Dilatancy, representing the plastic flow direction of granular material, is an important part in elastic-plastic constitutive model. So far, the dilatancy equation of rockfill is mainly obtained by the conventional triaxial test, and it is not clear whether these dilatancy equations can reflect the dilatancy law of rockfill under different stress paths. In this paper, tests with four different stress paths, including constant confining pressure , constant axial stress , constant mean effective stress p, and constant principal stress ratio are conducted to study the influence of stress paths on the dilatancy. The results show that: the dilatancy ratio is linearly associated with the stress ratio under different paths, but there is no consistent relationship between the dilatancy ratio and the stress ratio; the dilatancy line translates and rotates with the stress increment direction in the - space, and the slope parameter and the intercept parameter are increased with the increase of ; the existing dilatancy equations cannot well describe the dilatancy relationship under different stress paths, and a modified dilatancy equation considering the stress increment direction is proposed and verified.

To study the effects of basalt fiber on energy absorption and fractal characteristics of cement-soil, a series of impact compressive tests and dynamic tensile tests was conducted on cement-soil with different basalt fiber contents by using a Φ50 mm Split Hopkinson Pressure Bar (SHPB) apparatus. The relationship between the basalt fiber content and three factors (i.e., energy absorption, failure mode and fractal dimension ( ) of cement-soil) was analyzed. The test results show that energy absorption firstly increased and then decreased with the inclusion of basalt fiber, and due to the existence of weak-surface made by excess basalt fiber, the energy absorption capacity was unresponsive to an increase of basalt fiber content when the basalt fiber content was more than the optimum content. The fragment-size distribution of cement-soil had a fractal property with statistical sense of self-similarity. In the impact compressive test, mean diameter of fragments increased with the increase of basalt fiber content but its appropriate had a decreasing trend. In the dynamic tensile test, when the basalt fiber content was from 0 to 2.0%, the mean diameter of fragments increased and the value of decreased. However, the mean diameter of fragments decreased and increased when more than 2.0% of basalt fiber was added. Also, there was a close relationship between the energy absorption and . In the impact compressive test, energy absorption firstly increased and then decreased when was from 2.20 to 2.26. When was from 1.85 to 2.20, the energy absorption continuously decreased in the dynamic tensile test, which shows a negative correlation between and energy absorption. The optimum content of basalt fiber plays a positive role in the dynamic properties of cement-soil, therefore, this study presents a suggestion that the optimum content of basalt fiber is 1.5% to 2.0%.

Applied with a new large-scale interface apparatus, the influence of normal stiffness on 3D monotonic and cyclic behavior of the gravel-structure interface was investigated in detail. Under constant normal stiffness condition, the interface contracts first and then dilates, and the normal stress accordingly reduces and then increases during monotonic shearing. The irreversible volumetric change of the interface grows continuously, the normal stress, peak shear stress, shear strength of the interface decreases overall due to cyclic shearing while the peak resultant stress ratio remains invariable despite of shear cycle. It is indicated that the normal stiffness plays a vital role in 3D monotonic and cyclic behavior of the interface. With larger normal stiffness, the normal stress and the peak shear stress increase more during monotonic shearing; the irreversible volumetric change accumulates more slowly and its ultimate value is accordingly smaller. Meanwhile, the shear strength of the interface decreases faster to zero and the corresponding cycle number at which the shear strength becomes zero is smaller. The normal stiffness has a markable impacts on the value of performance parameters of the interface such as the irreversible and reversible volumetric change, shear stress, resultant shear stress, except the friction angle. In addition, good consistency exists in the relationship pattern between volumetric change, reversible volumetric change, resultant shear stress and resultant stress ratio versus tangential displacement, regardless of normal stiffness.

Hydraulic conductivity is one of the critical parameters for evaluating flow properties of water-bearing media. The variation of this parameter generally leads to uncertainties of ground water flow and solute transport in fractured rock masses, and furthermore influences justification of important issues involving migration and diffusion of high-level radioactive wastes (HLW) in hard-rock repository. In this paper, we mainly focus on the permeability of meso-scale fault zones in granitic rock mass, which belongs to Jiujing, one of the pre-selected areas for Chinese HLW repository in Gansu Beishan. We carry out fluid flow tests on the undisturbed fractured samples collected from one of these fault zones via non-standard test apparatus and obtain the variability of hydraulic conductivity. We then realize the identification of dominant flow paths by slicing the samples and extracting internal flow parameters using staining solution. The results illustrate that three sets of fractures can be identified within the fault zone (Shiyuejing fault). Hydraulic conductivities of the fractured samples with more set I fractures are mainly over 10?4 cm/s, while those of samples with more set II or III fractures are respectively in the range of 10?5-10?4 cm/s and lower than 10?5 cm/s, mostly 10?6-10?7 cm/s. Permeability of the three kinds of samples thus decreases successively. Three types of flow states, namely the laminar flow type (samples 4, 6, 10-12), the infilled type (samples 2, 7), and the erosive type (samples 1, 5, 8, 9, 13, 14), are indicated by the corresponding characteristics of P-Q (pressure-flux) curves. Permeability of these three types also successively drops.

Dynamic loading tests and mesoscopic tests were carried out to study the correlation of strength indices and mesostructure parameters, which commonly degrades for disturbed structural clay. It is found that cyclic torsional and simple shears cause a remarkable strength degradation for structural clay, in the range from 20% to 50%. The strength of silty clay after external disturbance is still greater than that of the reconstituted silty clay. Cohesion and friction angle of the disturbed silty clay degrade dramatically and then decrease to a stable value with the increasing of disturbance times. The investigation of five typical mesostructure parameters show that the growth rate of void for transverse sections subjected to the torsional shears is similar to the longitudinal profile. However, the void growth of longitudinal profile is greater than the transverse value subjected to simple shears. There is a linear attenuation between post-disturbance cohesion ratios and void number at the early period, and then the cohesion will become a constant value. By contrast, there is no convergence between friction angle ratios and void number ratios.

To investigate the mechanisms of floor failure and further induced risks of water inrush by the strong unloading effect of high-stress rock mass in deep coal mining, the influence of unloading on floor disturbance and failure was analysed with the theory of unloading rock mass mechanics. It calculated the strong disturbance characteristics of floor rock mass unloading damage in deep coal mining by using the discrete element method (DEM). Based on triaxial unloading tests and the concept of damage factor, we obtained the relationship between unloading percentage and damage factor, determined the propagation and failure condition of rock mass, and achieved the unloading disturbance partition of floor. Then the disturbance hazard of floor rock mass unloading damage and failure in deep coal mining were further studied. The results show that with mining depth increasing, both unloading starting point and unloading stress of floor are increased, but the unloading percentage is reduced, in which the lower unloading percentage causes damage severely in deep coal mining. When the unloading percentage of rock mass is greater, its unloading rate and displacement and the permeability coefficient become higher, which easily induces floor rock mass instability propagation. When the dip angle of crack and the ratio of horizontal stress and vertical stress are low, it easily reaches the propagation and failure conditions of floor rock mass unloading.

An experiment using the rings of 34 mm in thickness, 50 mm in external diameter, and 8-30 mm in internal diameter was designed via the ring test, to analyze the stress characteristics around the hole. Strain gauges were used to record the strain changing around the hole during the test, and the mechanical properties of specimens were studied. The results indicate that the peak load of the specimens decreases with the increase of internal diameter. Both the discs and ring specimens with relatively small internal diameters have abrupt failure when they reach the first peak load. However, when the diameter is greater than 16 mm, there is no clearly defined stress drop after the first peak stress, but a distinct stress drop after the second peak stress is reached. The stress at the weakest point in the ring specimen is a structural parameter rather than a material parameter, and it changes with different internal diameters. The Hobbs’ equation based on elastic mechanics may not be suitable for determining the tensile strength of rock. Rock specimen needs adequate tensile deformation to fail until it reaches the limit stress. The failure of the borehole in the rock may be evaluated by the tensile deformation instead of tensile strength. The results provide important reference for mechanical characteristics of rock under compression-tension stresses.

As a connecting part between surrounding rock and the segment, the backfill layer is used to stabilise the lining, transfer the load, and absorb the deformation. During the construction of shielded TBM tunnel, the backfill layer had two main states: loosened before grouting and consolidated after grouting. The effect of the backfill layer and characteristics of the segment stress depend on the state of characteristics of segment stress. The similar model test was used to analyze the mechanism of backfill at different states, and the following conclusions were obtained. When the backfill is loosened before grouting, due to the radial compression and circumferential movement, the load value of the surrounding rock to the segment is reduced, and the distribution is more uniform. At this time, the backfill is used as the "compressible layer" to reduce pressure and to make the pressure uniform. The backfill can significantly reduce the force and deformation of the segment. When the backfill becomes consolidation after grouting, the backfill layer can bear a small amount of load and deformation, but the bearing capacity is limited. At this time, it becomes the "transfer layer" between the surrounding rock and the segment. The extrusion of the shield rock TBM tunnel construction may use the backfill compressibility before grouting, and reduce the segment force and deformation. Shallow and subway tunnels should be grouting as soon as possible, so the lining and the surrounding rock can form a stable force system. The increase of elastic modulus of the backfill layer can improve the support stiffness of the backfill to the segment system, but the effect is not obvious.

To investigate the permeability evolution of deep coal under the influence of mining disturbance, two forms of permeability model including the damage and fracture effect were established. These two forms were exponential form and cubic form, respectively. These two permeability models were based on the previous coal permeability model in three-dimensional (3D) stress state. The derivation process included two aspects, i.e., the fracture deformation caused by adsorption and the deterioration of elastic modulus from matrix caused by damage. Meanwhile, the internal swelling ratio and the damage constitutive based on Drucker-Prager failure criterion were introduced into the models. According to permeability tests under conventional triaxial compression, loading-unloading under mining disturbance and changing the gas pressure, the permeability of coal in the tests were analyzed in detail. The results show that these two models can reflect the permeability evolution in the conventional triaxial compression and loading-unloading tests. Moreover, these two models can represent the decrease of coal permeability with the increase of gas pressure under the constant effective confining pressure condition. In the loading-unloading and changing the gas pressure tests, the fitted results in exponential form are slightly better than those in cubic form. This study provides a useful reference for developing the technology of deep coal mining and gas extraction.

This paper investigates the strength characteristics of water-rich sandy gravel subjected to freezing, as this soil is often encountered in Beijing. A series of triaxial compression tests has been performed on sandy gravel samples obtained at mining station of Beijing Metro at different temperatures (?5℃, ?10℃, ?15℃, ?20℃) and confining pressures (0.0、0.3、0.8、1.3、2.0、3.0、 4.0 MPa and 8.0 MPa).The results show that: the behavior of frozen sandy gravel is dominated by strain softening, and the ideal plastic failure mode occurs only when the soil experiences high negative temperature and confining pressure; the strength, cohesion and friction angle of the soil all increase with the decrease of temperature. The variation of strength with temperature satisfies an exponential distribution, while the changes in cohesion and friction angle follow a linear relationship; the strength and elastic modulus of frozen sandy gravel increase as the confining pressure increases, but the increasing rate descends gradually. The Mohr - Coulomb criterion can still be used effectively to characterize the soil’s compressive response at low confining pressure. The failure mode of frozen sandy gravel is represented by shear failure with diagonal fractures on the lateral sides of the specimen. Tensile failure occurs when the specimen is subjected to a low confining pressure, and it is influenced by the formation of ice significantly. The mechanism of volumetric inflation has been found when a high level of temperature and confining pressure is applied to the specimen.

Tunnel surrounding rock seepage boundary conditions can be roughly divided into four types based on water level, drainage design and construction approach, and the seepage boundary conditions to adapt to different construction conditions are discussed in detail. An analytical formula to calculate pore water pressure in tunnel surrounding rock and tunnel water inflow under four kinds of boundary conditions is obtained by adopting the method of conformal mapping of complex function. Comparison between analytical solution and numerical solution confirms the correctness of the analytical solution. Based on the relationship between tunnel water inflow with buried depth diameter ratio ( ), as well as the relationship between surrounding rock pore water pressure and under different boundary conditions, the influence of boundary conditions on shallow-buried tunnels and deep-buried tunnels is analyzed. Selection of boundary conditions for shallow-buried tunnel seepage calculation is also discussed. The conclusions for tunnel seepage calculation and drainage design reported in this article provide theoretical guidance for engineering practice.

Since the emergence of reinforced soil, reinforced soil retaining walls, which are composed of panel facing, reinforcement and soil, have been widely studied and used in civil engineering such as road engineering and railway engineering. Soil compaction has a significant influence on the deformation, earth pressure, and reinforcement tensile force of reinforced soil retaining walls. In order to study the influence of soil relative compactness on reinforced soil retaining walls, three groups of centrifugal model tests with different soil relative compactness are carried out and the following conclusions have been drawn by analyzing the experimental data: the horizontal deformation of the panel facing decreases as soil relative compactness increases, especially in the loading period; the tested horizontal earth pressure values behind the panel facing are greater than the design values because of soil compaction; the tested reinforced soil retaining walls are conservative because the interface friction coefficient between the reinforcement and the soil is less than the value recommended by design codes; analysis shows that the connection force between reinforcements and panel facing is smaller than the value of horizontal earth pressure obtained from the model tests.

Hydrogeological conditions of the coal mining are becoming increasingly complicated, especially, the water pressure in a confined aquifer is getting higher and higher. When the disaster of water-inrush occurs, under the condition of the high hydraulic gradient, it brings the problem of high-velocity non-linear water flow through the water-inrush channel of fractured rock mass. An experimental apparatus was designed to study the behaviour of high-velocity non-linear water flow through the porous media under the condition of the high hydraulic gradient (up to 600). One-dimensional (1D) uniform flow in the homogeneous porous media was experimentally investigated. The porous media was constructed by six types of smooth balls with the diameters ranging from 1 mm to 6 mm which were used to simulate the broken rock mass. Experimental results indicated that, for the porous media with the porosity between 0.44~0.45, when the hydraulic gradient is greater than 145, the process of water flow through the porous media could be divided into three stages: the linear laminar flow, nonlinear laminar flow and turbulence by analyzing the curve of hydraulic gradient and velocity, the curve of hydraulic gradient and Reynolds number. Moreover, the obtained critical flow velocity of the transition from linear laminar flow to non-linear laminar flow is 0.23~0.78 cm/s, the critical hydraulic gradient is 3~8. While the critical flow velocity of the transition from laminar flow to turbulent is 1.6~4.8 cm/s, the critical hydraulic gradient is 90~145. As the particle size increases, the critical flow velocity increases gradually, but the critical hydraulic gradient decreases. The results also show that the permeability is a linear positive correlation with the square of the particle size as well as the non-Darcy flow influence coefficient with the reciprocal of particle size. Moreover, with the increase of permeability, the non-Darcy flow influence coefficient decreases exponentially. Finally, the conclusions can provide some significant references for the problems of water-inrush in high water-pressure confined aquifers in practical engineering and the theoretical study of non-linear seepage flow through the porous media.

The application of rigid-drainage pile, combining vertical drainage and rigid pile, is a new technology for mitigation of liquefaction. Shaking table tests were carried out to investigate the performance of the rigid-drainage pile against liquefaction. The response of excess pore water pressure, acceleration and lateral displacement of pile top were monitored and analyzed. The results indicated that the use of rigid-drainage pile was an effective method to mitigation of liquefaction. There was much water drainage from the drainage pile when the shaking motion was applied, yet no water drainage for the ordinary pile. The mean value of peaks of excess pore water pressure decreased 12% for the rigid-drainage pile comparing to the ordinary pile. The value of excess pore water pressure approximately decreased 13% when the excess pore water pressure became stability. The effect of drainage was mainly in the previous period of shaking. The lateral permanent displacement on pile top decreased 27% for rigid-drainage pile compared with ordinary pile. The liquefaction, shear-strain hysteresis loops at previous stage were more pronounced than that of post liquefaction stage. the secant modulus of rigid-drainage pile is larger than the ordinary pile. The results of the tests illustrated the effectiveness of rigid-drainage pile in mitigation of liquefaction.

Aiming at the influence of anchorage length on stress conditions in bolt as well as the calculation method for its critical value, a nonlinear stress-slipping model of anchorage interface was introduced to develop shear stress, axial force and displacement solutions of bolts using load transfer method. The influence of anchorage length on stress conditions in bolt, mainly including load-displacement relationship, shear stress distribution as well as softening load and ultimate bearing capacity, was discussed. The calculation method for critical anchorage length was proposed and verified by the engineering applications. The results indicate that the load-displacement relationships of bolts with small anchorage length perform as unimodal curves with low bearing capacities. A slowness changing of the segment aroused accompanying with the increasing of anchorage length. Shear stress distributes uniformly along bolts with small anchorage length and the bearing capacity is very small. The non-uniform characteristics occur with the anchorage length increase and the bearing capacity also increases. The softening loads, ultimate bearing capacities and the bearing capacities of bolts approximate toward constant values after the anchorage length reaches critical value. The calculation results of the critical anchorage lengths show good agreement with the actual values in engineering cases for bearing tests, thus this proposed method is feasible and effective.

The soil-pile interaction has always been of critical importance in geotechnical engineering related to pile foundations. However, there’s a lack of research and insufficient understanding regarding the load bearing performance for energy piles due to the unusual loading conditions where both the thermal and mechanical loading apply. Based on the ideal elastoplastic model and the hyperbolic model, a new pile-soil load transfer model considering Masing’s rule was proposed. The proposed model adopted the piecewise nonlinear method to modify the pile-soil load transfer backbone curve. Extensive numerical investigations were conducted to investigate the impact of the loading on the thermo-mechanical behavior of the energy piles. In addition, a physical model test was conducted to provide an in-depth understanding of the load transfer mechanism between the soil and the energy pile, and the thermo-mechanical behavior of energy piles. The axial stress and shaft resistance were measured as the temperature and depth changed. The results compared with those from the improved-approach-based numerical calculations indicate that thermo-mechanical behavior of energy piles can be described by the modified pile-soil load transfer model. The results obtained by the numerical simulation are in alignment with that of the physical model test, indicating that the modified model is suitable for the energy piles considering both the mechanical and cyclic thermal loading.

Based on Leclaire’s extension of the Biot model for saturated porous elastic medium, the propagation characteristics of the body waves in a three-phase porous elastic medium with two types of solid phase components are studied. Firstly, based on the Helmholtz decomposition of the displacement vector, the characteristic equations of the body waves in saturated frozen soil are established. Then the effects of the volume fraction of each phase, the shape of the particles and the contact between the particles on the inertial parameters, viscous parameters and elastic parameters are studied. The model of saturated frozen soil is degraded. The characteristic equations and propagation characteristics of body waves are analyzed assuming only liquid water or ice in pores. Finally, a numerical calculation is carried out to explore the relationship among phase velocity, attenuation coefficient of waves and parameters of soil consolidation, saturation, porosity, particle contact, wave frequency etc. The calculation results show that, different from saturated soil, there are 5 types of body waves in saturated frozen soil, i.e. 3 compressional waves and 2 shear waves. All body waves present dispersion and attenuation. The dispersion and attenuation of P1 wave and S1 wave are much smaller than those of P2, P3 and S2 waves. Body wave propagations are significantly affected by cementation parameters, saturation and porosity, but are slightly affected by contact parameters.

Three-point bending (TPB) specimens can realise out-of-plane fracture through pre-establishing a crack surface which is perpendicular to the under-surface while inclined to the front and back surfaces. The finite element method (FEM) software ABAQUS is applied to calculate stress intensity factors (SIFs) of mode I, mode II and mode III crack front along the thickness of the specimen with different inclined angles θ. It is clear that mode I and mode III dimensionless SIFs can get a larger value, while mode II dimensionless SIF is insignificant when it is close to the mid-point of the specimen thickness. As a result, this kind of specimen can be used to investigate mixed-mode I/III of materials. Numerical results are compared with the analytical formula of the conventional TPB specimen and the approximate formula of the TPB specimen with the inclined crack surface. The accuracy of numerical results is proved and the problems of the approximate formula are discussed. Mixed-mode I/III fracture behaviour of sandstone is studied in 7 groups of 28 specimens. The results show that the critical SIFs of mode I and mode III increase with the increase of inclined angle then decrease, while the variation tends are different; mixed-mode I/III effective fracture toughness also changes with the inclined angle and reaches the maximum value when θ=20°. The crack surface tilts when the crack propagates, and the lager θ is, the greater tilted angle can get.

Expansion is an important strategy to increase the capacity of a landfill, but the induced deformation by expansion can threat the stability of the landfill and its internal structure. Synthetic municipal solid wastes (MSWs) which exhibited engineering characteristics similar to MSW in China were developed, and a series of centrifugal model tests on the deformation of expanded plain-type landfill under self-gravity stress was performed. The settlement of landfill under self-gravity stress decreased as the MSW age increased with a maximum settlement of approximately 20% of the initial landfill height. Differential settlement of the interface between the old landfill and the new landfill decreased with the increase of old landfill MSW age. The maximum value of horizontal displacement on the interface occurred under the slope shoulder, and increased with the increase of slope ratio and decrease of filling age. The engineered berm restricted the settlement of the old landfill before expansion, but the settlement restriction was weakened as the height of landfill increased after expansion. It might induce large difference of the horizontal displacement on the interface. The results of the tests are slightly larger than those of one-dimensional settlement calculation of the landfill, and can provide reference for the expansion and liner system design, stability assessment and landfill operation.

Hardening soil model is commonly used in geotechnical numerical analyses. In order to study the effect of loading path and drainage condition on the shearing behaviors of undisturbed granite residual soil. Four series of triaxial tests, including the conventional consolidated drained tests, the conventional consolidated undrained tests, the consolidated drained laterally unloading tests and the consolidated undrained laterally unloading tests have been conducted on the undisturbed samples of granite residual soil in Shenzhen. The values of model parameter for different conditions were also calibrated from the test results. It was observed that the specimens first contracted and then dilated in the shearing stage of the conventional triaxial test, but always dilated in the laterally unloading tests. The values of model parameters were closely related to the loading path. The effective internal friction angle measured by the CDLU tests was 20% higher, and the effective cohesion was 46% smaller than those by the CD tests. The reference secant modulus determined from the CDLU tests was 2.9 times, and the unloading-reloading reference secant modulus was 1.8 times those from the CD tests. The values of model parameters were also affected by the drainage conditions. The effective internal friction angle obtained from the CU tests was similar to that from the CD tests, but the effective cohesion obtained from the former was significantly larger than that from the latter. The reference secant modulus determined from the CU tests was twice that from the CD tests, and the unloading-reloading reference secant modulus obtained from the former was 3.8 times that from the latter. Hence, the values of parameters should be determined in accordance with the real loading and drainage conditions for geotechnical numerical analyses.

Given that rock bulking is of great significance to water storage capacity and ground surface subsidence of coal mine underground reservoir, the 22615 working face in one mine of Shendong coalfield was selected as the engineering background. The stress and the bulking coefficient distribution laws of caving rock in goaf were analyzed by using the similar material model test, and then the stress-bulking coefficient relation of caving rock was established, which was verified by rock compaction experiment. Moreover, the compaction characteristic of saturated rock was revealed. The results show that: along goaf advancing direction, overlying strata subsidence is limited by the structures of cantilever beam near the boundary where the stress of caving rock is relatively low (0.32 MPa), and the corresponded maximum bulking coefficient reaches 1.48. Due to the instability of main roof structure, caving rock is compacted by overlying strata in the middle area, rock stress trends toward 1.5 MPa, while bulking coefficient reduces to 1.09. It is clear that the height exhibits a negative correlation with caving rock stress but a positive correlation with bulking coefficient in goaf vertical direction. There is a negative logarithmic relationship between stress and bulking coefficient of caving rock along either advancing direction or vertical direction. By comparing with natural rock, the bulking coefficient damping of saturated rock shows obviously under loading, which has a difference of 8.514%. This study provides a theoretical basis for water storage capacity and ground surface subsidence predictions of coal mine underground reservoir.

Due to irregular shape, calcareous soil particles are prone to produce interlock, which results in different earth pressure transmission from ordinary cohesive soil. To study the distribution and response of calcareous soil pressure in road foundation and on the retaining wall under different loading conditions, the soil pressure under the vehicle dynamic load was monitored at a coral reef site. The study is focused on the transfer and distribution of earth pressure in calcareous soil under the weight of fill and the moving load of the vehicle and the vibration compaction load of the roller. The results show that the lateral pressure coefficient is 0.2-0.3 and the average value is 0.25. The observed earth pressure on the roadbed is much higher than that calculated according to the theoretical formula. At the depth of 3.28 meter in the roadbed after rolling, the additional load of heavy vehicles is small. The increment of the additional soil pressure in the foundation at the depth of 2.73 meter is extremely small. However, when the 22-ton vibratory roller is vibrated and rolled, the additional stress increment of the foundation at a depth of 2.73 meter is extremely small. Hence, it is difficult to increase the compactness of the soil at this depth. Just the shallow soil can be effectively compacted.

To investigate the effect of sandy fillings on the shear strength of rock joints, direct shear tests were conducted on single-joint fine-grained marble specimens infilled with four types of sands with different frictional coefficients. The results show that the peak shear stress of unfilled marble joints was greater than those of infilled marble joints under a same normal stress. It is indicated that the existence of sandy fillings reduced the shear strength of rock joints. A new empirical formula for the shear strength of the unfilled joints was proposed, expressed by the three-dimensional roughness parameter of maximum valley depth of the joint surfaces, and its calculated shear strength of the unfilled joints roughly coincided with their test values. An empirical formula of peak shear strength for infilled fine-grained marble joints was also obtained, expressed by the friction coefficients of infilled sands. the predicted shear strength of infilled rock joints was in accordance with the test values. Above conclusions have some helps to evaluate the stability of infilled jointed rock mass in rock engineering.

In addition to the critical slip surface, the potential slip surface of each step and other slip surfaces which do not meet the specification requirements of bench-shape slope also need to be considered. Based on strain softening theory, the development of shear strain in bench-shape slope is simulated by FLAC3D, and the multi-slip surfaces have been obtained. Meanwhile, the strength parameters and evolution of safety factor of slip surface in strain softening process have been analyzed by using vector sum method. Examples of double-step slope and complex multi-step slope show that: the critical and secondary slip surfaces can be obtained; the strength parameters in the slip surfaces gradually change from peak strength to residual strength as the strain softening progresses. However, the speed is different. With the development of strain softening process, the safety factor of all slip surfaces reduces gradually, and finally tends to a constant value.

The long-time weathering causes significant deterioration of earthen building materials, which poses a great threat to the durability of earthen monuments. This process, however, keeps unknown under the real weathering conditions because of their complexity and large time scale. Soil micro-structure changes with the natural exposure and its evolution is an important feature characterizing the deterioration process. The loess road cuts, which were exposed to similar weathering for different years, were selected as analogy model to capture the evolution of micro-structures of undisturbed soil samples from surface and internal parts, respectively. Scanning electronic microscope (SEM) was used to observe the fabric and texture of soil samples. Mercury intrusion porosimetry (MIP) was used to measure the pore size distribution (PSD) quantitatively. The experimental results show that the micro-structure of surface soil changes much more significantly with weathering time compared to that of internal soil. The fabric of surface soil is in lamellar form and its PSDs are bimodal (i.e., inter-aggregate pores and intra-aggregate pores). The inter-aggregate pores volume accounts for a larger proportion in the surface soil and shows a decreasing trend with weathering time. Fractal analysis of pore surface indicates that building age has a tendency to decrease the irregularity and roughness of micro-pore walls in the surface soil samples, which could lead to a reduction in friction forces between soil aggregates or particles. Consequently, surface weathering, like crusts or peeling off, or other diseases would be engaged at the macro-scale.

During construction of anchorages for a high rock slope, whether the anchorage force can be maintained is the key to the slope anchorage engineering, and thus it is essential to understand time-dependent variation mechanisms of the anchoring force. Firstly, we discussed the high slope anchorage engineering projects which had significant sustained loss of anchoring prestress, analyzed the occurrence mechanism of such rapid variation of the anchoring prestress, and found that it is inevitable to consider the effect of high slope strong unloading on the initial anchoring prestress loss process during the calculation. Then, based on an improved visco-elastoplastic model, a new model was established by introducing conversion time K and a prestressed anchor cable in parallel. Finally, through the anchored cable’s prestress monitoring data of LE1915 drainage hole and L2J connect hole 0 + 126 m on the left bank of Jinping I hydropower station, the newly developed model is verified to be suitable to be applied in high slope anchoring engineering, and also confirm its accuracy and broad application by comparing with the original model. Not only the newly developed model provides theoretical guidance and technical means for the control and compensation of anchor cable’s anchorage force, but also has an important significance to the long-term safe operation and early warning of high slope anchoring project.

Design of vertical hole supporting structure in foundation should be based on its active earth pressure. So it is often necessary to calculate the active earth pressure on the hole wall after excavation of vertical holes. The foundation containing vertical hole is a typical axisymmetric problem, the traditional Rankine or Coulomb solution which is based on plane strain assumption is inapplicable, the existing methods for axisymmetric active earth pressure often presume the ratio of earth pressure and the major principal stress (tangential stress coefficient ?) is constant, such as Harr-Von Karman hypothesis and other similar methods, this assumption is not rigorous in theory and the calculated results have large enough error. In this paper, the slip line field equations for axisymmetric problem are established, the method of maximizing the active earth pressure and the iterative method are used to solve the circumferential compressive stress coefficient the ?, the effects of soil parameters and vertical hole geometry parameters on ? are analyzed, then the accurate value of active earth pressure can be determined. This method is more rigorous in theory and the result is more reasonable compared to that under plane strain assumption condition.

The fractional Kelvin-Voigt viscoelastic model is introduced to describe the rheological characteristics of saturated soils. One-dimensional consolidation characteristics of saturated soils with fractional viscoelastic model under symmetric semi-permeable boundaries is studied. By applying these two models, the analytical solution to the one-dimensional consolidation is obtained in the Laplace transform domain. Crump’s method is adopted to perform the inverse Laplace transform to obtain semi-analytical solutions in the time domain. By reducing the proposed solution to one dimensional consolidation equation of saturated soils under symmetric semi-permeable boundaries using these two models, it is shown that the present solution is reliable and in a good agreement with the existing solutions from literatures. Finally, several numerical examples are provided to investigate the consolidation behavior of saturated soils with the fractional viscoelastic model under symmetric semi-permeable boundaries. It can be found that the one-dimensional consolidation process is affected by the semi-permeable boundary parameters, fractional order and viscosity coefficient, and the modulus of compressibility has a significant effect on the final settlement of saturated soil.

In order to study the elastic modulus degradation and dynamic characteristics of permafrost at different temperatures, the stress-strain hysteresis curve and fatigue damage life under dynamic load were obtained by cyclic loading and unloading test of frozen soil samples under different below-zero temperature conditions. Fatigue damage parameters of permafrost at different temperatures were determined according to the relationship between fatigue life and stress amplitude. According to the law of elastic modulus degradation of permafrost, the governing equation of dynamic model was proposed and the phenomenological model of fatigue damage of permafrost was established. According to the characteristics of cyclic loading and unloading hysteresis curve measured by permafrost, the method of joint analysis of damping ratio under ideal and non-ideal hysteresis loops was proposed. Based on the Kelvin model, the mathematical relationship between the evolution of the hysteresis loop and the elastic modulus degradation and loading time was established. The study shows that: the phenomenological fatigue damage model, which takes into account the effects of the elastic modulus attenuation, describes the accelerated fatigue damage characteristics of permafrost. Equivalent hysteresis and non-ideal hysteresis damping ratio analysis method is good for taking account of the actual evolutionary characteristics of hysteresis loops. The Kelvin rheological model based on elastic modulus degradation establishes the mathematical relationship between the hysteresis loop and the unloading time.

The characteristics of the nonlinear accelerated creep stage of rock cannot be represented by the traditional model combined by the linear element, which brings great challenges to engineering applications. We proposed a new nonlinear viscous dashpot element with a strain trigger which was further connected with the Bingham model to form a new one-dimensional (1D) constitutive model. The newly established model can represent the constant and accelerated creep characteristics of rock, and the corresponding 3D constitutive equation was deduced in detail. Then, the attenuation law of the elastic modulus during the triaxial compression process was introduced into the 3D creep constitutive equation to obtain 1D nonlinear creep constitutive model which can reflect the whole process curve of rock creep. The model parameters were identified by the triaxial compression creep experimental data of mudstone. From the comparison of results calculated by this model and experiments, it can be concluded that the improved Bingham model not only can describe preciously the three creep phases including deceleration creep, stable creep and acceleration creep of soft rock, but also has the advantages of few components and simple combination form. This study provides a new study reference for the nonlinear creep constitutive model of soft rock.

The excavation-induced settlement of soil behind retaining wall is analytically deduced based on displacement boundary problem under plain strain condition. The analytical formula of ground settlement caused by the rigid movement or parabolic flexible movement of retaining wall is derived by the fundamental solution for ground settlement caused by rigid horizontal movement of retaining wall. If the retaining wall influences infinity, the analytical formula and the fundamental solution are in the same. The fundamental solution induced by rigid horizontal movement of retaining wall is used to verify the analytical equation. The solutions of integrated form under deformation conditions of rotation with respect to bottom, rotation with respect to top, triangle-bugling movement and parabolic flexible movement are also used to verify the analytical equation, respectively. The results are in good agreement. Finally, the analytical formula is applied to prediction of measured data in the field. The extent of application is illustrated by the comparison between the analytical equation and in-situ measured data. When the wall deflection is small, the proposed analytical equation can predict settlement well. When the wall deflection is large, the normalized settlement curves derived from the analytical equation can predict settlement anywhere behind retaining wall safely. The results prove that the proposed analytical equation is practicable.

Undrained creep pore-pressure equation is almost a blank in the field of mathematical modelling of rheology behaviors of clay. Based on the theoretical framework of critical state soil mechanics, the movement of the state boundary surface (SBS) with time was formulated. Then the undrained creep pore-pressure equations for normally consolidated clay were presented, which is independent on the shape of the SBS and constitutive models. The undrained creep pore-pressure of normally consolidated clay is interpreted by the coupled effect of volumetric creep and shear compaction, the former is relating to the parameter and the latter is relating to the shape of SBS. Two kinds of equations with double log and single log forms which can be easily used in pore-pressure test data analysis were then presented. Using the SBS of modified Cambridge model as an example, the slopes of the pore-pressure curves in double and single log scales, defined by m and m′ respectively, were compared with the parameter . The proposed method statistically simulated the pore-pressure coefficients of Leda clay obtained by Walker, and interpreted the pore-pressure coefficients by the two mechanisms.

Elastic coefficient (k) of cemented filling materials and roof-untouched filling height (h) are key impact factors on the roof stability in cemented filling mining. Based on the principle of flexible supporting, roof deformation was divided into two stages, i.e., under the gravity stress of overburden rock and the roof presented flexural deflection. Both roof and cemented filling materials under the gravity stress of overburden rock were contacted with each other. Accordingly, mechanical models were established for each stage. Panlong Lead-Zinc deposit in Guangxi was selected as the case study to investigate the characteristics of roof deflection with different roof-untouched filling heights and elastic coefficients. The results show that roof-untouched filling height is the dominant factor which affects the deflection of the roof when k≥0.1 GN/m3, and the elastic coefficient would play the key role when k≤ 0.1 GN/m3. Cemented filling materials can effectively control the movement of roof strata and reduce the strain energy stored in roof strata when k≥0.1 GN/m3 and h≤300 mm. The theoretical analysis results are consistent with the in-situ drilling, indicating the feasibility of this study.

In order to accurately obtain the distribution rule of initial geostress field of Sangzhuling tunnel site, a two-stage back method to calculate initial geostress in rockburst area is presented. Based on the least square method, multiple linear regression is used to analyze the initial geostress field and with superposition principle, the initial geostress field is obtained. The wall stress after tunnel excavation is measured through stress relief method. According to the site of rockburst, the lateral pressure coefficient is acquired and then compared with its equivalent value from the primary inversion in the corresponding position. If both values are larger than or equal to or less than one, then the lateral pressure coefficient is assumed to be the calculated value of primary inversion and the value is taken as the constraint condition to modify the initial geostress. When the calculated secondary wall stress acquired from the modified initial geostress is close to the measured one, the secondary geostress is obtained through the regression analysis with the modified initial geostress and in-situ geostress. The conclusions show that when a small number of boreholes are used for in-situ geostress and with a large computational domain, there are some errors between the measured stress and the calculated stress from the primary inversion in positions far from the boreholes. Furthermore, based on in-situ geostress, the secondary inversion modifies results by using measured secondary wall stress as a complement, and then the calculated stress in positions far from the boreholes shows better agreement with the measured stress, which can be presented as an inversion method to provide reference for similar research projects.

Considering the impact of the shaft friction on rock-socketed section in karst area, a series of methods was developed to determine the safe thickness of cave roof. Firstly, considering the bending stiffness of the entire rock roof, the equation of anti-bending thickness can be acquired by using elastic theory and the first strength theory. Secondly, considering the contribution of the shaft friction for altering the distribution of the load on pile, the Griffith criterion and Mohr criterion were introduced to check computations of the anti-punch-shearing and the anti-shearing capacities of the cave roof respectively. Then, the accuracy and correction of the method verified by ABAQUS, and the integrated analyzing model for the cave roof and the rock-socketed pile is simulated. The calculated result agreed well with the simulation’s result. Finally, the effect of the ratio of roof thickness and span on the thickness of the safe roof were investigated, while the effect of the nature roof thickness on anti-punch-shearing and anti-shearing capacities and the effect of coefficient of rock-socketed friction on safe cave roof thickness were analyzed as well.

To investigate the water seepage characteristics and formation mechanism in an ancient building base (ABB), site investigation, in situ monitoring, laboratory test and numerical methods are employed to study the water field in an ABB. The causes of water seepage, spatial-temporal distribution and migration of water during the rainfall are analyzed in detail. The research results show that the causes of water seepage of the ABB are rainfall infiltration rather than plants irrigation. The rainfall has a greater influence on 2.0 m depth rammed soil underneath the base top than the influence at the other positions, and the water has a tendency to migrate from the base top to base bottom. It is indicated that the impervious layer has been in disrepair for long years and the leakage pathway in the rammed soil has been generated. During 2 hydrological years, 3.0 m depth rammed soil adjacent to the side wall of ABB was saturated and was easily influenced by the rainfall infiltration, which caused bloom of the crystalline materials and occurrence of peeling and water seepage. After 10 hydrological years, the water migrated from the base top to the crown of city-gate, and water seepage and peeling happened. The evolution law and formation mechanism of water seepage hazards are analyzed in details through different approaches, and the results can provide scientific base for seepage prevention and restoration measures of the ABB.

Conventional gob-side entry retaining technology has some limitations, such as mining speed restriction and risks of working in the goaf. In this study, we proposed a modified gob-side entry retaining technology named pier column reserving technology in the wide roadway. First, a wide roadway is excavated, and a row of pier columns are established in the middle of the roadway. One side of pier columns is the conveyance roadway of the working face, and the other side is the rail roadway of next working face. Then the rail roadway with the support of pier columns can be retained to use for the next working face. The results show that the pier columns can maintain the stability of surrounding rock during roadway drivage. Meanwhile, the safety is improved greatly by avoiding working behind the working face. During the roadway excavation, the technology of roadway secondary excavation and the bolt-column combined support are used to guarantee the roadway stability. At the stage of gob-side entry retaining, the high strength pier columns have great performance on roof cutting and supporting. When the distance between pillars is 1.5 m, the required pressure of pier column for roof cutting is 21.53 MPa, which is lower than the compression strength of pier columns. The bearing capacity of the pier column meets the requirements of gob-side entry retaining. The relative displacement of the top and bottom plates is 652 mm, and the maximum convergence of pier column is 164 mm. The pier column can play a certain role in relieving pressure and has good support to the roof, which can be well adapted to the roof activity law of gob-side entry retaining.

In view of the “eight” shaped micro-pile composite structure with a roof connection, relying on the upgrading project of the Guangtong-Dali railway, in-situ test of micro-pile combined structure to reinforce stage excavation landslide was carried out to study the anti-siding mechanism. The results show that under the action of sliding thrust, the axial force distribution of each row of piles was different, and the distribution law of anti “S”, “double bow” and “S” was successively presented along the thrust direction. The peak axial force of each row of piles was tension, and the proportion of the side piles of the mountain: the middle piles: the roadside piles was 2.5:4.1:3.2. The maximum axial force of the side piles of the mountain was at the lower part of the piles, the middle piles appeared at the middle and upper part, and the roadside piles appeared at the upper part of the pile body. The coordination effect of the top cap on the inclined pile group was more significant than that of the general vertical pile group. The pile group under horizontal load was prone to large flexure deformation. Under the combined influence of pile group effect and slip surface, the transfer of tension and pressure forms of pile body were generated. The force mechanism of the composite structure is that: the first two rows of piles are subjected to tension, the bottom embedded section of the third row piles is compressed, and the compression zone demonstrates upward trend with the continuous load. Our results also show that the axial force of the single pile is dominated by the tension force, which is beneficial to the exertion of the internal steel in tension.

To deal with the difficulty of quantifying the complex influence relations between multiple influencing factors of the stability of stope roof in the gently inclined thin to mid-thick deposit, Shanghengshan Mine is selected as a case study. Firstly, the influencing factors of stope roof’s maximum tensile stress ( ) and maximum settlement ( ) were determined through the numerical results of the single factor test program, and their impact features were analyzed. Secondly, according to the physical meaning analysis of the influencing factors, the dimensional model and dimensional model were defined, respectively. Based on these models, the numerical simulation uniform test of influencing factors of stope roof’s stability was designed, and the dimensionless equations of stope roof’s and were deduced through experimental results. Finally, the dimensionless equation of stope roof’s was verified through the comparisons with the measured settlement from several gently inclined mines. The verified results show that the predictions results from the dimensionless equation are basically consistent with measured results with an average error of about 9.68%, which shows good prediction effectiveness. This study can provide a reference for the selection of mining parameters and the management of stope roof of gently inclined mines.

This paper is focused on scattering and diffraction of Rayleigh wave caused by local topographies. For this purpose, a substructure replacement technique based on the theory of soil-structure interaction is used to evaluate the effects of canyon, vertical fault fracture zones and mountains on scattering and diffraction of Rayleigh wave. Based on the substructure theory, the scattering problem is decomposed into three parts: solving the dynamic stiffness of the ground of excavation, solving the dynamic stiffness of the complex structure and solving the input wave of the free field. The dynamic stiffness of the ground of excavation and the complex structure are solved using scaled boundary finite element method (SBFEM). In order to validate the proposed method, two examples are solved and the results are in good agreement with those reported in the literature. Then the scattering of Rayleigh waves by a variety of complex terrains, such as canyons, vertical faults and mountains are analyzed. Numerical results are presented in graphical form for the surface displacement and displacement spectra. Conclusions in this study can be useful in engineering practice. The proposed method can be applied to the design of seismic isolation ditch and seismic adaptability analysis of dam and bridge.

In the present work, a numerical study is presented to solve the problem of ambient vibration isolation using piles as wave barriers. Based on the periodic theory of solid-state physics and finite element method, the attenuation zones of rows of pile barriers are studied. The governing equations and boundary conditions are formulated as coefficient forms of partial differential equations (PDE), and solved by the aid of COMSOL PDE interface. First, the influences of some related parameters, such as physical parameters of soils and pile configurations on the attenuation zone are thoroughly discussed. Second, a periodic pile-soil system accounting for a practical ambient vibration is designed and the isolation effectiveness is numerically simulated both in frequency domain and in time domain. Results indicate that the periodic theory can be used to reveal the dynamic performances of pile barriers, which opens a new window for the application of pile barriers in ambient vibration attenuation; the equation-based modelling COMSOL PDE method can be used not only to calculate the attention zone of periodic structures, but also to analyze the responses of finite periodic structures both in frequency domain and in time domain.

Energy pile is an innovate technology which can simultaneously support building load and acquire geothermal energy. In the practical use, expansion or contraction of the piles induced by thermal load will be restrained by the upper structure and bearing layer of pile bottom. Thus, the pile stress and displacement will be significantly influenced. However, there are only few studies focusing on this issue. Based on model test and numerical simulation methods, the thermal stress and displacement of two types of heat exchange piles (U-shaped and W-shaped) under different pile head and pile tip restraints were analyzed. Furthermore, the position of null point influenced by the pile head stiffness restraint and pile tip soil stiffness restraint were evaluated. The results show that as the pile head load stiffness restraint increased, the null point moved upwards, and the thermal stress decreased with the increasing of depth. As the pile tip soil stiffness restraint increased, the null point moved downwards, and the thermal stress increased with the increasing of depth. Compared with the case with no load, the null point will move upward with a working load.

Within the ongoing effort towards a better understanding of the influence of the stress shadow on the choice of fracture spacing in alternative fracturing, an optimised particle flow theory of fluid-solid coupling was applied to simulate the distribution of the induced stress due to the stress shadow around double hydraulic fractures. Numerical results were compared with the theoretical analysis solution to verify its rationality. Numerical simulations under different anisotropic stress fields and initial hydraulic fracture spacing were carried out to investigate the effect of the stress shadow on the initiation pressure and extension forms of the induced fracture with double hydraulic fractures. Experimental results showed that the anisotropic stress field did not change the stress field around the fractures and also did not affect the initiation pressure of the induced fracture. With the decrease of initial hydraulic fracture spacing, the stress shadow effect was enhanced, and the initiation pressure of induced fracture was also increased. Both of the anisotropic stress field and initial hydraulic fracture spacing affected the extension forms of the induced fracture. With the increase of initial hydraulic fracture spacing or the hydraulic differential stress, the influence of stress shadow on the extension direction of new hydraulic fractures gradually weakened. The initial hydraulic fractures exhibit a limitation on the extension direction of the induced fracture, to some extent, which was not conducive to the formation of a complex fracture network. Based on the above results, the optimisation of fracturing spacing in alternate fracturing was qualitatively discussed.

To improve the level of soil tensile testing, a set of microstructure change test system for soil tensile failure process is developed. The system consists of soil tensile loading device, image acquisition device and image processing program. Tension loading device provides uniform and stable external force and observation surface. Image acquisition device can continuously take the microscopic structure images under different stress states during the entire stretching process by the use of tracking platform, and determine the evolution area of tensile fracture zone (i.e., the observation area) using relative displacement field calculation based on the digital speckle correlation method. Image processing program includes enhancement, fusion, splicing and segmentation of the captured images, as well as the extraction of quantitative feature parameters of soil particles and pores. Based on the developed test system, the tensile failure test of clay is carried out. The results show that the particle structure changes first, and then the pores evolves during the whole process of tensile failure. The formation and penetration of the pores eventually lead to tensile failure of the sample. The porosity and fractal dimension distribution of pores increase with the amount of tensile deformation, and the fractal dimension distribution of particles decreases with the increase of tensile deformation, both can be divided into different stages. To be specific, the entire process of tensile failure can be divided into three stages: initiation, development and breakthrough of the fracture zone.

The similar material is a key to landslide model test. Based on previous studies of similar material, combined with fuzzy comprehensive evaluation method, a similar material for reservoir landslide model test has been developed through various trial of recipe. The similar material can simulate the similarity both physical and mechanical properties and seepage behavior. The similar material is mixed with standard sand, sliding mass soil, bentonite and water solution. A laboratory landslide model test was performed to verify the similarity of the similar material. The variations of the pore-water pressure, seepage, slipping surfaces and development process of cracks were recorded during the fluctuation of reservoir water level. The model test results indicated that weakening process of water and seepage force point to the free face are the main factors for landslides. The failure mode during rapid drawdown of water level was the multiple retrogressive mode. The seepage path is consistent with theoretical calculation during the fluctuation of reservoir water level. It is an ideal similar material for reservoir landslide model which can generate the similar result of landslide deformation and failure process effect of reservoir water level. And its physical and mechanical characteristics and seepage behavior have met the test similar requirements. The experimental results can provide scientific support to large-scale landslide model test study.