Using of the modified true triaxial apparatus in Xi’an University of Technology, the intact loess strength, deformation characteristics and failure modes of intact loess are investigated through lateral unloading plain stress tests of loess under different moisture contents and different confining pressures. The stress-strain relationship curve under different confining pressures shows hardening behavior at the different moisture contents, similar as ideal plasticity curves. The lateral deformation of loess has a non-linear relationship with its vertical deformation. Lateral strain increment is larger than the vertical strain increment, indicating dilatant volume deformation. The failure strain is smaller in the lateral unloading plain strain test than vertical loading plain strain and conventional triaxial test. In brief, the failure strength of loess is closely related to moisture content, confining stress and spheric stress state. With the moisture content increasing, cohesion reduces and internal friction angle decreases slightly. The intact loess is develops dilatant slip failure modes under lateral unloading conditions.

A series of experimental tests were conducted on grey medium grained granite to investigate the influence of failure support forces, support failure timing and support failure rates on rockburst ejection using the self-developed true-triaxial rockburst test system. The difference of stress paths before and after the support failure of an underground cavern was simulated. The whole rockburst processes were tracked and the ejection kinetic energy was estimated by the high-speed camera system. The results indicate that the greater the support force, the larger ejection kinetic energy once the support fails. With the increase of axial stress, the later the time of removing the minimum principal stress on a single side is (i.e., the later the time of support failure is), the greater the kinetic energy of rockburst ejection is. With the increase of support failure rate, the kinetic energy of rockburst ejection increases, and the failure mode of rock specimen changes from static brittle failure to dynamic rockburst failure.

The existing plane-strain apparatuses can not avoid the friction between the soil specimen and the constraint panel, which influences greatly the accuracy of soil deformation measurement. This paper presents a brief review of the plane-strain apparatuses. The plane-strain apparatuses are classified into four types according to their loading models. The advantages and disadvantages are discussed for each type of the plane-strain apparatus. A newly developed plane-strain apparatus with modified loading chamber uses the special designed front and rear panels with 3 mm water film to reduce the friction. Friction between soil sample and panel can be eliminated during the test, since the rubber film touches the water-sealing silicone membrane instead of touching the panel. A digital image measurement system is integrated into the apparatus to measure the deformation distribution on soil specimen surface with high accuracy and capability of identifying shear band and its characteristics. The improved and conventional chambers are employed to measure the deformation of Fujian standard sand, respectively. The peak values of the stress-strain curves obtained by the new plane-strain apparatus can be reduced by 60%. Both triaxial and plain-strain tests on the soil specimen with same dry density under different confining pressures measure the soil’s shear strength. It is shown that the shear parameters obtained by using the new type of loading chamber are closed to that of the triaxial test. However, the results by using the old one are obviously unreasonable.

A biaxial servo testing machine is used to simulate rockburst of a granite tunnel, and the acoustic emission (AE) system is applied to acquire the waveform signal. The dominant-frequency characteristics of AE signals from initiation to occurrence of rockburst are analyzed using the spectrum analysis theory. The results show that the dominant frequency interval of AE signal is from 0.4 to 110 kHz, and more than 99% of the dominant-frequency concentration is in the range of 35-65 kHz. The distribution of the dominant-frequency of the AE signal can be divided into three stages with the evolution of rockburst. In the early stage of rockburst initiation, the dominant frequency is in the range of 35-65 kHz and 15-25 kHz, a few of low frequency AE signal close to 0.4 kHz occurs, and high frequency around 110 kHz seldom appear. In the middle period of rockburst initiation, the low frequency around 0.4 kHz nearly disappears, but the high frequency around 110 kHz begins to appear. In the final stage of rockburst occurrence, the number of dominant-frequency in the range of 35-65 kHz plummets, the low frequency approximate to 0.4 kHz almost disappears, but the high frequency close to 110 kHz appears intensively. The study provides the fundamental understanding of optimizing the frequency band of AE monitoring, which has important theoretical significance with respect to monitoring and early warning of tunnel rockburst.

Foundation will be subjected to resistance during the process of uplift or pullout. Adhesion is a contributing component of the resistance and a key factor in determining the pullout capacity of soils. In order to study the laws and factors of adhesion, the compound adhesion-measuring disc is modified to eliminate the effect of the pore water pressure of soils on adhesion during its pullout by venting the bottom of the inner disc. Adhesions of soil are measured with different water contents and pullout velocities. Test results show that the drawing stress of soil on structure increases linearly with the increase of the displacement of pullout until it reaches adhesion limit. The adhesion of soil is zero when the water content is low and increases when the water content exceeds plastic limit. It decreases to a constant value after it reaches its maximum. The maximal cohesion under constant pullout velocity increases and the corresponding water content decreases as the pullout velocity increases. When the water content of soil is the same, the relationship between adhesion and the logarithm of pullout velocity is in an S shape. The ratio of adhesion to undrained shear strength increases with the increase of water content. The test results provide a sound basis for understanding the laws of adhesion and can be used in practical engineering.

Moisture content of subgrade gradually changes from the initial compaction moisture to equilibrium moisture content during in-service period, which leads to the evolution of the subgrade soil road performance. By summarizing the measured results of shear modulus with compacted soil moisture content in literatures and complement experimental data, this paper investigates the effect of moisture content and the degree of compaction on the shear modulus of compacted soil. The results show that, when the degree of compaction is a constant, the shear modulus of subgrade soil decreases with increasing of moisture content. The shear modulus of subgrade soil decreases larger as degree of compaction increases. Shear modulus increases with increasing degree of compaction in low moisture contents. However, shear modulus increases first and then decreases with increasing of the degree of compaction in higher moisture contents. The degree of compaction corresponding to the peak modulus decreases with increasing moisture content. Moisture content corresponding to peak shear modulus is slightly less than the optimum moisture content corresponding to maximum dry density. Shear modulus of compacted soil increases first and then decreases with the increasing of liquidity index. But liquidity index corresponding peak shear modulus of different soils shows a good function with the clay content of soils.

Laboratory model tests are performed to study the characteristics of movement and accumulation of landslide-debris under different constraints. The effects of the gradient of slope and the chute sidewall on the accumulation scope and accumulation characteristics are investigated. Testing results show that when slope angle increases, the final run-out and accumulation area increase for the fine particles deposit, but for the coarse particles deposit, they increase first and subsequently decrease. However, for both of deposits, the accumulation width decreases and the thickness increases. The landslide movement is obviously influenced by the chute width. With the increase of the chute width, the final run-out slightly increases, the accumulation area and width significantly increase, while the accumulation thickness becomes smaller. The chute outlet width is a significant factor to influence the final accumulation scope, while the influence of the chute entrance width is relatively small. Theoretically, experimental results contribute to the study of accumulation scope and the form of landslide-debris.

Since many pre-existing fractures (i.e. more than 15) are required by the hydraulic testing of pre-existing fractures (HTPF) method, the application of HTPF method to various stress measurement conditions is restricted. To overcome the shortcomings, a mechanical equation is developed to describe the shearing stresses intrinsically occurring on geological discontinuity planes. The least square method and the trial searching algorithm code are used to calculate the frictional coefficient of pre-existing fractures and further to calculate in-situ stress tensors by the inversion technique. Theoretically, the hydraulic test on each pre-existing fracture is utilized to establish two mechanical equations, and three tests on pre-existing fractures is used to determine the in-situ stress tensor. Practically, to guarantee the convergence of the inversion code, at least five pre-existing fractures are required. Thus, the developed method is called the modified-HTPF method, which is further applied to measure in-situ stress in Weifang area, Shandong Province. During the process of stress measurement, the complete in-situ stress tensor is determined by the shut-in pressures from the hydraulic fracturing test on pre-existing fractures and the azimuth and dip angle data from Televiewer logging of five geological fractures. The in-situ stress tensors are characterized as 8.85 MPa, N58.12°W∠14.18°; 6.61 MPa, N26.2°E∠ 21.54°; and 5.01 MPa, N62.86°E∠63.86°. Compared with the data by the classic hydraulic fracturing (HF) method, the medium and minimum principal stresses determined by these two methods are similar, but there exists a large difference between the maximum principal stresses. The orientations of the maximum and minimum principal stresses determined by the modified-HTPF method are in good agreement with the classic HF method. The modified-HTPF method offers a new access to determine a complete stress tensor using a single borehole.

Brillouin optical time-domain reflectometer (BOTDR) techniques have numerous advantages such as distributed measurement, long distance and real-time online, which are widely used in the structural engineering field and show extensive application prospects. However, the application of BOTDR is relatively limited in the field of geotechnical engineering, and thus some relevant technologies need to be improved. In this study, the relationship between strain measurements by the optical fiber distributed along the direction of axial tunnel and the deformation of tunnel roof subsidence is investigated based on the strain monitoring technology of BOTDR. Firstly, according to the deformation regularity of tunnel roof, three mathematical models, namely the circular arc model, the parabolic model and the triangle model, are established for the relationships between the strain along tunnel axial direction and the deformation of tunnel roof subsidence. Secondly, experiments are conducted to examine the relationship between the optical fiber strain and the deformation of tunnel roof subsidence. The final comparative analysis reveals that the theoretically calculated values show well agreement with experimental data. The optical fiber strain can be linked with the roof subsidence by using these three analytical models, which has theoretical significance and practical engineering value for the application and improvement of BOTDR technology.

A large number of ancient landslides in the Three Gorges Reservoir Area present long term and slow deformation characteristics with significant creep properties when undergoing internal and external geological agents. It is commonly thought that the soil on the slip plane of a reactive ancient landslide have already reached the residual state. Mechanical properties and stress state of the soil in the rupture zone dominate the main kinematic feature of a slow-moving landslide. Creep behavior, therefore, has an important value for evaluating reactivation potential and landslide prediction. In this paper, intact soil samples are collected from a reactive ancient landslide. Residual strength of intact sliding zone soil is studied and residual-state creep test is performed afterward. Various RCSR (the ratio of the applied constant creep stress to the residual strength) levels are chosen to study the correlation between RCSR and creep rate. The results show that creep rate of soil is positively dependent on RCSR. As RCSR approaches 1, a pronounced secondary creep occurs in a short time followed by an accelerative creep stage for some tests, namely tertiary creep. At the same RCSR, soil with higher normal stress level has larger creep rate. Burger’s model is employed to simulate the creep behavior and the parameters of Burger’s model are obtained. The long-term shearing resistance is investigated by analyzing the isochronal curves, and the value of long-term shear strength of intact sliding zone soil is found to be approximately 0.95 times as much as that of residual strength. Additionally, consolidation duration can affect the creep rate, which decreases with increasing consolidation duration. This reveals that the mobilized shear strength and residual strength are regained to some extend during consolidation or with shear displacement.

Because initial static shear stress exists in a sloped ground, soil is more possible to be liquefied and largely deformed than the level ground when subjected to a strong earthquake. So it is necessary to study the effects of initial static shear stress on the liquefaction and large deformation of liquefied soil. A series of cyclic torsional shear tests examine the saturated silts. The single amplitude shear strain exceeds 50% in the tests. The testing results show that the pore pressure of the specimens can reach the effective confining pressure under the combined effect of initial and cyclic shear stresses, namely the effective stress equals zero. Moreover, it is found that the cumulative strain increases gently during initial stage, and grows greatly later. Two types of large deformation of saturated silt can be distinguished: the cyclic liquefaction and the cumulative strain. At the same time, it is shown that, the cyclic shear strength decreases with the increasing of initial static shear stress ratio until initial static shear stress ratio reaches cyclic shear stress ratio, and starts to increase thereafter.

Based on damage mechanics and the concept of damage threshold, rock behaves elastically at the beginning of loading, and successive damage is followed when the stress reaches the yield state. Until rock is completely damaged, the stress-strain curve shows deformation characteristics of residual strength. In this study, three-parameter Weibull distribution function is adopted to describe the evolution of rock damage. Meanwhile, the Lemaitre strain equivalence hypothesis is modified by considering the friction force caused by the relatively slipping deformation of rock along pre-existing local cracks. Finally, a new constitutive damage model is proposed to precisely describe deformation characteristics of residue strength and the elastic deformation at the low confining pressure. Furthermore, the proposed model is also verified by experimental results, which indicates that the model can be widely applied to practical engineering projects.

Discontinuous cyclic loading/unloading fatigue tests were conducted on salt rock to investigate the evolution laws of mechanic characteristics (i.e., deformation and elastic constants) at different time intervals by using a multifunctional testing machine. The results show that compared with the residual deformation in the normal loading/unloading circle, residual deformation in circle after interval is greater than that in circle before interval. The behavior of the radial and volumetric residual deformation follows the same rule as that of axial deformation. Modulus of elasticity in circles after interval is larger than that in circles before interval generally, while Poisson’s ratio does not change obviously with interval which shows a similar upward trend before and after the time intervals. Interval accelerates the accumulation of residual deformation. The longer the interval is, the faster the residual deformation accumulates during fatigue process, and the shorter the fatigue life of salt rock. The interval without applied stress is beneficial to regression of crystal lattice under the function of residual stress and to generating new slip planes. Less energy consumption is caused when the crystal lattice returns to its initial position corresponding to previous peak stress value. Salt rock samples break more easily and have shorter fatigue life at the macro level.

Investigations into damaged geotechnical structures after earthquakes reveal that the sheet pile wall has good seismic performance, especially reinforced by anchor cables. However, the research about sheet pile wall mostly focuses on its behavior under static conditions at present, while scarce achievements on dynamic response and seismic working mechanism yet. The comparative study of seismic response characteristics regarding two types of sheet pile wall, namely sheet pile wall and anchored sheet pile wall, has not been reported in literatures. In this paper, sheet pile wall and anchored sheet pile wall are tested in a large scale shaking table test, and dynamic characteristics of these two types of structures are analyzed. The experiment results show that the dynamic responses of time histories of earth pressures, anchor cable tensions, and displacements of pile from these two types of structures are closely relate to input seismic parameter characteristics, e.g. curve shape and variation trend. The occurrence time between peak value and peak ground acceleration is consistent. The installment of anchor cables can stabilize slope and restrict displacement of pile efficiently, especially in high seismic intensity zones where soil nonlinearity increases. Prestressed anchor cables can constrain displacement of pile. The displacement of sheet pile wall is 2.4 times of displacement of anchored sheet pile wall when the seismic coefficient reaches 0.4. The application of prestress in anchor cables can generate pseudo-active counter pressure from pile to soil, resulting in increased internal force in cantilever segment. Under the conditions of static loading and 0.1 of seismic coefficient, the landslide thrusts and soil resistance of two types are close. The maximum difference of measured intensity is less than 20 percent, indicating minor anchor cable effect. When seismic coefficient is larger than 0.2, anchor cables improves the compatibility of deformation. In this situation, the interactive force between pile and soil increases, and resistance of soil decreases greatly, and the slope is more stable. Meanwhile, the cable tension makes internal force larger in cantilever segment. Thus cantilever segment should be strengthened in structural design, and embedded segment can be weaken appropriately. The achievement of analysis provides reference for seismic design, rebuilding after earthquake, and revision of related specifications in high seismic intensity zones.

Recycled tire wastes mixed with soils are applicable as lightweight filling material for slopes, sub-bases of pavements and retaining walls to improve the safety of the retaining walls. Under the seismic loadings, e.g., earthquake or traffic loads, the dynamic responses of granulated rubber/soil mixtures, such as the evolution of stress-strain, rule of cumulative pore water pressure, dynamic shear modulus, and liquefaction resistance, are essential in the design of such a system. This paper investigates the dynamic responses, liquefaction resistance mainly, of recycled rubber tire powder through mixtures with different tire powder sizes in saturated condition using cyclic triaxial tests. The results show that the larger tire powder size significantly improved liquefaction resistance of granular materials. Meanwhile, the incorporations of tire powder changes the deformation pattern and the evolution of pore water pressure compared to the pure sand. The attempt is to further explain the evolved dynamic behavior of the mixture. And the results as a supplement enrich the database of dynamic behavior of soil rubber mixture as lightweight filling material in saturated condition. Finally, the results are interpreted from the microscopic view of the point.

The hydraulic conductivity of mine leachate through the geosynthetic clay liners (GCLs) was tested using the flexible wall permeameter under different effective stresses. The result of test shows that the increase in the hydraulic conductivity of the GCL permeated with simulated mine leachate was strongly related to the effective stress applied on the GCLs. Under a relatively low effective stress of 24 kPa, the hydraulic conductivity of GCL permeated with simulated mine leachate was up to 1.52 m/s, about 340 times greater than that of GCL permeated with tap water. The GCL was not able to satisfy the requirement specified in the standard for pollution control on the storage and disposal site for general industrial solid wastes. However, the hydraulic conductivity decreased to 26, 21, 14 and 10 times of the number for tap water when the effective stress increased to 93, 162, 231, and 438 kPa, respectively. All the hydraulic conductivity values of GCL obtained during these test stages were lower than the specification in standard. The results of this study indicated that the stress state for GCL expected in the field should be considered when evaluate the hydraulic performance of GCLs that considered as a liner for a tailing impoundment.

Aquitards are an important part of an aquifer system. Hydraulic properties of an aquitard, such as hydraulic conductivity and specific storage must be determined before the investigation of strata deformation and groundwater depletion. Based on the proposed one-dimensional schematic diagram of an aquifer system, a dimensionless analytical solution for flow in the aquitard is derived under the boundary condition of drawdown in adjacent aquifers showing a linear increase with time. The dissipation process of time-lag drawdown in the aquitard is analyzed. The type curve of cumulative aquitard compaction versus time is derived based on the mass balance equation of water. A new type curve method is further derived for estimating the hydraulic conductivity and specific storage of the aquitard. The type curve method reflects the time-lag drainage within the aquitard. This method is tested by a field application to the Shanghai aquifer system to obtain the hydraulic parameters of the second aquitard at the f10-7 extensometer site. Field test results show that the hydraulic conductivity and specific storage are 4.26 m/s and 2.22 , respectively. For an aquifer system with long-term observed water level and deformation data, the new type curve method can be used to some extent.

The three-dimensional (3D) structural model is a good way to represent the spatial morphology of geological entity, and is an effective carrier of geological structures, compositions, tectonics, and geological data in a 3D visualization space. Geological slices based on the Boolean operation (vector shear) can be used to extract crisscross virtual geological sections directly from a 3D geological model, which intuitively shows the spatial morphology of the stratigraphic structure and geological tectonics at a certain location. However, isolated geological sections cannot properly characterize spatial continuous changes of a geological structure, tectonics and phenomena. Therefore, we propose a visual analysis method of 3D geological models based on sequential sections. Corresponding to each scanning direction, the Boolean operation of geological structures, tectonics and attributive characters on each virtual section is implemented by using a multithreading-based real-time vector shearing technology. Thus the visualized geological sections which contain spatial topological structures and attributive characters are obtained. Multi-group sequential sections are successively generated, and the continuous and dynamic display of 3D geological models is performed by means of sequential sections eventually. This method possesses high flexibility, controllability and automaticity since the scanning direction, threads, section frames and other parameters can be controlled through a custom interface. Therefore, real-time and multi-angle dynamic scanning of 3D geological models can be achieved using the sequential sections as well as more intuitive, efficient and flexible visual analyses of geological space are implemented.

The ratio of shear/normal stress reflects the deformation and failure characteristics of the friction material. By analyzing the shear/normal stress ratio under the change of magnitudes and directions of principal stresses, a nonlinear elastic model of soils considering the direction of principal stress axis is proposed based on the hyperbolic relationship between the shear/normal stress ratio and shear strain component. Considering the initial shear modulus and the strength of soil are closely related to the loading history and direction of stress, a method is given to determine the parameters of the model, and then a stress-strain relationship in the form of component is obtained. The rationality of the model is validated through stress path controlled triaxial test, pure principal stress axis rotation test and shear test with fixed direction of major principal stress. Comparisons of the predictions with the experimental results show that the deformation characteristics of soils under complex stress paths can be well quantified by the proposed nonlinear elastic model.

The dynamic response of X-section cast-in-situ concrete (XCC) pile-raft composite foundation embedded in sand under sine wave loading simulating a moving train axle load with different frequencies is investigated based on large-scale model tests. This study measured the variation of velocity and dynamic soil pressure with depth, and analyzed the response in velocity, dynamic soil pressure and dynamic stress of XCC pile under different load frequencies. It is shown that the amplitude of velocity response of the raft increases approximately linearly with increasing loading frequency. The dynamic stress and dynamic load magnification factor of subsoil also increases gradually with increasing loading frequency. In addition, the dynamic stress on top of the XCC pile increases with increasing loading frequency. The results provide an insight into high-speed railway pile-raft composite foundation regarding to theoretical analysis and calculation, and the determination of dynamic load magnification factor.

Most reliability analyses of geotechnical structures considering soil heterogeneity mainly focus on inherent variability, namely the heterogeneity in soil parameters. Another type of soil heterogeneity, i.e. geological uncertainty, is not well studied. The geological uncertainty is very common in reality. It appears in the form of one soil layer embedded in another or the inclusion of pockets of different soil types within a more uniform soil mass. Hence, a borehole-based method is proposed to evaluate the uncertainty in probability of failure (Pf) and statistics of factor of safety (FS) for a slope when geological uncertainty is considered. Firstly, different borehole layout schemes are designed using available borehole data. A coupled Markov chain model is constructed to simulate the geological uncertainty. Secondly, slope stability analyses are conducted using a finite element – strength reduction method. Finally, the effect of borehole layout scheme on the uncertainty in FS and Pf of a slope is analyzed. The borehole data in Perth, Australia are adopted to illustrate the effectiveness of the proposed method. The results show that the borehole layout scheme has a significant influence on the uncertainty of FS and Pf of the slope. The FS of the slope in the presence of the geological uncertainty can be described by a Johnson distribution. The Pf and statistics of FS do not necessarily vary with the number of boreholes monotonously. The boreholes within the influence zone of slope are the most effective in evaluating the uncertainty in the FS. The mean of the FS converges to an accurate value as the borehole number increases.

The evaluation of rock burst proneness is the basis of risk assessment of rock burst in underground engineering. However, existing numerous evaluation indexes with different characteristics results in application errors frequently. After clarifying the concept of rock burst proneness, the evaluation indexes of rock burst proneness were summarized and categorized through a comprehensive literature review. From the perspective of acquisition methods of their values, the index of rock burst proneness (Wet) and the coefficient of intensity brittleness (B) were analyzed. The inflection point of volumetric strain, as unloading control point in test process, was recommended to determine the value of Wet. Thus, the traditional difficulty that the unloading point was hardly controlled during the test process, was solved. According to testing results, this method was proved to be scientific and effective. By comprehensively investigating the values of Wet and B for different kinds of rock, the relationship of these two indexes was analyzed and the evaluation standard of B value was further improved. Therefore, this study provides a significant guidance for scientifically and reasonably evaluating rock burst proneness.

Mechanical properties and temperature field of inclined frozen wall provide reliable basis for solving technical difficulties of inclined frozen mine construction in the water-rich sand stratum. Taken the inclined frozen engineering in northern Shaanxi as an example, thermo-physical and mechanical properties of frozen sand were studied by the combination of laboratory tests, field measurement and the finite element simulation. The variation and causes of freezing pressure in inclined frozen sand well were analyzed and the measured temperatures were compared with numerical results obtained in thermometer holes. It is found that the thermal conductivity of frozen sand initially increases and then decreases with the decrease of temperature, and the internal friction angle of frozen sand was greatly influenced by freezing temperature. The freezing pressure was significantly affected by the freezing temperature, shaft depth and groundwater. The effect of the concrete hydration heating on the frozen wall was in the range of 460 and 475 mm. The results provide evidence for the optimization design and stability of inclined mine construction by frozen in the water-rich sand stratum.

To identify boundaries of homogeneous soil layers is critical to geotechnical design. The piezocone penetration test (CPTU) data are often used for soil classification, boundaries identification, property evaluation, etc. Statistical methods for soil boundary identification are developed to detect the boundaries of the homogeneous soil layers based on CPTU data. To generate intra-class correlation coefficient index, i.e. RI statistics and Bartlett statistics, it is necessary to perform statistical analysis on CPTU data with intra-class correlation method and modified Bartlett statistic test respectively. The boundaries of homogeneous soil are identified by mechanical layered method using critical RI statistic and critical modified Bartlett test statistic for homogeneity test of soil layers. The CPTU data in three construction sites are assessed to identify boundaries of homogeneous soil layers with the proposed methods. The results compared with the results of the soil classification layered method show that the mechanical layered method can discriminate all primary boundaries decided by the soil classification layered method, and reveal potential secondary soil boundaries.

The roadway experienced the whole evolution process, including the stability before excavation, excavation disturbance and support stability or failure. It is found that the steady state of the roadway was affected by the interaction of the in-situ stress field, excavation-induced stress field and supporting stress field. In this study, the finite difference program FLAC3D was employed to analyze distribution characteristics of supporting stress fields in surrounding rock which were induced by the bolt and anchor cable under different conditions of pre-tightening force and inter-row distance. Furthermore, the coefficient k of rock stress expansion was defined to characterize the stress diffusion effect of surrounding rock. The coupling support effect of the bolt and anchor cable was revealed as well. A new approach was put forward by considering the special geological conditions and engineering characteristics of deep roadway in Zhujixi Mine. This approach was named as a step-by-step combined support technology consisting of cable anchor spraying, U type steel support, grouting, floor anchor and injection. A three-dimensional (3D) similar material model test was conducted to verify the approach, which revealed the deformation and failure of soft surrounding rock and the evolution laws of supporting structure under high stress conditions. This scheme was also successfully applied to a practical engineering project, which solved the support problem of deep soft rock roadway under high stress. The monitoring results indicate that the combined support scheme effectively control the large deformation and floor heave of deep soft rock roadway. Eventually, the long-term stability and safety of the roadway surrounding rock and supporting structure can be guaranteed.

Seismicity as an important parameter in a mine indicates rock damage, which is widely used for prediction and control of the stability of surrounding rock mass during mining. To investigate failure mechanisms of surrounding rock during mining, we propose solutions to key issues concerning applications of the moment tensor theory. A moment tensor three-component decomposition model is introduced to solve the uncertainty of the solution of equations of moment tensor decomposition due to the uncertainty of mining-induced stress states. The deficiencies of the criterion of rock failure modes proposed by Ohstu are discussed and thereby a revised criterion is proposed to analyse rock failure modes in a mine. Failure mechanisms of surrounding rocks in Dongguashan Cooper Mine are studied by the proposed seismic moment tensor method. The results show that the major rock failure of Dongguashan roadway is shear failure, in combination with the failure mode of the combined action of multiple factors. When tunnels are located in different rock contact zones, microseismic events cluster in the contact zone and a shear band occurs in the seismic event clustered area. However, when tunnels are located in one stratum, the distribution of microseismic events is more dispersed. The failure is caused by the stress concentration, and the failure mode is the local surrounding rock caving.

To overcome difficulties in calculating the failure probability of slopes such as determining the performance function and solving multiple integration, a Copula-based method for analyzing slope reliability through the g-line failure domain was proposed in the present paper. Firstly, the Copula theory was briefly introduced and the procedures of Copula-based slope reliability analysis were presented. Then we discussed the g-line curve-fitting shapes of general homogeneous slopes and the range of shear strength parameters which represented the slope failure domain. It is found that the g-line curve can be fitted as the quadratic polynomial and the slope failure domain under the g-line curve can be represented by the friction angle and cohesion. Taking a homogeneous slope as an example, the failure probabilities of three different types of Copula functions were obtained by integrating the g-line failure domain. The results approximate to those calculated by traditional methods such as FORM and MCS, which demonstrate the reasonability of the Copula-based method for analyzing slope reliability using the g-line failure domain. Finally, we discussed the characteristics of the failure probabilities calculated by different Copula functions change with the safety factor. When the failure probability was low or the safety factor was high, the results are sensitive to the type of Copula function. Therefore, attention should be paid to the study of the different results caused by different function types and of the optimization problem.

Cyclic stress generated in soft foundation after cyclic wave loading is transferred to the intercalated soft layer through embankment and the backfilled sand layer. The strength of saturated soft clay degrades and soil loses bearing capacity. A 3D elasto-plastic dynamic model of steel sheet pile considering post-cyclic undrained strength degradation is developed using the dynamic finite element method. The maximum excess pore pressure and post-cyclic strength degradation of the intercalated soft layer are investigated. A method for dynamic stability analysis of steel sheet pile-soft foundation system is proposed to investigate the failure mode, stability and settlement of steel sheet pile-soft foundation system. The results show that the maximum excess pore pressure is generated in soft clay around the cell. Post-cyclic strength degradation occurs at the bottom of the main cell, arc cell and some soil-pile interaction areas. Safety factors of stability of steel sheet pile-soft foundation system decrease significantly with considering post-cyclic strength degradation of soft foundation. It is suggested that the post-cyclic strength degradation should be considered in practical design.

Both experimental and numerical results demonstrate that particle breakage has significant influence on the macro mechanical response of granular soils. In this study, a novel computational method was proposed to simulate particle breakage phenomenon in granular soils. The proposed method based on the discrete element method (DEM) and the scaled boundary finite element method (SBFEM) has advantages of each method. Individual grains of soil are modelled by a single star-convex polygon with an arbitrary number of sides. The DEM is used to determine the motion of particles and the interaction among particles, whereas the SBFEM is applied to obtain stress states of grains at the end of each time step. Since the SBFEM flexibly describes the morphology of each grain with a single polygon consisting of an arbitrary number of sides, it greatly reduces the necessary computational resources for stress analysis. When the stress state has been confirmed, Hoek-Brown criterion is chosen to determine the ‘plastic points’ within each particle. Once the ratio of ‘plastic points’ reaches a predefined threshold, the particle breakage is triggered. As a straight breakage line is assumed for simplification, the particle is split into two when breakage occurs. The newly generated polygons are directly modelled by the DEM and SBFEM without any change of the formulation, and thus this method does not need to predefine sub-particles and re-meshing elements. At last, the feasibility of the newly developed method is verified by a biaxial benchmark test.

Under the certain strain path, granular materials may exhibit non-localized failure mode corresponding to an abrupt occurrence of failure with the stress states within the Mohr-Coulomb yielding surface. Using the discrete element method (DEM), mechanical properties of granular material with different rolling friction coefficients are examined under proportional strain loading paths. For particle assemblies of different densities, looser assemblies tend to have diffuse failure, which qualifies Hill’s second-order work criterion. A contact model considering rolling friction is adopted in DEM analysis. By changing the rolling friction coefficient, micro-macro mechanical properties of particle assembly are studied under a specific proportional strain-loading path. The enhancement of particle rolling resistance reduces the likelihood of diffuse failure. At the macro level, stress path changes from strain softening to strain hardening as the rolling friction coefficient increases, and the looser particle assembly exhibits the similar mechanical behaviours as the denser one. The micro-structure shows the corresponding mechanism of action. As the rolling friction coefficient increases, the angular velocities of particles and their distribution will be well controlled. Although the coordination number decreases, the contact forces are enhanced, and the instabilities and anisotropies of the force chain distribution can be improved in the system. All the microscopic parameters manifest a stable structure, which can resist the increasing load, thus the specimen will not form a loose contact state and diffuse failure will not occur.

A three-dimensional (3D) discrete element model (DEM) is established to simulate micro- and macro-scale mechanical behaviors of railway ballast. In this model, the clump models with irregular shape are built to simulate the real ballast particle geometry morphology captured by using a 3D laser scanner. A full-scale model of high-speed railway ballasted track is conducted to validate the DEM model. The deformation and vibration response of railway ballast are obtained under the static load and the cyclic load in the laboratory. The amplitudes of the ballast acceleration and its attenuation law with the depth acquired by DEM simulation and experimental tests are close. Numerical results of the vertical deformation of railway ballast under the static loads and the permanent deformation under cyclic loads are good agreement with experimental data, which demonstrates that the established DEM model is reasonable. Therefore, the obtained vibration response and deformation of railway are reliable and relatively accurate. This DEM model can be used for subsequent analysis on the micro- and macro- mechanical behaviors and deformation of high-speed railway ballast.

Fully coupled governing equations are developed for hydro-mechanical analysis of deforming porous medium with fractures based on the stress balance equation, the seepage continuity equation and the modified Biot effective stress principle. The flow of the fluid within the medium, and fracture satisfies the Darcy law. The final nonlinear fully coupled equations reflect not only the coupling effect of the physical quantity within the porous medium, but also the coupling between the medium and the fracture. Since the extended finite element method (XFEM) has a unique advantage in dealing with fracture problems, both XFEM and the ordinary finite element method (FEM) are used to establish the numerical calculation system. During the spatial dispersion, the displacement and the pore pressure in the medium are discretized by FEM. To reflect the strong discontinuity of the fracture surface and the stress singularity at the crack tip, two kinds of additional displacement functions are introduced in the displacement model of the fracture area based on XFEM. The pore pressure enhancement function is also applied to represent the weakly discontinuous features of the normal pore pressure. Time discretization is performed using a backward difference scheme. Finally, numerical examples are provided to prove the correctness and effectiveness of the model and algorithm. Moreover, the delay of the fluid flow, the feature of the opening displacement and the pore pressure in the fracture are analyzed, and the effect of changes of the permeability and external flow on numerical results are discussed.

Block in matrix (BIM) soil is composed of block stone, gravel, sand, clay and other solid particles. The model for seepage erosion in BIM soil is assumed as the form of Sterpi Formula, and the content of block stone as one of the most important parameters of BIM soil needs to exist in the model. However, due to the complexity of grain sizes in BIM soil and the limitation of traditional experimental setup in the laboratory, it is hard to conduct experiments directly to study seepage erosion in BIM. Therefore, a new method is proposed to obtain these parameters by means of numerical simulation on BIM soil and experiments of seepage erosion on gravel soil matrix without block stones. BIM soil from a landslide in Yunnan Province is selected as an example. Firstly, an experimental setup is designed to perform a series of seepage erosion tests on gravel soil matrix without block stones to obtain its seepage parameters. Then, based on the governing equations of particle migration, coupling seepage and porosity, numerical simulation is carried out to characterize the process of seepage erosion in BIM soil under the assumption of block stones with poor permeability. Numerical results show that when hydraulic gradient and time are consistent, the average initial velocity of BIM soil is inversely proportional to the content of block stone, but the density of liquefied particles is proportion to the content of block stone. Finally, a formula is presented for seepage erosion in BIM soil with the content of block stone as one of parameters.

The determination of three-dimensional (3D) critical slip surface and its associated factor of safety (FoS) of slopes are essential to their stability analysis. However, it is difficult to obtain 3D slip surface conveniently and reliably by using existing analytical methods. In this paper, the FoS of slopes is calculated based on the stresses from the finite element method (FEM). A new method is developed to search 3D critical slip surface of slope by constructing an extended ellipsoidal slip surface and adopting self-adaptive differential evolution (SaDE) algorithm in combination with the opposite-movement scheme. The extended ellipsoidal slip surface is easy to construct and flexible to search, and meanwhile it is more coincident with the actuals than spherical and ellipsoidal slip surface. In addition, the whole calculating process is explicit without the convergence problem. The application of the developed method is verified by re-analyzing benchmark slope stability examples from the literature. The results obtained in examples prove the SaDE algorithm has high efficiency and global optimization ability, which are also in good agreement with limit equilibrium and strength reduction methods. It is also demonstrated that this method is suitable to be applied in stability analysis of slopes under complex lithology and environmental conditions by analyzing actual engineering slopes.

It is well known that the constitutive relation plays a key role in the nonlinear finite element analysis, and a time integration is particularly required to solve the problem whose stress response is deduced by its strain increment. The hypoplastic rate constitutive model is represented by Jaumann stress rate and deformation rate, and on the basis of this model, we develop adaptive implicit and explicit integration methods with local error control respectively. Meanwhile, the consistent tangent modulus is given for the implicit integration. Based on two different element tests, results of two types of numerical simulations of integration algorithm are compared by using ABAQUS. Moreover, a UMAT-VUMAT interface is developed to implement the transition from ABAQUS/ Standard to ABAQUS/Explicit and then the flow chart of this development is presented. Therefore, the existing UMAT subroutine can be used for large deformation or high-degree dynamic problem analysis. Finally, the accuracy of numerical results is verified by a case study.

The inconstant well resistance effect, namely the changing discharge capacity of PVD with the foundation depth and consolidation time, is observed in drainage well under the vacuum preloading condition. Meanwhile, the partition of vertical drain zone and smear zone in 3D model is another challenging problem of finite element simulation. In order to simulate the actual conditions of vacuum preloading, a model with dimensionless parameters and considering well resistance in 3D finite element analysis is developed in this paper. An adaptive grid unit simplifies the drain zone and an equivalent method simplifies smear zone in simulation. The proposed procedure is applied to build the 3D finite element model of the reclamation project in Tianjin Port, and is verified by comparisons between the calculated data and the observed data.

Shaking table test is considered as an effective tool for investigation of soil-structure interaction problems and validation of research methods under earthquake loading. It is essential to choose an appropriate soil container, because the soil container directly affects the boundary of the model and the accuracy of the simulation. A 3D circular laminar shear container is deployed consisting of 19 layers of aluminum alloy frames with dimensions of 1 800 mm in height and 4 500 mm in diameter. The upper and lower layer frames are connected by supports in three direction. In order to investigate the boundary effect of the laminar shear container on the seismic response, a shaking table test is conducted to acquire the test data from accelerometers embedded in the sand bed at various depths and distances from the edge of the container. In the shaking table test, the ground acceleration corresponding to design spectra of AP1000 nuclear power plant is applied as the input for earthquake ground motion. The acceleration time-histories compare with response spectra at different monitoring points. The relative error of PGAs and response spectra recorded at monitoring points from center to the edge of the container are calculated. It is shown that the designed 3D laminar shear container could effectively simulate the infinite boundary condition of actual site in three directions, which overcomes the shortcoming of the former laminar shear container inputting one-direction or two-direction excitation.

A large size visual direct shear testing apparatus is developed to carry out direct shear tests of geosynthetics and soil under various conditions. The loading modes and reaction system of the apparatus are improved to explore the interface properties and loading transfer mechanism of reinforcement soil. The front visualization of the shear box and automated data acquisition system are achieved to measure the strain of geotextile material. Direct shear tests are conducted on geogrid and coarse-grained soil by using the newly developed apparatus. The results show that the interfacial cohesion of reinforced soil increases, but its internal friction angle decreases compared with plain soil. The geogrid strain increases with the increase of shear displacement. Moreover, the rapid increase of embedded resistance between the geogrid transverse rib and the soil is caused by the rapid increase of the geogrid strain. However, the maximum strain of the geogrid generated by direct shear is far less than the yield strain of the geogrid. The direct shear interface thickness of plain coarse soil is less than that of the reinforced soil. The movement of coarse grained soil particles is mainly translational on the reinforced soil around the direct shear interface, and meanwhile some small particles are in the horizontal rotational movement mode.