To further investigate the rheological consolidation mechanism of saturated clay, the Koeller spring-pot element based on Caputo’s fractional derivative is introduced to replace the Newton dashpot element of the classical Merchant model. The flow model with the non-Newtonian index is employed to describe the non-Darcian flow in the process of rheological consolidation. Accordingly, a one-dimensional rheological consolidation equation is obtained, and its numerical analysis is conducted by the implicit finite difference method. In order to verify its validity, the numerical solutions by the present method for some simplified cases are compared with the results in the related literature. Then, the effects of the parameters of non-Darcian flow and fractional-order Merchant’s model on the rheological consolidation are investigated. Numerical results indicate that the fractional order and the viscosity coefficient more greatly affect the ground settlement than the dissipation of pore water pressure. The rate of ground settlement lowers as the fractional order decreases or the viscosity coefficient increases. The flow described by non-Newtonian index delays the dissipation of pore water pressure and reduces the rate of ground settlement compared with the Darcy flow. Moreover, the development of ground settlement is always slower than the dissipation of pore water pressure considering the rheological effect.

The excavation unloading activities in deep hard rock tunnels often induce high-intensity rockburst disasters, which has become a key issue affecting the safety construction of tunnels. The physical model test is an important method to study the deep tunnel excavation, and the properties of model materials have great influences on the testing results. Thus, it is the key to prepare materials suitable for the physical model test. Based on the development of the traditional rockburst model materials, this paper introduces the rockburst proneness index and brittleness evaluation index. Combing with the orthogonal design method and sensitivity analysis, the experiments were carried out to investigate the rockburst model materials with low-strength and high-brittleness. We analyzed five influencing factors, including the quartz sand content, barite content, water content and the mass ratio of high-strength gypsum and cement. Each factor was set at five levels, a total of 25 matching schemes. The material strength, mechanical parameters, rockburst proneness index and brittleness evaluation index of model materials were measured in each matching scheme, and the variation of these parameters and indexes were studied under different design levels. Finally, the relationships among the influencing factors, rockburst proneness and brittleness of the selected rockburst model materials were discussed. The results show that: 1) According to the rockburst proneness index and brittleness evaluation index, the prepared model materials meet the requirements of the physical model tests. 2) It is important to control the contents of barite powder and water and to adjust the mass ratio of high-strength gypsum to cement properly.

The multi-field coupled heat-moisture-salt behavior of unsaturated soils under steady state is investigated using porous media theory. It considers that the pores are filled with liquid water, dissolved salts, water vapor, and dry gas. The mass conservation equations of moisture, gas, and salinity in unsaturated soils and the energy conservation equations are presented. Considering one-dimensional steady-state problems, the state equations are obtained by using the temperature, pore pressure, pore water pressure and salt solution concentration and their first-order derivatives as the state variables. Under given boundary conditions, the coupled nonlinear differential equations for the varying coefficients are solved by shooting method. The validity of the model is verified by comparing with the existing experimental results. Based on numerical examples, the influence of moisture content, temperature boundary and porosity on the distribution of temperature field, water field and salt field in unsaturated soils was discussed in detail.

The particle breakage of rockfill materials is one of the significant factors influencing the deformation behavior of rockfill high dams. The stress paths and saturation of rockfills vary during the process of construction and impoundment. A series of large-scale triaxial tests was systematically conducted to investigate the influences of stress paths and drying-wetting states on particle breakage behaviors. The results show that the particle breakage index under different stress paths is not the same for the same axial strain. The particle breakage index of the constant ?3 test is larger than that of the constant p test and the particle breakage index of constant ?1 test is the least in the three stress paths. The particle breakage index of saturated specimen is higher than that of the dry one with the same initial condition and the gap increases with the confining pressure. The evolution of particle distribution under different stress paths and saturation states is the same. The established relationship between particle breakage index and plastic work considering the strength of the parent rock can well unify the particle breakage index under different stress paths and saturation states. The results can provide valuable references for the elastic-plastic constitutive model considering the particle breakage under complex stress paths and dry and wet conditions.

Microwave absorption tests were carried out on 11 typical rock-forming minerals using the 2450 MHz frequency multimode resonator. The microwave sensitivity of the minerals were studied according to the heating rate and temperature increment. This study determined the mineral compositions of Chifeng basalt, Anshan gabbro, and Kunming sandstone, respectively. Based on the obtained mineral compositions, the microwave absorptivity of three types of rocks was predicted and further verified by the microwave radiation testing results. Then the uniaxial compressive strength of three types of rocks was measured, and the relationship between the strength reduction and microwave absorption capacity of rock was analyzed after the microwave treatment. The results show that the microwave absorption capacity of the main rock-forming minerals can be divided into three categories. The microwave absorption capacity of rock can be predicted according to the mineral compositions of the rock. The rock containing the mineral with strong microwave absorption capacity also has a strong microwave absorption capacity. The stronger the microwave absorption capacity of the rock is, the greater the reduction of uniaxial compression strength after microwave radiation.

The shear strength and compressibility of soils are largely controlled by intergranular interactions. For clayey soils, however, the intergranular stresses remain elusive experimentally due to the complex physicochemical interactions between the clay minerals and pore water. To explore the effect of NaCl solution with different concentration on clay compression and to determine the intergranular stresses, a series of oedometer experiments was performed on the remolded samples prepared from a slurry mud. It is shown that at the same vertical stress, the deformation during osmotic consolidation increases with pore water concentration, and at the same concentration, the deformation during osmotic consolidation decreases as the vertical stress increases. Based on Terzaghi’s effective stress principle, the average intergranular stress is calculated based on the osmosis-induced deformation, and the dependence of intergranular stress (or the generalized osmotic pressure) variation on the pore water concentration and void ratio (i.e., dry density) is determined. This paper provides a simple and yet effective approach to determine the intergranular stresses for clayey soils, which is helpful in calibrating the constitutive model of soils with multiple coupled physicochemical processes.

This study is aimed to investigate the spalling failure mechanism of surrounding rock in the rectangular tunnel of deep hard rock. A cubic granite specimen (100 mm×100 mm×100 mm) was prepared with a precast rectangular hole (40 mm×40 mm), and then the simulation test was carried out by using the TRW-3000 true triaxial electro-hydraulic servo mutagenesis testing machine. In the simulation test, the in-situ stress of the depth of 1 000 m was selected as the initial loading stress state, and the horizontal stresses of the rectangular hole were kept constant in the radial and axial directions. After that, the vertical loading was applied until the surrounding rock on both sidewalls of the hole was destroyed, and the whole specimen remained in a stable state. During the loading process, a real-time video surveillance system was employed to monitor the failure process of the internal structure of the rock specimen. The results showed that when the maximum principal stress was at the vertical direction and the intermediate principal stress was at the horizontal axis, the obvious spalling failure appeared on the surrounding rock of both sidewalls of the rectangular hole. Moreover, it was found that the failure zone of the surrounding rock was symmetrical, whereas the roof and the floor remained stable. Meanwhile, the failure of surrounding rock was parallel to the vertical direction, showing typical tensile cracking and spalling characteristics. The entire failure process was divided into the calm stage, the particle ejection stage on the shoulder angles of the hole, the sidewall crack propagation stage and the crack penetration spalling stage at both sidewalls. When entering the crack penetration spalling stage, the spalling failure may continue to develop regardless of the loading or load-holding process. During the test, the spalling failure of the surrounding rock on the both sidewalls of the specimen presented a static failure mode. Besides, the failure zone gradually developed towards the deep part of the wall along the horizontal direction, and finally formed a penetrating symmetric arc notch along the axial direction.

The process of dead-weight consolidation of the soil layer involves many complex nonlinear problems. However, the existing analysis methods are generally based on the linear assumption to simplify the consolidation governing equation, which is unreasonable for the large strain consolidation. In this article, the boundary conditions of Gibson's large strain governing equation are deduced first. Then, the changing compressibility and permeability relationship of soil mass is taken into consideration. The finite difference method (FDM) in Crank-Nicolson scheme is used to disperse and solve the nonlinear governing equations. Verification of FDM solutions shows an excellent agreement with the CS2 simulations, in the aspects of void ratio, settlement and relative discharge velocity. Moreover, the effects of initial layer height and initial void ratio on the consolidation behavior are investigated. The results reveal that both a larger initial layer height and a larger initial void ratio result in a larger final settlement of the foundation. Compared with the traditional method, the method presented in this article realizes the fast solution of the highly nonlinear equation of large strain consolidation, and it can be widely used in the analysis of practical engineering.

The current design methods for the railway stepped reinforced soil retaining walls are still immature, which fails to satisfy the requirement of railway slope reinforcement practice. For the design of reinforced soil retaining walls, accurate determination of the potential failure surface is the key issue. However, though current specifications clearly address the shape and location of the potential failure surface, they limit their use only in single walls with a height of no more than 10 m. This paper attempts to identify the characteristics of potential failure surfaces in stepped reinforced soil retaining walls under railway loads by the use of model test. The model was designed with a large scale of 1:4 and the railway load was stimulated by a specific cyclic surcharge load. The shape and location of the potential failure surface were determined by the comprehensive analysis of the slope surface lateral displacements, vertical settlements at the slope crust and strains of the geogrid at different investigation points. The result illustrated: the potential failure surface in the lower stage wall is similar to that given by the “0.3H” method but has a deeper location and a more gentle inclination of the bottom part, which indicate a larger potential unstable area; while the shape of the potential failure surface in the upper stage wall is generally similar to the Ranking’s active rupture, however it thrusts into the lower stage wall rather than thrusts out from the foot of the upper stage wall. The test results and conclusions drawn in this study can provide theoretical reference for the design of railway stepped reinforced soil retaining wall.

This study is aimed to investigate the unloading and dilatancy characteristics of rock under high-stress level and the variation law of the dilatancy angle. A series of triaxial pre-peak unloading confining pressure tests was carried out at different initial confining pressure levels, and the conventional triaxial compression tests were also conducted at corresponding confining pressure levels. Based on the experimental results, the effect of the unloading stress path on the dilatancy characteristics of sandstone was analysed, the variation law of dilatancy angle under the unloading stress path was summarized as well. Moreover, the dilatancy angle function under the unloading stress path was proposed, and its numerical realisation method was established. Finally, the feasibility and rationality of the proposed dilatancy angle function was verified by the numerical simulation of the triaxial pre-peak unloading confining pressure tests. Under different confining pressure levels, the volumetric strain values of pre-peak dilatation were similar under the loading paths. While under the unloading stress paths, the volumetric strain of pre-peak dilatation increased from the minimum value of 3.15×10?3 to the maximum value of 9.65×10?3 with increasing the confining pressure level. The volumetric strain of pre-peak dilatation under the unloading path was about 1.1-4.0 times than that under the loading path. The volumetric strain corresponding to the peak of the deviatoric stress was substantially zero or close to zero under the unloading condition, while the volumetric strain was negative under the loading condition. Under the unloading stress path condition, the proportion of the volume expansion strain before the peak of deviatoric stress in the total volume expansion strain was significantly larger than that under the loading path. The dilatancy angle firstly increased and then decreased with increasing the plastic shear strain under the two stress paths. Under lower confining pressure conditions, both the maximum dilatancy angle and the dilatancy angle corresponding to the peak were greater than those under the higher confining pressure conditions. Compared with the loading path, the dilatancy angle reached the maximum value faster, and the maximum dilatancy angle and the dilatancy angle corresponding to the peak were larger under the unloading path. According to the unloading test results, the linear fitting method was used to establish the dilatancy angle function with the confining pressure and post-peak plastic shear strain as independent variables. The experimental results showed good agreements with the simulation results from the established function and the strain softening constitutive model under the unloading path. The results indicate that the function can better describe the expansion characteristics of sandstone under the conditions of the triaxial pre-peak unloading path. This study can provide a theoretical basis for deformation prediction, stability analysis and support design of deep underground engineering.

Based on the failure characteristics of buried pipelines under multi-point non-uniform seismic excitation, the three-array shaking table test of underground pipelines under non-uniform excitation was developed and carried out for the first time. Firstly, according to the experimental conditions and purpose, the similarity ratio of the model system was determined, the suspensions continuum model box for the multi-array shaking test of long linear structure were designed and the location of the sensor were determined by special research. Secondly, the design of the model material selection, earthquake motion input and test loading system were analyzed. Finally, the dynamic characteristics and boundary effects of the continuum model box were analyzed. The experimental results show that the scheme design of the shaking table model test of the buried pipeline under the non-uniform excitation is reasonable. The research has laid a foundation for the development of the shaking table test of the buried pipeline under the non-uniform excitation and also have some reference value for similar experiments in the future.

The cyclic loading and unloading axial compression tests of coal specimens with the pre-existing transfixion fissure were carried out by triaxial loading coal rock seepage testing device. The permeability variation of coal specimen with pre-existing fissure and the difference with permeability of intact coal specimen were analyzed. The results show that the relationship between permeability and axial compression is a negative exponential function and the stress sensitivity of permeability decreases with the increase of the loading and unloading numbers for coal with pre-existing fissure. The permeability difference of the loading stage and permeability difference of unloading stage decrease with the increase of the loading and unloading numbers. There is a positive correlation between permeability difference and stress sensitivity coefficient. There exists a significant permeability difference during the loading and unloading stage, which indicates that there is apparent loss in permeability and it decreases with the increase of the loading and unloading numbers. The permeability and stress sensitivity coefficient of coal specimens with vertical fissure are higher than those of the coal specimens with horizontal fissure and the intact coal specimens. The permeability of coal specimen with horizontal fissure is similar to that of the intact coal specimen, but the stress sensitivity coefficient is higher than that of the intact coal specimen. The permeability difference and the loss quantity of permeability of coal specimens with vertical fissure are higher than those of the coal specimens with horizontal fissure and intact coal specimens. The permeability difference of coal specimens with horizontal fissure is higher than that of the intact coal specimens, but there is slight difference in the loss quantity of permeability between them. After the cyclic loading and unloading axial compression, the loss rate of permeability is the largest for intact coal specimen, followed by the coal specimen with horizontal fissure and last is the coal specimen with vertical fissure. The recovery rate of permeability is the largest for the coal specimen with vertical fissure, followed by the coal sample with horizontal fissure, and last is the intact coal sample.

Advanced support is often used to ensure the safety of tunnel construction in soft surrounding rock. In order to evaluate the tunnel stability under the advanced support, a joint failure model of truncated cone and logarithmic helix under the advanced support effect was established. The objective function of the tunnel safety factor was deduced based on the limit analysis upper bound method and the comprehensive strength reduction method, and considering the influence of the unsupported section of initial support. The function was solved using Matlab programming to judge the tunnel stability. Compared with model test results and existing theoretical research results, the rationality of the proposed method was verified, meanwhile, the factors affecting the safety factor of the tunnel stability were also analyzed. The research results show that with increasing the soil cohesion and internal friction angle, the applications of tunnel face bolt and arch pre-consolidation measures have a significant effect on the stability of the surrounding rock, while the increase of unsupported length and excavation height is not conducive to the stability of surrounding rock. When the internal friction angle is small, it is more beneficial to improve the stability of tunnel to reduce the excavation height by bench method.The increase of reinforcement strength of bolt in the working face plays a more significant role in improving tunnel stability. Finally, the construction design proposal drawing of the advanced support was given, which can provide a reference for the preliminary determination of the advanced support parameters and construction methods.

In order to study the seismic response of the interaction systems assembled by multi-ribbed composite wall structure and subsoil in frequency domain, a series of shake table tests was carried out using a model scaled in 1/15. The dynamic responses of the structure and subsoil were studied by inputting white noise, El-Centro wave, Tianjin wave in the tests. The response curve was obtained in frequency domain by Fast Fourier Transform, and the dynamic characteristics of the foundation and structure as well as their dynamic responses from 7 degree to 9 degree along horizontal axis loading were analyzed. The frequency response curves of the acceleration and displacement under different loading conditions were comparatively investigated. The dynamic frequency responses of the foundation and structure and their influencing factors were also examined. It was found that the fixing effects of subsoil for the superstructure are lessened, and the vibration frequencies decrease after the subsoil crack affected by the earthquake wave. The acceleration responses are amplified at the subsoil surface and the structure top with increasing the intensity, the frequencies corresponding peak response vary remarkably. The amplification effect of foundation on acceleration is remarkable, and the amplification effect of superstructure on displacement is significant. Therefore, the dynamic amplification effect is closely related to the destruction of subsoil and earthquake ground motion characteristics when considering the interaction between subsoil and structure.

At present, there are few similar materials that can reasonably simulate the rheological behavior of soft rock. It is also still in the exploratory stage to study the long-term rheological behavior of soft rock engineering based on the model test method. In this paper, a new rheological similar material of soft rock was developed, which compose of the iron powder, barite powder and quartz sand as aggregate, the rosin alcohol solution as binder and the hydraulic oil as viscous agent. This material processes a low strength and a significantly rheological property, which can not only simulate the transient elastoplastic properties of soft rock, but also simulate the rheological properties well. With a constant aggregate proportion, a series of gradient compounding tests were conducted by adjusting the concentration of rosin alcohol solution m and the content of hydraulic oil w. The tests results indicate that the main parameters associated with the instantaneous strength and deformation of the similar material as well as the rheological parameters of Nishihara model are all affected by the factors m and w. The higher the concentration of the rosin solution, the larger the strength and the smaller the rheology of samples are. A higher hydraulic oil content leads to lower strength and more obvious rheological behavior. Compared with the concentration of the rosin alcohol solution m, the hydraulic oil content w exerts more remarkable influence on the parameters of Nishihara model. Finally, the developed similar material was applied to the model test of the shield inclined shaft in the weak sandy mudstone in Shenhua Xinjie coal mine. The model test results show that, the instantaneous mechanical properties and rheological properties of the material meet the test requirements, which provides guarantee for good results.

The incompatibility and the lag of type development of anchorage slurry have become the key problems restricting the development of anchorage technology in earthen sites. To improve the compatibility and enrich the types of anchorage slurry, the fluidity of SH-(CaO+C+F) anchorage slurry composed of traditional quicklime, clay and fly ash was tested, so did the physical and mechanical properties of stones. During the tests, the mass concentration of SH binder was 1.5%. Then, the anchorage slurry with water cement ratio of 0.5 was selected as the preferred slurry. Based on this, the in-situ anchorage test was performed in which six different kinds of anchorage systems composed of the selected slurry and two different kinds of anchorage bolts were tested at three variable lengths. The in-situ test aimed to obtain and analyze the failure modes, ultimate load and ultimate load-displacement characteristics and the distribution characteristics of stress along anchorage depth of six kinds of anchorage systems. Finally, compatibility and anchorage performance of this type of anchorage slurry were compared and evaluated through analysis of anchorage mechanics mechanism. The research results provided a reference for the selection of anchorage slurry diversity of earthen sites.

Due to the insufficient research on the stress relaxation characteristics of the nonholonomic hard rock, the stress relaxation tests were carried out on the gabbro specimens with pressure relief holes and rock burst tendency. The tests included the modes of pre-peak loading, relaxation and reloading, and re-relaxation. The pre-peak stress relaxation characteristics, relaxation model and ultrasonic variation law were obtained, and the mechanism of pressure relief hole in the stress relaxation process was revealed. Results showed that the stress relaxation process of hard rock with pressure relief holes experienced three evolution stages of rapid attenuation, attenuation and stability. With the gradual increase of pre-peak loading, the stress relaxation degree generally increased, the energy dissipation increased, and the proportion of energy used for damage and fracture evolution of hard rock increased. The deformation, damage, and fracture of hard rock in stress relaxation process can be reflected by the comparative analysis of the wave velocity, wave amplitude and waveform. The Burgers model can better express the stress relaxation characteristics of hard rock with pressure relief holes. Compared with the stress relaxation testing results of intact gabbro specimens, the hard rock containing pressure relief holes had higher stress relaxation degree, greater energy dissipation, and faster dissipation velocity. The research results provide significant guidance and reference for the long-term stability analysis, rock burst prediction and solution of hard rock with or without pressure relief holes.

The stress analysis of the circular hole is one of the classical problems in the mechanics, and as well in tunnel and roadway engineerings. With the development of fracture mechanics, the research on the hole with cracks has been deepened. However, previous studies mainly focused on the two-dimensional problems or holes with surface cracks, and there are few reports on the hole problems with three-dimensional internal cracks. Firstly, based on the 3D-ILC method, the deep internal cracks were generated in brittle materials containing circular holes. The uniaxial compression tests were performed on the specimens with internal cracks. The experimental results are compared with the existing literatures, and the theoretical and numerical simulation studies are carried out. Results show that: 1) Compared with traditional methods, the 3D-ILC method has more realistic crack characteristics and lays a foundation for solving the three-dimensional internal crack problem in fracture mechanics. 2) The main crack shapes of intact specimens are the primary crack and remote crack. 3) For the specimenes with internal cracks, the main crack shapes are the wing crack, secondary crack, anti-wing crack, anti-secondary crack, vertical torsional crack and primary crack. 4) The ultimate failure load of the specimen with cracks is 76.49% of the intact specimen, while the crack initiation stress is 96.72%. 5) The simulation results are in accordance with the experimental results. This study provides an experimental basis for the corresponding theoretical research.

Scaled model test for the influence on an existing shield tunnel induced by surface surcharge is carried out, and vertical earth pressure and soil settlement for the stratum above the shield tunnel are analyzed. Results show that under uniform surface surcharge, the less of the vertical distance from the top of the tunnel, the more extent for the nonuniform vertical earth pressure in the stratum above the shield tunnel, and the more extent for the nonuniform soil settlement of overlaying soils of the shield tunnel. The overlaying soils show vertical earth pressure transference for vertical shearing force among soil elements, which is induced by vertical relative movement among soil elements as the stratum above the shield tunnel has nonuniform soil settlement, so the vertical earth pressure in the stratum above the shield tunnel is nonuniform. As vertical shearing force among soil elements for overlaying soils is related to vertical relative movement among soil elements and soil mechanical property, the extent of nonuniform vertical earth pressure in the stratum above the shield tunnel is affected by the extent of nonuniform soil settlement and soil mechanical property of overlaying soils when the tunnel suffers from surface surcharge, so the tunnel deformation is influenced.

Three types of Wudang group schist with different macroscopic characteristics were selected to make the standard cylindrical test specimens possessing different schistosity angles. Firstly, P-wave velocity of the specimens were tested after dried and soaked to investigate the velocity anisotropy of Wudang group schist in different water bearing states. Then, combined with mineral composition and microstructure characteristics of three kinds of schist obtained by polarizing microscope and scanning electron microscopy, he wave velocity anisotropy affected by internal and external factors were further investigated. The results indicate that the major minerals of Wudang group schist are hard granular quartz, feldspar and soft muscovite. The higher content of hard mineral or the smaller porosity of schist, the larger P-wave velocity and vice versa. The P-wave velocity of dry samples shows significant anisotropy. As the angle between the direction of wave propagation and foliation decreases, the wave velocity increases gradually. Wave velocity in different directions can be predicted by the formula expressed as wave velocity circle. The wave velocity anisotropy is essentially caused by the directional and the interval distribution of micro fissures, of which the degree k can be evaluated indirectly through the orientation coefficient of muscovite. There is a linear positive correlation between and , and the upper limit of the p-wave anisotropy of the Wudang group schist is 2.90. Due to the increase of the equivalent volume modulus of schist after the pores filled by water, the P-wave velocity of the soaking sample is generally increased. And the increasing effect of velocity depends greatly on the porosity and distribution of micro fissures, leading to the difference of P-wave velocity among different kinds of schists and a inverse correlation between the anisotropy degree of wave velocity for the same kind of schist and the soaking time.

Natural sedimentary clays exhibit anisotropic consolidation properties since most clay minerals are platy and the clay particles and fabric elements tend to be horizontally oriented in the deposition and subsequent consolidation processes. In this paper, the anisotropic consolidation properties of Ariake clay in Japan were studied by the constant rate of strain (CRS) consolidation test using vertically and horizontally cut specimens. The test results show that the ratios of the preconsolidation pressure of horizontally cut specimen (pch) to that of vertically cut specimen (pcv) are in the range from 0.5 to 1.0, which is mainly due to the anisotropic yield locus of natural sedimentary clay and the different stress paths experienced by the vertically and horizontally cut specimens. In the normal consolidation range, the ratio of coefficient of consolidation obtained from horizontally cut specimen (ch) to that from vertically cut specimen (cv) is approximately 1.43, and the ratio of hydraulic conductivity obtained from horizontally cut specimen (kh) to that from vertically cut specimen (kv) is approximately 1.40, while the coefficient of volume compressibility obtained from horizontally cut specimen (mh) is approximately equal to that from vertically cut specimen (mv). Therefore, the anisotropy of coefficient of consolidation of Ariake clay mainly arises from the anisotropy of hydraulic conductivity, which is essentially induced by the anisotropy of microstructure.

A nonlinear creep model is researched and proposed on the basis of a new proposed strain softening index. Firstly, according to the triaxial experimental data of rock, a strain softening index R1 is presented to describe the relationship between the softening of the post-peak mechanical parameters and the plastic strain. Secondly, by analyzing the relationship between the tertiary creep and the general post-peak stage, a strain softening index R2 in the tertiary creep is put forward to establish a non-linear viscoplastic element. Thirdly, by connecting the nonlinear viscoplastic element with the Hook and the Kelvin viscoelastic models, a nonlinear creep model is established inserting into the ABAQUS software. Finally, the proposed model is applied to simulate the triaxial creep experiments of sandstone and mudstone. The numerical results are in good agreement with the experiments indicating that the proposed model is capable of characterizing the accelerated creep behaviors of hard and soft rocks. The parameter β can adjust the curve form of the tertiary creep, showing the function to model the brittle-ductile failure. Furthermore, the parameters in the model can be readily identified by the conventional compression failure test and the creep test.

This paper attempts an in-depth analysis on the hydrodynamic behavior of clays considering the multiple driving forces of pressure and induced electrical potential (IEP). Electrokinetics is employed to quantify the processes of ion migration, fluid motion, and potential distribution, which are described by the coupled equations of the Nernst-Planck (NP), the Navier-Stokes (NS), and the Poisson-Boltzmann (PB), respectively. The numerical investigation shows that employment of Debye-Huckel approximation may be inappropriate for clays in calculation of double layer potential since their relatively high surface charge density. IEP is caused by the requirement of electroneutrality for the clay-water system, and is directly proportional to the separation of cation-anion resulting from the differential hydraulic migratability between them. IEP contributes to decelerating cation, accelerating anion, and producing a negative electroosmosis that counteracts in partial the positive flow driven by pressure. At those conditions including low concentration, small porosity, and high surface charge density, double layer effects may be enhanced, leading to significant effects both in IEP and its flow reduction.

To reduce stratum disturbance and settlement during shield tunneling in silty sand layer, a new construction technique of slurry-EPB shield was proposed for the silty sand layer with large permeability and high internal friction angle. 3 groups of slurry permeability test were carried out on mixed soils with different slurry additions using the self-made soil chamber penetrating test device. The variation of pore water pressure in mixed soil and stratum, and the distribution rule of pore water pressure were analyzed. Based on the laboratory testing results, in situ pore water pressure was monitored to study the effect of slurry addition on the pore water pressure in the stratum. The effect of filter cake appears on the excavation surface when the amount of slurry added is more than 25%. The larger the amount of slurry added during the tunneling process, the smaller the change rate of pore water pressure in the stratum. The change rate of pore pressure is only 25%-45% when the addition amount reaches 8 cubic meters per ring. Only the type of infiltration cake occurs in case of slurry-EPB shield, and undergoes slurry particles lost before the film formation. The research results have important significance for the application of slurry-EPB shield in practical engineering and extension to sandy gravel stratum.

Soft clay is characterized by high water content, large compressibility and Poisson's ratio. For thick soft soil foundation, it is difficult to ensure that the lateral deformation remains zero under vertical loading. The condition of flexible constraints with proper consideration of lateral deformation is more realistic with engineering practices. Therefore, in this paper, a consolidation test with flexible lateral constraints was conducted on the undisturbed and remodeled soils. The influences of the lateral constraints on the settlement characteristics and deformation parameters of soft clay were investigated. The results show that both the primary and secondary consolidation deformations of the soil under flexible constraints are greater than those under the K0 lateral confining conditions, as well as performing a shorter consolidation time and more nonlinear isochronous curves. The theory of non-Darcy flow was introduced to modify the Terzaghi’s consolidation theory, so that nonlinear governing equations considering the certain lateral deformation effect were deduced. Furthermore, the parameters of the calculated model were obtained from the flexible lateral restraints consolidation tests. Finally, the validity of the proposed model was verified by the laboratory test results.

The experimental study on the relationship between P-wave velocity and physical parameters of calcareous sand has important theoretical guiding significance and engineering application value for non-destructive testing of calcareous soil foundation and geophysical exploration. By controlling the state of the tested specimens under different conditions, the P-wave velocity was measured to investigate the relationship between the P-wave velocity and physical parameters. Experimental results show that the water content is the main factor that affects the variation of compression wave velocity in a certain density range, and there is a quadratic curve relation between P-wave velocity and water content. Generally, the results of CT scanning show that the larger the particle size, the more abundant inner pores in the particles, which leads to the larger the void ratio and the smaller the P-wave velocity. The P-wave velocity has a negative correlation with particle size and pore ratio. When the density is fixed and uniformity coefficient is different, the compression wave velocity is basically the same in well-graded sand. After compression, a good quadratic relationship is established between P-wave velocity and void ratio under the constant water content. The P-wave velocity is linearly related with soil density. Therefore, the results can be applied to the nondestructive detection of calcareous soil foundation compactness.

For inclined retaining walls under translational motion, the earth arch formed behind the wall is assumed arc-shaped. Nonlinear functions of displacement with internal and external friction angle, considering the interlayer shear stress, were established. The horizontal layer analysis method was used to obtain the solution of non-limit active earth pressure distribution, the total earth pressure, point of forces applied. The analytical solution and experimental values are in good agreement comparing to other methods. The results show that regardless of the inter-layer shear stress is considered or not, the magnitude of the earth pressure decreases as the wall displacement increases. The total of earth pressure does not change the magnitude but the distribution of earth pressure varies. The earth pressure considering the shear stress is less than the one in the upper part of the wall without considering the shear stress, and higher than the lower part. Shear stress acts as a hindrance to the soil, and it first increases significantly and then decreases slightly as the internal friction angle increases. Shear stress increases as the external friction angle and displacement increase. With the increase of the wall dorsal obliquity, the shear stress decreases first, then increases in the opposite direction, and the earth pressure increases accordingly. The height of the resultant force point considering the soil arching and shear stress together is between only considering the soil arching effect and the Coulomb solution.

There are many factors affecting the permeability coefficient (k) of cohesive soil, and different test methods have great influence on the test results. To solve the problems existing in present test methods, a hollow cylindrical torsional shear apparatus (HCA) was used for seepage tests. The significance, feasibility and experimental procedures for HCA seepage test were demonstrated, and remolded kaolin was used to carry out a series of experiments to explore the standard rules for permeability tests. Finally, a preliminary study of the dynamic test was explored. The results show that: (1) If 3 600 s is taken as the unit of time, the difference in average permeability coefficient in the unit time is less than 2% in continuous 24 h. Therefore, it is accurate to take the average of permeability coefficient obtained in this stage as the final permeability. (2) The hydraulic gradient range in HCA permeability test for kaolin is suggested between 10 and 15 after comprehensive consideration of test efficiency, comparability, and the accuracy. (3) After 100 000 cycles of dynamic traffic load, the permeability coefficient of kaolin is 12.79% lower than that of the same axial strain in static compression test, indicating that it is important to study the influence of dynamic characteristics on permeability coefficient.

It is of great significance to understand the influence of matric suction on shear strength behavior of ion-absorbed rare earth unsaturated ore body. Hence, the weakening of the strength of the ore body caused by water can be recognized. The soil-water characteristic curve and shear strength of the ore body were measured in the field. The influence of matric suction on the shear strength of the ore body was obtained. As the matric suction increased, the inner friction angle of the ore body increased slightly, and the cohesive force increased greatly. According to the analysis of the physical meaning represented by the air entry value, we could see that when the matric suction was lower than the air entry value, the contribution rate of matric suction to shear strength could be regarded as a constant. When the matric suction was higher than the air entry value, the contribution rate of matric suction to shear strength decreased gradually. The improved model of unsaturated strength was proposed by taking the air entry value as the boundary point. The absolute error between the calculated value obtained by this model and the measured value was within 15%, and better than the other models prediction results

For underground excavations in sand and blocky rock masses with low cohesive strength, the loosening pressure above a shallow tunnel varies with the developing ground deformation due to evolutions of ground arching. However, the normal ground arching method fails in determining the existence of the ground arch, resulting in critical deformation when the ground arch reaches the ground surface and the variation of the loosening pressure as a function of the developed arching effect. This paper presents a modified method by introducing a continuously developed ground arching mechanism. Rotations of the principal stress and the correlation between orientations of the principal stress and the shear surface are used to determine the stress state within the arch. Previous methods determining the rotation of the shear surface as a function of the ground deformation was also modified to better reflect the test results. On the basis of the above three steps, a modified method is proposed. Comparisons of the results among the previous methods, the proposed method and the experiments examined the validity of the proposed method. Parametric analysis studied the initial loosening pressure, the evolution of the loosening pressure and the critical deformation. A case study by the proposed method indicates its practical use. Some important conclusions are: (1) the initial loosening pressure comes from the weight of the ground within the arch. The area of the initial-loosening zone is independent on the cover-depth ratios. Instead, the area is controlled by the friction angle of the ground. Grounds with low friction angles tend to have large initial-loosening zone with a high initial loosening pressure; (2) the loosening pressure increases with the developing ground deformation, and a lower raising rate is found for a deeper, smaller tunnel ( ); (3) the critical deformation increases with the raising cover-depth ratio and the increasing friction angle, indicating that a stronger arching effect is expected in such grounds; (4) for Xiabeishan tunnel, the arching effect exists, the initial loosening pressure is 0.37 , the critical value is 0.41 , the ultimate is 0.54 , and the critical relative deformation is 5.7%.

The anisotropic elastoplastic constitutive model of saturated soil is extended to describe the mechanical properties of the unsaturated soil by using the degree of saturation and effective stress as the state variables. Through the theoretical simulation of the existing dynamic triaxial tests of the unsaturated soils under completely undrained conditions, the correctness of the proposed constitutive model of unsaturated soils is verified. Finally, based on the proposed constitutive model, the influence of initial saturation on the dynamic mechanical behavior of unsaturated soil is discussed under the undrained condition. The results show that the void ratio of unsaturated soil will reduce under the dynamic loading, which will result in the increase of saturation. When the initial saturation is high, the unsaturated soil will be converted to saturated soil, and the liquefaction will happen. The research results obtained in this paper are of great significance to study the mechanical behavior of unsaturated soils under dynamic loads such as earthquakes.

The approximate function of normal stress distribution of symmetrical slope slip surface based on grid element is constructed, which provides a theoretical basis for establishing the limit equilibrium method based on the assumption of normal stress on slip surface in GIS(geographic information systems). Combining GIS's powerful spatial data analysis capabilities, a three-dimensional slope stability analysis model is established based on grid element. Under the assumption that there is no force, the distribution of normal stress on slip surface is deduced. With an analysis example, we can draw a conclusion: in the perspective of the sliding direction of the sliding body, the distribution of the normal stress on slip surface comprises several portions. The largest portion is the dead-weight of the sliding body and the external force, as a known function. The other portion that accounts for a small percentage is consisted of the force between the columns, as an unknown function. Therefore, the approximation function on the distribution of forces between the columns can be performed by a third-order Lagrange polynomials. In the direction perpendicular to the sliding body, the normal stress distribution on slip surface is approximated by parabolic approximation, and then we construct an approximation function of the normal stress distribution of slip surface based on grid element. This kind of approximation function is easily expressed in the GIS. In the end, the rationality of the approximation function is verified by an example.

For the water conservancy project in the alpine canyon basin, the deformation of high-steep slopes and its influence on the dam safety are important scientific problems during the construction and operation period, which can be divided into two aspects. One is the stability of high-steep slopes, which can be evaluated by the reliable monitoring data obtained through the monitoring technology and methods of the high-steep slopes deformation. On the other hand, the effect of the deformation of high-steep slopes on the dam safety are also need to be studied. The influence mechanism, range and degree of the deformation of high-steep slopes on the dam safety are investigated through the interaction between the slopes and the dam. In the summary of the research progress in recent years, the time-varying monitoring method, four key scientific problems are concluded and proposed to be investigated, such as the high precision numerical simulation, the intelligent optimized inverse analysis and the theoretical calculation method for the influence of high-steep slopes on dam body. To provide ideas for the research, the interaction mechanism between the high steep slopes and dam body should be further studied as well as the strengthening measures.

At present, the method of uniform isometric piles is used in most group pile designs. This method has major defects in foundation stress and deformation. Considering the increase of group pile foundation stiffness and reducing the differential settlement of group pile foundation, the group pile foundation displacement function is combined with the pile length optimization function. Under the method of line transformation and squared transformation, different group pile designs are determined by setting different pile length ratio ξ and connection curvature η. The scheme is used to analyze the variation law of axial stiffness ratio and differential settlement ratio of group pile foundation under different schemes. The reliability of theoretical analysis results is verified by finite element method. In addition, parametric analysis of axial stiffness ratio and differential settlement ratio of pile group foundations are based on different pile-soil stiffness ratios and different pile spacings. The results show that the optimal transformation mode of different pile groups and different pile lengths have different effects on the optimization results of group pile foundations. When the optimization purpose is to increase the pile group foundation stiffness, the optimization method of line transformation should be chosen. When the optimization purpose is to decrease the differential settlement of pile group foundation, the optimization method of squared transformation should be chosen. The axial stiffness of pile group increases with the increasing of pile-soil stiffness ratio and the decreasing of pile spacing. The differential settlement ratio of pile group decreases with the increasing of pile-soil stiffness ratio and the decreasing of pile spacing.

The left bank of Baihetan hydropower station is a high slope, which is a three-dimensional (3D) complex block system with strongly unloaded rock mass. The 3D geomechanical model test was adapted to investigate the slope deformation characteristic, failure process and mode, destruction mechanism, slope stability, and reinforcement effect. The model test shows that the slope failure exhibits the mode of the block sliding failure, which demonstrates the shear slipping among the bottom surfaces, the tensile crack along the trailing edge surface, and the block sliding along the bottom surface and side surface. The failure process basically experienced three stages, including the initially crack of discontinuities, crack expansion throughout the block boundaries, and the instability of the slope. The general safety factor of the left bank slope was obtained through the comprehensive geo-mechanical model test. The safety factors of given blocks were compared with the calculation results of both 3D-LEM and BEM, which shows good agreements. Simultaneously, the relative displacements at the interface of LS337 were monitored. From the results, we can see that by the reinforcement of the deep concrete replacement caverns, the sliding deformation among the bottom surfaces is effectively controlled, and the safety factors of the combination blocks of related discontinuities are improved, and the effect of slope reinforcement is more obvious. This paper provides significant guidance for the stability and reinforcement of the left bank slope of the 3D complex block system with the strongly unloaded area in Baihetan or other similar engineering slopes.

More and more attention was paid to the behavior of bedrock-dam materials interface in earth rockfill dams. The hyperbolic hardening rule for constitutive model of coarse grained soil is introduced into the model for soil-structure interface and thus a simple elasto-plastic interface model is suggested. The expression of stiffness matrix of interface model is derived. The performance of proposed model is demonstrated by comparing its predictions with direct shear test results for different types of granular soils, including sand and rockfill materials, during shearing. Within the framework of thin layer element finite element scheme, the interface model is applied in numerical finite element program. Combining Rumei high core-wall dam example, shear sliding property of shear band between dam materials and valley is analyzed. Simulation results show that tangential displacements of middle zone of slope is relatively large while the edge zone is relatively small. These are in accordance with the sliding law of coarse-grained soils, which provide a favorable reference to research on shear sliding property of bedrock-dam materials interface and deformations calculation of earth-rock dam.

The saturated loose deposits formed by engineering waste and earthquake landslide deposits under rainfall conditions have strong mobility, their movement speeds are fast, and the damage scopes are larger than expected. Their internal mechanisms have always been a hot research issue in international academic circles. In this paper, the saturated deposit shear dilatancy model constructed by Iverson based on the limit state soil mechanics principle is integrated into the physical model of the Savage-Hutter slide motion physical model. The finite volume method is used to solve the landslide kinetic equations and achieve full simulation of the motion evolution of the saturated loose accumulation body. Finally, a back in-situ analysis of the catastrophic construction solid waste landslide that occurred in Shenzhen in December 2015 is presented and evolution process of the landslide is reproduced. The results show that the dilatancy effect is the main reason for rapid movement of the saturated loose accumulation bodies and the initial state (void ratio or volume fraction of solid phase) of the saturated loose deposit has a crucial influence on its motion-accumulation evolution process.

In order to improve the accuracy and applicability of inversion analysis model of material parameters for rockfill dam, an adaptive model based on quantum genetic algorithm (QGA) and multi-output mixed kernel relevance vector machine (MMRVM) is established. By introducing mixed kernel function, the MMRVM can accurately simulate the nonlinear relationship between the material parameters and the settlement of rockfill dam. Therefore, the finite element method (FEM) can be replaced by the MMRVM to reduce time consumption. Then, the kernel parameters of the MMRVM is optimized by the QGA, thus the QGA-MMRVM is adaptable to different inversion analysis problems. The parameters of constitutive model of dam materials can be inverted by fully utilizing QGA's global searching ability. Finally, the influences of the signal-noise ratio and the number of measured points on the calculation result are analyzed. The examples of Gongboxia dam show that the parameters of constitutive model of material can quickly and accurately calculated by the QGA-MMRVM. With its adaptability, the QGA-MMRVM has good application prospect and popularization value in practical engineering.

In this study, a multi-degree of freedom model method was proposed to construct the differential equation for similar dynamic responses of complex stereoscopic goaf of metal ore under blasting load excitation. The correction factor matrix λ of the shear effect and the action coefficient matrix B were also introduced to describe the shearing effect of surrounding rock under external loads. The Newmark-β method was applied to solve the differential equation for similar dynamic responses in the goaf. The self-contained Matlab program was used to realize the fast calculation, which solved the problems of low efficiency and poor accuracy of the dynamic responses of the multi-degree of freedom goafs. An example of the 3×3 unit goaf in a metal mine was compared with the numerical simulation method. The results show that this method can directly reflect the dynamic response laws of the particles in the stereoscopic goaf group, and the displacement and velocity curves are basically consistent with the numerical simulation results. The maximum displacement is the area with the application of the blasting load. The comparison between the calculation results of the multi-degree of freedom model method and the field displacement monitoring results reveals that their displacement changes are similar, their peak values are at the same order of magnitude, and the latter displacement is slightly delayed. This research provides a new way to study the dynamic responses of the complex stereoscopic goaf group.

Aggregate shape not only reflects the formation history, but also plays an important role in the mechanical properties of granular materials, and the effect of aggregate shape deserves further study. In this research, the three-dimensional particle flow code, FPC3D, is used and five particle models are generated according to the actual aggregate shape. The process of obtaining different relative density samples in numerical experiments is proposed. The effect of sphericity on the maximum and minimum void ratio is discussed, and the conclusion is basically consistent with the statistical results of the existing experiments. Numerical tests of isotropic compression and triaxial compression are carried out on the samples consisting of different shape aggregates, and the void ratio and relative density are selected as density control indexes respectively. The evolution of four micromechanical indexes with strain including coordination number, particle orientation, deviator fabric and branch vector is studied. The data show that when the particles are well-rounded, the sphericity has less influence on the peak friction angle. Instead, it mainly affects the residual friction angle. When the aggregate shape changes, the coordination number affects the strength but does not play a decisive role. The particle shape mainly influences the macroscopic performance by affecting the degree of anisotropy of contact and contact force in sample.

Numerical biaxial tests of cohesionless granular materials were conducted using a flexible boundary model to investigate the evolution of the quantity and directional probability of force chains with varied axial strain, under different confining pressures. It has found that the quantity of high-stress particles which don’t form force chains decrease as the deviatoric stress increases, indicating that more loads are born by force chains. Statistically, the maximum length of force chains is 9 particles. As axial strain increases, the probability of force chains oriented in the direction [60o, 120o] evolves alike with deviatoric stress. While the probability of force chains oriented in the two directions [40o, 60o] and [120o, 140o] evolves contrary to deviatoric stress. Two types of shear failure were found in biaxial tests: single shear band and two conjugated shear bands. According to the comparison of the probability of force chains oriented in [40o, 60o] and [120o, 140o], a single shear band occurs within the angle range with obviously less probability, while two conjugated shear bands occur when the probabilities of force chains in these two directions have slight difference.

A soil slope failure usually experiences the initiation, development, and run-through of the slip plane. The extended finite element method (XFEM) has been applied to simulate the process of slope failure in recent years. However, there are still some shortcomings to be overcome in practical applications of XFEM to landslides. For example, the initial position of the slip plane needs to be prescribed, and the extending direction of the slip front-end cannot be tracked accurately. In this paper, the mechanism of slip-plane initiation and development is introduced, and the process of automatically determining the initial position of the slip plane based on the stress history and the relative relationship between the tensile stress level and the shear stress level in the soil element is proposed and described in detail. Then, a new method for determining the front-end propagation direction of the slip plane by using the sector control domain and the circular control domain is introduced, which effectively improves the simulation precision of the XFEM for the landslide failure process. Finally, two typical slope cases with different failure types are analyzed to verify the reliability and rationality of the proposed method further.

With the application of a plasticity model for large post-liquefaction deformation of sand to model the liquefiable soil and an equivalent nonlinear incremental model to model stone columns (SC), three-dimensional dynamic responses of stone columns composite foundation in liquefiable soil are numerically investigated using finite difference code FLAC3D. The analysis investigates the effect of the SC’s high stiffness and improved drainage on soil liquefaction mitigation, the excess pore water pressure (EPWP) build-up and dissipation, the deformation process of the liquefiable soil from small to large deformation in the pre- and post-liquefaction regimes, and the variation of stress distribution between SC and surrounding soils. The results show that the model and the program can reasonably reproduce the seismic response of stone columns composite foundation in liquefiable soils and its effect of liquefaction mitigation. The vertical stress and horizontal shear stress gradually concentrate to SC during earthquake shaking and vertical effective stress ratio may decrease to 1/6-1/3, the deformation in soil and SC is incompatible and the ratio of shear strain in the soil and SC may reach 7-10. A ratio of SC permeability to soil permeability larger than 100 significantly decreases the EPWP, while the stiffness of SC slightly decreases EPWP but helps reduce the surface peak acceleration.

School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China