To investigate rock breaking mechanisms induced by cutters of tunnel boring machine (TBM) under a biaxial state, TBM indentation tests were conducted on granite specimens using a triaxial testing platform. Then, detailed morphological measurement was carried out to analyze the morphology and volume of the fractured surface using a surface profilometer. It is found that the increase of differential stress results in the increase of consumed energies, the growth of groove volumes and the efficiency of indentation when the Sig_1 (i.e., the smaller confining pressure) was fixed. The energy of indentations increases as the differential stress decreases, but the groove volumes are decreased, and thus the indentation efficiency is restrained by the decline of the differential stress when the Sig_2 (i.e., the bigger confining pressure) was fixed.

Sand and gravel soils in a dam foundation with a suspended cutoff wall may lead to fine grains loss due to the effect of suffusion, which further results in the reduction of strength and deformation modulus. As a result, the cutoff wall and the dam above the foundation experience an adverse impact. The effect of loss amount of fine particles on the stress-strain relationship of soil is known as one of preconditions to quantitatively assess the impact. In this study, an experimental program was presented to study the constitutive model. Triaxial and confined compression tests were conducted to investigate the effect of the loss amount of fine particles on the strength and stress-strain relations of sand and gravel soils. It is found that stress-strain characteristics of soil are not influenced by fine grain loss, but both the strength and deformation modulus are decreased. By establishing the relationship between model parameters and the amount of the loss, a single model was utilized to describe the stress-strain relationships of sand and gravels with spatio-temporal changes of particle loss amount. Based on Duncan E-B model, we proposed an expression to quantitatively describe the relationship between the loss amount of fine particles and the stress-strain of the soil, and parameters of the constitutive model were given as well.

The permeability of calcareous sand is important for the formation of underground fresh water on the reclaimed islands in the South China Sea. The relationships among gradation, void ratio and permeability of calcareous sand were studied through a series of permeability tests with constant head in laboratory. Soil samples with different void ratios but the same particle size distribution were examined to probe the influence of uniformity coefficient and curvature coefficient on permeability. The experimental results show that a linear relationship exists between permeability coefficient and void ratio of calcareous sand. Correlations were observed among with the permeability coefficient, the uniformity coefficient, curvature coefficient, and particle size. A formula was developed for the determination of permeability coefficient of calcareous sand by analyzing lab data. The equation provides references for the assessment of soil permeability and the formation of underground fresh water on the recently reclaimed islands and reefs.

In this study, large-scale triaxial consolidation drained (CD) shear tests under 0.2-3.5 MPa confining pressure for the rockfill of Shuibuya Dam were performed to investigate the stress-strain behaviors of rockfill, i.e., deviatoric stress-axial strain relationship and volume strain-axial strain relationship. Stress-strain relationships under different confining pressure conditions are determined using relationships of failure strength and volume strain to confining pressure. Critical deviatoric stress and critical deviatoric strain normalize the stress-strain relationships of experimental results and verifies the proposed equation. The experimental results show that, for the dense rockfill, a certain elastic stage occurs in the initial deformation, and its slope is strongly dependent on confining pressure. More strain softening is observed under low the confining pressure. The rockfill presents strain hardening and shear contraction within 0.8≤ ≤3.0 MPa of confining pressure. Dilatancy behavior occurs depends on the critical confining pressure (between 0.45 and 0.8 MPa). The deformation of rockfill under >3.0 MPa presents strain softening and shear contraction. Analysis show that the rockfill strength decrement caused by particle breakage is greater than the increase caused by confining pressure increment. The relative breakage rate is above 15%. Peak principal stress ratio is reduced as the confining pressure increases, consistent with the increase of axial strain. The fracture strength is observed linear with confining pressure. Predictions by proposed equation show that the formula given in this paper is correct.

Dynamic experiments were conducted on single cleavage drilled compression (SCDC) specimens of sandstone using large-diameter split Hopkinson pressure bar to obtain the whole dynamic fracturing process of Mode-I crack. A crack propagation gauge was used to measure the key moments of dynamic initiation, propagation, arrest and re-initiation, respectively. A fractal model of crack extension was applied to analyze the propagation speed of a tortuous crack. Finally, we determined the dynamic initiation toughness, dynamic propagation toughness, dynamic arrest toughness, and dynamic re-initiation toughness using the experimental-numerical-analytical method. The results demonstrate that the crack propagation path is torturous in the process of crack propagation. For this irregular curve path, the value of the universal function, which was characterized by the crack propagation velocity, was smaller than that with a straight path. It is found that the dynamic propagation toughness obtained by the fractal model was close to its real value. The dynamic initiation toughness was greater than the dynamic arrest toughness, and the dynamic initiation toughness was slightly greater than the dynamic re-initiation toughness. The reason probably was that the naturally formed crack at the second re-initiation was sharp, while the artificial notch for the first dynamic initiation was blunt at a certain degree.

The interfacial properties between geo-grid and soil are important for representing the reinforcement of the geo-grid and are of great influences on the stability and the deformation-failure characteristics of geo-grid structures. At present, various specifications and standards fail to consider the influences of mesh sizes on the parameters selection of geo-grid soil interface, leading to artificial selection of geo-grid in practical engineering. In this paper, the numerical model studies the characters of geo-grid interface through comparative analysis between indoor experiments and numerical methods. The results show that the mesh size of geo-gird has dramatic influences on the characteristics of geo-grid interface. Through analyzing the principles of the influences of different mesh sizes on the interface characters, it shows that the friction effects of geo-grid interface should be excluded from the comprehensive friction on the interface to explore the effects of reinforcement more directly. Meanwhile, the reasonable mesh size of geo-grid should ensure that the effective contact between geo-grid and soil should be one-third of the whole interface.

The surrounding rock of diversion tunnel in Danba Hydropower Station is mainly composed of quartz mica schist at the high-stress zone, which is typical transversely isotropic rock mass and has distinct layered characteristics with apparent dilatancy and high energy. Based on the MTS815 system, triaxial unloading tests were conducted to investigate the characteristics of dilatancy and energy change, and the loading direction was parallel and perpendicular to the schistosity of rock samples, respectively. The results demonstrate that the characteristic stress of both groups increased with confining pressure, which exhibited a good linear relationship with confining pressure. The crack closing stress, damage and expansion stress and peak stress of the parallel group were superior to those of the vertical group, whereas the crack stress was inferior to that of the vertical group. The dilatancy parameters of the parallel group were higher than vertical group. However, expansion characteristics of these two groups were weakened with the increase of confining pressure. Moreover, the index of expansion showed great agreement with confining pressure by an exponential distribution, and dilatancy angles had a linear relationship with the partial stress ratio. At the peak point and the residual point, the energy values of these two groups enhanced with confining pressure, and the energy values revealed good exponential distribution with confining pressure. Furthermore, under the same confining pressure, the energy characteristic value at the peak point and the residual released energy of the parallel group were greater than those of the vertical group. However, the residual dissipated energy of the parallel group was lower than that of the vertical group. For both groups, the relationship between the dissipated energy value and the dilatancy angle, together with the energy characteristic value and the dilatancy index, demonstrated good exponential distribution, which fit at the peak point as well as the residual point.

In this study, uniaxial cyclic loading and unloading experiments were conducted on dry and saturated sandstones from Xiaojihan coal mine in Shaanxi province, respectively. The strength and deformation characteristics of rock and its corresponding energy evolution and distribution during the process were analyzed. It is found that the peak strength of dry specimens under cyclic loading and unloading condition was 19.47% lower than that under uniaxial compression condition. The results demonstrate that the saturation affects both the strength and deformation of sandstone specimens. Compared with dry specimens, the average peak strength of saturated specimens was 39.55% lower, meanwhile, the saturated specimens present more obvious compaction stage. The loading elastic modulus and unloading elastic modulus tend to increase for dry and saturated sandstones. However, the elastic modulus of saturated specimens was lower than that of dry ones. When the peak strength was normalized, the elastic strain energy Ue and the dissipation energy Ud of dry specimens were larger than those of saturated specimens at different stages of stress loading. During the loading process, the proportion of elastic strain energy Ud of saturated specimens was greater than that of dry one. In addition, the Ud proportion of saturated specimens declined gradually during the loading process. The Ue proportions of dry and saturated specimens achieved an appropriate level prior to failure.

Through dynamic triaxial test, we investigate the effect of clay content on unconfined compressive strength, sensitivity, dynamic residual strain, and residual pore pressure of two mucky silty clays with different clay contents. Result shows that the unconfined compressive peak strength of specimen with high clay content is lower than that of specimen with low clay content; the sensitivity of sample with high clay content is greater than that of sample with low clay content. Dynamic residual strain, dynamic residual pore pressure and difference of dynamic residual strain between reconstituted and undisturbed sample increase as dynamic loading increases. Ratio of reconstituted dynamic residual strain to undisturbed dynamic residual strain also increases with increasing of load, and this value is greater than their sensitivity. The dynamic residual strain of reconstituted sample is greater than that of undisturbed sample under the same load. Also the dynamic residual strain of sample with more clay content is larger than that of the sample with less clay content in the case of similar dynamic stress. We conjecture that cementation and lubrication between clay particles cause different results for samples with different amounts of clay, use power function model to fit the curves of gradually stabilized dynamic residual strain, and develop a empirical formula, incorporating cycle stress ratio and number of cycles, for the dynamic residual strain.

Experimental studies were carried out on coal specimens, rock specimens and coal-rock specimens to solve the invalidity of burst tendency index on evaluating burst danger in the deep coal seam. The charge signal was monitored in the fracture process of coal-rock specimen to explore the corresponding relation of force-charge and the charge burst tendency of coal-rock specimens. The results show that roof and floor rocks significantly influence burst tendency of the coal seam. The greater the thickness of rock is, the higher the measured burst tendency index of coal-rock is. It is found that force change of coal-rock specimens was consistent with charge change in the fracturing process of specimens. Moreover, the stronger burst tendency of the coal-rock specimens is, the greater the charge signal amplitudes vary in its stress intensification until failure. Thus, the charge rate burst tendency criterion after the stress peak was proposed. The monitoring results of charge in stope face show that the rapid rise and attenuation of charge coefficient variation in the process of rock burst occurrence are consistent with quantitative analysis results on charge change rate after the stress peak. The validity of the charge rate after stress peek as burst tendency criterion was further verified. Therefore, this study provides experimental instruction for the formation of charge prediction method to pre-judge burst danger and its occurrence probability, and offers the experimental basis for failure prediction of coal and rock mass and early warning of mine power appearance.

Shale widely distributed in Chongqing Region particularly accounts for a relatively large proportion in the surrounding tunnel of rock mass. The stratification and water significantly affect mechanical properties of shale, this study is to investigate the damage process of shale and its deterioration mechanism under the influence of stratification and water content using the MTS815 testing system and PAC acoustic emission (AE) instrument. AE experiments were performed in the damage process of layered shale under uniaxial compression. The damage mode of shale was further analyzed comparatively using the commercial software 3DEC. The damage process of shale was determined by its mineral component, mineral arrangement and loading direction. The distribution of macro-cracks was dominated by the distribution of pre-existing micro-crack, the size of mineral grain and loading direction. Moreover, the macro-cracks governed the damage mode of shale. The pre-existing micro-fissuring group towards the stratification direction inside the shale triggered the damage zones of shale. The secondary micro-cracks were generally found along the mineral boundary, which basically had the same direction as the loading direction. These micro-cracks were formed the macro-cracks, which connected the damaging surfaces of stratifications. The AE events of generation and distribution of layered shale were closely related to the distribution of micro-cracks inside the trial piece. The initial compression phase accumulated near the stratification in the central section of shale, then developed towards its ends or both sides along the normal direction of the stratification. It finally coalesced to the core along the turning point and intersection position of macro-cracks. The stratification and water had different damage and deterioration mechanism on shale. The effect of stratification on shale was essentially the damage effect of pre-existing micro-cracks group distributed along the stratification. However, the damage effect of water on shale is primarily depending on the water absorption and capillary pressure.

The determination of ultimate bearing capacity of foundation near slope is an important subject for foundation design. Bearing capacity of ground is conventionally calculated using linear Mohr-Coulomb failure criterion. However, measured data show that the strength envelopes of geomaterials are nonlinear. In this paper, the upper bound theorem of limit analysis with nonlinear failure criterion and a multi-tangential technique were employed to evaluate the bearing capacity of strip footings adjacent to slope . The unilateral rigid blocks sliding mode of strip footings adjacent to slope was considered according to the characteristics of the asymmetry failure mode. The velocity comparability and plastic flow rule satisfy the corresponding velocity field. A mobile permissible velocity field and the ultimate bearing capacity calculation formula of strip footings adjacent to slope were developed. A new method of determining ultimate bearing capacity of strip footings near slope was implemented using sequential quadratic programming optimization algorithm. The proposed method shows superior to other existing methods. The feasibility, rationality and universal applicability of the approach verified by comparison and analysis with current research results. Nonlinear failure parameter significantly impacts the bearing capacity. The rigorous multi-tangential technique method optimum calculated results.

A self-developed multi-field coupling physical simulation testing system was employed to investigate the gas pressure, coal temperature, the deformation and other parameters evolution characteristics of coal reservoir during the process of extracting different adsorption gas. The results demonstrate that the gas pressure of coal reservoir decreased rapidly at the early stage of extraction, and formed a gas pressure equivalent plane with the center of the drill hole. The gas flow rate and pressure drop rate declined with the increase of distance. The stronger ability of adsorption, the lower the gas pressure drop rate and the longer the duration. The time evolution law of coal reservoir temperature and the time evolution law of gas pressure were consistent. Coal reservoir temperature decreased significantly at the early stage. At the late stage of extraction, under the influence of desorption of the adsorbed gas and heat exchange, the coal bed temperature appeared to decrease initially and then increase slightly. The closer position from extraction drill hole, the greater the pressure drop, the more obvious the coal bed temperature decreased and the greater the amount of coal deformation. The stronger the ability of adsorption is, the greater the deformation of the coal caused by gas extraction.

Description and construction of blocks play a significant role in the analysis of rock mass stability. The equation representation is an effective approach to describe all possible blocks geometry. However, this approach has not been applied to block construction in the literature. Although it is possible to construct arbitrarily complex block geometry, it is hard to obtain a precise geometrical information of blocks, due to the lack of appropriate parametric description method. Therefore, we proposed a geometric construction method for convex polyhedron block. First, an equation representation for convex polyhedron was established by defining two input variables of boundary planes of polyhedron. Then, a simplified algorithm was developed to solve the convex polyhedron equation and a procedure was further presented to identify these two input variables. Finally, an analytic method was proposed for geometrical construction of convex block by introducing four control variables. A numerical example was conducted to verify the effectiveness for parametric representation and geometrical construction of block geometry in engineering rock mass .

In this study, a simplified nonlinear calculation method was developed to analyze the single pile in non-homogeneous soil under excavation, considering the unloading rebound of soil and changes of soil property caused by excavation. The calculated results show good agreement with testing results obtained by the present method, which indicates that the validity of this method is verified. Moreover, we studied the responses of the single pile after excavation under vertical load using the simplified method. It is found that the ultimate vertical bearing capacity and vertical stiffness of the pile loaded after excavation are overestimated by both the conventional loading test method and loading test with the sleeve method, which could lead to an unsafe design. In addition, excavation causes rebound of soils around the pile and then results in tension force in the pile. To avoid the pile be pulled apart, the reinforcing bars in the middle-lower part of the pile should be raised when the excavation depth is deep. The unloading rebound of soil around caused a great decrease in stiffness of the pile top.

Energy dissipation and shear modulus variation of ice-rich frozen silty sand with different water contents are investigated in a comprehensive experimental program of triaxial loading-unloading cyclic tests under various confining pressures at the same temperature and strain rate conditions. The results show that the plasticity of frozen silty sand firstly increases and then decreases as the water content increases. The frozen soil presents mostly plastic failure mode with a water content threshold of 30.6%. The energy dissipation as shear strain increases is mainly induced by deviator stress variation, and less energy dissipation overcomes the effect between ice particles in the deformation process of frozen soil. Shear modulus always decreases as shear strain increases. The decreasing rate of shear modulus has an apparent change point at low water content.. Three types of effects of water content on shear modulus can be observed. These testing results can provide important implications for the parameter selection on engineering design in permafrost region with ice-rich soil.

For determination of the ground horizontal resistance coefficient, m, of a pile under lateral loading, we usually assume horizontal surface for natural soil foundations. However, there has been no relevant standards or experiences for evaluating the coefficient m for inclined ground. In order to evaluate the coefficient of ground horizontal resistance of gravel soil on slopes, static lateral loading tests are conducted in laboratory to examine the horizontal bearing behaviors of a pile embedded in the gravel soil slope. The variation of m value of the subgrade with slope gradient is discussed. A formula modified using m value for horizontal gravel soil ground is used to determine the m value of gravel soil foundation on slopes with different gradients. The suggested range of m value is provided in the procedure. The applicability is verified by field test. It is shown that the m value ranges from 23 to 65 MN/m4, and decreases as the gradient of slope increases.

There has been controversy concerning the methods of estimating water and earth pressures together. This article quantitatively analyzes the error of existing methods of water and earth pressures calculation for the normally consolidated saturated clay under fully undrained or steady flow conditions. In most cases, the predicted results by existing methods were found non-conservative and errors can be over 40%. After that, the formulas for estimating the water and earth pressures together for both the normally consolidated and over-consolidated clay were derived using principle of equivalence. The results of proposed equations are found in consistent with those by WEI Ru-long. The formulas are also verified by method using undrained shear strength used by other scholars in foreign countries with good agreement. The proposed approach tends to overestimate the total pressure of water and earth pressure in both normally consolidated and lightly overconsolidated clay subject to steady flow. On the other hand, this approach may underestimate the total pressure in heavily overconsolidated clay. The critical state occurs when the negative excess pore pressure fully dissipates. The developed equations calculate the total active or passive pressure of saturated clay under fully undrained condition using of the total stress parameters. The formulas do not consider the influence of seepage on water and earth pressure. The significant impact of seepage on the water and earth pressure suggests it should be considered in engineering practices.

It is known that the phenomenon of leakage frequently occurs in the roof of the fully mechanized working face with large mining height in thin bedrock coal seam of Huainan mining area. In this study, laboratory tests, theoretical analysis, and field measurements were conducted to investigate the mechanism and control technology for the leakage in the thin bedrock mining face. The results show that coal seam with large mining height in the thin bedrock had a periodic weighting phenomenon in the roof of the fully mechanized working face. The deformation potential energy of the immediate roof was proportional to the dead weight of the overlying strata next to the immediate roof, while was inversely proportional to the elastic modulus of rock mass. When the periodic weighting of working face roof took place, the deformation potential energy of the immediate roof increased. As a result, the primary cracks propagated and the secondary cracks developed, which caused the growth of the probability of the roof leakage. Therefore, a combined procedure of waste steel wire rope and grouting was applied to reinforce weak areas in the immediate roof, forming a unique spatial grid reinforcement structure. It turns out that this technique presents an obvious reinforcement effect and can prevent the occurrence of the phenomenon of roof leakage effectively.

There are significant differences between the double pile-column foundation and the common pile foundation in abrupt slope. And the bearing capacity and deformation behaviors of double pile-column foundations in abrupt slope are more complex. Simplified models were developed to analyze the bearing mechanism of lengthways and lateral double pile-column foundations in abrupt slope, and were derived using the internal force of common pile subjected to the horizontal uniform force applied on the shaft. The proposed model was verified and its influencing factors were analyzed by a typical engineering project, including pile diameter, sliding body thickness, residual sliding force, proportional coefficient of ground level resistance modulus, on the pile-top horizontal displacement and pile maximum bending moment. The results indicated similar impact by these factors, and salient potential sliding body on the load acting section, and subtle influence of the depth on the load bearing section. Larger pile diameters within 2.5 m are preferred to control the pile deformation and bending moment. Foundation locations can also be changed to reduce the influence of residual sliding force, and lower the instability risk of the pile-column foundation in abrupt slop. The results under different conditions imply optimization design in engineering practices.

In this study, the seismic ground motion of the scarp topography under inclined P waves was analyzed using numerical simulation method. The effects of the incident degree, the slope angle, and the incident direction of seismic ground motion were discussed as well. It is found that from the bottom of scarp to the top, the amplification factor increased gradually, whereas it had no influence on the incident degree, the slope angle and the incident direction. When the incident degree was constant, the amplification factor of the scarp upside region was greater than that of the scarp downside region, regardless of the incident directions. At the same time, the amplification factor at the crest of the slope increased with the increase of the slope angle. When the slope angle was constant and the waves travelled away from the slope, the amplification factor of x component increased, while the amplification factor of z component decreased with the increase of incident angle. The results show that for waves travelling into the slope, the maximum amplification factor is generally found around the crest of the slope. For waves travelling away from the slope, the maximum amplification factor shifted from the slope crest. Moreover, the larger the slope angle, the farther the departure. The amplification factor of x component was larger for waves travelling away from the slope as compared to waves travelling into the slope, but the amplification factor of z component had no obvious change with the incident direction.

The structural and mechanical properties of the soil foundations on the construction site are critical for the investigation on the deformation and failure of structures in the goaf region. A series of true triaxial tests on the unconsolidated soils from Nanpiao mining area was conducted using TSW-40 apparatus. The variations of stress ratio and structural parameters of unconsolidated layers soil under true 3D stress state were measured under different conditions of the confining pressure, the moisture content and the intermediate principal stress ratio. A mathematical model of the structural parameters was established. The results show that undisturbed soil present three types of relationships between q and???s, i.e., strain softening, ideal elastoplasticity, and strain hardening. However, the remolded soil and saturated soil exhibit strain-hardening type of q???s relationship. The structural parameters m? decrease with increasing the shearing strain, moisture content, confining pressures, and intermediate principal stress ratio. In the initial stage of shearing, the structural parameter m? decreases significantly. Then mh tends to be stable gradually as ?s is equal to 5%. The m? equals to 1 when ?s equals 15%. The proposed mathematical model shows that of the number of mh is significantly dependent on confining pressures, whereas less sensitive to the moisture content, and the intermediate principal stress ratio. The proposed model describes well on the structural parameter of unconsolidated soils under different experimental conditions, and compares well with the experimental measurements.

It is important to locate the slip surface in stability analysis of soil slope. The current method, circular slip surface method, results in a major error in the simulation analysis. In this paper, a method for seismic stability analysis of soil slope is proposed based on the theory of slip line field and dynamic finite element. Firstly, the stress field of soil slope is determined under seismic loading. Then, the method of slip line field is used to search the critical slip line under different conditions, and safety factor for every slip line is achieved. Finally, the seismic stability analysis of soil slope is quantified by the minimum mean safety factor. The proposed procedure is used to determine the critical slip lines and safety factors of an example slope at different moments. Seismic stability of the soil slope is evaluated by using the minimum mean safety factor. The study indicates that the shear band is composed of the slip lines with safety factors below 1.2. The shear band is consistent with the plastic zone of soil slope.

The Wujiang landslide at right bank of Wujiang Canyon is located at the entrance region extension project of Centian river reservoir., The distance from the downstream slope to dam is only 300 meters, which is a typical ancient landslide with a total volume of 1 327×104 cubic meters. The stability of Wujiang landslide significantly affects the operation and safety of the dam and discharge structure. The observed displacement of landslide is analyzed in this paper. The strength parameter of landslide is determined by limit analysis method with an assumption of safety factor of 1.0 during slow creep. The internal displacement of landslide is observed creep annually in the borehole observation. Assuming that the landslide satisfied Mohr-Coulomb yield criterion, viscoplastic strain rate is calculated using based on the assumption of Perzyna, the finite element calculation program of elasto-viscoplastic is adopted to analysis the landslide combined with the finite element model of typical profile of landslide, thus the elastic modulus and viscosity coefficient of landslide and sliding zone are obtained with inversion by the combination of orthogonal design and optimization algorithm, the results can provide the basis for stable deformation analysis and monitoring of the landslide and offer reference for similar projects.

The rigorous and efficient method of discontinuous deformation analysis (DDA) by Shi has been widely used in geotechnical engineering due to its advantages in calculating discontinuous deformation and large displacement including sliding, rotating and opening. However, some precision problems inevitably occur in the early stage, and follows mountains of work done by Shi and many other scholars in order to explain and solve these precision problems. In this paper, the research findings of the scholars in the world are summarized, and the effectiveness and efficiency of the improved methods are discussed mainly in the following five aspects: (1) Precision control of stress-field inside the DDA blocks; (2) Improvement of contact handling method among blocks; (3) Reasonable selection of artificial parameters; (4) Consideration of energy dissipation; (5) Modification of artificial boundary. Advanced research hotspots and trends are also discussed beyond the above work. Authors hope that this paper can bring some ideas for further development and improvement for the DDA method.

The hydro-mechanical (H-M) coupled numerical simulation was conducted for the prediction of the tunneling construction in water-rich areas using the earth pressure balance (EPB) shield. First, a zone state index (ZSI) was established based on the achievements of other scholars. Then, the yield approach index and failure approach index was unified to safety evaluation system (negative values mean failure), which achieved a complete expression of elastic, yield and failure states. By combining the strain-permeability equation with ZSI, the variable of permeability coefficient was calculated during the coupled process, which made up for the deficiency of permeability coefficient in FLAC3D seepage simulation. Taken the 202 section of Dalian Metro, Xianggong street station to Shahekou railway station, as an example, the H-M coupled numerical simulation was realized by using program in FISH language. The deformation and failure characteristics of excavation face and surrounding rock during tunnel excavation were analyzed. The stability of excavation face was further evaluated according to numerical results of ZSI. The results indicate that the proposed method can be used to well simulate and analyze the H-M coupling process, which are in good agreement with measured results.

A numerical model for analyzing microscopic fluid flow in granular media is developed using a coupled discrete element method (DEM) and computational fluid dynamic (CFD) approach to investigate fluid-particle interaction. The CFD-DEM coupling algorithm was implemented using open source code LIGGGHTS and OpenFOAM, within the framework of open source code CFDEM. A rigorous rolling resistance model was incorporated into the DEM code to approximately represent the effect of particle shape. Two benchmark examples, i.e., sand pile formation and upward seepage flow in sand, were presented to demonstrate the effectiveness of rolling resistance model and validate the CFD-DEM coupling model, respectively. The results show that the prediction of the relationship between seepage flow velocity and hydraulic gradient is consistent with classical Ergun theory. The incorporated rolling resistance model shows capability of representing the particle shape effect on the sand pile repose angle and packing porosity of sand columns.

Based on qualitative understanding of the so-called pot-cover effect on moisture transport in the road subgrade soil, a mathematical model is proposed to analyze multi-phase transportation, heat conduction, and water-vapor transition. A one-dimensional finite element model for subgrade soil column is developed to investigate moisture transport and phase change under temperature gradient, as well as the mechanism and influencing factors of pot-cover effect. The numerical results indicate that the temperature profile and soil texture may have significant influence on pot-cover effect. Pot-cover effect is more likely observed in silt subgrade than in sand or clay subgrade. The temperature profile of lower temperature at the top subgrade more easily leads to the pot-cover effect. These results provide reference for further understanding the pot-cover effect in subgrade soil.

In this study, a new FDEM-flow method is developed by considering the permeability of rock matrix, and it fully utilises the unique topological connection between joint elements and triangular elements in the original combined finite-discrete element method (FDEM). First, the joint elements were used as a natural channel for fluid flow, and the fluid flow in rock matrix and fissures were characterized by fluid flow in joint elements based on the cubic law. While the permeability of rock matrix was determined by calibrating the appropriate aperture of the joint element. Then, a numerical example of the free surface steady flow with the analytical solution was employed to validate the proposed seepage algorithm and the calibration method for rock matrix permeability. Finally, a hydraulic fracturing example was conducted to demonstrate that the permeability of rock matrix and fracture was considered simultaneously in the modified FDEM-flow method. Moreover, by using simple pure fracture seepage this method solved the complex issues of hydraulic fracturing. Therefore, the application scope of the new FDEM-flow method is broader than that of the original FDEM-flow method. This method provides a new solve tool for simulating hydraulic fracturing in shale gas exploration and geothermal exploration in hot dry rock.

A coupled viscoelastic-plastic model is composed of viscoelastic model and a series of plastic elements, which can be regarded as a limit condition of the viscoelastic-viscoplastic model when the viscosity-related parameter of viscoplasticity is close to 0. This model provides an alternative scheme for analysing the structural collapse of viscoelastic materials by numerical solution at the certain circumstance. First, the strain increment was decomposed into viscoelastic part and plastic part in this viscoelastic-plastic model. Then the integral type viscoelastic constitutive equations were linearized over the time interval, by taking the history of viscoelastic strains into consideration. Meanwhile, the shear and bulk modules were clearly defined, which are functions of the time increment. The recurrence formulas for stresses on viscoelastic strains were deduced as well. The numerical integration of viscoelastic-plastic constitutive equation was transformed into the similar format with the general elastic-plastic circumstance. The plastic part of the viscoelastic-plastic model was assumed as the hyperbolic Drucker-Prager plasticity with isotropic hardening. Finally, the fully implicit stress update algorithm and the associated consistent tangent operator, as well as the final formulas, were derived by the combination of the viscoelastic predictor and the plastic return mapping. The comparison and analysis of numerical examples indicate that the algorithm had a good convergence, since only the simple function calculation was performed in each iteration process. After two iterations, the value of yield function reached to 10?10 degree, and the stress point returned to the yield surface.

It is known that mesoscopic characteristics of rock materials have a significant effect on its macroscopic mechanical properties. Based on the electron micrograph of mesostructure of typical rock materials, a mesoscopic simulation model was established to investigate the shock compression behavior of rock materials with different mesostructures, such as particle morphology, porosity and water. Numerical studies of mesoscopic behaviors were conducted on rock materials during the compressive processes using ANSYS Autodyn software. We obtained the effect of particle morphology, porosity and water on shock compressive properties at mesoscale. The Hugoniot parameters of rock materials with different mesostructures were determined, which were further applied in the impact cratering process simulations. The results show that both the Hugoniot parameters at mesoscale and the results of cratering process simulation are in good agreement with existing experimental counterparts in the literature. It is found that the porosity and water content have an obvious negative effect on the shock wave propagation in rock materials. The Hugoniot parameters determined by the mesoscopic simulation are applied to predict dynamic responses of rock materials, which can effectively reflect the effect of particle morphology, porosity and water content on impact cratering.

Seismic loading may result in liquefaction-induced deformation in saturated sand, including seismic settlement and lateral spreading. The permeability coefficient of sand may change after liquefaction. Variation of the permeability coefficient has not been included in the existing models. This is one of the main reasons for the underestimation of the seismic settlement in the numerical simulations comparing to the experimental observations. To analyze the effect of the variation of permeability coefficient on the liquefaction-induced settlement, the settlement in free-field condition is simulated using OpenSees platform, and compared with centrifuge experiments. The proposed model with variable permeability coefficient allows the maximum permeability coefficient during the liquefaction several times of its initial value. Compared with the model with fixed permeability, the proposed model properly describe the evolution of settlement and excess pore water pressure, and improve the accuracy of the settlement prediction in the numerical simulation. The results show that the adopted variable permeability model is capable to simulate the behavior of the sand in the free-field condition under seismic loading with an acceptable accuracy.

Based on bounding surface plasticity theory, both the size and shape of the bounding surface are allowed to change with temperature in the thermo-mechanical model. The thermo-bounding surface model can capture many vital aspects of thermo- mechanical behavior, including volume changes during heating and cooling, and thermal effects on shear behavior. In order to analyse thermo-fluid-solid coupling phenomena, a thermo-bounding surface model is implemented in the software COMSOL. The implementation techniques include modification of the built-in material equations of COMSOL, coupling analysis of pore fluid flow and stress, the addition of partial differential equations to compute plastic strains for any stress path within the bounding surface. The developed model was used to analyze one-dimensional consolidation, isotropic compression test at constant temperature, drained heating and cooling tests and undrained triaxial compression tests at different temperatures. By comparing with the computed and measured results, it is evident that the proposed model is capable to capture key features of the coupled soil behavior.

The determination of positions of critical slip surfaces is a hot spot of research on geotechnical engineering. In two-dimensional slope stability analysis applied with finite element-strength reduction, the points with the maximum equivalent plastic strain along depth are mostly on the critical slip surface for a slope at limit equilibrium state. One set of wavy signal function consisting of points with the maximum equivalent strain can be constructed by deploying a series of parallel lines approximately perpendicular to the slope surface. The wavelet analysis smoothens these points on the critical slip surface. Through the classic example analysis and comparisons with Spencer’s method and other previous research, the results show that the method in this paper is reasonable and effective, and can be used to locate the critical slip surface.

Since the current device for geotechnical direct tension tests is limited, a new direct tension device was developed in this study. The testing device consists of four components: sample preparation, loading, control and data acquisition system. With the novel design of “dovetail” groove and a double sliding plate on the device, direct tension tests can be conducted on prepared samples with different lengths. Due to the chosen sampling forms and their corresponding stretching fixture, the problems of relaxation and stress concentration on the ends of the specimen can be solved during the drawing process. The phenomenon of eccentric stress appearing in the drawing process can be avoided using the double rail stretching device. The minimum tensile rate of the device is 0.001 mm/min assisted by the two-stage gearbox design. Therefore, the device can be used to describe the evolution of uniaxial tensile failure and to determine tensile strength and tensile stress-displacement curve in the whole process. Direct tension tests were carried out on clay specimens using the developed device. The results show that the uniaxial tensile failure mode of clay is not purely brittle fracture, but there exists a softening stage after the tensile strength, and at this moment, clay specimens still have the certain bearing capacity. With the increase of the length of stretching section, the tensile strength decreases logarithmically while the peak displacement increases logarithmically. With the increase of tensile rate, tensile strength increases logarithmically while the peak displacement increases linearly. Both tensile strength and the peak displacement increase linearly with increasing compactness. With the growth of moisture content, tensile strength increases initially and decreases afterward, but the peak displacement linearly increases.

Compared with cyclic triaxial and torsion shear apparatuses, the cyclic simple shear apparatus has obvious advantages, e.g., simulating in-situ conditions under earthquakes, and directly applying shear stress and measuring shear strain. However, applications of current cyclic simple shear apparatuses are still limited due to technical problems, such as non-uniform shear stress or strain, boundary condition un-determined, potential shear plane, and size effect of specimen. In this study, a new cyclic simple shear apparatus with hinged structures for a cubical specimen was developed to resolve these problems. The design concept and loading principle were proposed by considering the loading mechanics and stress-strain condition of current simple shear apparatuses. Several main components of the apparatus were presented in detail, including pressure cell, loading system, measurement system and automatic control system. The shear strain distribution of soil specimen subjected to loading from three different loading devices was analyzed by the three-dimensional finite differential program, which proved that the shear strain distribution of soil specimen subjected to loading from the new simple shear apparatus were more uniform than the other two. Finally, a series of cyclic simple shear tests on intact loess specimens were conducted with this developed apparatus under different vertical pressures, water contents and shear strain amplitudes. The results show that the apparatus is reliable and accurate in loading control. The dynamic load input can be reproduced with the acquired data. The formation process of seismic subsidence of loess and the corresponding influencing law are revealed by the relationships between vertical strain, shear stress, shear strain and the number of loading cycles.