Suffusion will occur in the internally unstable sandy soil because of the groundwater seepage. Soil failure caused by the suffusion has adverse effects on the building structures or foundations. In this paper, a model that can calculate the force acted on fine particles in seepage field was established by considering the effective stress of soil and the stress reduction of fine particles. According to the equilibrium state of ultimate stress, the formula for calculating the startup critical hydraulic gradient of fine particles migration in sandy soil during the suffusion process was obtained. A DEM-CFD coupled method and the existing experimental data were used to validate the proposed model. The results showed that the fine particles in the sandy soil started in rolling mode in the beginning, and the startup critical hydraulic gradient is found to be affected by the seepage flow, soil characteristics, and the properties of the particles. The startup critical hydraulic gradient of fine particles on the surface of sandy soil was found greatly affected by the buried depth. The difference between the highest and lowest startup critical hydraulic gradient of the fine particles buried in 1 cm depth was 10.169%, and the difference was reduced to 1.061% when the buried depth was 10 cm. The maximum standard error of the calculation method was 6.038% while compared to the numerical simulation results, the maximum standard error compared to the seepage test results was 11.211%. Therefore, the proposed model can accurately predict the startup critical hydraulic gradient of sandy soil fine particles.

This study focuses on tunneling under challenging conditions, particularly with regard to the stress distribution and deformation in the humidity stress field. The swelling phenomenon during tunneling has been treated as a coupled humidity–mechanics process, where the humidity diffusion and stress dilatancy are considered together to obtain stress and deformation fields for tunnels crossing the formations with high swelling potential. A solution to the nonstationary process of humidity transfer has been derived according to Fick’s second law. The swelling pressure has been included in the form of body force, and a non-associated flow rule has been adopted to obtain the analytical solutions. Next, considering the examples of rock tunnels that are excavated in two different quality rock mass, we have investigated the impact factors on stress and deformation in swelling surrounding rock. Numerical results show that the inclusion of the swelling stress increases the plastic zone of the surrounding rock and the maximum stress at the elastic-plastic boundary, whereas the stress convergence has been decreased. After a certain increase in swelling pressure, a tensile stress zone appears in the plastic circle. The deformation of surrounding rock caused by swelling pressure can be much more significant than that caused by in-situ stress. Furthermore, the effect of dilatancy on the deformation rock cannot be negligible especially when the support resistance is small. This paper presents a new possible workflow to quickly evaluate the elastic-plastic stress and deformation of tunnels in swelling surrounding rock.

The discrete element numerical method has been usually used for some parameter sensitivity analysis of geo-materials in the compression test and the Brazilian splitting test. However, there have been limited studies systematically focusing on mesoscopic influencing factors and 3D fracture process in mode I fracture toughness tests. The 2D discrete element methods cannot reflect the real mechanical behavior of a 3D model. Therefore, a three-dimensional flat joint model (FJM3D) is used in this paper to investigate the effects of microstructure parameters and bond mesoscopic parameters on mode I fracture toughness tests with different notch shapes. The microstructure parameters include the square root of average particle radius ( ), model resolution ( ), and maximum/minimum particle diameter ( ). Bond meso-parameters include average coordination number (CN), slit element fraction ( ), bond tensile strength ( ), bond cohesion ( ), friction coefficient ( ) and friction angle ( ). Results of parameter sensitivity analysis show that the mode I fracture toughness ( ) is positively correlated with , CN, and , and negatively correlated with and . There are no obvious linear relationships between and , , , . In addition, suitable ranges of and are recommended to obtain an appropriate mode I fracture toughness with a low level of variation. Based on the results of parameter sensitivity analysis, the mechanical behaviors of the Kowloon granite with notched semi-circular bend (SCB) and cracked chevron notched semi-circular bend (CCNSCB) specimens are calibrated. The failure process of mode I fracture toughness tests with different notch shapes indicates that the pre-peak and post-peak behaviors of the SCB test is more consistent with the laboratory test.

Clay contains a variety of clay minerals. The charged surface of clay particles makes the clay particles show active hydraulic properties, which can lead to the formation of a double layer on the surface of the soil. So clay particles are stacked on each other under various forces during the deposition process to form non-connected pore structures such as isolated pores and blind pores. As a result, when seepage occurs in the soil, the fluid only flows through the interconnected pores, but not through the unconnected pores. Unfortunately, the Kozeny-Carman equation (K-C equation) uses the total specific surface area of the particles as seepage specific surface, therefore, the K-C equation is not suitable for calculating the hydraulic conductivity of clay any more. In this paper, only the pore specific surface area of the interconnected pores in which the fluid can flow through is taken as the seepage effective specific surface area. And then, the seepage effective specific surface area is used to modify the original K-C equation. Test results show that the modified K-C equation has obvious advantages over the original K-C equation in describing the seepage law of clay.

Due to the complexity of fracture distribution in engineering rock mass, the physical modeling of fracture network is one of the key problems in rock mechanics experiments. In this study, a 3D printing method of fracture network model based on water-soluble materials with polyactic acid materials as supporting base is proposed. Based on the water solubility of printing material, a method for preparing rock-like model specimens containing fracture network is established. Through digital image correlation (DIC) method, the deformation and fracturing characteristics of rock-like model specimens during loading process are quantitatively studied, and the influence law of filling material is further analyzed. The experimental results show that 3D printing technology is capable to prepare complex fracture network model with satisfied repeatability of mechanical properties. The stress-strain curve of fracture network rock-like model presents several evident stress reductions before its peak strength, whereas the plastic strain softening is encountered after peak strength. DIC technology can capture the global strain field of fracture network rock-like model during the whole loading process. Moreover, the progressive evolution of strain localization is observed in the process of deformation and fracturing, which reflects the law of crack initiation, propagation and coalescence. The mechanical parameters and strain field distributions of model specimens are influenced by different filling conditions. The advantage of the proposed method is reflected by the fact that the filling material can be filled into the fractures in accordance with the actual engineering condition.

In order to consider the influence of the displacement effect of the retaining wall on the seismic earth pressure, according to the conclusions of previous experimental research, the friction angle is expressed as a function related to the displacement and the position height of retaining wall. Then based on the pseudo-dynamic method and the horizontal layer analysis method, the calculation expressions of the seismic non-limit active earth pressure and resultant force point of the wall in the RT mode are derived. The calculation model can describe different non-limit displacement state conditions in which the friction angle gradually develops along the wall height. And the relationship between the displacement of the retaining wall, the seismic load, and the earth pressure is established. The parameter analysis discusses the effects of vibration time, the displacement state of retaining wall, the seismic acceleration parameters and the soil friction angle on the seismic active earth pressure distribution, the resultant force and the height of the resultant action point. Compared with the traditional limit state seismic earth pressure theory, the proposed method describes the development process of seismic earth pressure with retaining wall displacement more reasonably. It has certain reference significance for the development of non-limit earth pressure theory and the improvement of seismic calculation methods in slope engineering.

The soil freezing characteristic curve (SFCC) is a mathematical description on the relationship between the unfrozen water content and the freezing temperature in frozen soil. It is an important basis for the research of hydrothermal migration, frost heaving and constitutive relations of frozen soil. The empirical expressions of SFCC are widely used in the literature, while the investigation on its physical understanding is relatively rare. By considering the adsorption and capillary interaction between the soil particles and the ice interface, a new SFCC model for saturated frozen soil is proposed from the pore scale based on the equilibrium pressure of ice water phase transition composed of adsorptive and capillary pressure. The calculation results of the model show that the unfrozen water content will decrease continuously at the same temperature, and the SFCC will become steeper as the particle radius is gradually increased. The SFCC of monodisperse silica microspheres was tested based on a nuclear magnetic resonance equipment. The experimental results were compared with the mathematical model, which showed that the proposed SFCC model is in good agreement with the experimental results. The new SFCC model manifests a clear physical meaning and provides a theoretical basis to reveal the mechanism of frozen soil.

In the analysis of consolidation of naturally saturated soft clay with strong structure, the influence of sedimentation on self-weight stress, the nonlinear variation of compressibility and permeability were considered. The one-dimensional large strain consolidation equations under arbitrary loading conditions were derived and solved by a semi-analytical method. Then the solutions were degraded into solutions of a non-structured saturated soft clay consolidation theory. By comparing the degraded semi-analytical solutions with the existing large strain consolidation solutions, the solutions of the one-dimensional large strain consolidation equations were proved to be right. At last, the consolidation behaviours of semi-analytical solutions were compared with the theoretical solutions of small strain consolidation theory and the the theoretical solution of the consolidation theory without considering the structure. The comparison results show that the settlement at any time of large strain consolidation theory is greater than that of the small strain consolidation theory, and the difference between the two increases with the increase of the load. When considering the structure of the soft soil, the settlement of large strain consolidation is smaller than the calculated value without considering the soil structure.

This paper aims to investigate the evolution law of soil cracks in the rainfall-evaporation process. Based on a full-scale slope model test, the surface moisture content of soil was measured, and the crack ratio was extracted by image vectorization technology. The critical water content during the repeated cracking process was studied by dividing the cracked soil into soil matrix and crack domains, respectively. The critical cracking matric suction and water content of the soil matrix domain were deduced and calculated according to the horizontal strain increment constitutive model of unsaturated soil. The results show that the soil cracking during the rainfall-evaporation process has repeatable characteristics, and the crack rate generally increases with the increase of rainfall-evaporation times; the cracking water content in the crack domains increases with the increase of rainfall-evaporation cycles, while the matrix domain has the opposite result. The matrix suction can both inhibit or promote the generation and propagation of the cracks. In the soil matrix domain, the cracking water content range calculated based on the constitutive model of the homogeneous isotropic unsaturated soil strain increment is close to the measured value, and the model can explain the variation law of cracking water content in soil matrix and crack domains.

Dry density has an important influence on strength properties of coarse granular material, especially in three-dimensional stress state. In this study, the effects of dry density on strength properties of coarse granular material were investigated using large-scale true triaxial tests under equal intermediate principal stress coefficient (b=0.25) loading condition with equal minimum principle stress and large-scale triaxial tests at different dry densities. The results show that the stress-strain curve of large-scale true triaxial test presents basically of climbing shape which is higher and steeper than that of large-scale triaxial test and shows strong hardening behavior. The strength of coarse granular material increases linearly with the increase of initial dry density or minimum principal stress. The strength of large-scale true triaxial test increases by 20%–97% compared with that of large-scale triaxial test, and the smaller the minimum principal stress, the greater the strength increase. If the cohesion of coarse granular material is 0, the internal friction angle increases linearly with the increase of initial dry density and decreases with the increase of minimum principal stress. The failure stress ratio linearly increases with the increase of initial dry density and decreases linearly with the increase of minimum principal stress. The failure stress ratio of large-scale true triaxial test is smaller than that of large-scale triaxial test.

Weakly cemented soft rock show significant creep characteristics under water rich condition, which seriously affect the safety of mining and slope engineering. A series of multi-stage loading creep tests was carried out by using GDS HPTAS creep triaxial apparatus to investigate the creep behavior of the weakly cemented soft rock with different moisture contents. Creep deformation, creep rate and failure mode were analyzed. Thus, the long-term strength and its variation were determined according to the inflection point of the creep rate vs. stress curves of the weakly cemented soft rock with different moisture contents. Based on the test results and fractional calculus theory, a new four-element fractional-order creep model was proposed by using Abel clay pot instead of Kelvin clay pot element, and the plastic element was applied instead of the elastic element, the three-stage creep behavior of weakly cemented soft rock was described. The Trust-Region method was adopted to determine the model parameters of the four-element fractional-order creep model. The relationship between the model parameters, moisture content and loading stress was analyzed by the multivariate nonlinear regression method. The effect of moisture content and loading conditions on the creep behavior of the weakly cemented soft rock was also discussed. From the perspective of comparative analysis, the numerical results calculated by the four-element fractional-order creep model are in good agreement with the test data, the proposed model can accurately simulate the whole creep behavior of weakly cemented soft rock.

In order to further understand the mechanism to cause shock hazard of coal-gas outburst gas-solid two-phase flow and the propagation law of the two-phase flow, a self-developed large-scale multi-field coupling coal mine dynamic disaster simulation testing system is used to study the impact force and movement characteristics of the outburst gas-solid two-phase flow under different gas pressure conditions. The results show that during the process of outburst coal-gas two-phase flow, the peak impact force at the front end of the roadway fluctuates within a small range from 20 kPa to 50 kPa, and the impact force has no obvious linear relationship with the gas pressure. The peak impact force sharply increases in the range from 3 944 mm to 4 944 mm in the roadway. After 4 944 mm, the peak impact force shows a trend of oscillating attenuation along the roadway, and its average attenuation coefficient gradually decreases with the increase of gas pressure. The flow patterns of the outburst two-phase flow can be divided into suspended flow, stratified flow, dune flow and slug flow, and the higher the coal seam gas pressure is, the more obvious each flow pattern is reflected. The process of pulverized coal flow movement can be divided into three stages: initial acceleration, medium-term attenuation and late secondary acceleration. The gas pressure mainly affects the migration rate of pulverized coal flow and the migration distance into the second acceleration stage. The higher the gas pressure, the faster the migration rate of pulverized coal flow, and the shorter distance to reach the second acceleration stage.

The formation mechanism and evolution of force chain in the granular media system of fault fracture zone are important foundations for studying the occurrence of geological disasters such as creep, stick-slip and earthquake. By photo-elastic test device of particles under biaxial loading and bilateral flowing conditions, the macro-mechanical characteristics, the network structure and evolution, the spatial distribution and strength of force chain in the fracture zone are studied under shear. The results show that in fault fracture zone, the interaction between particles of rock mass is transmitted through the force chain. There are easy sliding section and non-easy sliding section between the fracture zone and the fault-induced fracture zone, which reveals the non-uniform characteristics of spatial deformation of the fracture zone under shear. The rearrangement of rock particles in the fracture zone results in the dynamic evolution of easy sliding sections and non-easy sliding sections. The larger-sized breccia particles in the fracture zone carry the main compression and friction between the upper and lower plates of the fault, which plays the role of “skeleton support”. With the increase of shear force, the direction of the strong force chain is deflected in the vertical direction. Rock particles near the middle of the fracture zone are more likely to be destroyed, fractured and rearranged when the fault is in a high stress state, which results in the change of spatial orientation of strong force chain. With the increase of vertical load, the spatial orientation of strong force chain changes from obvious anisotropy to uniform isotropy. The change of vertical load has little effect on the force chain ratio and the distribution of particle contact force frequency in fault fracture zone, but has great influence on the spatial distribution and strength of the force chain.

The freezing method is an important construction method for crossing water-rich soft rock formations. The long-term stability of the frozen wall plays an important role in engineering safety. Creep damage is one of the remarkable features of induced deformation of frozen walls. It is of great theoretical and engineering significance to study the characteristics of frozen rock creep. Taking the cretaceous saturated frozen sandstone as the research object, triaxial creep mechanical tests with different confining pressures (0, 2, 4 and 6 MPa) were carried out under the low temperature freezing condition of –10℃. The creep deformation of saturated frozen sandstone was analyzed. According to the existing viscoelastic-plastic model, the parameter identification was carried out and the variation law of creep parameters was studied. A creep constitutive model considering temperature and damage effect was then proposed. The results show that the low temperature freezing weakens the mutual cementation force between the particles during the creep process, and the creep characteristics are obvious. However, the confining pressure inhibits the development of the internal damage of the saturated frozen sandstone to some extent, resulting in the steady creep rate. The increase in confining pressure shows a significant downward trend. With the increase of confining pressure, the creep failure morphology of saturated frozen sandstone shows a change process from shear failure to tensile failure to local shape hardening failure. On the basis of the viscoelastic model, the creep parameters , and are increased first and then decreased with the increase of the load, and the inflection point is the yield stress. The parameter appears after the yield stress and undergoes increase to decrease. Combined with the frozen rock creep data, the parameters of the stress and low temperature coupled creep constitutive model are identified, and the numerical results of the model are compared with the creep experimental data to verify the correctness and rationality of the established nonlinear model.

In order to explore the critical state characteristic of high soluble salt loess in Ili area, a series of triaxial consolidation shear tests controlling suction and net confining pressure is performed on the unsaturated undisturbed Ili loess with different soluble salt contents. The results show that the strength of the unsaturated undisturbed Ili loess has a peak value with the increase of soluble salt content under the consolidation shear of constant suction. The q-p or e-p critical state lines are parallel lines of unsaturated soil with a certain soluble salt content under different suctions. The q-p' critical state lines under different suctions can be normalized as a straight line represented by the saturated critical state line, and the slope of the straight line decreases as a power function with the increase of soluble salt content. The slope ( ) of e-p critical state line of unsaturated soil is larger than the counterpart ( ) of saturated soil, both first decrease and then increase with the increase of soluble salt content. Under the same effective net mean stress, the ratio of critical state void ratio ( ) between unsaturated soil and saturated soil and gas saturation (1– ) can be normalized. The initial and subsequent yield curves in the q-p plane can be approximately assumed to be ellipses that symmetrical to the line. The hardening effect produced by suction and stress on the yield curve is isotropic.

Because of long-term cyclic loads resulting from waves and ships, additional stress and deformation are inevitably induced in existing piles. Centrifugal model tests are conducted in this study to investigate deformation mechanisms of single piles and pile group embedded in saturated clay due to lateral cyclic loading. It is found that the horizontal cyclic loading-unloading induces plastic deformation of the soil around the pile, which in turn leads to unrecoverable horizontal displacement and bending deformation of the pile. As the cyclic loading increases, the maximum pile head horizontal displacement and residual pile head horizontal displacements increase as well, but the residual pile head horizontal displacement is much smaller than maximum pile head horizontal displacement. For single piles and a pile group, ratios of the residual lateral displacements to the maximum lateral displacements range from 0.17–0.22 and 0.30–0.84, respectively. The residual bending strains are also much smaller than the maximum bending strains. For single piles and a pile group, ratios of the residual to the maximum bending strains induced in the piles vary from 0.13 to 0.50 and 0.23 to 0.82, respectively. The maximum and residual bending strains induced in the front piles are up to 3.2 and 3.1 times as large as those in the rear piles. Thus, protection measures should be used for the front piles to ensure long-term serviceability of pile foundations.

The physicochemical interactions between different phases of the soil have an important impact on the geotechnical engineering related to environment and energy. The principle of effective stress is always the most important and effective theory to solve the relevant problems. However, the change of inter-particle stress caused by physicochemical effects cannot be accurately described by current effective stress equation. In response to the above problems, a mean intergranular stress expression that uniformly describe capillary, adsorption and osmosis effects between soil particles has recently been proposed. The purpose of this research is to realize the quantitative calculation of the mean intergranular stress and verify its stability and effectiveness. Firstly, the physical meaning of each part in the expression of mean intergranular stress is analyzed. Through analyzing the parameter in the expression, the variation rule of each part of mean intergranular stress with the water content and the concentration of pore water are obtained. Then, the formula characterizing the solid-liquid interface interaction for the surface force potential is derived, which can be used for the quantitative calculation of the mean intergranular stress equation. Finally, the mean intergranular stress of unsaturated soil in the critical state is calculated, and applied to simulate the coupled chemical-mechanical loading test of unsaturated soil. The calculated results show that there is a unique relationship between mean intergranular stress and shear strength in the critical state, and the chemical-mechanical calculation results give good agreement with the experimental results, verifying the stability and effectiveness of the mean intergranular stress.

A systematic process for obtaining the proportion of the rock-like material with properties of deformation and brittleness similar to the prototype sandstone using orthogonal test has been proposed. The indexes of and have been introduced to quantitatively represent the properties of deformation and brittleness, respectively. The rock-like material is composed with cement and microsilica as the binder material and quartz sand as the aggregate. First, orthogonal tests have been performed, and the various indexes of and with different levels of water-binder, sand-binder and microsilica-cement ratio have been divided by statistical data of natural sandstone. Second, range analysis has been applied to describe the trend of the two indexes with different levels of these three factors. Third, multivariate polynomial equations have been used to obtain the proper proportion of the rock-like material with properties of deformation and brittleness similar to the prototype sandstone. The specimens with the determined proportion are found to be within the allowable error margin compared with the prototype sandstone, and properties of deformation and brittleness of the proposed rock-like material are consistent with the sandstone. Therefore, the newly proposed rock-like material can substitute rock blocks in the following laboratory test.

Granite residual soil is widely distributed in southern China, and it has many poor physical and mechanical properties. Slopes of this type of soil are prone to deformation and failure under the action of rainfall. Therefore, it is of great significance to study the rainfall infiltration mechanism in granite residual soil slopes. On the basis of Green-Ampt model, the initial moisture content, underground water level and unsaturated characteristics of the soil are comprehensively considered. An infiltration model suitable for different rainfall conditions is established, and verified by comparison between numerical simulations and other models. Then, the proposed model is used to analyze granite residual soil slopes under three typical rainfall conditions. The results show that the initial water content has little effect on the migration rate of the wetting front when it is far from groundwater level, whereas the migration rate increases gradually when the wetting front is near groundwater level, presenting an exponential trend. In the same rainfall time, under the condition that the rainfall intensity is slightly greater than the saturated permeability coefficient of soil, the wetting front migration depth is the largest and the slope stability factor decreases the most.

Slaking of mudstone in acid rain area is significantly stronger than that in non-acid rain area, and the slaking mechanism needs to be studied. Based on the formation and development characteristics of hydro-chemical coupled damage under acid rain, this paper took a landslide at Panzhihua city airport as an example, which is in a typical acid rain area. Silty mudstone rock samples located in the sliding zone were selected and processed. After that, a series of slaking experiments was comparatively carried out under different pH conditions. In order to explore the micro-mechanism of acid rain-aggravated slaking behavior of silty mudstone, we adopted a series of analytical methods, including analyzing cation composition changes in different pH slaking fluids, observing micro-structure change of samples before and after acid rain treatment as well as analyzing slaking failure modes of silty mudstone. Finally, an index named specific surface area increment index was introduced to reflect the impacts of acid rain-induced chemical damage on slaking behavior of silty mudstone. The results highlight that: the acid rain-induced chemical damage in silty mudstone was mainly caused by the dissolution of specific minerals, which provided extra paths for the slaking of silty mudstone. With the decrease of pH value of slaking fluid, the acid rain-induced chemical damage of silty mudstone increased, the slaking paths increased, the slaking failure mode changed, and the slaking residues were broken into finer fragments. The specific surface area increment index could well capture the fragmentation degree of slaking residuals. The more breaking the slaking residuals, the higher the specific surface area increment index, and the greater the slaking degree of silty mudstone. Conclusions of this paper provide theoretical reference for the evaluation of geotechnical engineering properties and reinforcement design in acid rain areas.

Dynamic response of saturated porous medium is of great significance in many engineering fields. The consideration of varying porosity helps to reasonably reveal the related mechanical behavior of saturated porous medium such as soil. Dynamic porosity model is combined with u-U-p equation representing the dynamic characteristic of saturated porous medium. And a new nonlinear dynamic model is established. Comsol Multiphysics PDE is used to obtain its numerical solution. On this basis, the change of porosity, deformation and pore water pressure of two-dimension saturated soil are developed under two different kinds of permeable conditions and excited by harmonic load on the surface. The result shows that the porosity relates directly to the volumetric strain and pore water pressure of soil. The loading process decreases soil porosity, and enhances the interaction between solid skeleton and pore fluid increases, therefore increases the resistance applied on solid skeleton. The dimensionless vertical displacement and pore water pressure are also low under constant porosity condition. It is useful to increase the research rationality of mechanical behavior of saturated porous medium such as soil if the dynamic porosity is considered. On the other hand, pore fluid can discharge freely from permeable top surface. So, the load that is born by soil skeleton is greater, the porosity, deformation and pore water pressure are also greater comparing with the condition under impermeable top surface .

The fractal dimension is determined based on the slope of the double logarithmic curve using synchrotron radiation small angle X-ray scattering (SAXS) and liquid nitrogen adsorption for sodium-based bentonite in Gaomiaozi, Inner Mongolia, as a backfill material for nuclear waste buffering. Based on the FHH (Frenkel-Halsey-Hill) model, the fractal dimension of liquid nitrogen adsorption was calculated. The calculation of bentonite expansion deformation and the required parameters are summarized. Based on the electric double layer model and fractal model of bentonite expansion deformation, the K value of the expansion force parameter of bentonite was calculated by SAXS fractal dimension and liquid nitrogen adsorption fractal dimension. The difference of the calculated expansion force of the fractal dimension measured by the two methods was compared. The results show that the fractal dimensions measured by SAXS and liquid nitrogen adsorption are close, which are 2.600 and 2.636 respectively, and the difference between the two is small. There is a good linear relationship between scattering intensity and scattering vector in the double logarithmic relationship. In the correlation between void ratio and expansion force, the predicted values obtained by the two methods are smaller than the experimental measured values. Under the same bentonite density, the fractal dimension is calculated by SAXS. The predicted value of the expansion strain is greater than the value predicted by the fractal dimension from the liquid nitrogen adsorption test.

Based on the on-site monitoring data of deformation and electromagnetic radiation of Zhongyi Railway Tunnel of Lijiang-Shangrila, a statistical analysis was done on the characteristics of electromagnetic radiation, the relationship between the events of maximum peaks of EME intensity (N) and horizontal convergence deformation, and the relationship between the events of maximum peaks of EME intensity exceeding the average intensity (M) and horizontal convergence deformation during the deformation of the tunnel. The results show that: 1) The maximum average value of electromagnetic radiation intensity (E) increased with deformation expanding before the initial support yielded, while there was an opposite trend after the initial support yield failure. The turning time point of rising first and then falling of the maximum average value of electromagnetic radiation intensity was close to the initial support yielding. 2) The events fluctuation rate of maximum peaks of EME intensity ( ) and maximum peaks of EME intensity exceeding the average intensity ( ) were positively correlated with convergence deformation rate of the tunnel. There were positively linear relationships between the percentage of events of the maximum peaks of EME intensity ( ), the maximum peaks of EME intensity exceeding the average intensity ( ) and the cumulative deformation of the tunnel as well. Research conclusions are important in the perspective of advancing the understanding of electromagnetic radiation characteristics during the deformation process of underground cavern and enhancing the field application level of monitoring technology of electromagnetic radiation.

The dynamic cone penetration test (DCPT) has been widely used in predicting the relative compaction of the foundation soils. However, the current formulas might not be suitable for the calcareous sand soils. To address the problem, a series of in situ and model DCPT were conducted to obtain the relationship between the light dynamic penetration index and relative compaction for the calcareous sand soils. The results show that the effect of particle size on the penetration of calcareous sand is more significant than that of the quartz sand soils. Under the similar relative compaction, the penetration of calcareous sand soils is smaller than that of the quartz sand soils with similar gradation. For engineering applications, a method which could transform the penetration index between the different kinds of DCPT is proposed according to the improved Butterfield's dimensional analysis theory. Then the light dynamic penetration index is transformed to the heavy dynamic penetration index using this method, so that a relationship between the heavy dynamic penetration index and relative compaction of the calcareous sand soils is obtained. Finally, the relationship was verified based on the results of the field heavy dynamic penetration test.

The dynamic characteristics of subgrade is aggravated under the interaction of immersed infiltration and dynamic loads of trains, which affects the safety of train operation and long-term stability. Based on the engineering background of cement-stabilized expansive soil subgrade of Hao-Ji heavy-haul railway(Haolebaoji-Ji'an), field excitation tests of subgrade with four million cycles were carried out under dry and immersed conditions to investigate the dynamic characteristics. Large-scale excitation equipment, combined with dead weights, were used to simulate the dynamic behavior of heavy-haul trains with 25-30 t axle load. The test results show that the variations of dynamic stress and acceleration along the depth of subgrade are consistent, and decay rate is 80% at the base of subgrade. The influence of immersed infiltration and dynamic load of train is more significant at the interface of between the subgrade bottom and fill. Under the same loading conditions, the dynamic stress at the interface under the immersed condition is 28% larger than for the dry condition. The acceleration is much less sensitive to the immersed environment than the dynamic stress. At the same time, the dynamic stress level along subgrade depth is much lower than the critical dynamic stress of fill in the same location. The cumulative deformation of subgrade surface under cyclic loading of 4 million times is less than 5 mm and remains stable, which indicates that the improved expansive soil with 3%-5% cement content can be used as the subgrade bottom and fill to meet the dynamic stability requirements of subgrade. The research results can provide theoretical reference for high-quality construction and aintenance of expansive soil roadbed improved by heavy-haul railway.

Based on the static load test data of 716 test piles collected from 139 projects, the practical calculation method of bearing capacity and settlement of large-diameter post-grouted piles was studied. The improvement coefficients of the side friction and base resistance of soil layer were given primarily based on statistics analysis, and the practical calculation approach for the bearing capacity of large-diameter post-grouted piles applicable to different grouting types was presented. The reliability of the proposed approach was verified by a large number of measured data. Moreover, the influence coefficient of post-grouting settlement was introduced based on the settlement calculation method of large-diameter pile foundation without grouting. Based on the statistical analysis, the recommended range of influence coefficient of post-grouting settlement was given, and an empirical estimation method for calculating settlement of large-diameter post-grouted piles suitable for different soil layers was proposed. Finally, the applicability of the proposed method was verified using engineering examples. The research results have been incorporated into the industry standard of the People's Republic of China Code for design of ground base and foundation of highway bridges and culverts (JTJ 3363－2019) and the industry standard of national project construction Technical specification for post-grouting of cast-in-place pile of highway bridges (T/CECS G: D67-01－2018), which can promote the wide application of post-grouting technique.

According to the soft soil engineering cases in Shanghai, several vibration field measurements of the vertical acceleration of tunnels and buildings is carried out to evaluate the damping effect of urban subway transit. Then, the combined finite element method and the infinite element method are adopted to investigate the variation of structural vibration induced by urban subway transit with the floor level. Comparing the numerical results and the field measurement, it can be concluded that: 1) The vibration level in tunnel decreases by 16 dB and the vibration level in the floor decreases by 10.9-21.1 dB after the damping, which indicates that the damping effect is obvious; 2) The vibration level in the floor decreases and then increases as the floor increases; 3) The vibration level of the floor calculated by the proposed numerical model shows a better consistency with the measurement result, which shows the proposed analysis method is reasonable and feasible, and it provides an effective way for predicting the vibration level of buildings around the subway.

In this paper, a new method is proposed to calculate the optimal anchorage direction angle for wedge sliding in rock slope. Taking the maximum anti-sliding increment provided by the unit length of the free segment of anchor cable as the target control variable, the characteristic parameters of slope surface and two sliding surfaces and the anchor cable design parameters are adopted as the optimization control independent variables, the pre-tensile force of the anchor cable is decomposed through the linear equations system established through coordinate system transformation. Then a new three-dimensional optimization calculation equation for the anchorage direction angle is obtained. Based on the equation, for case of the anchor cable reinforcement direction is perpendicular to the strike direction of the slope, derivative method is used to optimize the anchorage direction angle. And when the anchor cable reinforcement direction has no restrictions, the fmincon function offered by Matlab is adopted to optimize the anchorage direction angle. Finally, through the comparation of calculation results and engineering measurement, the validity and advancement of the proposed calculation method of the optimal anchorage direction angle are proved. The proposed method can further improve the anchoring effects and reduce the total usage of the anchor cables and the the slope supporting costs.

In order to more realistically describe the explicit relation between the displacement of the reservoir bank accumulation layer landslide and its influencing factors, and overcome the shortcomings of the existing superimposed component response model which is difficult to construct the displacement regression function, a new decomposition mode—fluctuation ratio is defined, while the displacement increment is expressed as the product of the fluctuation ratio and the trend item increment. Wangyemiao landslide, a typical accumulation landslide in the Three Gorges Reservoir area, is investigated as an example. The lowpass FFT filtering method is used to obtain the trend term displacement component. The monthly rainfall, the monthly reservoir water level and the previous month's fluctuation ratio are determined as the core factor combination. The K-means algorithm is used to establish the correlation function between each single factor and the fluctuation ratio. Then a multi-factor generalized model composed of the evoked factor term and the control term is proposed. Compared with the actual monitoring displacement and the values predicted by several other methods, our model has better prediction effect and simple operation; furthermore, the displacement components can be clearly explained. Four other typical landslides in the Three Gorges Reservoir area are selected for comprehensive comparative study, the results further verify its rationality. This method can accurately reflect the comprehensive response of landslide displacement with time lapse, multi-factor influence and state constraint, which provides a new idea for studying the evolution mechanism and time-space prediction of this type of landslide.

Based on Newmark principle, a 3D seismic displacement method of stepped slopes reinforced with piles is proposed. Firstly, based on the limit analysis, the explicit expression for the yield acceleration parameter of stepped slopes reinforced with piles is derived through the horn failure mechanism. Then the influence of different factors on is investigated through parameter analysis. The results show that multi-step slopes are safer than single-step slopes. In addition, the formula of angular velocity is derived by means of the principle of moment balance, and the angular displacement within the time of earthquake action is obtained through the quadratic integral of the angular velocity. Combined with the engineering practice, the influence of earthquake on the 3D seismic stability of stepped slopes reinforced with piles is investigated, and the corresponding engineering suggestions are also given. Finally, the sensibilities of the factors influencing on the stability of slope are analyzed, and the reference is provided for the seismic design of 3D stepped slopes reinforced with piles.

Basin-shaped freezing technology is applied to form a water-proof structure, which consists of two parts: the frozen curtain (basin wall) around the excavation zone and the horizontal frozen body (basin bottom) at the bottom of the excavation zone. In this paper, physical model test and numerical simulation were used to study temperature field expansion of basin-shaped technology under static water and 0.5 m/d seepage condition in water-rich sandy gravel stratum of Beijing. As a new application of freezing method in the field of municipal engineering, basin-shaped freezing technology can effectively play the role of water proofing. Different parts of basin structure show different frozen orders under different seepage conditions. Under the condition of static water, the basin wall is frozen prior to the basin bottom. While under the condition of seepage, the order of the freezing intersection of different positions is basin wall along the seepage, basin bottom, basin wall on the back surface and basin wall on the face surface in sequence, the freezing of basin wall is the key factor to restrict the basin-shaped freezing under this condition, and basin wall should be focused in the actual engineering. Freezing thickness is the most direct index to evaluate freezing effect. The freezing thickness of the basin wall tends to be stable under the condition of static water, and the freezing thickness of the basin bottom gradually exceeds the length of the freezing tube at the basin bottom and develops in both directions of in and outside the basin structure. Under seepage conditions, the freezing curtain of the basin wall with the smallest thickness appears on the front-water surface, while the local thickness of the freezing curtain on the basin wall of the back-water surface increases, and the horizontal freezing plate thickness at the basin bottom is only one-way develops inside of the basin.

Currently, the semi-empirical design method based on the linear elastic analysis assumption is commonly employed, which is incapable of examining the stability of the long pile embedded in complex ground mediums accurately. To this, this research adopts the nonlinear finite element method to establish an efficient pile element model for nonlinear analysis of piles. This approach can be utilized in nonlinear buckling stability analysis without assuming effective length factors. This paper elaborates the basic theory of the pile element. It’s worth noting that, the continuous springs along the element are integrated into the pile element formulations for considering the soil structure interaction (SSI) responses, which can significantly improve the computing efficiency. The element tangent stiffness matrixes are accordingly formulated for predicting displacement, and the secant relations are developed for eliminating accumulative errors in a Newton-Raphson incremental-iterative numerical procedure. The Updated- Lagrangian (UL) approach is developed for simulating large deflections of piles. Finally, several benchmark examples are provided for verifying the accuracy and efficiency of the proposed pile element model in analysis and design of piles with nonlinear surrounding soil.

To investigate the vertical bearing characteristics of expansive concrete piles embedded in coral sand foundation, the vertical static load test of single model pile was carried out in laboratory. The load-settlement curve, axial force and frictional resistance of single expansive concrete pile were analyzed, and compared with the numerical results from PLAXIS 3D software simulation. The effect of the linear expansion rates was discussed. The results show that the load-displacement curves of expansive concrete piles in coral sand show a slow change. During the loading process, the load is mainly borne by the side friction resistance of the pile. The axial force decreases with the increase of the depth, and the side friction resistance of the pile first increases with the depth and then gradually decreases, and gradually plays a role as the load increases. With the increase of expansive agent dosage, the linear expansion of pile shaft increases gradually and the pile-soil interaction becomes more obvious. Adding 25% HCSA expansive agent can increase the ultimate bearing capacity by nearly 20% and the ultimate value of pile side friction by 56%. Increasing the linear expansion rate of the pile can effectively increase the ultimate bearing capacity and side friction resistance of the pile. This study provides a reference for the pile foundation projects in calcareous sand foundation.

Geotechnical engineering informatization urgently needs to strengthen the integration and sharing of big data and multi-disciplinary cooperation. The successful experience of BIM technology in the field of engineering construction enlightens us to apply BIM technology to development of geotechnical engineering informatization. However, the main problem is that the data standards of geological model and BIM model are not unified. In order to solve this problem, we propose the idea of adopting BIM data standard IFC for geological models. This paper established an extended IFC-3DGeoMdl model by using entity extension and attribute set extension schema for 3D geological models. On account of the existing IFC object types, the model derived the corresponding geological-physical elements and geological-spatial structural elements, and yielded spatial expression forms of geological physical elements. In addition, with the use of the existing relationship classes in IFC, the relationships of geological physical elements and spatial structural elements were defined. Further, based on the attribute expression in IFC, the extension of attributes such as stratigraphic information and physical mechanics parameters of geological elements was realized. Finally, the paper gave a concrete implementation process of modelling, and used the actual engineering examples to verify the practical application of the extended model. The result shows that the model can effectively realize the integration of 3D geological model and BIM structural model, so as to provide effective integration and sharing of geological information for structural design and geotechnical engineering construction.

Granular materials are mostly composed of irregularly shaped particles, such as sand, grain and so on. Resistance to the rotation is an inherent characteristic of irregularly shaped particles. Previous studies have shown that the anti-rotation characteristics of particles have a significant effect on their macro-mechanical responses. Therefore, the non-spherical particles or the spherical particles with a contact model considering rolling resistance are widely employed in the mesoscopic numerical simulations of granular materials. In this paper, the combined finite and discrete element method (FDEM) and discrete element method (DEM) are used to simulate the triaxial tests of ellipsoidal particles and spherical particles with rolling resistance, respectively. The limitations of the rolling resistance model capturing particle shape effects are pointed out, and the meso sources of shape influence are revealed from the perspective of particle configuration structure. Peak deviatoric stress and dilatancy both change monotonically with rolling friction coefficient and the degree of deviation from a spherical shape, but the influence of particle shape on them shows obvious convergence. The mesoscopic fabric analysis also shows that although both particle shape and rolling resistance can significantly enhance the fabric anisotropy, but there are significant differences in the fabric anisotropy evolution mode between the two particle systems. The difference of the above results lies in the different influence mechanism of rotation resistance. Rolling friction enhances the stable bearing capacity of particles by limiting the rotation of particles, while non-spherical particles form a stable local arrangement structure through interlocking. Since the middle of ellipsoid particles can transfer greater contact force than the end, the particles rotate during shearing, and the long axis of the particles tends to be orthogonal to the direction of the largest principal stress, presenting a staggered arrangement, which means that particles lock together.

To explore the boundary effect of the strain transmission between embedded optical fiber sensor and tunnel lining, the study was conducted from three aspects: theoretical, experimental studies and field applications. The results were verified in actual engineering. The strain transfer model of optical fiber in the concrete lining was constructed, and the mechanism of optical fiber strain transfer was analyzed. The strain transfer efficiency of optical fiber was then calculated and compared that with the numerical modeling results, which verified the accuracy of the mechanical calculation model. The concrete lining of tunnel was simulated with the reinforced concrete beams and distributed optical fibers were embedded on the surface of the concrete beams. Two groups of tests were carried out in this study. The test beams were loaded in stages and the optical fibers were tested by BOFDA technology. The test results show that the embedded fiber optic sensor has a boundary effect. The two ends of the beam structure are the low efficiency strain transmission area of the optical fibers, which cannot fully transfer the strain of the test beam. The middle part of the test beam is the high efficiency strain transfer area of the optical fibers, which can completely transfer the strain of the test beam. Based on the research results, the engineering application research was carried out. A distributed optical fiber sensor was installed in the tunnel lining in the CRD construction method section of the subway tunnel of the Beijing New Airport Line using the embedded fiber technology. The monitoring results show that the boundary effect has little influence on the monitoring results. The placement method of the distributed embedded optical fiber is feasible. This research can provide a reference for the application of distributed optical fiber technology in underground engineering structure monitoring.