In the context of the “carbon peaking and carbon neutrality” goals, the specific heat capacity of soil, as one of the important thermophysical parameters, plays an important role in many fields such as energy geo-structure, subway ventilation calculation, buried pipelines, nuclear waste disposal, artificial ground freezing, agricultural irrigation, etc. A specific heat capacity test was carried out on clay samples with different initial dry densities and initial water contents under different temperature conditions, and the variation patterns and mechanisms were investigated. The test results indicate that the specific heat capacity of clay increases linearly with the increase of initial dry density and initial water content, and is proportional to the third power of temperature. The mechanism of the variation of specific heat capacity is related to the variation of three-phase percentage, solid-phase lattice vibration, and water-ice phase transition. A model for predicting the specific heat capacity of clay considering multi-factors is established and cross-validated with back propagation artificial neural network (BP-ANN) model, simplified theoretical model and other empirical models. The comparison shows that the prediction model has better performance in terms of applicability and accuracy, which can provide a reliable reference for specific heat capacity determination in theoretical calculations, numerical simulations, and engineering practice.

This study aims to explore the seepage characteristics of fractured sandstone before and after grouting and the change rule of mechanical properties after grouting. Firstly, Rock Top multi-field coupling tester was used to conduct triaxial compression test on sandstone under different confining pressures at a constant rate of 0.02 mm/min to obtain fractured sandstone and conduct seepage test. Then, the self-developed grouting reinforcement system was used to reinforce the fractured sandstone, and the Rock Top multi-field coupling tester was used to conduct the triaxial compression seepage test on the fractured sandstone under different confining pressures. The results show that: (1) The permeability of fractured sandstone decreases significantly after grouting compared with that before grouting, with a decrease range of 24.26%-96.55%, but it is greater than the original rock permeability. (2) The permeability of fractured sandstone before and after grouting shows different periodic changes with the increase of hydrostatic pressure. When hydrostatic pressure reaches 40 MPa or above, the permeability difference within 5 MPa has a little effect on permeability, and the permeability curve tends to be horizontal. (3) After grouting, the fractured sandstone only exhibits brittle failure characteristics similar to the original rock only under 10 MPa confining pressure, but loses the brittle failure characteristics of the original rock under 20−60 MPa confining pressure, showing strong ductility failure and plastic flow phenomenon after the peak. (4) The peak strength and strain of the fractured sandstone after grouting both increase with the increase of confining pressure and show nonlinear variation characteristics satisfying the quadratic function relation. The peak strength ranges from 44% to 59% of the peak strength of the original rock. (5) The failure mode of fractured sandstone after grouting is mainly slip-shear failure, and new failure modes will appear under low confining pressure. With the increase of confining pressure, the failure effect weakens. (6) Scanning electron microscopy test on rock-slurry interface shows that ettringite and C-S-H (calcium silicate hydrate) gel are bonded to form stable hydration products, thus improving the bearing capacity of rock.

Currently, the simplified analysis for the deformation response of adjacent piles by excavation has seldom considered the influence of supporting action, especially the geotechnical influence caused by the rainfall environment. Based on the stratified hypothetical Green-Ampt model applicable to different rainfall conditions to simulate the rainfall infiltration process, a two-stage method was proposed to analyze the interaction between the excavation and the adjacent pile under the influence of rainfall. In the first stage, considering the influence of soil unloading, retaining, and supporting of excavation, the Mindlin solution was used to analyze the additional stresses in the soil at the adjacent pile foundations caused by the excavation of the foundation pit under the rainfall. In the second stage, based on the Pasternak foundation model, the interaction between pile foundations and soil was explored to obtain the horizontal deformation response of single piles and groups of piles under the influence of rainfall with the rainfall duration. The monitoring data from existing engineering were compared to the theoretical calculation results with good agreements. In addition, the parameters of rainfall (rainfall intensity, saturated permeability coefficient, initial water content, matric suction) and pile (boundary conditions, brace stiffness, pile diameter, excavation depth, distance between piles and foundation pit) were analyzed to investigate the influences on pile deformation. The results show that the proposed theoretical method can better reflect the deformation response of foundation excavation on adjacent pile foundations under the rainfall. The rainfall has a significant influence on the deformation of the adjacent pile, and the sensitivity of rainfall parameters is as follows: rainfall intensity > initial water content > saturated permeability coefficient > matric suction. With the increase of the rainfall duration, the development depth of the wet front continues to increase, and its development rate shows a gradual weakening law until it approaches the saturated permeability coefficient. The displacement of adjacent piles caused by the excavation becomes larger and larger, and the change rate of the top displacement first gradually decreases and then converges to a specific value. The smaller the support stiffness and pile-excavation distance, the greater the influence of rainfall duration on piles. The influence of rainfall duration on piles with different pile diameters is basically the same. The greater the excavation depth, the greater the influence of rainfall duration on piles.

The tunnel slope is prone to be damaged under the action of earthquakes and rainfall. It is necessary to study the dynamic response characteristics of the reinforcement structure of the tunnel portal slope. A tunnel portal slope in southwest China is experimentally studied as an example. The dynamic response and failure mode of the tunnel portal slope reinforced by prestressed anchor sheet-pile wall under earthquakes and rainfall are analyzed through shaking table test. The main conclusions include: (1) The failure process of the slope can be summarized as: tension cracks at the slope crest-shear cracks shear cracking, the foot of the slope, and overall sliding failure of the slope. Under the seismic action, the local damage occurs easily near the slope surface due to the infiltration of rainfall. The failure mode is tension-shear. (2) The peak acceleration amplification factors along the pile shaft increase significantly with the increase of peak acceleration, thus the inertial amplification effect of the structure should be considered properly. (3) The peak earth pressures behind the pile increase as the input peak acceleration becomes larger and the earth pressure changes from the S-shaped distribution to the inverted triangle distribution. When the peak acceleration is greater than 0.4 g, the axial force of anchor cable increases gradually and the tension effect is fully exerted. (4) The amplitude of Fourier spectrum of soil pressure and acceleration of pile are concentrated in the low frequency band. There is a high-frequency filtering effect of seismic wave propagation along the elevation. (5) The displacement spectrum amplitude of the pile increases as the peak acceleration becomes greater and increases larger along the pile height. The main frequency of the displacement spectrum is 1–4 Hz and the dominant frequency is 2.5 Hz, which is close to the dominant frequency of the seismic load. (6) The correlation between pile accelerations is well related and the correlations of pile acceleration, dynamic soil pressure, strain and axial force of anchor cable decrease with the increase of peak acceleration.

Effective shear zone of structural plane directly affects its shear performance. Based on the previous analysis of roughness and contact state of structural plane, the quantitative analysis method of effective shear zone of matching structural plane is studied by combining the topographic features scanning and illumination technology. The results show that: (1) Under the light source irradiation, the bright part of the structural surface reflects the effective shear zone during the shearing process. Statistical analysis of 3D bright area percentage (BAP^3D) at different incidence angles shows that with the increase of incident angle, BAP^3D is approximately S-shape. (2) The ratio of effective shear area to total area of structural plane is defined as structural plane effective shear coefficient JEC. By combining with the Patton model, the optimal incident angle of light source was theoretically determined as φ_B=90°–(φ_b+i ) (φ_b represents basic friction angle of structural plane, and i represents average undulating angle of structural plane). At this point the bright area is consistent with the actual effective shear area, the corresponding BAP^3D is effective shear coefficient JEC of the structural plane. (3) Considering the effective shear coefficient, the Barton model is modified and a modified shear mechanical model of structural plane is established. Validation analysis shows that the model can accurately estimate the shear strength of matching structural plane．

In the natural state, the moisture content of the soil in the unsaturated loess ground is low, resulting in the poor compaction effect of the loess ground by the heavy ramming method, which cannot meet the requirements of ground bearing capacity. Thereby, how to humidify the loess ground has become the focus of the research. In order to study the humidification effect of unsaturated loess under the action of water vapor, the water vapor humidification model experiment was carried out with the unsaturated loess as the research object, and the variation of water vapor diffusion rate, temperature and gas transport with time under different water vapor pressure gradients, the number of flower tube openings and the spacing of open holes were analyzed. The results show that the humidification of water vapor is a dynamic change process in which the moisture content gradient, pressure gradient and temperature gradient are coupled and interact with each other, of which the temperature gradient is the main factor affecting the transport of water vapor. After the water vapor is introduced into the soil, the volumetric moisture content, air pressure and temperature at each measurement point with the passage of ventilation time, all show two stages of rapid rise-gradual stabilization. In the test, Increasing water vapor pressure results in significant changes in the degree and range of humidification, and raising the number of open pores, the uniformity of soil humidification increased. Reducing the spacing between the opening pores and the degree of humidification does not change much. The research results can provide certain experience for the engineering of water vapor humidification of unsaturated loess foundations.

In order to study the crack initiation mechanism of rock under hydraulic coupling, hydraulic coupling triaxial test and acoustic emission test were carried out on Xiluodu basalt. The test results show that the peak strength of basalt increases with the increase of confining pressure, showing a typical hard brittle behavior. When the confining pressure remains unchanged, the peak strength decreases gradually with the increase of initial water pressure, and the hard brittleness decreases at the same time. The acoustic emission test results show that the crack initiation of basalt under hydraulic coupling is tensile failure, which is mainly tensile failure and supplemented by shear failure in the stable crack propagation stage, and these failures mainly occur in the middle of the rock. In the post peak stage of unstable crack propagation, the rock fracture is mainly characterized by shear failure. Based on the understanding of crack initiation mechanism, the critical hydraulic failure criterion of rock crack initiation under hydraulic coupling condition is derived with the help of the single circular hole theory, which is then introduced into the numerical simulation of basalt hydraulic coupling triaxial test. The hydraulic coupling failure process and water pressure distribution law of basalt are analyzed. The rationality of the critical hydraulic failure criterion is verified, and it has a good reference value for the study of rock failure process under hydraulic coupling.

The exploitation of geothermal resources will change the temperature and pressure of the thermal reservoir, affect its consolidation deformation characteristics and cause environmental geological problems. In this study, porous geothermal reservoir in the sandstone thermal reservoir exploitation area in northwest Shandong Province was studied as a research object. Consolidation deformation experiments under different stress and temperature conditions were carried out to analyze the characteristics of consolidation deformation, and the preconsolidation pressures calculated by Casagrande method and energy method were compared. The results showed that the consolidation deformation of geothermal reservoir was negatively related to water content and temperature. The self-weight compressibility of geothermal reservoir is about 10% of the standard compressibility. When calculating the preconsolidation pressure, the energy method can be used for low compressibility soil, and the Harris model, Gaussian model and energy method can be used for medium and high compressibility soil. There is a negative correlation between preconsolidation pressure and temperature. In the range of 25–80 ℃, the higher the initial temperature is, the faster the preconsolidation pressure decreases due to temperature rise.

To explore the accelerated disintegration mechanism of Gansu red-bed clay-bearing rock under drying-wetting cyclic, water immersion test and slake durability test were carried out. The main factors affecting rock durability were analyzed by comparing clay-sulfate rock with argillaceous sandstone, shale, and gypsum rock. Furthermore, the mineral inclusion effect during the disintegration process was discussed. The results of the experiment show that the natural disintegration rate of undisturbed clay-sulfate rock is relatively slow, and the disintegration rate of the sample is 0.11 after soaking for 3 h. After drying at a high temperature (163 ℃), the mixed gypsum minerals will be dehydrated with the volume shrinkage, and the rock mass will completely disintegrate within 2 hours when it is soaked in the water again. The clay-sulfate rock belongs to highly durable rock and its slake durability index of the second cycle I_d2 is 0.80. However, an accelerated trend can be observed in the disintegration, and the relative slake durability index of the fifth cycle I₅ is up to 0.56. The durability of rock is greatly affected by the mineral composition and cementation strength. In the process of rock disintegration driven by mineral expansion, argillaceous blocks are prone to uniform crushing, while sandy blocks are prone to uneven crushing. Because the clay minerals inclusion is dense, disintegrating of the clay-sulfate rock is intensive. The sulfate mineral inclusion is corrosive, and its solution shows weak acidic. Therefore, the main reasons for the accelerated disintegration of clay-sulfate rock are micro-cracks produced by gypsum corrosion and the abscission of calcareous nodules in the acidic environment.

The size effect and anisotropy of the mechanical parameters of fractured rocks are difficult tasks that need to be solved in the field of rock mechanics and engineering. Making full use of the advantages of rapid prototyping and batch preparation of complex internal structure rock models with 3D sand printing technology, the rock-like specimens with different sizes and different rotation angles of the fracture network model are produced by using 3D sand printing, the quartz sand and furan resin are employed as the printing materials. The uniaxial compression test is performed on the 3D sand printed specimens to study the size effect of the mechanical properties of the fracture network rock mass, the correlation between fracture density and strength is revealed and the anisotropy of the mechanical properties of rock masses at the representative elementary volume (REV) scale is analyzed. The test results show that the mechanical properties of 3D sand-printed specimens are similar to those of natural rocks, the stress-strain curves of the fractured network model-like rocks can be divided into four stages: original crack closure stage, linear elastic deformation stage, crack initiation and extension stage, and post-peak stage. There is an exponential decay relationship between uniaxial compressive strength and size of the specimens, and there is an obvious characteristic of size effect. There is a significant negative exponential relationship between fracture density and compressive strength, and the size of the REV determined based on the fracture density and compressive strength is well consistent. The failure patterns and compressive strength of the fractured rocks have obvious anisotropic characteristics. The research approach provides a reliable method for the laboratory experiments to study the size effect and anisotropy of complex fractured rock masses.

Particle morphology is an important parameter affecting the mechanical properties of coral sand. Studying the multi-scale morphological characteristics of coral sand is helpful to interpret its mechanical properties from the microscopic perspective. Based on the particle dynamic image analysis technology, this study carried out particle morphology scanning and comparative analysis on more than 200 thousand coral sand and terrigenous quartz sand (including artificial broken quartz sand and natural quartz sand) particles in different particle size ranges, and proposed the classification standard of particle shape suitable for coral sand. The difference of particle morphology between marine coral sand and terrigenous quartz sand was revealed from particle shape, roundness and convexity. The findings indicate that: (1) Coral sand is mainly composed of blocky, flaky and bar-shapes particles, taking the elongation ratio and flatness ratio of 0.5 as the threshold for the classification of coral sand particle shape, the accuracy of this classification method can reach 90%. (2) The proportion of blocky particles in coral sand is the largest and the content is more than 50%. With the increase of particle size, the proportion of blocky particles increases, and the proportion of flaky particles decreases, while the proportion of bar-shaped particles basically remains unchanged. With the increase of particle size, the proportion of blocky particles in quartz sand is higher than coral sand, which is determined by the mineral properties of the particles, rather than the weathering and crushing mode of the particles. (3) Artificial broken quartz sand and coral sand have relatively similar particle roundness, and slightly less than that of natural quartz sand. The roundness of blocky particles is the highest, followed by flaky particles and the lowest is bar-shaped particles. Therefore, the roundness of aggregate increases with the proportion of blocky particles. (4) The convexity of coral sand is between 0.85 and 1.00, which is lower than that of quartz sand. With the increase of particle size, the convexity of coral sand decreases obviously, while the convexity of quartz sand changes little.

To investigate mechanism of compressive deformation of red clay contaminated by heavy metal Cu²+, CuSO₄ solutions with concentrations of 0, 2.5, 5.0, and 10.0 g/L were used to prepare the contaminated soil, and consolidation tests, thermal analysis tests, and scanning electron microscopy (SEM) tests were conducted. The results show that the changes of compression coefficient and total compressive deformation of red clay and the changes of pore water (free water, weakly bound water and strongly bound water) content in the clay show the same trend of decreasing first and then increasing with the increase of Cu²+ concentration. The structural connection between soil particles in clay soil is mainly based on adsorption water film contact. Cu²+ changes the water film thickness of pore water in soil, which leads to the change of pore water content. The water film becomes thinner, the distance between soil particles shortens, the higher the structural strength of soil body, and the greater the ability of soil body to resist compression deformation. With the increase of Cu²+ concentration, the microstructure of soil body gradually evolves from loose block-like and flaky units to stacked aggregates with face-to-face contact. When the concentration of Cu²+ increases to 10.0 g/L, scale-like units start to appear, the contact mode between units is mainly point-point contact and edge-face contact, the cohesion between soil particles becomes poor, and the structural stability of soil body decreases.

To obtain three-dimensional anisotropic deformation field characteristics of bedded shale, uniaxial compression experiments were carried out on laminated shale of Longmaxi Formation in Sichuan Basin. The digital images obtained by in-situ scanning through Micro-CT were used as the deformation information carrier. The deformation field of bedding shale under uniaxial compression conditions was calculated based on local DVC and global DVC. The bedding effect of shale deformation evolution was explored. The following results indicate that: with the increase of load, the gradient of the overall displacement field of shale specimens gradually evolved towards the bedding direction. The high-strain concentration zones of shale specimens with different bedding exhibit different patterns. As for the 0° specimen, there is obvious strain concentration in the middle zone and the fracture is concentrated in the middle zone under the joint influence of tensile and shear action. As for the 45°specimen, the concentration zones of tensile strain and shear strain appear at the same time during the late loading period; there is an obvious bending at the bedding plane for fracture development and the fracture evolution is jointly controlled by tensile and shear action. For the 90° specimen, there is obvious tensile strain concentration during the whole loading process; the cracks developed parallel to the vertical bedding plane, and the failure of the specimen is controlled by the tensile action. The deformation field and strain field obtained by Micro-CT high-resolution in-situ scanning images combined with local and global DVC can reflect the deformation and failure law of anisotropic shale, which provide a method for studying the bedding effect of shale deformation evolution.

The MX-80 bentonite powder was pretreated by thermal aging at 200 ℃ for different durations (t =0, 15, 30, 60, 90, 120 d). Then, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the variations of bound water, mineral composition, and microstructure in MX-80 bentonite with the thermal aging time t. Based on the crystal structure theory of montmorillonite, the micro-mechanism of high-temperature ageing time effect in MX-80 bentonite was revealed. The results show that, 1) the free water, weak bound water, and strong bound water in bentonite have different degrees of desorption with thermal aging time t increasing. The desorption changes significantly from 0 to 15 days and tends to be stable after 15 days. After 120 days, desorption values of three types of water decrease by 82.6%, 68.8% and 96.5%, respectively. 2) With increasing the thermal aging time t, montmorillonite, the main mineral component of bentonite, is transformed into sodium mica with good stability, and it changes significantly from 0 to 15 days, and tends to be stable after 15 days. After 120 days, the changes of montmorillonite and sodium mica are –12.57% and +12.47%, respectively. 3) In the process of high-temperature aging, the distance between crystal layers of montmorillonite decreases, resulting in the contraction and deformation of lamellar minerals, and the microstructure of bentonite changes with the increase of thermal aging time t. 4) Under the condition of high-temperature aging, the fundamental reason for the changes in the macroscopic physical and mechanical properties of bentonite is the interaction and mutual influence among the mineral composition transformation, bound water desorption, and microscopic morphology change of bentonite.

Organic matter is a common component in soil and has a significant effect on the thermal properties of soil. To clarify the influence and mechanism of organic matter on the thermal conductivity of clay, bentonite was used as the matrix to prepare soil samples with different organic matter contents by adding humus. Thermal conductivity coefficient λ was measured by thermal probe, and the variation of λ with dry density ρ_d, water content w (degree of saturation S_r) and organic matter content w_u were examined. By analysing the adsorption characteristics of bentonite to organic matter, the influence mechanism of organic matter on soil thermal conductivity was discussed. The results show that the thermal conductivity coefficient λ  increases with the increase of dry density ρ_d water content w and degree of saturation S_r when w_u is the same. When the dry density ρ_d of saturated soil is the same, l decreases with the increasing of w_u, but is not a monotone linear decline. It can be divided into three stages: sharp descent stage, transition stage, and gentle descent stage. The approximate range of w_u corresponding to the transition stage is 7.5% to 15.0%. The saturated adsorption capacity w_u,1 of bentonite to compact organic matter is about 8%, and that of w_u,2 to compact + stable organic matter is about 14.0%. In other words, the two thresholds (w_u,1, w_u,2) of the variation of organic matter occurrence form are consistent with the w_u corresponding to the transition section of the λ-w_u relation curve. Mechanism analysis shows that in addition to the content of organic matter, the change of organic matter occurrence form is also an important factor affecting the thermal conductivity of the soil. The applicability of several theoretical prediction models of thermal conductivity for clay soil containing organic matter was analysed.

Using the self-vibration column apparatus, the experimental investigation on the 165 undisturbed clayey and silt soil samples obtained from 41 boreholes in Xuzhou urban area were conducted to evaluate the characteristics of dynamic shear modulus ratio G/G₀ and damping ratio l with the shear strain amplitude γa . Special focus is given to the influence of effective confining pressure, plasticity index, and geological age on the G/G0-γa  and λ-γa  curves of Q₃ and Q₄ clay soils, Q₄ silty clay soil and Q₄ silt soil. The results indicate that the larger the effective confining pressure is, the larger the plasticity index is, the newer the geological age is when the depth is similar, and the weaker the nonlinearity of soils is. The upper and lower envelopes of the G/G0-γa  and λ-γa  test data of three soils were proposed. The influence characteristics of soil type, effective confining pressure, plasticity index, and geological age on the G/G0-γa  and λ-γa  curves of three soils were quantitatively analyzed, and the corresponding empirical formulas for predicting G/G0-γa  and λ-γa  curves were established. The results are beneficial to understand the dynamic characteristics of various soils in Xuzhou urban area, and have a helpful reference for the evaluation of seismic site effects in this area.

In order to deeply understand the shear failure mechanism of intermittent joints, shear tests and acoustic emission monitoring of intermittent joints with different joint angles are carried out. Based on the dominant frequency of acoustic emission signal, the quantitative analysis of fracture degree in the failure process is realized. By combining the shear failure strength, shear failure structures and the evolution process of fracture degree, the shear failure characteristics of intermittent joints are studied. The results show that the variation trend of SR1 at stage I of intermittent joints presents horizontal transverse S-shape, and SR2 presents symmetrical joint angle distribution. When the joint angle is positive small angle, SR1 is greater than SR2, while when the negative angle and positive large angle, SR2 is greater than SR1.The failure structures of intermittent joints can be divided into plane failure structure, zigzag failure structure and block failure structure, three failure structures are actually determined by four crack propagation modes. Joint angle controls the occurrence of large-scale failure, intermittent joints will have large-scale failure in stage I and stage II when subjected to large joint angle. However, the large-scale failure only occurs in stage I when the joint angle is small. The failure process of intermittent joints can be divided into four categories. With the increase of joint angle, the failure process develops from " unimodal abrupt " to " bimodal stable-stable ", then to " bimodal abrupt-stable ", and finally to " bimodal abrupt-abrupt ".

In order to study the fracture characteristics and energy consumption characteristics of the fully tailings cemented backfill under impact loading, uniaxial impact tests on fillers with different cement-sand ratios at moderate strain rates were carried out with the help of a split Hopkinson pressure bar (SHPB) test system. The results show that the pre-peak strain energy, absorbed energy, prepeak strain energy density and absorbed energy density of the backfill body all increase exponentially as increase of incident energy when the cement-sand ratio is the same. When the incident energy is less than 16 J, the absorbed energy density, pre-peak strain energy density, absorbed energy and pre-peak strain energy of the backfill body with the cement-sand ratio of 1:6 are greater than those of the cement-sand ratio of 1:4 and 1:8. The fracture toughness of the backfill body gradually grows with the increase of the cement-sand ratio for the same peak strength, incident energy, pre-peak strain energy and absorption energy. The fracture toughness of the backfill body increases linearly with the increase of dynamic peak strength, absorbed energy density and pre-peak strain energy density, and increases exponentially with the increase of incident energy, pre-peak strain energy and absorbed energy. The increase of fracture toughness with energy absorption density and pre-peak strain energy density of the filled body with cement -sand ratio of 1:4 is two to three times that of cement-sand ratios of 1:6 and 1:8. Based on the growth law of strain energy density, energy consumption and strain, the damage and failure evolution process of the backfill can be divided into four stages: nonlinear compression, linear elastic deformation, elasto-plastic deformation and post-peak damage. Through regression analysis of the backfill body test results, a calculation formula for the fracture toughness is derived from the perspective of energy consumption, which can provide a reference for the stability analysis of the underground backfill body.

Thixotropy is a research hotspot in the rheology of dispersion systems. Clay thixotropy is an extraordinary phenomenon of clay, which shows that the strength of clay decreases after being disturbed, and the strength recovers gradually after standing. To discuss the influences of clay content, water content, void ratio, and sensitivity on the thixotropy of clay, we designed orthogonal test on Zhanjiang Formation structural clay with strong, medium, and weak sensitivities to implement unconfined compressive strength tests with different curing ages. The experimental results show that: in terms of the thixotropic strength of clay, there are power function relationships between clay content, moisture content, void ratio, and thixotropic strength of clay, and it decreases as the values of these three parameters increase. There is a logarithmic relationship between sensitivity and the thixotropic strength of clay, and it increases with the increase of sensitivity. For the above four parameters, R² is greater than 0.95, which has a good correlation. In terms of the thixotropic strength ratio of clay, it increases with increasing the clay content, water content, and sensitivity, and decreases as the void ratio increases. In addition, for samples with the same sensitivity, the void ratio has the greatest impact on thixotropy, followed by water content, and finally clay particle content. Finally, we used the least squares method to perform multiple regression fitting and developed a multiple regression prediction model for the relationship between the factors and the intensity of thixotropy.

Bolts-grouting is a common reinforcement and waterproofing method in water-rich tunnel engineering. At present, there is still a lack of analytical theories that can simultaneously consider the mechanical interaction between rockbolt and surrounding rock, as well as the waterproof and impermeable effects of grouting. Based on Darcy’s law and "smeared" method, a differential equation of rock bolts-grouting composite surrounding rock was established by substituting the pore water pressure in the surrounding rock after grouting reinforcement and the interaction force between the rockbolt and the surrounding rock into the stress equilibrium equation of the reinforced surrounding rock. By solving the proposed differential equation, the closed-form solutions for pore pressure, displacement, and effective stress on bolts-grouting composite surrounding rock, and stress on the rockbolt are obtained and compared with numerical solutions and the solutions of other scholars. The comparison results show that the analytical results are consistent with the finite element solution; and bolts-grouting reinforcement can improve the stress state of surrounding rock compared with grouting only. Furthermore, based on our closed-form solutions, and the effect of bolts-grouting reinforcement parameters, support pressure, impermeability pressure of lining, and diameter of the tunnel on safety factor is elaborated. These laws indicate that with the increases of bolts-grouting range, rockbolts density factor and supporting pressure, the safety factor increases in the ways of first fast then slow, quasi-linear and first slow then fast, respectively. The increase of impermeability pressure on secondary lining can reduce the water inflow, but it is not conducive to the stability of the tunnel. Finally, based our closed-form solutions, we propose the method of parameter optimization for the bolts-grouting reinforcement in the tunnel as well as case study.

As an essential parameter for evaluating subgrade performance and pavement design, the dynamic resilient modulus is complex and changeable due to the significant influence of the physical and mechanical state and external environment. An efficient and straightforward monitoring method is urgently needed. In this paper, a series of dynamic resilient modulus tests and shear wave velocity tests were conducted on thawed silty clay under different degrees of compactness, moisture contents, and freeze-thaw cycles. Dynamic resilient modulus, shear wave velocity, and their conversion relationship of thawed silty clay were obtained. The results show that the dynamic resilient modulus and shear wave velocity of silty clay are closely related to its physical state. Both decrease sharply with the increase of moisture content and freeze-thaw cycles, and increase with the rise of compactness. The dynamic resilient modulus of silty clay is also affected by the stress condition, and it increases with the growth of confining pressure and decreases with the increase of cyclic deviator stress. A three-parameter composite model was used to predict dynamic resilient modulus of frozen and thawed silty clay, and a model for predicting shear wave velocity was also established. The conversion relationship between the dynamic resilient modulus and shear wave velocity was constructed, which could provide an effective way to determine the dynamic resilient modulus of subgrade soil based on shear wave velocity.

Rainfall-induced accumulation landslide is one of the most widespread geo-hazards. In recent years, due to more extreme rainfall events brought on by climate change, the scale and frequency of the rainfall-induced accumulation landslides have further increased. Centering on the slope failure mechanisms due to the extreme rainfalls, this research carries out a series of model tests in order to explore the influence of different gradations of the slope materials on the slope failure mechanism. A series of large-scale triaxial tests is carried out first, where three different colluvium materials are remolded, with the clay content fixed at 10% and the rock contents at 30%, 50%, and 70%, respectively, so that stress-strain relationships of the samples considering different gradations can be obtained. Thereafter, three slope models are built, consisting of the designed gradations. Extreme rainfalls are then applied to cause the slopes to fail, aiming to reveal different slope failure modes. Meanwhile, the changes of the water content, soil pressure, and pore water pressure inside the slope during the slope failure process are also monitored and analyzed, and the changes of fines content and its moving trajectories during the rainfall infiltration process are also illustrated. Finally, the failure mechanism of the accumulation landslide under extreme rainfall is summarized, which can hopefully provide some theoretical basis for the early warning of the accumulation landslide.

JRC-JCS model provides a good idea for estimating the shear strength of joint surface, but it often overestimates the shear strength of jointed rock mass with poor consistency. The JRC-JMC model further considers the effect of joint matching degree on shear strength, which provides a good idea for estimating the shear strength of joint surface with poor joint matching degree. However, there are still difficulties in quantitative analysis of joint matching degree at present. Based on the analysis of the morphological characteristics of joint plane and the variation law of shear performance of joint surface, the quantitative calculation method of joint matching degree was proposed. The results show that: 1) Under the action of repeated shear, the shear strength of the jointed rock mass and the morphology parameters of the joint plane show a trend of decreasing first steeply and then slowly, and the matching degree between the upper and lower walls of joint surface decreases gradually. 2) According to the comparative analysis of joint surface topography before and after shear, the effective contact area of joint surface during shear process is determined, and the quantitative calculation method of joint matching coefficient JMC is proposed. 3) The comparative analysis shows that combining JRC and JMC can better reflect the influence of joint morphology characteristics on shear performance compared with the consideration of JRC alone. The related research methods and analysis results can provide a reference for the shear behavior analysis of joint surface.

In this study, the nano-SiO2 (NS)and lime were used to solidify the coastal petroleum-contaminated soil. The effects of nano-SiO2 and lime on the solidification of coastal petroleum-contaminated soil(PCS) were studied through Atterberg limits tests, unconfined compressive strength tests and pH tests. The microstructure and mineral composition of typical modified petroleum-contaminated soil were analyzed by scanning electron microscopy and X-ray diffraction tests. The results indicate that the unconfined compressive strength of petroleum-contaminated soil with 5% petroleum content modified by NS-lime increases significantly. By adding 1% or 2% NS to the 3% lime-modified petroleum-contaminated soil, the 7-day saturated unconfined compressive strength of lime-modified petroleum-contaminated soil reaches 421 kPa and 727 kPa, respectively, more than 3 times and 5 times of that without NS. Meanwhile, adding NS reduces the pH of lime-modified petroleum-contaminated soil and the harm of lime to the environment. Furthermore, the scanning electron microscope test and X-ray diffraction test also prove that, compared with adding lime alone, when NS and lime are combined, the NS accelerates the hydration reaction of lime, promotes the formation of hydrated calcium silicate, and greatly improves the strength of coastal petroleum-contaminated soil.

At present, the microstructure and compression characteristics of marine soft soils in onshore and shallow seas are widely studied, while those of deep-sea soft soils are less studied. However, with the development of marine engineering to deep water, the characteristics of deep-sea soft soils deserve attention. Diatomite is widely distributed in the deep sea and it is a kind of deep sea soft soil. It has diversity and does not follow the characteristics of classical soft soil laws. Currently, there are few studies on in-situ undisturbed samples. To investigate the microstructures, compression characteristics and secondary consolidation properties of deep-sea diatomite, scanning electron microscope (SEM) analysis, mercury intrusion porosimetry (MIP) tests, traditional oedometer tests and multistage oedometer tests (7-day loading for each stage) were carried out on diatomite sampled from the western Pacific Ocean at the depth between 4 423 and 4 674 meters. The experimental results show that the compression index of deep-sea diatomite ranges from 1.7 to 1.95, which is about 0.6 to 1.2 larger than that of other terrestrial and shallow marine soft soils. In addition, in the creep stage after consolidation, diatomite still has volume deformation for a long time, and there is no stable trend of deformation convergence, which may be caused by the continuous breaking of the shell of diatom particles. This hypothesis has been confirmed by SEM and MIP tests observation results in the loading stage.

Natural cementation is a typical characteristic of marine calcareous sediments, such as calcareous rock and soil, and the degree of cementation has an important influence on its mechanical properties. Due to the great heterogeneity and low cement strength of cemented calcareous sediments, it is difficult and expensive to obtain natural cemented calcareous sediments from the oceangoing island, limiting research on their physical and mechanical properties. To effectively solve the above problems, this paper attempted using physical, and biological dominate method in the laboratory. It was found that microbially induced carbonate precipitation (MICP) and enzyme induced carbonate precipitation (EICP) can promote the production of calcium carbonate crystals, generating artificially cemented specimens similar to the natural ones. The mineral composition, porosity and unconfined compressive strength of the biological artificially cemented specimens were analyzed by scanning electron microscopy (SEM), computed tomography scanned by X-ray (X-CT) and unconfined compressive strength test. The mineral composition and crystal morphology of the artificial cementation were the same with the natural cemented calcareous sediments. The peak unconfined compressive strength of the artificially cemented sample could reach to the level of the natural weakly cemented calcareous sediments. The relationship between cemented time, porosity, degree of cementation and unconfined compressive strength was quantitatively determined. Therefore, the biological dominate method can shorten the natural cementation process from tens of millions of years to a period that can be reproduced in the laboratory, providing scientific value for exploring the formation mechanism of naturally cemented calcareous sand and reef limestone. However, it should be noted that there are some limitations in artificially cemented specimens, such as the degree of cementation is not fully uniform and dolomitized calcareous rock cannot be simulated.

In order to investigate the influence of multi-factor coupling effects on frozen Lanzhou loess dynamic parameters, Lanzhou loess distributed in seasonal frozen soil region of western China was investigated experimentally. The dynamic parameters of frozen Lanzhou loess under different conditions were examined by dynamic triaxial test, including confining pressure (0.1, 0.2, 0.3 MPa), soil temperature (−1, −3, −5 ℃), soil water content (14%, 16%, 18%) and vibration frequency (1, 2, 4 Hz). Based on the test results, the changing rules of the maximum dynamic elastic modulus, equivalent viscous damping coefficient and reference strain amplitude of frozen Lanzhou loess under the coupling influence factors of temperature, confining pressure, water content and loading frequency were analyzed. Test results show that the coupling factors including temperature, water content, loading frequency and confining pressure have different influences on the dynamic elastic modulus, reference strain amplitude and equivalent viscous damping coefficient of frozen Lanzhou loess. It can be found that the dynamic elastic modulus and reference strain amplitude of frozen Lanzhou loess are influenced most significantly by soil temperature, and the equivalent viscous damping coefficient is the most sensitive to the loading frequency. Moreover, based on the experimental results, the four factors affecting the frozen Lanzhou loess are normalized and dimensionlessized, and the prediction formulas of the dynamic parameters of the frozen Lanzhou loess are proposed using multiple regression analysis method. This will be beneficial to quickly predict the changing characteristics of the dynamic parameters of the frozen Lanzhou loess under the influence of the coupling effect of multiple factors. The formulas are helpful for rapid prediction of dynamic parameters of frozen Lanzhou loess under the multi-factor coupling influence effects.

As a new type of subgrade fill, steel slag-stabilized soil was characterized by high heterogeneity and discontinuity. It is difficult to directly study the microscopic characteristics of its failure mechanism through traditional mechanical testing and theoretical analysis methods. In order to reveal the damage mechanism of steel slag-stabilized soil, uniaxial compression tests were conducted combined with a real-time X-ray computed tomography (CT) test, and the dynamic evolution characteristics of microscopic cracks under four typical strain levels were analyzed based on image processing and three-dimensional visualization. The results show that the steel slag-stabilized soil experienced four stages, including initial compaction, elastic deformation, plastic yield and residual deformation. A localized shear band appeared in the middle of the specimen in uniaxial compression process. The two-dimensional porosity and dispersion degree of crack distribution continuously improved with the increasing axial strain. Three-dimensional reconstruction models vividly revealed that the cracks experienced three development stages, including initial germination, rapid expansion and stable state. Three-dimensional porosity and crack connectivity are exponential function and linear function respectively with axial strain. The pore size distributions show that the primary cracks gradually expand and penetrate through the entire specimen and contribute to a main fracture that leads to the structural damage. Thus, the expansion and connection of cracks are the internal reasons of strength softening and instability failure of specimen under uniaxial loading. The uniaxial compression-CT real-time scanning results can effectively reveal the damage evolution characteristics of materials. The research results provide a new perspective for understanding the failure mechanism of soils and have important reference for promoting the application of industrial waste slag in geotechnical engineering.

Sludge is a kind of soil with very poor engineering properties and difficult to solidify rapidly. Through unconfined compressive strength test, consolidated drained triaxial test, micro test and mercury intrusion test, the strength development law of sludge solidified by composite rapid soil stabilizer (CRSS) and the influence of the content of soil stabilizer on the strength are studied, and the micro mechanism of strength development is preliminarily discussed. The results show that the strength of CRSS-solidified sludge increases logarithmically with the curing age, the early strength develops rapidly, and the unconfined compressive strength can reach 3 MPa after curing for 1 h; with the increase of stabilizer content, the triaxial shear stress-strain curve of solidified sludge gradually develops from strain hardening type to strain softening type, and the failure deviatoric stress and cohesion increase linearly. The microstructure shows that the hydration products of stabilizer can cement soil particles, fill soil pores and enhance the integrity of soil. The mercury intrusion test results further reveal the mechanism that the cohesion of solidified sludge increases linearly with the increase of the content of stabilizer through the connection of the most probable pore size. CRSS-solidified sludge has significant advantages of fast hardening and high strength, which provides a theoretical basis for the application of rapid solidification of sludge.

The interaction of pre-existing fissures and engineering cracks caused by excavation-induced disturbance, unloading and hydraulic fracturing is very common in rock engineering. Establishing a propagation criterion suitable for engineering cracks encountering pre-existing fissures is the key to explaining the propagation mechanism of engineering cracks and investigating the weak-surface shear-slip of rock mass. The study used two concrete filling materials with different strengths to simulate the pre-existing fissures of strong and weak cementation. The mode I static fracture toughness of the filled cemented rock was determined by the semi-circular bend method under the quasi-static tensile stress. By analyzing the propagation trajectory of engineering cracks, the relationship between the critical crack initiation angle and the stress approach angle was obtained; the interaction propagation mode and initiation criteria of engineering cracks interacting with preexisting fractures were further discussed. The results show that the interaction between engineering cracks and pre-existing fissures under tensile stress is jointly affected by the stress approach angle, the crack initiation approach distance, and the cementation strength of the filling. The static fracture toughness of the filled cemented sandstone first increases and then decreases with the increase of the stress approach angle. When the crack initiation distance is large, the fracture toughness changes little with the stress approach angle; while when the crack initiation distance is short, the fracture toughness first increases and then decreases with the increase of the stress approach angle. The stress approach angle affects the fracture toughness of the cemented rock filling, but the magnitude of the influence is not as great as those of the crack initiation approach distance and the cement strength of the fillings, and there is a limited influence distance. Even if the rock material is under tensile stress, there is also shear localization at the front of the crack. Therefore, whether or not an engineered crack crosses a pre-existing fissure depends on the shear strength of the cracks and the friction properties of the pre-existing fissure under the combined effect of the stress approach angle, the crack initiation approach distance, and the cementation strength of the filling materials.

To understand the effect of drying-wetting cycles on the expansion characteristic of confined compressive clay-sulfate rock, a series of cyclic drying-wetting tests was carried out by a self-designed instrument. The test samples were special clay-sulfate rock collected from the Tianshui No. 2 tunnel of the Pingliang (Gansu) to Mianyang (Sichuan) expressway. The macroscopic expansion regulation and mesoscopic expansive mechanism of the samples during the drying-wetting cycles were analyzed. The results show that: (1) The self-designed instrument can couple the drying-wetting cycle in a confined compressive stress state in the whole process of the test. Meanwhile, there is no free surface of the specimens, which accords with the real occurrence of the underground rock mass. (2) When the normal pressure is less than the expansive stress of clay-sulfate rock, the volume of the sample increase significantly after the first wetting process, and the proportion of recoverable expansive deformation is small in the subsequent drying process. (3) After the first drying-wetting cycle, the mineral particles of specimens degenerate from cementation to flocculent accumulation, which is an argillation process, with a proportion of decrease in expansion stress exceeding 80%. (4) Normal pressure can reduce the expansion deformation of clay-sulfate rock, however, it cannot inhibit the degeneration of mesostructured of clay-sulfate rock. (5) The loaded drying-wetting cycles may eliminate the expansibility of clay-sulfate rock, at the expense of some unrecoverable deformation. However, it maybe reduce the shear strength of the surrounding rock at the same time. The main conclusions of this study play a guiding role in tunnel construction and geological hazard prevention in clay-sulfate rock areas.

Study on the phase transition properties and rheological model of submarine sediments during rheological testing is of great significance to the safety assessment for submarine structures. Using the soft clay in South China Sea, five group samples with different water contents were prepared, and a series of rheological tests under different temperature was carried out using the MCR302 rheometer. The results show that shear stress increases rapidly then increases slowly with increasing shear rate, while apparent viscosity decreases rapidly then decreases slowly. The shear stress and apparent viscosity decrease with increase in water content, and they increase with decrease in temperature. Phase transition happens in soft clay during shearing and can be divided into static and dynamic yield stresses, and the models for static and dynamic yield stresses were established on the basis of experimental results. In addition, Dual-Bingham rheological model considering effects of water content and temperature for soft clay from South China Sea was established, and the efficiency of model was verified. The results of this paper can provide basic model for the numerical analysis of submarine structure stability in South China Sea.

Geopolymer is characterized by high strength, denseness, low thermal conductivity, and resource conservation, and it meets the needs of coarse-grained fill improvement for high-speed railway roadbed engineering in terms of seismic safety and feasibility of resource acquisition. The unconfined compression strength tests of geopolymer-stabilized fine-grained fillings with different mixing ratios of metakaolin and alkali-activator and the dynamic triaxial tests of geopolymer-stabilized coarse-grained fillings with different rock block contents and confining pressures were carried out. The mixing ratio of raw material and alkali activator for composing metakaolin-based geopolymer and their optimum mixing ratio in fine-grained fillings were analyzed. The impacts of rock block content and confining pressure on the dynamic characteristics of the geopolymer-stabilized coarse-grained fillings were discussed. The results indicated that the optimum ratio of metakaolin and alkali activator for composing geopolymer was 2:1, and their optimum content in fine-grained fillings was 15%; the maximum dynamic shear modulus of geopolymer-stabilized coarse-grained fillings had an approximately linear relationship with the rock block content and a non-linear relationship with the confining pressure; when the shear strain was normalized, the dynamic shear modulus ratios of the geopolymer-stabilized coarse-grained fillings were distributed in a narrow band, while the damping ratio showed a relatively high dispersion in values. The results of this study can provide the design parameter basis for the application and popularization of geopolymer-stabilized coarse-grained fillings.

In order to explore the correlation between soil-water characteristics and microstructure of soil-rock mixtures in Qinling Bashan Mountains, unsaturated infiltration test and mercury intrusion test were carried out on soil-rock mixtures with different void ratios and rock contents. The test results show that the soil-water characteristic curve of soil-rock mixture under high compaction and low rock content is obviously higher than that under low compaction and high rock content. The pore size which affects the soil-water characteristics of soil-rock mixtures is within the range of less than 200μm. For the soil-rock mixture sample with low rock content, increasing the compaction degree will cause the pores to concentrate in the range of small pore size, thereby making the soil-water characteristic curve steeper in this pore size range. For the sample with high rock content, increasing the compaction degree mainly compresses the large pore (d>80μm), which has almost no effect on small pores, resulting in the consistency of soil water characteristic curve within the research scope. When the compactness is high, increasing the rock content causes the pore size distribution of the soil-rock mixture to be more uniform, and the soil-water characteristic curve changes from steep to gentle. For the soil-rock mixture with low compactness, the structure of small pores under different rock content conditions has little difference, which makes the soil water characteristic curve from different samples relatively consistent.

The coal mass around deep roadways are often disturbed by mining activities from far to near, while bearing high ground stress loads. As a result, the internal crack damage continues to develop in a stress path similar to the gradual loading and unloading of high stress. If they are still under the influence of water and rock interaction, their bearing capacity will further deteriorate. The water absorption characteristics, wave velocity comparisons, mechanical experimental analyses, and acoustic emission monitoring of deep coal samples from a mine indicate that the deep coal samples containing water exhibit characteristics including rapid water absorption, easy saturation, and overall integrity enhancement after water saturation, and they are mainly characterized by the tensile failure of the open main control crack, which causes the overall failure of the specimen. According to the above characteristics, a loading beam main control crack model is optimized and established herein by combining some factors such as the water content, crack parameters, and system size. The mechanism of the instability characteristics mentioned above deep water-bearing coal samples was elaborated, and the sensitivity analysis and strength verification were conducted. The obtained results were in good agreement with the experimental data, which can serve as a reference for similar experimental research, theoretical modeling, and mining design of fractured coal-rock mass located in deep high stress disturbed water-rich roadways.

The research of the coal-rock system composed of deep coal seams and surrounding rock masses has become one of the popular research directions in deep mining. In this study, the L-shaped mold is used to carry out the unilateral confinement compression test on the rock-coal-rock combination, and the digital image correlation technology (DIC) and the particle flow PFC2D are used to analyze the test strength, failure characteristics and crack distribution of the coal-rock combination. (1) The main strain areas of coal-rock combination are all concentrated on the free side of the sample coal seam. (2) Under unilateral confinement, the joint restriction of the two rock layers on the coal seam decreases as the height-to-width ratio of the coal seam increases. The damage of the sample is gradually transferred from the middle of the coal seam to the end of the coal seam. (3) When the ratio of coal-rock combination is 1:1:1 and 1:2:1, the failure mode of the calculation model shows a <-shaped fracture, which appears on the free side in the middle of the coal seam. When the rock-to-rock ratio is 1:4:1, the macroscopic damage gradually shifts to the middle and upper part of the coal seam, and evolves into shear failure. (4) The microscopic cracks of the calculation model are mainly located on the free side, which appear as tensile cracks. The number of the tensile cracks inside the model are about 4.5 times that of the shear cracks.

In order to obtain the meso-damage evolution law and mechanical response of tunnel surrounding rock in unloading failure process, the numerical simulation of the internal meso-damage of the surrounding rock during unloading was carried out by the particle discrete element method, and the effect of the initial stress on the failure and mechanical properties of the surrounding rock was analyzed by combining the failure characteristics of thick-walled cylindrical surrounding rock specimens. The results show that: (1) The cracks induced by unloading were distributed around the inner wall of the specimen. Under the influence of unloading stress adjustment, the cracks accumulated and gradually diverged and expanded to the outer wall, showing an "hourglass-type" damage failure. (2) The number of cracks generated by unloading increases exponentially with the increase of stress, and the growth rate of the number of cracks after unloading was significantly higher than that of the number of cracks during unloading. (3) When the unloading stress level was lower than 80% of the uniaxial peak strength of the surrounding rock, the stress was fully adjusted during unloading and remained stable after unloading. When the unloading stress level was higher than the uniaxial peak strength of the surrounding rock, the stress was not sufficiently adjusted in unloading stage and continued to be adjusted after unloading, resulting in "V-shaped" destruction of the surrounding rock. (4) The initial stress level has a significant impact on the excavation unloading-induced damage failure and mechanical properties of the surrounding rock. The larger the stress level, the earlier the time of damage rupture of the surrounding rock after unloading.

The geosynthetic reinforced soil technology used in mixed reinforced soil abutment can shorten the bridge span and improve the overall performance of the abutment. To study the influence of reinforcement spacing, horizontal constraint of wall toe and way of geogrid around pile on abutment deformation, as well as the influences of road surface load, four static load model tests are carried out. The results show that the mixed reinforced soil abutment is stable and the overall deformation is small under the pavement load. The monitoring results show that the existence of pile in the reinforced soil abutment reduces the lateral deformation of the abutment. The existence of horizontal constraint of wall toe can limit the deformation of abutment, while reducing the reinforcement spacing and way of geogrid around pile with rigid casing can enhance the stiffness and integrity of the reinforced soil, reduce the horizontal displacement of the wall face and improve the working performance of the mixed reinforced soil abutment. The research results have reference value for the engineering design of mixed reinforced soil abutment.

In order to explore the interaction mechanism between soil and structure, indoor direct shear tests under three median sizes of particles d₅₀ (1.21，4.56，8.91 mm), three joint roughness coefficients (0.4, 9.5, 16.7) and three shear rates (1, 5, 10 mm/min) were designed. The stress changes and volume variables in the shear process were monitored, and the effects of roughness on the shear characteristics of sand-concrete interface with different particle sizes under different shear rates were studied. The results show that, when the median size of particle is 1.21 mm, the shear strength of sand-concrete interface first increases and then decreases with the increase of JRC. When the median size is 8.91 mm, the interfacial shear strength increases with the increase of JRC. The internal friction angle of sand-concrete interface increased with the increase of JRC. With the increase of particle size, the internal friction angle of sand-concrete interface first decreases and then increases. At different shear rates, the final dilatancy increased with the increase of particle size. When the shear rate was 5 min/mm, the final shear expansion of sand-concrete interface was the smallest. The shear strength of sand-concrete interface increased with the increase of JRC after reaching a critical particle size.

The selection of tamping parameters can be the vital procedure for economic efficiency and ground reinforcement effect of dynamic compaction treatment. At present, stop-tamping criterion and parameters adjustment mostly depended on in-situ test result of dynamic compaction. In this study, a one-dimensional stress wave propagation model with non-radial plane emission was developed; the distribution of wavefront stress along soil depth under single tamping was derived; the mechanism of three independent energy-consuming factors, including compression deformation of foundation soil, lateral diffusion of shear wave and soil damping, were revealed; and classification standard for ground reinforcement depth (GRD) was proposed based on the rule of stress attenuation, which was then used to characterize stress wave propagation and energy dissipation process. Research results indicate that GRD can be notably increased as static ground pressure increase from 40.8 kPa to 122.3 kPa, while excessive increase of drop height and tamper radius has limited influence on GRD under equivalent static ground pressure conditions. Parameters combination of dynamic compaction characterized by heavier-tamper and lower-drop height, can be more beneficial to stress wave propagation deeper. Time-history curves of stress wave show various characteristics at different depths, including shock reinforcement, vibration compaction and elastic vibration. The shock reinforcement depth can be estimated by using the result of ground area enveloped by 5% volumetric strain isogram. The theoretical solution under single tamping is modified by using arbitrary Lagrange-Euler method-based simulation results, then calculation procedure of GRD under continuous tamping can be derived. Therefore, dynamic compaction parameters can be optimized through comparison with in-situ test results so as to improve construction efficiency and economy.

The aim of this article is to validate the predictive effectiveness of Sun's proposed coupled hydraulic-mechanical intrinsic model for unsaturated soils with respect to the density state. The loess in the eastern suburbs of Xi’an City, Shaanxi Province was selected as the research object. The isotropic compression test, triaxial compression test and triaxial tensile test were carried out on unsaturated loess samples. The model prediction results were compared with the experimental results, which confirmed the validity of the model proposed by Sun to predict the stress-strain and water-holding behavior of unsaturated loess. The experimental results show that the loading-collapsing (LC) yield curves obtained by Sun model and BBM model were compared, and it was found that the prediction results of Sun model were closer to the experimental data points. The loess samples with different initial void ratios were subjected to isotropic compression tests and humidified, and Sun model could better predict the collapsible deformation trend of loess. Comparing the prediction results of the model with the results of triaxial compression test and triaxial compression test of unsaturated loess, it was confirmed that the model could better predict the stress-strain behavior of unsaturated loess, and depict the change of saturation degree.

Bucket foundation has promising application prospects in offshore engineering. The calculation of penetration resistance is essential to such foundation installation feasibility analysis. The relationship between the calculation methods of penetration resistance of bucket foundation based on soil strength index and cone penetration resistance is established through theoretical derivation. For clay, the side wall penetration resistance coefficient can be determined by the ratio of cohesion factor to resistance coefficient of cone tip; and the tip penetration resistance coefficient can be determined by the ratio of strip foundation bearing capacity coefficient to resistance coefficient of cone tip. For sand, the side wall penetration resistance coefficient is in proportion to the lateral pressure coefficient and interface friction coefficient, and in inverse proportion to the foundation shape factor and surcharge bearing capacity factor; and the tip penetration resistance coefficient is the reciprocal of the foundation shape factor. The theoretical values of penetration resistance coefficient determined by the geological conditions of the North Sea are close to the empirical values, which provides a theoretical basis for the penetration resistance coefficient. According to the geological conditions of seabed in China, the penetration resistance coefficient is also studied.

In order to investigate the bolting effects of prestressed bolt on coal-rock combinations (CR), four sets of uniaxial compression tests were carried out on CR containing prestressed bolt (CRPB) and bolt (CRB) at different interface inclination angles (15°, 30°, 45° and 60°), and the mechanical responses of the CRPB and CRB were analyzed from failure mode, stress-strain curve and acoustic emission (AE) characteristics. The results show that the ratios of residual stress to peak stress for the CRPB are higher. Additionally, the application of prestress increases the energy release before the peak stress, and effectively inhibits the energy release after the peak. Moreover, the prestress also reduces the damage of the contact surface between the combination and the bolt when the sliding failure occurs, and weakens the stress fluctuation. The proportions of low-frequency and high-amplitude (LF-HA) AE signals of the CRPB and the CRB both increase first and then decrease with the application of load. However, the prestress inhibits the concentration of LF-HA AE signals when the slide occurs at interface between coal and rock. Moreover, under different interface inclination angles, the proportion of LF-HA AE signals of the CRPB and the corresponding standard deviation are lower, indicating that the prestressed bolt effectively inhibits the initiation of microcracks before the peak of the combination and reduces the sensitivity of the microcracks evolution to the variation of interface inclination angle.

The boundary dry density (including the maximum and the minimum dry density) is an important parameter affecting the mechanical properties of sand. When the method for determination of dry density in the Chinese specification is applied to the coral sand from the island reefs, the particle breakage of coral sand cannot be ignored during the procedure of measuring dry density, which will introduce great errors to the results. In this paper, the specifications of China, the United States and Japan were adopted to conduct a comparative study of methods for determining the boundary dry density of coral sand. Furthermore, the results of ISO standard sand were compared, thereby proposing a recommended method which was suitable for determining the boundary dry density of coral sand. The results demonstrate that the results of the minimum dry density determined by the three specifications mentioned above are ρ^jis_dmin＜ ρ^GB_dmin＜ ρ^ASTM_dmin  for coral sand and standard sand with different particle sizes; and the maximum dry density results determined are ρ^JIS_dmax＜ρ^GB_dmax ≈ρ^ASTM_dmax . The dry density difference (Δρ_d) between coral sand and standard sand measured by the three specifications varies dramatically with the particle size. With the increase of moisture content, the maximum and the minimum dry densities of coral sand both present the trend of ρ^JIS_d＜ρ^GB_d ＜ ρ^ASTM_d ; and the difference in dry density between different specifications increases with increasing moisture content, and remains stable subsequently. The Chinese specification for particle breakage in the dry density determination process is much larger than the American specification and the Japanese specification. In summary, the determination method of dry density adopted by the American specification has the advantages of clear definition of sand sample state, simple operation, wide range of particle size, ideal dry density results, less particle breakage and small discreteness of dry density results, thus it is a suitable method for the determination of dry density of coral sand.

Aiming at the insufficiency of hard rock stress relaxation characteristics and rock burst research, we carried out cyclic loading and unloading tests on stress relaxation process of straight-wall-top-arch roadways (tunnels) under low, medium and high loads, derived the stress relaxation law, established the stress relaxation model, and explored the stress relaxation mechanism. The test results show that the stress relaxation process of the straight-wall-top-arch roadways (tunnels) subjected to cyclic loading and unloading under a low load presents three evolution stages: rapid decay, gradual decay and stability, and the stress relaxation trends are consistent;, the time required for stress relaxation increases, and the degree of stress attenuation loss decreases as the number of cycles increases; the stress relaxation process under low load is a process of simultaneous attenuation of tensile and compressive stresses in the surrounding rock of roadway(tunnel), with no internal damage and no overall rupture. Under a medium load, the stress relaxation process of straight-wall-top-arch roadway (tunnel) subjected to cyclic loading and unloading also presents three evolutionary stages similar to those under the low load; compared with low load scenario, the stress relaxation process lasts longer under the medium load and internal damage occurs, but subsequent cycles do not lead to surrounding rock failure. Under a high load, the surrounding rock of the straight-wall-top-arch roadway (tunnel) presents a continuous increase in tensile stress and a continuous decrease in compressive stress, the roadway (tunnel) continues to damage and rupture, and the side walls produce stratified burst, eventually forming a V-shaped burst crater, overall, two significant burst failures can be observed. The fractional-order calculus theory is used to describe the stress relaxation process under cyclic loading and unloading. A fractional-order model, namely the stress relaxation equation, is established, and the fitting effect is basically basically satisfactory. Furthermore, we define the degree of stress relaxation that fully can depict the whole process of stress relaxation and the degree of relaxation. Based on the findings of this paper, engineering measures should be taken to stop the deformation of the relaxation process of the rock explosion rock mass from developing to a critical state in engineering practice.

Obtaining the 3D profile of the rock joint in the field is crucial for slope stability evaluation. Constrained by the high usage costs, cumbersome operational procedures, and stringent requirements for measurement subjects, precision equipment such as 3D laser scanners are difficult to widely apply to engineering sites. The paper proposes a method to obtain the 3D roughness of rock joint based on the profile measurement. The shear characteristics of rock joint are assessed using Tatone's peak shear model. The goal is to determine a suitable profile interval for reconstructing the rock joint, ensuring that the relative error of the peak shear strength between the reconstructed and original rock joint is less than 5%. Then, two-dimensional profile measurement of the rock joint is obtained by using a mechanical hand proflograph. The coordinate data for each profile measurement is extracted by considering the relationship between the size of the image digitization matrix and the actual length. The existing data is subjected to spatial interpolation using the Griddata function to generate a reconstructed three-dimensional rock joint, facilitating the study of relevant roughness. According to both the theoretical analysis and the direct shear test, the relative error of the peak shear strength of the two rock joint is less than 5%, which meets the requirements of engineering applications. The study shows that the method can accurately obtain the three-dimensional roughness of the rock joint and has the advantages of simple operation, low cost and low influence by the measurement environment, which provides a reference for related rock joint roughness analysis and shear strength research.

In order to investigate the effect of anchor spacing on the interaction between full-length bonded anchor rods, an approximate solution of stress distribution in the anchorage section of double anchor rods based on the Mindlin solution was derived. By combining with the single and double anchor static load pullout model tests, the effect of changing anchor spacing on the stress distribution, ultimate bearing capacity and final damage pattern of double anchor rods were obtained. The results show that the decrease in spacing makes the axial stress and lateral friction resistance of the anchor rods uniform. The axial stress increases with the decrease in spacing, and the middle of the anchorage section has the largest increase. When the anchor system enters the damage phase, the depth of the rock damage around the anchor system increases with decreasing spacing, and the area of the damage cone increases and changes from inverted cone damage of a single anchor to compound damage mode. When the spacing is too small, the increase in the number of anchor rods is very limited for improving the bearing capacity. In order to exert the joint effect of anchoring, the spacing of anchor rods should be not less than 10 D (D is the diameter of the anchor rod), and the spacing should be larger in soft rock.

The construction of reservoirs by "gully land consolidation" leads to soil salinization, and the permeability of saline soil is an important factor affecting engineering design and construction safety. Therefore, it is important to clarify the remolded loess permeability under different salt content and type conditions. In this study, a series of indoor variable head permeability tests was carried out to investigate the variation of permeability coefficient of remolded loess with salt content by preparing sodium and calcium salt remolded loess specimens with different salt contents. The results indicated that with the increase of salt content, the saturation permeability coefficient of remolded loess gradually decreases, and the two are negatively correlated. Moreover, the permeability coefficient of salt-containing remolded loess decreased to varying degrees compared with that of remolded loess without salt. Under the same salt content, the permeability coefficient of calcium-salt loess was smaller than that of sodium-salt loess. The variation of pore water fugacity and pore structure with salt content and type within the specimen was tested using nuclear magnetic resonance (NMR) techniques. When the salt content was below 2%, the permeability of remolded loess decreased rapidly with the increase of salt content, due to the changes in pore water occurrence state and pore structure. However, when the salt content exceeded 2%, the permeability of the remolded loess increased with the change of pore water occurrence state, while the permeability of the remolded loess decreased with the change of pore structure, and the change of pore structure had a dominant influence on the permeability, thus the permeability coefficient of the remolded loess decreased slowly. Furthermore, under identical salt content, the changes in the pore water occurrence status and pore structure of the calcium salt remolded loess were more significant than those in the sodium salt remolded loess.

Because of changes in pore structure, the permeability coefficient of soil with different dry densities varies. In the same site, the pore structures of soil at different positions are quite different. In order to obtain the permeability coefficient of soil at different positions, it is necessary to do the falling head permeability test on soil samples from different positions, which is a time-consuming process. Therefore, it is crucial to propose a model for quickly estimating the permeability coefficient of soil with different pore structures. In this paper, a capillary model for rapid prediction of the permeability coefficient of soil using T₂ distribution is developed based on the advantages of nuclear magnetic resonance (NMR) in quickly determining pore size distribution. With the permeability coefficient of a certain dry density soil and the T₂ distribution curves of different dry density soils, the model is able to estimate the permeability coefficient of soil under any dry density condition. The research results show that the capillary model is highly efficient for estimating the permeability coefficient of soil at different dry densities since it does not need to calculate the transverse surface relaxation strength ρ₂; The probability of each T₂ time value is the same as that of the corresponding pore volumetric probability, and the permeability coefficient can be calculated directly by substituting the T₂ time into the capillary model. The predicted results of the model are basically consistent with the measured values, indicating that the method is fast, reliable and unaffected by human behaviors.

The soft clay with low strength is widely distributed in the offshore area of China, the evaluation of its engineering properties will directly affect the design and safe operation of wind turbine foundation. Piezocone penetration test is the most widely used in-situ test method in offshore geotechnical investigation, which has less disturbance on soil. The disadvantage is that soil parameters can only be obtained through interpretation, which are site specific. Based on an offshore wind power project in Jiaxing offshore area of Hangzhou Bay, Zhejiang province, this paper carried out laboratory tests, in-situ piezocone penetration test. The range of calibrated CPTU cone factor Nkt for muddy silty clay in Hangzhou Bay offshore area is from 14.15 to 30.18, with a total average value of 20.25. The calibration results show that the cone factor N_kt is negatively correlated with pore pressure ratio B_q, but positively correlated with water content w, void ratioe, liquid limit w_L, plastic limit wp and plasticity indexI_p. And a multiple regression formula between N_kt and pore pressure ratio Bq, plasticity index I_p are obtained. By applying the N_kt correlations into the wind farm at Pinghu offshore area near this project, the results show that the correlations between water content w, void ratio e and cone factor N_kt and multiple regression formula between N_kt and pore pressure ratio B_q, plasticity index I_p have better interpretion quality on the strength of soft clay in Hangzhou Bay offshore area. The established correlations are not only suitable for the muddy silty clay, but also for the muddy clay and silty clay, which have good site applicability.

In soft soil area, the uplift of foundation pit bottom drives the lattice column to deform upward, which generates additional bending moment for concrete support. However, the secondary stress caused by the vertical deformation of lattice column is often not considered in the design of foundation pit at present, and there are few studies on this kind of problem, lacking the understanding of the deformation mechanism of lattice column and its influence. To clarify the deformation mechanism of lattice column is helpful to improve the understanding of the deformation of foundation pit in spatial supporting system, and to provide a theoretical basis for the deformation control of lattice column in design and construction. Combined with the monitoring data of deep foundation pit of open tunnel in Wenyi West Road, Hangzhou, and by changing model variables such as soil layer distribution, pit bottom reinforcement range, supporting structure depth, column pile depth and pile diameter, the influence mechanism and law of field monitoring and model variables on lattice column deformation were analyzed. The results show that: 1) The distribution of soil layer has a significant influence on the lattice column. The weaker the soil layer of foundation pit bottom is, the greater the influence on the lattice column deformation is. 2) The deformation of lattice column can be effectively reduced by increasing the depth and diameter of column. 3) Pit bottom reinforcement can reduce the deformation of lattice column, but there is a critical depth of reinforcement. 4) The depth of ground wall has a certain constraint effect on the upward uplift of lattice column, but the effect is not obvious.

Climatic characteristics of rainfall, transpiration, evaporation and temperature were summarized and analyzed in arid and semi-arid areas in the past 50 years. A full-scale extreme rainfall test of capillary barrier cover was carried out in a landfill in Northwest China to verify the impermeability with extreme rainfall accidents. Long-term anti-seepage performance of the cover was analyzed. The high-risk meteorological conditions of anti-seepage in arid and semi-arid areas were identified and screened. The meteorological mechanism of high-risk permeable meteorological period causing percolation was revealed. Results show that: (1) The precipitation in arid and semi-arid climate area of Northwest China is more from April to November, and less from December to April of the next year, with dry winter and wet summer. It is beneficial to the storage and release of water. (2) The threshold value of extreme accidental continuous heavy precipitation in the northwest non humid area is 56.1–118.5 mm. The cumulative rainfall of field cover extreme rainfall test is 194.85 mm, and the soil layer storage is 148.22 mm. With the condition of extreme accidental continuous heavy rainfall in this area, the capillary barrier cover can meet the anti-seepage standard. (3) In the arid and semi-arid climate region, August to November is the high-risk meteorological period for capillary barrier cover, followed by November to December. The possibility of percolation is the lowest from January to July. In the anti-seepage design of soil cover and the management of landfill, August to November can be regarded as a key meteorological period for verification and control.

The ground fracturing of slope in front of the tunnel face, whose horizontal distance exceeds 5 times of the tunnel section size from the tunnel face, has become an urgent issue. To address this issue, the ground fracturing of slope in front of heading face of Yangda tunnel in Guangxi caused by the tunnel excavation was studied by means of geological exploration and slope monitoring as a project example, and the following simulation model of the finite difference software FLAC^3D based on ubiquitous-joint model was suggested to simulate the ground fracturing. The response of the slope caused by tunnel excavation considering the influence of dominant joints was calculated with the finite difference software FLAC^3D based on ubiquitous-joint model and the inverse technique, and the distribution characteristics of plastic zone was laid special stress on. The results from geological exploration showed that the dip direction of the dominant joint J1 was almost the same as the slip direction of main sliding body. The results from slope monitoring showed that the maximum buried depth of main sliding body was from 15 m to 18 m and the slope sliding area after slope reinforcement was given. The results from numerical simulation showed that the maximum buried depth of main sliding body was close to that from slope monitoring results, the 63 m linear length between the two ends of the top fracture of the slope was close to that of the actual fracture, and the distance from one of the ends of the top fracture to one of the heading faces, 99 m, was close to the actual distance 90 m. The results indicate that the suggested simulation model is feasible and available and it can be referred for similar engineering.

The interlayer cracking and collapse of the roof rock mass is one of the main diseases that cause the structural instability of the roof of flat-top caves in sandstone caves. Investigation on the flat roof caves in Northern Grottoes shows that lithology, tensile strength between rock layers, thickness of stripped body, opening width and connectivity rate between stripped body and bedrock are the main factors affecting the stability of cracking body. In order to effectively improve the safety reserve of the flat roof and enhance the overall stability of the roof, according to on-site investigation and quantitative calculation and analysis, the roof cracked rock mass is divided into four levels: low risk, medium risk, high risk and extremely high risk. According to the force characteristics and deformation failure mode, the roof cracked rock mass is simplified into two main failure modes: “cantilever fracture failure” and “falling failure”. Through the on-site grouting bonding test of the North Grottoes, it is found that the area coverage of the filling slurry is generally from 40% to 60%, and the bonding and reinforcement of the cracked rock with a thickness of no more than 11.4 cm can achieve ideal results. Considering of 8 degree for earthquake fortification intensity, the effective bonding thickness is not more than 10.89 cm.

Considering the two-dimensional seepage effect of chamber of earth pressure balance shield, the spewing problem of earth pressure balance shield is analyzed by using an analytical method. The seepage field of chamber is divided into two regions, and the water head of the chamber is obtained in the form of an explicit hierarchical solution by using the method of separation variables and combining the conditions of continuity between regions. The flow in the screw conveyor is regarded as one-dimensional seepage, and the analytical solution of the seepage field of the shield is obtained based on the water flow and head continuity conditions at the intersection of the chamber and the screw conveyor. The analytical solutions of the seepage field of the chamber and the screw conveyor are compared with the numerical software calculation results and test results respectively, and the results are in good agreement to verify the correctness of the solution. Analyzing the impact of shield and soil parameters on the screw conveyor discharge water flow and water pressure, it is found that a water pressure difference of 0 between the inside and outside of the soil discharge port of the screw conveyor, there is an approximately linear relationship between the screw conveyor water flow and water pressure and water head at cutter surface center; increasing the length of the screw conveyor and inclination angle, and reducing the diameter of the screw conveyor are conducive to prevent spewing. Based on the existing research results of the spewing, a typical shield spewing discriminant map is given. Through discriminating the shield spewing example, and comparing it with the spewing discrimination results of one-dimensional analytical solution of the shield, it is proved that discrimination based on this analytical solution is more accurate.

The lithology of the strata in the Three Gorges Reservoir area is complex, and there is significant difference in the occurrence environment of the rock mass. There are many factors that affect the quality of the rock mass. Under the periodic hydraulic action, the clastic rock bank slope rock mass has formed a unique structural feature, which is unfavorable to the long-term safety and stability of the bank slope. Based on the survey and statistics of the characteristics of clastic rocks in the reservoir area, a large number of in-situ borehole tests were carried out, the typical borehole imaging characteristics of clastic rock of bank slope in the reservoir area were classified and summarized, and the block size and fracture characteristics of borehole cores of rock masses with different fracture characteristics were analyzed in detail. Based on the corresponding relationship between core fracture characteristics and borehole imaging fracture characteristics, the rock mass quality evaluation index RQ is established, and its applicability is verified by comparing with the traditional RQD and acoustic testing results. The research results show that the borehole imaging characteristics affecting the rock mass quality of the clastic rock reservoir bank in the Three Gorges reservoir area mainly include four structural types: sedimentary layered structure, soft filling structure, primary fracture zone and borehole axial fracture cutting. RQ takes into account the different structural types to divide the length zones of blocks, and quantifies the contribution of rock mass ratio in different regions to the rock mass quality evaluation value. Based on the internal structural characteristics of rock mass, the rock mass quality of clastic rock bank slope can be evaluated more objectively, avoiding the error introduced by mechanical damage during drilling and coring. The research results are helpful to analyze the quality distribution characteristics of clastic rock bank slope rock mass in the Three Gorges Reservoir area, and provide a theoretical method and technical idea for quantitative description of rock mass quality evolution.

Landslide with stepwise deformation often occurs under water level fluctuations in reservoir areas. Its displacement curve is multi-step, with intermittent, sudden, (quasi) periodic characteristics. This study selects a typical reservoir landslide case with the stepwise feature. Based on years of on-site monitoring, the feature of stepwise deformation is revealed. A theory of stick-slip is introduced to reasonably explain the mechanism of stepwise deformation. Secondly, considering the limitations of existing methods in the early warning for this landslide type, a new method of threshold definition and warning is developed based on machine learning. The results show that the seepage effect controls the process of stick-slip of the sliding zone soils. It is the likely mechanism of stepwise deformation of the landslide. Moreover, based on artificial neural network (ANN) and C5.0 algorithms, a two-dimensional threshold scheme for water level factor is defined, and the inverse proportional relationship between water level and rate of water level change is founded. The accuracy rate of early warning reaches 86.7%. This case study provides references for the introduction of the concept of stick-slip into landslide mechanism studies and machine learning techniques into threshold definition.

The research on the failure criterion for the strength reduction method (SRM) is a hot issue in the field of slope stability analysis. Three types of commonly used failure criteria, namely, the marked displacement mutation criterion, the plastic zone penetration criterion and the calculation program nonconvergence criterion are considered in correspondence with three types of energy catastrophe criteria, namely, the energy catastrophe criterion for gravity potential loss, the catastrophe criterion of dissipated energy increment and the catastrophe criterion of kinetic energy increment, respectively. To unify the three types of energy catastrophe criteria, a new failure criterion-variational value criterion for the SRM was proposed based on the principle of minimum potential energy. The calculation formulas of the second-order variational value of the total potential energy of a numerical model were derived. A method for applying variation was found. A variational value calculation procedure was written. Then, the process of judging the stability or instability of the model based on the positive or negative of the variational value was given. The unity of the variational value criterion and the three types of energy catastrophe criteria was verified through a typical slope example. The generality of the unity of the variational value criterion and the three types of energy catastrophe criteria was discussed by changing the typical parameters of the numerical model, such as mesh density, slope angle and slope height. It is shown that the results calculated by the variational value criterion are close to those calculated by the three types of energy catastrophe criteria, with the relative error of less than 5%. The variational value criterion unifies the three types of energy catastrophe criteria, and provides a mechanical explanation for the unity of the three types of energy catastrophe criteria.

Based on the theory of porous medium and continuum mechanics, the dispersion equation of Rayleigh waves in unsaturated soils are established using the mass balance equations, the momentum balance equations and the effective stress principle. The influence of the saturation on wave velocity, displacement response and energy flow distribution are studied by numerical examples. The results show that the characteristics of Rayleigh waves mainly reflects the characteristics of compressed P₁ wave and shear wave, and its velocity, displacement and energy distribution are significantly affected by degree of saturation. The propagation velocity and attenuation of Rayleigh wave are dispersive, and the increase of the saturation in the unsaturated soil will cause a significant decrease of the displacement amplitude, as well as the shear wave component in the Rayleigh waves energy will increase with increasing the saturation.

The interface of primary coal-rock combination is heterogeneous and contains a lot of complex microstructure. In order to solve the complex physical field caused by heterogeneous coal-rock interface transparently, industrial CT was used to scan the specimens of primary coal-rock combination. The three-dimensional model of primary coal-rock mass interface was reconstructed, and the fractal dimension of heterogeneous coal-rock interface was calculated. Based on this, a numerical simulation model of primary coal and rock mass was established, and the stress and damage characteristics of primary coal-rock combination under uniaxial compression were simulated and analyzed. The reliability of the numerical simulation law was verified by the uniaxial compression test results of coal-rock combination. The results show that: the interface of primary coal-rock combination has complex microstructure and fractal characteristics, and the fractal dimension can reflect the macroscopic morphology of interface. Under uniaxial compression, the vertical stress in the primary coal-rock combination exhibits non-uniform distribution. The presence of coal-rock interface induces horizontal compressive stress in the coal body and horizontal tensile stress in the rock, and the horizontal stress near the coal-rock interface presents an arch distribution. The damage of the primary coal-rock combination mainly occurs in the coal, and the damage of the coal body first occurs in the coal far away from the interface and gradually expands to the interface. The higher the fractal dimension of the interface is, the smaller the axial compression is when the initial damage occurs. Due to the existence of compressive stress arch at the coal-rock interface, the strength of the coal-rock combination is higher than that of the coal mass, and the coal mass after failure is arched. The expected research results are of significance for the prevention and control of coal and rock.

The existing methods are mainly expressed in equation form for evaluating the soil liquefaction, among which the equation of liquefaction probability evaluation method is particularly complicated and conservative. However, for the liquefaction microzoning of large-area and multi-points, objective and simple methods are needed. Therefor an optimized Logistic liquefaction probability equation and the corresponding tabular liquefaction probability evaluation method were developed. According to the published results of shear wave velocity liquefaction field in-site tests, the liquefaction probabilities of samples were calculated as the basis for grading the liquefaction possibility, and three precision liquefaction probability criteria tables were constructed by decision tree method. Then the data set constructed by Kayen et al. was used as the judgment data set. The differences between the optimized equation and Kayen’s liquefaction probability equation were compared to meet the purpose of measuring the reasonableness of the optimized equation and criteria tables. The results show that the influence of misjudgment by the optimized equation on actual engineering is less than Kayen’s equation. All the three criteria tables can properly isolate more than 70% of the sites, and the evaluation of liquefied site and non-liquefied site are both well considered. The criteria tables simplify the evaluation process of liquefaction probability, improve the applicability of shear wave velocity liquefaction probability evaluation method, and realize the purpose of evaluating liquefaction probability without calculation. The tabular method will provide support for liquefaction microzoning based on shear wave velocity.

Aiming at the anisotropic characteristics of frozen soil, this paper established a modified linear bond contact model that can reflect the anisotropic characteristics of frozen soil based on the linear bond contact model, and generated a discrete element constitutive subroutine (DLL) for particle flow program (PFC^3D) calls through C++. Firstly, tensile and shear stimulations were carried out on a single contact. By comparing numerical and theoretical results, the calculation accuracy of the modified linear bond contact model for frozen soil considering orthotropic was verified. In addition, the triaxial compression tests of frozen soil at different temperatures were simulated and compared with the stress-strain curves obtained from the tests. The results show that the proposed modified linear bond contact model has good applicability to frozen soil. Based on the calibrated meso-parameters of the model, a series of triaxial compression discrete element numerical simulations was carried out. Using the simulation results, the influences of the inclination of the virtual weak surface on the stress-strain curve characteristics, strength and shear strength indexes of frozen soil were discussed, and the evolution laws of effective coordination number and meso-fabric quantity were analyzed. The research results can provide a basis for using numerical methods to study the orthotropic macro meso-mechanical properties of frozen soil.

Natural foundation usually contains irregular interfaces between the soil layers. Therefore, this paper proposes a thin layer method to calculate the three-dimensional (3D) dynamic response of stratified soils with irregular interfaces. Based on the double Fourier transform, the system of equations in terms of thin layer elements for the elastic medium are obtained in the frequency-wavenumber domain. The stiffness matrices of the semi-infinite thin-layer elements and the finite-length thin-layer elements are derived through the modal superposition principle. The perfectly matched layers (PMLs) are subsequently introduced to simulate the wave propagation in the bottom half-space. By using the semi-infinite and the finite-length thin-layer elements as well as the PMLs, a calculation model is finally developed to obtain the 3D fundamental solution for a harmonic point load acting on a layered half-space with irregular interfaces. The accuracy of the proposed method is verified by comparing with the existing methods. Finally, the dynamic responses induced by a harmonic load acting on a two-layer foundation with an inclined interface are investigated. The results show that the inclination of the inclined interface exhibits a significant influence on the dynamic response. The difference in the vibration level increases as the inclination and the load frequency increase. The irregular interface needs to be considered in the evaluation of dynamic response of natural foundation.

When determining the parameters of stone column composite foundation, the simplified method of superposition of gravel and undisturbed soil parameters according to the proportion of plane area is often used in engineering, but the application conditions are seldom focused on. Based on the soft foundation treatment project for the deep overburden layer of the high earth-rockfill dam of the Nyabarongo II Hydropower Station in Rwanda, the triaxial consolidated-drained test numerical simulation of composite soft clay samples with gravel core under different area replacement rates was carried out using the PLAXIS finite element platform, and the rationalization of the numerical simulation scheme was verified by laboratory triaxial tests. The pile-soil interaction mechanism of stone column improved soft soil composite foundation was analyzed and the calculation parameters of hardening soil model were obtained. These parameters were applied to analyze the deformations of the dam foundation, compared with the traditional parameter- superposition method and the stone-column-wall method. The study shows that the parameters determined by the numerical composite sample method are reasonable and the error is negligible to analyze the settlement of the composite foundation of the earth-rock dam. However, the traditional parameter-superposition method underestimates the settlement of composite foundation, and it is only suitable for the conditions of low stress level and high area replacement rate, and will also overestimate the strength parameters of the stone column improved soft soil composite foundation. The two-dimensional finite element analysis of dam foundation deformation using the parameters of numerical composite sample method shows that it is feasible to adopt different replacement rates of stone columns to reinforce the foundation according to the different heights of the dam.

A vibration response calculation model of elastic layered pavement under the falling weight deflectometer (FWD) load considering the unsaturated characteristics of the subgrade is established to provide the theoretical basis for accurately identifying subgrade performance deterioration by using FWD. The dynamic governing equations of the model are derived and solved by Laplace-Hankel transformation, and the dynamic stiffness matrices of the pavement and unsaturated subgrade are established. The global dynamic stiffness matrix of the highway structure is synthesized from the interlayer continuity condition, and the vibration response solution of the entire highway structure in the transform domain under the FWD load is derived by combining the boundary conditions. The Laplace-Hankel inverse transform is utilized to obtain the numerical solution of the vibration response in the space-time domain. The effects of FWD load frequency and subgrade saturation on the vibration response and the correlation between subgrade performance deterioration and pavement surface vibration signals under FWD load are analyzed. It is found that the vertical dynamic displacement of the pavement surface is mainly influenced by the low frequency component of FWD load and increases with the increase of saturation. The vertical dynamic displacement of the pavement surface is more sensitive to subgrade performance deterioration than the vibration velocity of the pavement surface and the vertical dynamic stress of the subgrade surface. Moreover, the change rate of vertical dynamic displacement of the pavement surface at 1.2 m from the load center reaches the maximum. The results of the study can provide a scientific basis for selecting feedback indicators and locations of subgrade performance deterioration.

A new type of electronically controlled borehole shear test apparatus was developed to aim at the shortcomings of traditional     borehole shear apparatus, such as difficulty in controlling the shear rate, large test error, and the value of test parameters relying on experience. The structure, testing principles and methods of the new apparatus were expounded. To test the stability of the new apparatus, the new apparatus was applied to the landslide site and compared with the test results of the traditional shearing apparatus. Some results are obtained as follows. The normal stress of the first stage can be equal to or slightly greater than the initial normal stress σ₀. The relationship between normal stress increment Ds and plastic stress σ_f , the initial normal stress σ₀ is (σ₀–σ_f) / Δ_s =4.0-4.5, which can guide the value of Δ_s. When the normal displacement vs. time curve tends to be the horizontal and the normal displacement rate tends to be 0, the consolidation is stable, and the soil consolidation time can be determined accordingly. According to the curves of shear stress vs. shear displacement, the stress state of the soil can be judged intuitively, thereby guiding the exerting of shear force. Compared with the traditional borehole shear test apparatus, the new instrument can obtain more reliable strength index values, while the cohesion value c measured by the traditional apparatus is very small or even negative. At the depth of 4.5 m, the numerical simulation of the shear plate being pressed into the soil and the shear process shows that the soil can be effectively consolidated when the normal stress is in the linear deformation stage of the normal displacement curve; the soil near the shear plate is dislocated, forming a strip-shaped plastic failure zone, and gradually developing into a plastic failure zone through an upper and lower when shear failure occurs.

 In response to the difficulties in driving piles into mudstone foundation, insufficient bearing capacity, and the difficulty in preparing a model foundation due to the disturbance of soft rock, a simulation pile driving and static load test device based on undisturbed soft rock was preliminarily developed. The device mainly includes undisturbed soft rock constraint model box unit, hammer-driven unit, guide rail support unit and static load unit. Calibration tests and application tests were carried out to verify the feasibility and stability of the device. The penetration and bearing characteristics of driven pile were analyzed, the mechanical characteristics of mudstone around pile caused by pile driving damage were defined, and further research prospect and engineering application suggestions were put forward. The study shows that: 1) The results of tests are consistent with that of field test, and the penetration characteristics and bearing characteristics are both the same as those of field test, which verifies the feasibility of the test device. 2) The stability of the load transfer factor α further proves that the load transfer of the test device is stable and reliable. 3) As mudstone has intensive soft and hard interbedding, as a result, there is a significant difference in penetration resistance represented by the number of blows per 10 mm of penetration, and the static load failure of low strength soft interlayers presents a precipitously increasing settlement. 4) The mudstone within 2d (d is the pile diameter) around the pile is damaged by pile driving; for every 0.5d interval, the strength loss is 66.0%, 40.5%, 17.0%, 7.0% and the elastic modulus loss is 80.5%, 54.5%, 26.5%, 11.0%, respectively.  5) The reduced values of the undisturbed mechanical parameters should be selected according to the damage characteristics induced by pile driving in the design and bearing capacity evaluation of mudstone. The test device has the advantages of stability, reliability and controllability, which can provide support for related research on pile driving in mudstone.