Mechanical properties of soft soil will change under freeze-thaw cycle with a certain confining pressure in artificial freezing engineering in coastal soft soil area. Therefore, it is of a great significance to study the influence of freeze-thaw cycle under different confining pressures on the mechanical properties of soft soil. This paper takes the typical muddy soil in Tianjin coastal area as the research object. Through a self-improved temperature controlled triaxial apparatus, the differences of mechanical properties of soft soil under conventional freeze-thaw without confining pressure and freeze-thaw with confining pressure are compared and analyzed. Furthermore, the effects of freezing temperature, number of freeze-thaw cycles and freezing-thawing confining pressure on excess pore pressure, stress-strain characteristics, strength and deformation index of soft soil are revealed. The influence mechanism of freeze-thaw confining pressure on the mechanical properties is explored by SEM. Then, the relationship of shear strength, reduction coefficient of elastic modulus of muddy soil and above influence factors is established by using an exponential function. The results show that the freezing and thawing confining pressure reduces the size and number of pores in the soil after freezing and thawing, which can weaken the damage of freezing and thawing to the soil structure to a certain extent. However, the freeze-thaw confining pressure has little effect on the stress-strain curve. With the decrease of freezing temperature and the increase of the number of freeze-thaw cycles, the strength and moduli of soil are greatly reduced. With the increase of freezing-thawing confining pressure, the freezing temperature and the decrease of the number of freeze-thaw cycles, the excess pore pressure decreases.

To explore the influence of true triaxial cyclic loading and unloading in principal stress directions on sandstone energy accumulation and dissipation, three cyclic loading and unloading tests in principal stress directions were carried out by using the self-developed true triaxial disturbed unloading rock testing system. Based on the stress-strain evolution law and the loading and unloading characteristics of true triaxial cyclic loading and unloading tests, the types of loading and unloading in the cyclic loading and unloading tests are classified. Through the comparative analysis of the surface cracks of rock mass after cyclic loading and unloading in three principal stress directions, it is found that the minimum principal stress cycle causes the severest damage to rock mass, followed by the intermediate principal stress, and the maximum principal stress causes the least damage. The elastic energy density, dissipated energy density, and input energy density of true triaxial cyclic loading and unloading are calculated by using the graph area integral method and the superposition method, respectively. The evolution laws of the above three densities with the increase of the number of principal stresses and the energy distribution during loading and unloading are analyzed. The rationality and accuracy of the proposed energy analysis method are verified by the true triaxial loading and unloading test, and the elastic energy released by unloading in three principal stress directions is analyzed. The damage caused by cyclic loading and unloading has little influence on the elastic energy stored in the rock mass. The influences of unloading independently in three principal stress directions on sandstone damage and energy dissipation are compared, and the advancing direction of the roadway is further discussed.

To describe the influence of intermediate principal stress on the mechanical behavior of overconsolidated soil, a novel elastic-plastic constitutive model was proposed to produce the characteristics of over consolidation and stress-induced anisotropy of soil. The shape function g（θ）  , which can uniformly describe the four yield criteria of Mohr-Coulomb, Drucker-Prager, Lade-Duncan, and Matsuoka-Nakai, is introduced into the subloading yield surface model to modify the M value so that the M value can change with Lode Angle θ  in the new model. The plastic deviatoric strain increment was selected as the iteration variable. The stress integration algorithm of the new model was achieved by Newton-Raphson iteration, and the UMAT subroutine was written. The new model has been implemented into a large commercial finite element software ABAQUS. The results show that: 1) The new model can simultaneously characterize the over consolidation, dilatancy, and stress-induced anisotropy of soil, and the predicted results are in a good agreement with the experimental data. 2) The physical meaning of the new model is clear and simple, which is convenient for engineering promotion and application; 3) The stress integration algorithm of the new model has a fast convergence speed, fewer iterations per incremental step, high convergence accuracy, and robustness.

In order to explore the difference in dynamic response of gas-bearing coal under impact loading, an observable gas-bearing coal split Hopkinson pressure bar (SHPB) test system was used to conduct uniaxial impact tests on coal bodies with different initial gas pressures. The energy dissipation law of the coal under different gas occurrence states was analyzed, and with the help of ultra-high-speed camera and digital image correlation (DIC) technology, the evolution characteristics of cracks on the surface of gas-bearing coal during the impact process were demonstrated. Combined with fractal theory, the influence of gas pressure on the fractal characteristics of crushed coal was obtained, and the intrinsic relationship between gas occurrence state and the characteristic size of crushed coal was revealed. The results show that under the impact loading, the stress-strain curve of the gas-bearing coal could be roughly divided into four stages based on the energy dissipation law. The deterioration effect of gas on the coal body was significant, and the crushing energy dissipation and crushing energy dissipation density function decreased exponentially with the increase of the initial gas pressure. Under the gas wedge effect, the evolution of the strain field of the gas-bearing coal subjected to the impact loading was more complicated, and the coal body damage gradually evolved from the transverse splitting failure to the composite transverse splitting-longitudinal splitting failure. Under the action of gas pressure, the internal damage of the coal body was intensified. After the failure, the average particle size and fragmented block size of the fragmented coal body gradually decreased with the increase in initial gas pressure. However, the fractal dimension increased exponentially, and the degree of coal body crushing was more intense. A multi-dimensional dynamic gas-bearing coal crushing model based on the conservation of energy consumption in the coal body crushing process was constructed, and combined with experimental data, the model was validated and it could better describe the characteristic dimensions of fragmented coal samples under the influence of gas. The research results have important theoretical significance and certain application prospects for the prevention and control of dynamic disasters in gas-bearing coal mines.

In this study, a novel rock physics model is proposed to simulate the coupling effect of wave-induced ice viscosity and unfrozen water mobility, as well as temperature influences on physical properties in warm and ice-rich frozen soil, by combining the Burgers viscoelastic constitutive relation, the BISQ model, and thermodynamic theory. The analytical expressions of phase velocity and attenuation factor of fast P-waves, slow P-waves, and S-waves in this frozen soil are derived, which extend the description range of conventional elastic models. Through numerical examples, the basic response modes of phase velocities and attenuation factors for these three body waves are simulated and studied in the frequency domain. On this basis, the effects of model parameters such as soil porosity, ice viscosity, and temperature on wave propagation are analyzed and concluded. It is confirmed that the temperature can affect the velocity and attenuation of the fast P-wave on aspects of central frequencies and intensities; the slow P-wave has almost no temperature dependency; and the S-wave attenuation has a clear dependency at low frequencies. Under laboratory conditions, the applicability of new model is well verified by comparing the theory with the measured data of a warm, ice-rich, frozen soil sample.

Fracture of rocks under dynamic loading is very common in rock engineering. To study the crack response of dynamic fracture of mode I cracks under impact loading, the dynamic fracture test of single cleavage triangle (SCT) granite specimens with lateral opening was carried out using a split Hopkinson pressure bar test system. The Hough transform method was used to quantitatively describe the length and angle distribution of the surface crack morphology, and the relationship between crack morphology and the energy absorbed was analyzed. The 3D point cloud data of the section was obtained by using the 3D surface topography instrument, and the section reconstruction method based on the fitting surface threshold detection was proposed, which effectively eliminates the error of the 3D point cloud data of the section. The relationship between section roughness and energy dissipation was discussed. The results show that the exponential distribution of crack length  tends to increase with the increase of absorbed energy; the angles of cracks are evenly distributed, with few cracks appearing in the horizontal direction; when the energy dissipation of the specimen is low, the cracks present obvious directivity, while the cracks bend more violently and the connectivity is better when the energy dissipation is high; the proposed section reconstruction method performs well at 0.03～0.08 of the points in x and y directions, and the threshold value is 0.25. The roughness statistical parameters of specimens A and B sections decrease with the increase of energy dissipation.

The study on the structure and characterization of ancient rammed earth, a special soil formed by artificial selection, tamping and environmental aging in the historical process, is a fundamental problem in the field of rammed earth site protection in the arid area of Northwest China. Fifteen typical sites of rammed earth distributed in three climatic regions and five dynasties were selected as the research objects. Through the basic physical properties test, confined compression test, unconfined uniaxial compression test and structural theoretical analysis, the preliminary research on the structure of rammed earth is carried out. The results show that the particle size distribution, liquidity index, structural yield pressure and the compressive strength of rammed earth at 15 typical sites show regular changes with building age and environment. The compressibility, strength and stress-strain characteristics of undisturbed and remolded rammed earth show larger differences; its structure index and the above-mentioned macroscopic properties index have a good consistency. The water-sensitive potential plays a predominant role in the change of structural potential, the disturbance potential and water-sensitive potential have a significantly linear relationship with the dating of construction and drought index.

To study the shear strength characteristics of unsaturated rubber silt mixtures, a series of direct shear tests was conducted on the rubber silt mixtures with different rubber particle contents and water contents. Based on the particle contact state theory, the meso contact mode of rubber silt mixtures was constructed, and the calculation method of rubber silt mixtures skeleton void ratio based on different rubber content was obtained. The test results show that the shear strength of rubber silt mixtures decreases with the increase of skeleton void ratio at a low water content, while the strength of rubber silt mixtures increases with the increase of skeleton void ratio at a high water content. Based on the soil-water characteristic curve of rubber silt mixtures, the corresponding relationship between matrix suction and water content is obtained. The shear strength of rubber silt mixtures increases with the increase of matrix suction at a low skeleton void ratio, and it exhibits decrease first and then increase with the increase of matrix suction at a high skeleton void ratio. Based on the influence of skeleton void ratio and water content on internal friction angle and cohesion, the shear strength development mechanism of unsaturated rubber silt mixtures was proposed, and the prediction formula of shear strength was established. The research results can provide theoretical support for the actual design and construction of rubber silt mixtures.

The interlayer dislocation zone has the characteristics of large extension scale and poor physico-mechanical properties. After reservoir impoundment, the rise of the water level imposes greater water pressure on the interlayer dislocation zone. Under the action of high water pressure, the shear strength of the interlayer dislocation zone and its evolution law need to be studied. In this paper, the newly developed direct shear test system HMSS-300 is used to conduct the direct shear tests under different hydro-mechanical coupling conditions on the interlayer dislocation zone of Xiluodu Hydropower Station. The characteristics and variation law of shear strength of the interlayer dislocation zone under the hydro-mechanical coupling conditions are discussed. The test results show that under the hydro-mechanical coupling conditions, the shear stress-shear displacement curve of the shear strength of the interlayer dislocation zone has an obvious peak value. The normal displacements mostly show the dilation first and then shrinkage as the shear displacement increases. With the increase in water pressure, both the effective internal friction angle and the effective cohesion of the interlayer dislocation zone decrease in a negative exponential relationship. Under the water pressure of 0−2.0 MPa, the degradation degrees of the effective internal friction angle and the effective cohesion of the interlayer dislocation zone are 7%−22% and 32%−93%, respectively. It indicates that the increase of water pressure has a greater effect on the effective cohesion of the interlayer dislocation zone. Under the coupling action of normal load and water pressure, the interlayer dislocation zone presents a shear-slip failure mode and a mixed shear-slip failure mode of medium and fine breccia particles. Under the hydro-mechanical coupling conditions, the softening and swelling of clay minerals, and water molecular layers formed by the water intrusion into the interlayer dislocation particles and the structural unit layers of clay minerals are the main factors that deteriorate the shear strength of the interlayer dislocation zone.

By means of uniaxial compression test, acoustic emission (AE) monitoring approach and X-ray diffraction technique, we analyzed the mechanical properties of granite at different corrosion times and obtained the variation law of AE characteristic parameters. The causes of internal structure deterioration of granite were analyzed from the perspective of corrosion mechanism, and the energy evolution law and fractal characteristics of fragmentation during the destruction of rock samples were investigated. The test results showed that with the increase of corrosion time, the uniaxial compressive strength and elastic modulus decrease by 25.6% and 38.3%, respectively. The cumulative AE ring count is reduced, and the duration of high-level AE ring count is shortened. The internal structure of the rock sample deteriorates due to the decomposition of mineral components, and the silica suspension delays this deterioration, resulting in a negative correlation between the reduction rate of mechanical parameters and the corrosion time. Before the plastic stage, the growth rate of dissipated energy of corroded rock sample is large, its internal damage has developed rapidly, and the dissipated energy is also at a high level. At the plastic stage, the degree of damage development is lower than that of non-corroded rock sample. The dissipated energy decreases with the increase of corrosion time, but the proportion of dissipated energy increases from 29.1% to 35.0%, and the ductility increases. The peak value and growth rate of total energy and elastic strain energy decrease with the increase of corrosion time, the deterioration degree of internal structure increases, and the energy absorption capacity and energy storage limit of rock samples decrease. The failure mode changes from shear splitting failure to shear failure. The mass proportion of medium and small particle size fragments is reduced from 44.6% to 22.8%, the fractal dimension of fragmentation is reduced by 9.5%, the degree of fragmentation is reduced, and the dissipated energy for fragmentation is also reduced.

Multi-row micro-pile frame structure is an effective means for slope treatment, and its theoretical research lags behind the engineering application. To study the deformation and stress characteristics and reinforcement mechanism of the structure in slope reinforcement, the centrifugal model test of the slope reinforced by multi-row micro-pile frame structure was carried out. The test results show that the deformation and failure mode of the slope in the test is creep-tensile thrust-type, which is divided into three stages: elastic deformation, plastic deformation and deformation stability. Compared with the unreinforced slope, the anti-slide stability of the slope reinforced by multi-row micro-pile frame structure is significantly improved, and the factor of safety for the slope is increased by 156%. The importance of the factors affecting the slope reinforcement effect in the test is the anchorage depth, the number of piles, and the pile spacing. As the forward thrust of landslide, the soil pressure approximately presents a triangle distribution of ‘small in the upper part and large in the lower part’ along the depth direction, acting on the pile-soil composite structure, and the bending moment curves of pile body and frame beam present the reserved ‘S’ and ‘C’ distributions, respectively. The bending moment distribution of frame transverse and longitudinal beams is significantly affected by pile arrangement. The maximum bending moments of frame transverse and longitudinal beams in 4 rows × 4 columns are similar, while the maximum bending moment of longitudinal beams in 4 rows × 3 columns is nearly three times that of transverse beams. The research results can provide theoretical guidance and design basis for the structure in engineering application.

A new mechanism is established and applied to the upper bound analysis of uplift piles in saturated clay. Upper bound solutions of uplift capacities of closed and open-ended piles are analyzed. The new mechanism is verified by comparing with elastoplastic finite-element, existing lower bound and API solutions. Its reliability is assessed through case studies including one centrifuge test and two field tests. The effects of the pile length-diameter ratio, pile surface roughness, non-uniformity of undrained soil strength and length of soil plug on the uplift bearing capacity are considered. A formulation predicting the net bearing capacity of closed-ended uplift piles in clay is proposed. The results show that an approximately linear relationship can be established between the normalized net bearing capacity coefficient and the pile length-diameter ratio for closed-ended piles. As for open-ended pipe piles, the ratio of the net bearing capacity coefficient of open-ended pipe piles to that of closed-end piles tends to increase with the increase of the pile length-diameter ratio. The increase in the length of soil plug leads to an increase in the net bearing capacity coefficient of open-ended pipe piles. Therefore, the effect of soil plug should not be ignored.

When the earth pressure balance shield crosses the high water-level Qiantang River silt layer, the high water pressure difference between the groundwater and the sealing chamber will generate excessive infiltration force toward the excavation surface. The excessive infiltration force will cause large deformation of the soil and thus leading to destabilization of the excavation surface because of the low cohesion of Qiantang River silt, poor self-supporting of the excavation surface and small modulus of the soil. The reasonable selection of soil constitutive relationship and model parameters in numerical simulations are very important for the reliability of numerical results. In order to study the stability of the excavation surface under seepage conditions, the parameters of the Mohr-Coulomb model and its strain-softening model of the Qiantang River silt were investigated based on laboratory tests. It was found that the shear strain of the Qiantang River silt was 1.5 times of the axial strain. According to the triaxial unloading test, the relationship between the strain softening internal friction angle and the shear strain is obtained. The internal friction angle reaches a peak value of 25º when the shear strain is 4.7%; the internal friction angle reaches a residual value of 21º when the shear strain is 7.4%; the internal friction angle decreases linearly when the shear strain is between 4.7% and 7.4%. Then the finite difference method was used to establish 39 groups of three-dimensional analytical models. By comparing with the ultimate support force and surface settlement of the centrifuge test, it was found that under the same water level, the minimum error between the ultimate support pressure calculated by the Mohr-Coulomb strain-softening model and the centrifuge test was 3.1%, and the error of the maximum surface settlement was 5.67%. It proves the feasibility of the Mohr-Coulomb strain-softening model and the reliability of the model parameters in the Qiantang River silt formation.

The constitutive relation of elasto-plastic zone is simulated by Mohr-Coulomb criterion (M-C), and the theoretical solutions of cavity expansion pressure and energy dissipation are derived. Based on the assumption of spherical cavity expansion, combining with energy theory and non-associated flow rule, the process of cavity expansion is regarded as an energy conversion problem, and the large-strain energy dissipation analysis of cohesive-frictional soils is carried out. Firstly, the elastic zone is analyzed by a small-strain theory. Then, considering the effects of elastic deformation and large strain in plastic zone, the relationship among cavity expansion pressure, energy dissipation and radius is obtained. Compared with the published results, the effectiveness of the study is verified. Finally, the effects of elastic deformation and large strain in the plastic zone on cavity expansion pressure and energy dissipation are studied. The results show that the cavity expansion pressure increases with the increase of the dilatancy angle, and most of the work done by the external force is transformed into energy in the plastic zone. The dilatancy angle has a significant effect on the change of the plastic zone and the cavity expansion pressure. With the increase of dilatancy angle, the radius of plastic zone and the cavity expansion pressure increase significantly. The energy dissipation analysis provides a new analytical method and necessary theoretical basis for understanding of the mechanisms of grouting, geotechnical test and driven pile.

Given the problems of post-construction settlement deformation of high liquid limit red clay low embankment in Southern China, the variation laws of vertical and lateral wetting strain of high liquid limit red clay under different confining pressures, ratios of axial pressure to confining pressure and compactness were studied using a self-designed test device which can test the wetting deformation of rock and soil under low stress conditions. A peak prediction model of vertical wetting strain of high liquid limit red clay considering the influence of confining pressure, ratio of axial pressure to confining pressure and compactness is further established, and the prediction model is validated. The primary conclusions are as follows: under the coupling action of seepage and stress, the lateral wetting strain and vertical deformation of high liquid limit red clay first increase and then tend to be stable. When the wetting deformation is stable, the high liquid limit red clay sample shows the characteristics of large upper part and small lower part. The duration of lateral wetting strain, peak value of lateral wetting strain and peak value of vertical deformation of high liquid limit red clay are positively correlated with confining pressure and ratio of axial pressure to confining pressure. The peak value of lateral wetting strain and peak value of vertical deformation of high liquid limit red clay are negatively correlated with the degree of compaction, and the duration of lateral wetting strain is positively correlated with the degree of compaction. The lateral wetting strain of high liquid limit red clay can be divided into two parts: the lateral wetting strain caused by humidification and the one caused by water absorption of expansive minerals. The importance of different factors on the vertical wetting strain peak of high liquid limit red clay is: compactness > ratio of axial pressure to confining pressure > confining pressure. This study has an important engineering significance for the prediction and control of post-construction settlement deformation of low embankment with high liquid limit red clay.

The importance of this study is to explain the fatigue damage mechanism while addressing the effect of fatigue on the fracture toughness (KIC) using the brittle Brazilian specimens and to show for the first time in the literature the behavior of macroscale cracks that open and close in brittle rock without leading to eventual failure. The KIC was reduced by 35% due to the cyclic loading, and the reduction of the indirect Brazilian strength was found to be reduced by 30%. The fatigue cracks were observed to open and close elastically without failure and have been recorded by a camera for hours in brittle rock specimens with sinusoidal loading for the first time in the rock mechanics field in this study. The findings of the scanning electron microscope (SEM) and computed tomography (CT) revealed that the failure of the Brazilian disc and chevron crack notched Brazilian disc (CCNBD) specimens was caused by the formation of the fracture process zone (FPZ), which included many microcracks rather than a single macrocrack propagation during the cyclic loading tests. Moreover, SEM and CT findings indicated the FPZ took place ahead of the kerf crack tip, leading to the visible fatigue crack opening and closing elastically in brittle rock specimens without any rupture. According to the experimental and numerical analysis results, the FPZ_max could be obtained with the 60º inclined notch crack. This demonstrates the maximum FPZ development possible with combined mode I-II (tensile and shear) loading.

In the current code, the determination of the correction coefficient of dynamic penetration needs to consider the influence of the measured number of hammer blow, which is rarely studied in the industry. During a blow, the dynamic penetration drop hammer and the probe rod transfer the mechanical energy through collision. Based on the one-dimensional collision theory, if the coefficient of restitution is not zero, the two will continue to collide under the action of gravity and soil resistance. The calculation method for the rod length correction coefficient under three calculation schemes is derived: only calculating the energy of the probe rod after the first collision, calculating the energy of the drop hammer and probe rod after the first collision, and calculating the finite number of collisions after the first collision. The results show that whether the soil resistance is taken into account in the collision process or between the two collisions of a single blow has an influence on the calculation of the rod length correction factor. The calculation function for calculating the sum of the energy of the falling weight and the probe rod after the first collision is used to fit the rod length correction coefficient in the current code, and the determination coefficients of heavy and super heavy are 0.993 5 and 0.975 1 respectively. Using the calculation method calculating the finite number of collisions after the first collision, only the influence of resistance of soil to probe rod between two collisions is considered. The calculated rod length correction coefficient decreases with the increase of the number of blows, when the coefficient of restitution is no greater than 0.3.

Due to the advantages of good integrity, high strength and low permeability, surrounding rock reinforced by high-pressure rotary jet grouting in shallow buried section of tunnels has been gradually applied to practical engineering. However, the slurry penetration process is closely related to porosity, penetration path and construction parameters, thus it is difficult to determine the slurry penetration range. Through considering the properties of rock and soil, the hydrodynamic characteristics of grouting slurry and penetration path, a plane analysis model of slurry penetration range was established based on cavity expansion theory, and the calculation formula of radial penetration range of high-pressure rotary jet grouting was derived. Its application scope and parameter determination were also analyzed. Comparing with the field excavation, rationality of the theoretical formula was verified. Furthermore, the primary factors affecting the penetration range of slurry were discussed. The results show that the radial range of slurry permeation from theoretical formula and field measurement is 0.63 times and 0.618 times of pile radius, respectively, and the deviation of between theoretical permeation range and measured one is only 2%, which indicates that the proposed formula can well reflect the property of surrounding rock at shallow buried section of tunnels and the effect of construction parameters. The penetration filling range of high-pressure slurry increases with the increase of porosity, slurry water-cement ratio, rotary jet pressure and the decrease of tortuosity. The proposed method can provide theoretical basis for designing pile spacing and pile diameter, and for the evaluation of reinforcement effect on shallow buried section of tunnels using high-pressure rotary jet grouting.

The research on the mechanical response of anti-slide piles has seldom considered the influence of intermittent heavy rainfall environment, and cannot reflect the multiple rainfall infiltration and solar radiation evaporation links, especially the nonlinear theoretical analysis method of anti-slide pile in the rainfall environment is relatively rare. Based on the improved Green-Ampt model, the mechanical response of anti-slide piles to intermittent heavy rainfall-induced landslides is investigated by introducing the nonlinear Pasternak foundation model. First, in consideration of the drying and wetting cycle and water evaporation theory, an improved Green-Ampt model for intermittent heavy rainfall is proposed to obtain landslide thrusts by taking the wetting front as a potential sliding surface and assuming the homogeneous landslide soils. Second, the pile-soil interaction is investigated based on the nonlinear Pasternak foundation model, and the Newton iterative difference method is used to obtain the mechanical response of anti-slide piles to intermittent heavy rainfall-induced landslides. Finally, the theoretical calculation results are compared with the field monitoring data, which shows a good agreement. In addition, the rainfall sensitivity parameters including the total number of intermittent rainfall events, intermittent duration, average temperature, slope inclination and rainfall intensity are focused to study their influences on the wetting front characteristics and the mechanical response pattern of the anti-slide pile. The results show that the displacement of the anti-slide pile increases by 43.15% when the temperature increases from 10 ℃ to 40 ℃, and by 116.82% when the rainfall intensity increases from 6 mm/h to 20 mm/h. The development of wetting front depth under intermittent rainfall exhibits a “step” upward trend, and there is an “unsaturated zone → saturated zone”. With the increase of the number of intermittent rainfall events, the wetting front of the slope soil keeps advancing downward and induces landslide when it reaches a certain position. The thickness of the sliding area and the landslide thrust increase simultaneously, the deformation and bending moment of the anti-slide pile also become larger and larger. Its development trend shows a gradual decrease to a specific value. The intermittent duration and the total number of intermittent rainfall events presents a negative correlation with the deformation and bending moment of the anti-slide pile, while the average temperature, slope inclination and rainfall intensity demonstrate a positive correlation.

The creep settlement dominates the long-term deformation of high fill foundation after construction and cannot be ignored. The reliable prediction of creep settlement provides an important guideline for judging whether settlement is stable and arranging subsequent construction. The modification of the traditional power law model for predicting the one-dimensional creep deformation of soil is proposed, which can describe the one-dimensional creep deformation of clay, sand and soil-rock mixture. The modified model satisfies the requirement that the growth of the creep deformation has an asymptote with respect to time; that is to say, the creep deformation grows continually and approaches a constant with time. The proposed model has only two parameters, which can be easily obtained from oedometer tests. Then, a simplified algorithm to predict the creep settlement of high fill foundation is developed based on the proposed model. The simplified algorithm has two parameters, which can be determined using the field settlement monitoring data. Based on the field settlement monitoring data of high fill in Longnan Chengxian Airport, Cangyuan Washan Airport and Lüliang Dawu Airport, the fitting and prediction results of the proposed simplified algorithm are compared with those of other three curve fitting algorithms commonly used in geotechnical engineering. The results show that the proposed simplified algorithm can predict the creep settlement of high fill foundation more effectively and accurately.

Scientific and effective safety assessment of existing civil air defense structures has become a key issue to ensure urban underground safety. In order to overcome the shortcomings of the existing safety evaluation methods, a safety evaluation method based on load structure method and strength reduction method is proposed. First, the load structure method is used to convert the impact of surrounding soils on the tunnel lining into load and foundation spring. The concrete damage plastic (CDP) model is used to simulate the damage of lining structure, and the value of safety factor (K1) of lining is obtained by load increasing method and stiffness reduction method. Meanwhile, the finite element modeling analysis of soil lining is carried out by using the strength reduction method, and the safety factor value (K2) of the structure or soil mass at failure is obtained. The overall safety factor (K) of the structure is the smaller value of both. Finally, the influence of different factors such as crack condition and water level change on the structural safety factor is analyzed by using the above methods. The results show that the load structure method and strength reduction method can be used for evaluating the safety of civil air defense structures. The safety factor of the structure is mainly affected by cracks and water level. The deeper the crack is, the more unfavorable it is to the structure, and the lower the safety level of the structure is. When the underground water level is above the structure bottom and there is water seepage inside the structure, the higher the water level is, the safer the structure is. When there is no water seepage inside the structure, the higher the water level is, the lower the safety factor of the structure is. The quantitative evaluation of structures is conducive to the subsequent disposal, and the research results provide a new way for the safety assessment of underground structures.

There are many studies on the spatial variability of mechanical parameters of jointed rock masses and the reliability of slopes with potential slip surface, but the research on the spatial variability of mechanical parameters of rock slopes and the uncertainty analysis of excavation unloading response (deformation and plastic zone) is limited. A probabilistic evaluation method for excavation unloading response of rock slopes considering the uncertainty of mechanical parameters is proposed. Based on laboratory rock mechanical tests and geological survey mapping data, the probabilistic statistical models of rock mass mechanical parameters of slopes are constructed by using Hoek-Brown empirical criterion and Monte Carlo analysis method, in which the uniaxial compressive strength (UCS) of rocks, the geological strength index (GSI) and the parameters of rock mass joints are input, and these probabilistic models are checked by the chi-square test. Based on the point estimation principle, the combination scheme of rock mass mechanical parameters is constructed, and the simulation analysis of slope excavation process is carried out by the numerical method to obtain the probability distributions of the slope safety factor as well as the displacement and plastic zone of rock masses after excavation. This method is used to analyze the rock mass mechanical parameters and excavation unloading response of a cutting slope along the Beijing-Qinhuangdao expressway under construction. The values and uncertainty distributions of rock strength, elastic modulus, cohesion and internal friction angle are obtained. By using the point estimation and FLAC^3D simulation method, the distributions of the slope safety factor as well as the displacement and plastic zone distributions of typical observation points are obtained. The comparison between the simulation results and the measured values shows the applicability of the proposed method. This study provides an effective way for the mechanical parameter estimation and stability evaluation of the rock cutting slope, and can provide a valuable reference for the decision-making process in practical engineering construction.

The influence of the incident angle of seismic waves on the amplification effect of rock slopes is obvious in near-source earthquakes. Based on the theory of viscous-spring artificial boundary and the principle of equivalent nodal force, a seismic input method for oblique incidence of seismic SV and P waves is established and implemented in the finite element method. Various influencing factors such as slope inclination, incident angle of seismic wave, and type of incident wave are considered, and then a numerical study is conducted to investigate the amplification effect of rock slopes. The results of the peak ground acceleration (PGA) amplification factor of the slope show that the amplification effect of the rock slope may be significantly underestimated if only the vertical incidence of seismic waves is considered. In addition, the slope inclination and the type of incident wave also have a significant influence on the amplification effect. By comparing the calculated results of the PGA amplification factor with those suggested by the Code for Seismic Design of Buildings (GB50011―2010), it is found that the values suggested by the seismic code may underestimate the amplification effect in some cases. The results of the spectral characteristics of the acceleration at the slope crest reveal that the incident angle of the seismic waves has little effect on the main frequency of the Fourier spectrum but has a significant effect on the Fourier amplitude. As the incident angle of the SV-wave increases, the Fourier amplitude of vertical acceleration at the slope crest increases, while the variation of Fourier amplitude of horizontal acceleration is not obvious. As the incident angle of P-wave increases, the Fourier amplitude of vertical acceleration at the slope crest decreases while that of horizontal acceleration increases. Finally, the spectral ratio curve is introduced to quantitatively evaluate the effects of different influencing factors on the spectral amplification of slope crest, and the variation pattern of the peak spectral ratio under different incident conditions is obtained.

The main challenge of simulating the processes of seepage and heat transfer in fractured rock mass is the heterogeneity of rock mass at various scales. In order to balance the efficiency and accuracy of numerical simulation, the two-dimensional fracture continuum method is extended to a three-dimensional one. Based on the depth-first search algorithm, the effective fractures contributing to the permeability of rock blocks are collected. The block permeability tensor is obtained by considering the contribution of effective fractures and rock matrix. The finite element software COMSOL Multiphysics is integrated with Matlab to generate a three-dimensional fracture continuum model that contains multiple blocks with various permeabilities. The simulation results show that due to the combination between stochastic continuum model and discrete fracture model, the fracture continuum model can avoid the complexity of addressing fracture networks and consider the spatial variability of rock mass permeability, thus both the simulation efficiency and accuracy are balanced. As the order of magnitude for the ratio of rock matrix permeability to fracture permeability ranges from 10⁻⁴ to 10⁻⁶, the discharge calculation error of the effective fracture network model exceeds 5%.

Laying expandable polystyrene (EPS) slabs on the top of high-fill box culverts to reduce earth pressure has been used in engineering practice, but the creep of EPS slabs will cause the earth pressure on the box culvert to change over time. The present design theory of box culverts cannot clearly reflect the long-term load reduction effect of EPS slabs and the long-term stress characteristics of box culverts. In this analysis, model tests were carried out to investigate the short-term stress characteristics of the box culvert with EPS slabs, and a numerical model was validated by the model test results. Then the verified numerical simulation method was used to analyze the stress redistribution of the culvert-soil system and the long-term stress characteristics of the high-fill box culvert. On this basis, the mechanical model of the culvert-soil system was proposed, and the calculation method of long-term earth pressure on the top of the culvert was deduced and compared with the numerical simulation results for verification. The research results showed that the earth pressure on the top of the culvert decreased gradually with time, then increased slightly and finally became stable. Compared with the earth pressure at the completion of filling, the long-term earth pressure decreased by 52.12%. The vertical and horizontal earth pressure on the culvert side increased gradually with time and tended to be stable, and the long-term horizontal earth pressure in the upper range of the culvert side increased by 28.32% compared with that when the filling was completed. The foundation contact pressure also increased slightly at first and then tended to be stable. The increase of horizontal earth pressure caused by the creep of EPS slabs should be considered in the design of sidewalls in practical engineering so as to avoid bending failure of box culver sidewalls in the long-term use.

To study the deformation and fracture behavior of ultra-deep drilling core, an ultra-deep drilling core geological environment true triaxial apparatus was developed. The apparatus was mainly designed to obtain the complete stress-strain behavior, cyclic loading and unloading fracture behavior, and time-dependent deformation behavior of specimens (25 mm×25 mm×50 mm) processed by ultra-deep drilling cores under a true triaxial stress, mainly solving the technical problems such as inaccurate measurement of specimen deformation, low stiffness of the apparatus, mutual interference between pressure chamber oil pressure and actuator pressure. The device was used to test the mechanical behavior of the cores from the Xiling engineering exploration hole at the Sanshandao Gold Mine of Shandong Gold Group under the true triaxial stress. It was found that the true triaxial cyclic loading and unloading weakened the brittle fracture characteristics of the specimen, and induced deformation in three directions to show anisotropy. In the multi-stage true triaxial creep test, the deformation of specimen in three directions showed primary creep, steady creep, and accelerated creep. The creep strain rates in the three directions increased approximately linearly with deviatoric stress.

The wetting deformation test on the large specimens of gravelly soil core wall material is a challenging task, because the physical properties of gravelly soil material lead to difficulties of saturation, consolidation and drainage for a specimen and a long test cycle. In this study, we tackled the above key issues from the aspects of test technology and test methods, analyzed and corrected the deviation of test results in previous research, and performed detailed exploration in the aspects of large discreteness of the wetting deformation of gravelly soil and the problem of stress saturation. Through strict control of key details such as volumetric deformation correction, water inflow correction, real-time saturation calculation and discrete processing of results in the process of wetting test, the wetting deformation test on the typical gravelly soil materials was successfully completed and reasonable wetting deformation results were obtained. Abnormal phenomena in the test, such as overall upward deformation of the triaxial pressure chamber during the application of confining pressure and no obvious wetting deformation under high stress, have been reasonably explained through data and theoretical analyses. The understanding of geotechnical test technology and wetting deformation of gravelly soil materials has been deepened.