Methane hydrate (MH) is usually formed in marine deposit under specific temperature and pressure conditions. MH can enhance the shear strength of its bearing sediments due to bonding effect. Based on the framework of damage mechanics, the structured sand constitutive model is employed to simulate the mechanical behavior of methane hydrate bearing sediments. By simulating the consolidated drained triaxial compression tests, a quantitative relationship between the initial yield parameter and the methane hydrate saturation is developed according to the stress-strain relationship. The primary damage law is modified to develop an elasto-plastic constitutive model for methane hydrate bearing sediments. Furthermore, another set of triaxial tests and isotropic compression test on methane hydrate bearing sediments are simulated by the established model. Results show that this elasto-plastic constitutive model can effectively describe the relationship between the mechanical behavior of methane hydrate bearing sediments and the methane hydrate saturation. When methane hydrate saturation increases, the peak shear stress and the secant modulus increase in the triaxial tests, and the yielding stress under isotropic path increases along isotropic compression path.

According to the similarity theory, punching properties of karst cave roof under pile tip were investigated through four series of large-scale laboratory model tests under different thick-span ratios. The load-displacement curves of pile foundation and roof and the strain displacement curves of roof bottom were obtained, and the bearing mechanism of punching feature in the pile-cave system was analysed. The experimental results show that there are two elastic-plastic zones in the pile curve during the loading process. According to the load-displacement curve of the roof, the displacement rebounds at thick-span ratios of 0.125 and 0.200 during the loading process. Meanwhile, the strain change is consistent with the development of cracks at the bottom surface. Punching failure of the test plate is the result of the combined action of the shear effect and bending effect. With the increase of thick-span ratio, the ultimate bearing capacity of the pile-cave system increases slightly, whereas the displacement distance decreases. Shear effect becomes more apparent, while bending effect gradually disappeares. The shapes of the punching cones change significantly with varying the thick-span ratio. When the thick-span ratio is higher than 0.250, the punching cone is relatively thick and destruct along the boundary. While with the thick-span ratio less than 0.200, the punching cone is not restricted. Finally, the relationships among the punching cone generatrix, the thick-span ratio ξ and the pile diameter d are established through analysing the punching cones under four different thick-span ratios. Therefore, this study provides the basis for the theoretical research and engineering practices of karst caves under pile tip in the karst area.

Studies of damages in shear bands are important for obtaining a full understanding of failure mechanisms of materials, and for accurate modeling of deformations in shear bands. To study the distribution and evolution of damages in shear bands in clay specimens in uniaxial compression, monitored lines are arranged according to positions of clear shear bands along their tangential directions at higher longitudinal strains. Smooth strain fields at these lines are obtained using a bicubic spline interpolation function from results based on a digital image correlation method. The damage variable-longitudinal strain curves for entire specimens and shear bands are compared. It is found that in total the damage variable-longitudinal strain curves for entire specimens are linear, while those for shear bands are convex upward, suggesting that damage developments in shear bands become faster and faster as longitudinal strains increase. The envelop of the damage variable-longitudinal strain curves for shear bands is like a horse-tail, revealing that interactions among shear bands become intensive as deformation proceeds. For specimens with low moisture contents, changes in damage variables for shear bands are generally synchronic for parallel or co-linear shear bands, especially for well-developed shear bands, however, the shear band spacing cannot be large enough. The damages in one shear band between two conjugate or intersecting shear bands are dominant at a certain stage due to competition between them. However, if the two shear bands have developed fully, changes in damage variables can be synchronic. For specimens with high moisture contents, changes in damage variables for shear bands are generally synchronic for parallel or conjugate shear bands, reflecting weak interactions among shear bands.

Vertical circular holes are often encountered in practices. The limit depth of without supporting is important for a stable vertical cylinder hole in cohesive soil. Firstly, if the failure surface is planar and pass through the slope toe, the stable limit height of the slope can be obtained by limit equilibrium analysis of vertical slope, and compared with Taylor’s results by circular sliding surface. Secondly, planar sliding surface is extended to the axisymmetric problem for vertical cylinder hole in cohesive soil. Assuming the failure surface is an inverted round estrade, and a relationship between cu /?h and h/r can be solved by limit equilibrium analysis, and provide the basis in engineering design. Thirdly, vertical cylinder hole with different geometrical parameters are numerically modeled and the lower limiting values of cu /?h are summarized. The results show that limit equilibrium method results coincided well with the numerical analysis results.

Generally, special requirements on the tunnel lining structure are needed for swelling rock. This study investigated the lining structure improvements for Lirang tunnel of Liangzhong-Chongqing highway composed of swelling rock. A new numerical simulation model was proposed based on the Noorany modified swelling model. Then we studied the optimum design of EPS buffer layer thickness and the stability of the tunnel structure by using the established model. FLAC software was employed to comparatively analyse mechanics states of three kinds of structures after excavation, including the primary support, buffer layer and secondary lining of the excavated tunnel. At last, the optimum thickness of buffer layer was obtained for the certain tunnel condition. In addition, the EPS buffer layer with a thickness of 40 cm was applied in practical supporting structure between the first and the second lining. The field monitoring results showed that the actual values of lining contact pressure were less than those of standard warning, which indicated that the reliability of optimum proposal for support structures was verified. Therefore, theoretical and applied studies demonstrate that the EPS buffer layer can be an effective improvement for lining structure and a control measure for preventing potential disasters of tunnels in rich-water and swelling rock. The optimisation scheme and the design method also have essential guidance for similar projects.

The ageing effect on the shear strength of Gaomiaozi (GMZ07) bentonite with different water contents were investigated in this paper. Water contents of 10%, 18% and 24% (saturated) of compacted bentonite specimens were kept constant during curing periods of 0, 5, 15, 30 and 90 days under constant volume conditions. Then, the shear tests on the aged specimens were performed at vertical pressures of 400, 800 and 1 600 kPa by using the shear testing apparatus. At the same time, the microstructure features of the aged bentonite specimens were characterized by means of mercury intrusion porosimetry (MIP) test. The test results show that the shear strength of Gaomiaozi bentonite decreases with the ageing time. The shear strength significantly decreases at the early ageing days and then tends to stabilize when the curing time is over certain days. According to the failure envelopes of three specimens with different water contents, the internal friction angles slightly reduce and the cohesion changes little for saturated specimens with the increase in curing time. For the specimens with water contents of 10% and 18%, the cohesion evidently decreases but the friction angles remain almost unchanged. According to the effective stress of unsaturated soils proposed by Alonso et al and the pore-size distribution, it is considered that the increment in the intra-aggregate pore is the reason for the decrease in the shear strength of the unsaturated bentonite with ageing time.

For the existing calculation methods for the stabilising pile, the interaction between pile and landslide body is simplified as the determined load. However, these methods all ignore the direct dependence of the interaction on the displacement of the pile. This study developed a method, in which m-method model was employed to simulate the interaction between landslide body and pile. Meanwhile, equations were established for the piles above and below the slip surface respectively, and their expressions of displacement and internal force were also solved with power series method. Meanwhile, the bending moment and shear force at the slip surface were obtained by using deformation coordinating conditions of the upper and lower piles at the sliding surface. Hence, the deformation, internal force of the pile and the interaction between pile and landslide body were easily computed. Finally, an example was calculated by the presented method and FEM, respectively. It was found that results were in good agreement, which verified the correctness of the method.

It is important to consider an aseismic issue, which is that transflective properties of the seismic wave propagating through joints embedded in rock in underground rock engineering. However, there is very limited research on transflective properties by using the continuously yielding nonlinear joints model. In this paper, a continuously yielding (CY) model was developed based on the time-domain recursive method (TDRM) for S wave using a nonlinear Coulomb-slip (MC) model. Verification of TDRM-based results was conducted in comparison with the simulated results via 3DEC code. Meanwhile, the influence parameters were also discussed. Finally, the results from MC model and CY model were compared under an idealised impulse excitation and a real ground motion record, respectively. It can be seen that TDRM-based results show good agreement with the simulated results by 3DEC, which proves that TDRM is reliable to study the subsequent parameters. In addition, CY model is significantly influenced by parameters of normal stress, incident wave amplitude, initial joint stiffness and joint spacing, respectively. Compared with MC model, CY model can better describe complex joint behaviours in the wave propagation, such as tangential stiffness degradation, shear strength deterioration, normal stress dependence and the hysteresis effect. Therefore, research results can provide useful references for the seismic design and analysis of rock underground engineering.

In this study, three-point bending beam tests were carried out under impact load. Dynamic stress intensity factor (DSIF) of type-I crack was determined by using the strain gauge method, which considered the stress field near the tip of propagating crack. When the orientation angle between strain gauge and the crack path was at specific acute and obtuse angle, the normalised strain around a propagating crack could be clearly described by a two-parameter formula, which was related to the velocity of propagating crack and the location of the strain gauge. Furthermore, the corresponding coefficient and DSIF formula were also given. The results show that the strain-time curve obtained by the theoretical method is in good agreement with experimental data. When characteristic time ?t is chosen at the time span of 3/4 peak strain before and after the peak value of strain-time curve, the consistency of theoretical calculations and experimental results is relatively high. DSIF is calculated by using the theoretical and experimental peak value of the strain-time curve. Meantime, the dynamic caustics method is applied for the determination of DSIF of type-Ⅰcrack and the obtained results verify the feasibility of the strain gauge method as well. In conclusion, this study provides an effective theoretical basis for the application of strain gauge method in the determination of dynamic fracture properties for rock mass.

The theory of fractional calculus has been widely applied to model the viscoelastic behaviour of soils subjected to static loading. However, limited work has been carried out on using fractional calculus to describe the cyclic elastoplastic behaviour of granular soils. Hence, a fractional rate for strain accumulation of coarse granular aggregates under cyclic loading is proposed, based on the analysis of the deformation of coarse granular aggregates subjected to cyclic loads by using the theory of fractional calculus. A fractional order bounding surface plasticity model for coarse granular aggregates under monotonic and cyclic loads is developed. It is noted that there are ten parameters of the proposed model, which can be experimentally determined by the traditional triaxial compression tests. To further validate the model, a series of laboratory test results of different granular aggregates from several independent literatures is simulated. It is found that the proposed model can well capture the monotonic and cyclic stress strain behaviour of coarse granular aggregates. It can also well predict the cumulative deformation under long-term cyclic loading.

Abandoned mine pits around the city are gradually constructed for large-scale public service projects. However, new technical problems emerge due to taking the slope as the foundation of buildings. A large-scale shaking table test was carried out to study the dynamic displacement and internal force of pit slope, single-span frame structure and multi-span frame structure. Results show that dynamic response of the model is influenced by seismic wave type, amplitude and direction. Moreover, different seismic waves have different impacts on the dynamic displacement and internal force of the model. It is found that dynamic displacement increases with the increase of excitation amplitude. In addition, dynamic displacement caused by the bi-directional excitation is larger than that of the single one, and the displacement in the same direction as the excitation is greater than that in other directions. Under the high-intensity earthquake excitation, the ability of multi-span structure to control displacement is stronger than that of single-span structure, while column internal force is higher. By considering the interaction between structure and foundation, the structure with good integrity and high stiffness can improve the seismic performance of the foundation. Results show that the peak and permanent displacements of multi-span structure foundation are 2.5%-8.8% and 13.6%-62.1% lower than those at free zone site, respectively. Therefore, this study is helpful to reveal the failure mechanism of pit slope under the earthquake, and provides a useful reference for the seismic design of the slopes and structures.

Compared with the traditional physical model test, centrifugal test can simulate the long term process of soil freezing with full-scale stress in a short time. However, there are few researches on the centrifuge modeling of cold regions engineering. At present, scaling laws and similarity conditions of thermal dynamics of freezing soil in geotechnical centrifugal modeling are still not completed, which has become an uncertain factor in quantitative analysis of frost heave by centrifugal technique. Based on hydro-thermal-mechanical interaction process in saturated freezing soil, dimensionless variables have been established by Butterfield dimensional analysis method. The scale factors of the pore pressure, thermal diffusion, pore water migration, consolidation of freezing soil in centrifugal modeling have been derived. In centrifugal test, the effect of water migration, thawing soil consolidation and heat diffusion have the unified time factor 1/N2 of the prototype model, and the scale of velocity of unfrozen water is N above the prototype model. In addition, an application of centrifugal modeling of frozen-thawing process about canals has been carried out by cold regions engineering centrifugal modelling facility.

In this paper, a series of triaxial compression experiments was performed to investigate the effects of fracture dip, trace length, gap width, confining pressure and temperature on mechanical properties of the single-fractured rock mass. Experimental results show that the mechanical parameters of rock mass exhibit the quadratic function with dips and the exponential distribution with trace length, respectively. Moreover, the fitting formula (3) is employed to calculate rock mass strength approximately. It is found that rock mass strength linearly increases with the confining pressure. However, Poisson ratio and elastic modulus under negative temperature are independent of the confining pressure. The strength of rock mass decreases with the increase of gap width when it is less than 0.1 mm or greater than 0.8 mm. However, mechanical parameters are irrelevant to the gap width when it locates between 0.1 mm and 0.8 mm. Water, existing in pores and fractures, freezes under negative temperature so that both the cohesion and friction angle between rock particles are increased. Hence, the change of water form is the reason why the rock mass strength increases with reducing temperature. Results also show that the fracture angle affects the initial position of failure surface, the trace length affects the expansion scale of failure surface, and the confining pressure influences the extension direction of failure surface. In addition, the crack dip is the most sensitive influencing parameter to the strength of rock mass, followed by trace length, with the least temperature.

Residual water content (RWC) is an important parameter for the study of seepage theory and strength theory of unsaturated soils. However, it is very difficult to determine experimentally from soil-water characteristic curve (SWCC) because the residual state can not be reached normally. In this case, the RWC is often estimated using the empirical methods including the model fitting, so the rationality of these methods is worthy to be studied. After Wuhan clay samples with different initial void ratios were prepared, SWCCs were measured by using the pressure plate apparatus and the RWCs were calculated by using the model fitting method. Water evaporation test was carried out in the natural state. Subsequently, the residual time was defined according to the rate of water loss and was used to determine the RWC. The micro pore characteristics were studied using the nuclear magnetic resonance (NMR) technique, which was used to explain the microscopic mechanism of the RWC. The results show that the model fitting method can be used to estimate the RWC, but its accuracy is directly related to the choice of model and the restriction of preliminary range in RWC. Water evaporation test is a direct and feasible method to determine the RWC. The micro pores of Wuhan clay are distributed in triple peak pattern, and RWC is closely related to the water content in those pores before the first peak. According to the T2 spectrum area with the relaxation time of less than 0.267 38 ms, the RWC can be predicted accurately, however, this method needs further demonstration and improvement for other type of soil.

This study investigated the relationship between bolt rib spacing and anchorage performance under different conditions of surrounding rock. Based on the thick-walled cylinder theory, pull-out tests were carried out on sinistral rebar bolt specimens with the spacing of 12, 24, 36, and 48 mm, which were anchored in the steel sleeves with wall thicknesses of 4.5 and 6.0 mm, respectively. Results of the drawing force, the displacement of drawing force more than 100 kN, the circumferential strain of the sleeves and energy dissipation were obtained. Experimental results show that the displacement of drawing force more than 100 kN, the circumferential strain and the energy dissipation value of the sleeve increase with increasing the rib spacing in different sleeves (different surrounding rock conditions), respectively. The pulling force of anchor rod is found to be the highest when the rib spacing is 24 mm. While with the same rib spacing, the stronger the surrounding rock is, the larger the pulling force is. The circumferential strain of the sleeve with a 4.5 mm thick wall is larger than that of 6.0 mm, which indicates that the effect of surrounding rock is significant on the deformation ability of bolts. Moreover, the anchorage performance can be improved by increasing the rib spacing under different surrounding rock conditions.

Because of the slope effect, conventional methods are not applicable to calculate the deformation of laterally loaded piles in the slope. The failure test of laterally loaded pile in slope is carried out to determine the failure mode. The soil wedge is divided into oblique elements along the direction of the slope. Strain wedge model considering the effect of slope is proposed. Key parameters, strain wedge depth and soil strain of strain wedge, are obtained by iteratively solving equations of pile-soil interaction using finite bar element method. When the difference between the ground displacement of the pile and the ground displacement of strain wedge model is less than a permissible value, the ground displacement and internal force of pile obtained through the finite bar element method are the final answer. By comparing the test data and results of the proposed method, the rationality of the proposed method is verified. Finally, the ratio of the depth of damaged soil and the slope is defined as the scope of slope effect, and the influence factors are compared and analyzed. Results show that, the scope of slope effect is related to the strength parameters of soil and the size of pile, it decreases with the increase of pile diameter and soil strength.

This study aims to establish a simulation method reflecting the initial macroscopic deformation of rock and propose a determining method for internal micro-cracks closure stress. Firstly, a deformation analysis model was established between rock matrix and micro-cracks, based on the stress and deformation characteristics of rock and its internal micro-cracks. Then deformation analysis methods were put forward for rock matrix and internal micro-cracks, respectively, according to the analysis of material deformation mechanics. Thus, an initially macroscopic constitutive model was deduced for rock, and its determining methods for the model parameters were also given. Secondly, a new method was proposed to obtain the closure stress of micro-cracks, due to the defects and deficiencies of those existing methods. Lastly, this study investigated the effect of confining pressure on the nonlinear concave degree of initially macro deformation of rock by using the established model. The theoretical result indicated that there was a negative correlation between them. Research results show that this established model can not only simulate the full deformation procedure of rock before failure, but also explain the deformation relationship between rock and their components. The new method can not only satisfy the theoretical significance of micro-cracks closure stress, but also avoid the interference of human factors. Moreover, this new method is easy to operate. Therefore, the above results verify the rationality and feasibility of the proposed model and method in this study.

Variable control method is used to comprehensively analyze the influence of all the microscopic parameters of parallel bond model on its macroscopic parameters, They are mainly manifested as: Parallel-bond modulus and particle contact modulus Ec are the main controlling factors of macro elastic modulus and there is a linear relationship between them. The Poisson's ratio is mainly affected by the particle stiffness ratio kn /ks and the parallel bond stiffness ratio and there is a logarithmic relationship between them. The bond strength of the particle bond determines the strength properties of the material. The cohesion c and tensile strength of interior materials are mainly influenced by the parallel-bond normal strength and the parallel-bond strength ratio ; they increase linearly with the parallel-bond normal strength and decrease logarithmically with the parallel-bond strength ratio 。 The friction angle is mainly affected by the friction coefficient u of the particles, and the two are in a logarithmic relationship. Analysis of fracture propagation characteristics shows that the relative sizes of the material's normal and tangential bond strengths determine the distribution of cracks. With the increase of parallel-bond strength ratio , the tensile failure area of the rock sample decreases, while the shear zone increases, and the failure surface breaks from the shear failure to conjugate damage. The smaller the dispersion of the strength of the material, the rock sample tends to focus on the destruction, the destruction of the surface is obvious, the ratio between the mean and the standard deviation of the parallel bond strengths more than 3.5 is appropriate; with the increase of parallel-bond stiffness ratio , the macroscopic damage develops to conjugate destruction. In addition to matching the strength parameters, the mesoscopic parameters need to consider the consistency of the failure modes. Considering the mutual influence of multiple parameters, the empirical formulas between the macro and meso parameters are established, the mesoscopic parameters are selected and optimized, and examples are verified. The values of peak loads, deformation parameters and shear strength obtained by indoor tests and numerical simulations are close to each other. The stress-strain evolution law is the same and the damage patterns are the same, indicating that the mesoscopic parameter results are reliable.

Van Genuchten model is one of the most commonly and widely used models. Existing research results show that different forms of parameter m and whether the correction factor is taken into consideration can have a great impact on the fitted parameters of Van Genuchten model. Therefore, three forms of parameter m (m refers to (a) without constraints; (b) ; (c) , respectively), as well as correction factor were studied in the paper. MATLAB was used throughout the calculation process. The effect of Residual matrix suction and on fitted parameters (i.e., parameters of a, m and n) were discussed based on sixty-seven types of SWCC data. The results show that if m is not constrained, a and n decrease and m increases with increase of . If m is constrained, a decreases and n increases with increase of . Furthermore, the discrete degrees of a and n increase and discrete degree of m decreases when applying the correction factor given a non-constrained m, while discrete degree of a increases and discrete degree of n decreases when m is constrained. The results also indicate that the parameter a under various conditions of m and shows a linear correlation of parameter a without any constraints, while for parameter n, the rule does not exist.

To explore the influence of seepage deformation on the permeability and compressibility of coarse grain soil, the whole process of seepage failure and compression experiment with lateral confinement on coarse grain soils with different gradations were conducted using seepage failure instrument developed by the authors. The critical hydraulic gradient, evolution law of permeability coefficient and damaged characteristics were obtained through analyzing the measured data and observed phenomenon during the test process. The results indicate that the seepage extrusion effect will generate firstly at the location of downstream along seepage path during seepage failure process and induce decrease of the permeability at the location. The permeability of the seepage extrusion part increases gradually with the increment of the experiment water head. The compression modulus of samples decreases after the seepage failure occurred. The degree of damage of the sample due to seepage failure is different on different grading samples. For soil samples after seepage failure, the structure of soil samples is reconstructed under the influence of gravity and seepage force.

To analyze the effects of bedding and water on the tensile strength of shale, specimens with four water contents were prepared with Longmaxi Formation black shale. Brazilian disc splitting tests were carried out on prepared specimens along the angles of 0°, 30°, 60° and 90°. Acoustic emission tests were simultaneously performed during the experiments, and results were further simulated by the discrete element software 3DEC. The results show that, compared with the bedding shale, the shale with both water and bedding presents a unique failure mode and special mechanical properties. Both the fracture pattern and tensile strength of Brazil shale ae related to the bedding angle and water content. Particularly, the failure mode is mainly controlled by the loading direction of bedding. Although water do not affect the failure mode, it lead to the formation of secondary cracks. The tensile strength firstly decreases and then increases with increasing the bedding angle, while it decreases with increasing water content. Moreover, under the combined effects of water and bedding, the more the shale is damaged by the bedding, the higher it is damaged by the water. The mechanism of the above changes is obtained based on the analysis of the microstructure of the shale at different water contents. When the internal mineral particles are swollen with water at the surface of the shale, the expansion force is generated, and internal structure of the shale became loose and broken. Furthermore, microcracks gradually increased and broadened. The macroscopic performance accounted for the increase of secondary cracks. In addition, the bond strength between mineral particles is also reduced under the action of water, which further decreases the tensile strength of shale.

Transmission line in Sichuan mountainous area always layout in steep slope, where Gravel soil and bedrock dual structure formation are common in the region. As such, proportional coefficient m of ground horizontal resistance coefficient is the problems to be settled urgently in the design of transmission line tower pile foundation in the steep slope. m value is obtained by the static horizontal loading test of single pile. Three methods including field experiment, indoor model test, and numerical simulation are used to investigate the changing rules, influence factors and accessor methods of the m value. The results indicate m value of slope site decreases linearly with the increase of slope, and the decrease of m in gravel soil is greater than in the gravel soil-bedrock foundation. The most influencing factors on m value are ground slope, soil compactness, pile length and pile diameter. The proposed prediction formula considers impact factors of m value of the gravel soil, gravel soil and bedrock in slope site, and provides the correction coefficient.

Water retention of undisturbed fully weathered mudstone, from Dayezhen landslide at Cenxi city, Guangxi province, is measured using pressure plate method, filter paper method, and vapor equilibrium technique with saturated salt solution. The water retention curves in a large range of suction are obtained. Mercury intrusion porosimetry is used to measure the pore-size distribution of the intact samples under different suctions. The test results show that the air-entry value of the fully weathered intact samples is about 30 kPa and the water retention curve in the full suction range can be measured by three methods. The undisturbed natural specimens exhibit a unimodal pore-size distribution with a main range of 10-1 000 nm in diameter and a secondary pore diameter distribution of 100-300 μm due to occurrence of primary crack. By comparing the results of the mercury intrusion porosimetry tests on the mudstones experiencing three different suctions, a method for predicting the water retention curve of undisturbed specimens during drying is proposed, and the predicted results are compared with the measured values. The comparison shows that the combination of three predicted curves is closer to measured results of the mudstone in the full suction range. The predicted curve using single pore size distribution curve cannot match measured water retention curve correctly in the full suction range.

In this paper, loading-unloading experiments were carried out on gas-contained coal under different stress levels by using self-made thermal-hydro-mechanical (THM) coupling equipment. The characteristics of the deformation, seepage and energy dissipation of coal and rock were analysed, and the damage variable equation was also established by considering the energy dissipation. Research results show that the cumulative residual deformation increases gradually with the advancing of cyclic loading-unloading. The relative residual deformation decreases firstly, then maintains stable at a certain value, and finally rises again when the coal sample is nearly destroyed. With the advancing of cyclic loading-unloading, the overall trend of permeability decreases spirally, and then increases until the coal sample is fractured. Moreover, a sharp increase is observed at the moment of destruction. The absolute recovery rate of permeability and relative recovery rate of permeability are defined as ?j and ?x to quantitatively analyse the changes of permeability in loading and unloading processes, respectively. It is found that ?j decreases firstly, and then increases at the critical moment of destruction. However, ?x increases steadily during the process, where ?x maintains at 85%-95% in the elastic stage, and ?x is more than 100% at the critical moment of destruction. With the advancing of cyclic loading-unloading, the cumulative dissipated energy grows exponentially, and the single-stage cycle of dissipation energy increases. With the increase of the axial stress, the principal stress difference increases, and the value of damage variable also increases. In addition, damage variable of coal Dc is 0.9 when coal is fractured.

Considering the excellent properties of supercritical CO2 has economic and technological advantages on the development of unconventional gas resources. This study aims to investigate the quantitative effects of CO2 and supercritical CO2 on the structure and mechanical properties of sandstone. Hence, acoustic emission (AE) and low-field nuclear magnetic resonance tests are carried out to analyse the damage of sandstone by soaking with CO2 and supercritical CO2 for 15 days. The results show that uniaxial strengths of samples under these two conditions decrease, and the results under supercritical CO2 soaking condition are even lower. In addition, samples subjected to supercritical CO2 soaking produce a large number of AE signals in the elastic stage. The growth points of accumulated AE curve (the cut-off between the crack closure and crack initiation) for all samples appeare in smaller strain stages. The AE energy probability densities P(E) of all samples satisfy the power law well, CO2 and supercritical CO2 soaking conditions do not change the scale invariance of AE energy for sandstone. The probability density curve is more inclined under the supercritical CO2 soaking condition, which reflects an increase in the proportion of small AE energy signals. The nuclear magnetic T2 waveforms of samples soaked with supercritical CO2 represent more developed porosity, internal microstructures and higher proton NMR signals.

Since there are multiple peaks and waveform intensive problems by using direct cross-correlation for locating the rock acoustic emission (AE) sources, no solution occurs in the solution process and the positioning accuracy is insufficient. In this study, an algorithm of AE source localisation was proposed to solve these problems, based on all-phase FFT analysis and multiple cross-correlation. The experiments were carried out on granite specimens with the size of 50×100×50 mm3. The wavelet transform was used to pre-process the spectrum of cross-correlation. Meanwhile, the phase invariance of all-phase FFT was also applied to find the waveform peak and obtain the time difference. Finally, the initial point of positioning was acquired by the least square method, and then the final positioning coordinates were obtained through the Geiger iteration. Eight measuring points were selected and monitored during the experiments. Results indicate that this method is easier to find the wave peak than the direct cross-correlation, and can obtain clear waveforms. The selection of initial points can effectively meet the strict requirement on the initial value of the Geiger iterative method. It is found that the obtained results are more accurate than those by the direct cross-correlation. The mean absolute error of this study was 2.40 mm lower, compared with Geiger positioning result by the PCI–2 AE system from the United States. The result was 3.31 mm lower, compared with the result of AE source localisation based on multiple cross-correlation and Geiger algorithm. The result was 1.74 mm lower, compared with time-delay positioning result by the all-phase phase difference method for AE sources.

A series of tests was carried out on reconstituted loess with a hollow cylinder apparatus equipped with high precision strain sensors with fixed principal stress direction. The mean principal stress p, principal stress direction ? and intermediate principal stress coefficient b were constant during shearing. A total of 21 specimens in 4 groups of experiments, including 3 groups with different main stress direction angles and 1 group with main stress coefficients, were completed. The stress, strain, strength, and small strain (2%. The initial stiffness was higher at the beginning of shearing and decreased quickly with the increasing of shear strain when shear strain >0.02%. Stiffness varying with shear strain could be simulated accurately with the exponential function.

Using the fiber Bragg grating sensors, a two-year in-situ monitoring for the subgrade permanent deformation in seasonally frozen regions was conducted. The combined effects of different sites, periods of a year, and different axial loads were considered. The results indicat that: 1) Affected by the air temperature, the subgrade’s temperature varies linearly but astatically with time in the freezing and melting periods. During a cycle of freezing and thawing, the range of ground temperature in the urban district at a depths of 30 cm and 75 cm are -9.0-14.4 ℃ and -1.9-15.4 ℃, respectively. The response of ground temperature to air temperature decreases and the hysteresis increases with the depth. 2) When the subgrade is fully frozen, the vehicle load-induced permanent deformation at both sites are small. However, when it is thawing, the deformation rises even under the same load. The maximum deformation is 4.5 and 4.2 times that of the frozen and normal period, respectively. 3) After two cycles of freezing and thawing, the subgrade has not reached a steady state. The permanent deformation under heavy vehicles can not be ignored. 4) Taking the maximum permanent subgrade deformation induced by a vehicle of 40 kN axial load as reference, the measured values caused by the 80 kN and 250 kN increase 17 and 215 times, respectively. There is a nonlinear relationship between the permanent deformation and axial load. 5) The combination of freezing and thawing cycles with heavy vehicle loading will produce the worst result, which can magnify the permanent subgrade deformation.

To study the deformation behavior of large-diameter grouted pile in extra-thick fine sand layer, load transfer of large-diameter grouted pile was analyzed in a case study of eight in-situ pile load tests of Shishou Yangtze River Highway Bridge. The BoxLucas1 load transfer function was used to calculate the relationship between load and settlement of the grouted pile considering the radius of the grout bulb and the thickness of cement grouting along the pile. The empirical range of enhancement factors for side friction and tip resistance in different soil deposits was also given. Then, case history was cited to demonstrate the validity of the method. Finally, according to the engineering example and calculation method of this paper, the bearing capacities of the large-diameter pile under extra-thick fine sand layer were further analyzed. The results show that the presented method can well determine the range of settlement of the grouted pile. It is suggested that the calculated lower bound can be used as an engineering design. The bearing capacity of the large-diameter pile is gradually increasing with the increase of pile diameter or pile length. When the pile diameter is constant, the increased range of bearing capacity of the large-diameter pile is decreased with the increase of pile length. The pile length reaches a certain value, the ratio of the mobilized base resistance to the total capacity is almost zero. This indicates an effective pile length problem by increasing the pile length to improve the bearing capacity of large diameter pile. Effective pile length, bearing capacity and percentage of load carried by pile tip of the large-diameter pile can be significantly improved by combined grouting of pile tip and side.

A new risk assessment method for karst ground collapse is presented in order to quickly and accurately assess the risk of surface subsidence in covered karst area. Firstly, the main factors were identified by mechanism analysis of karst ground collapse, and secondly the weight back analysis method was used to obtain the weights of main factors of karst ground collapse based on 100 typical engineering examples in Tangshan city. As a result, a score sheet of comprehensive hazard evaluation of karst ground collapse was established. Studies have shown that the weights of selected five main factors are as follows: karst development degree- 0.338, water-resisting capacity of impermeable layer-0.255, overburden thickness-0.186, depth of bedrock water level-0.174, and distance from the fault-0.047. The karst ground collapse hazard evaluation results of the 100 project examples based on the proposed score sheet have shown that the correct rate is 99% ,which can prove that the proposed method has a good performance in feasibility and effectiveness. In addition, the proposed method has the advantage of easy access of evaluation factors and high efficiency, and therefore it is worth popularizing and applying.

It is important to study seepage forms of confined water on translational landslide, which is helpful to accurately evaluate the slope stability and provides a reasonable theoretical guidance for studies on the disaster mechanism on translational landslide. Based on the variation law of seepage width of confined water, the seepage forms of confined water on slide plane of translational landslide are divided into the radiation flow and the non-radiative flow. According to different seepage forms, the translational landslide analysis models are established. Based on the theory of groundwater flow to canals, the water head line equation of confined water and the calculation formula of uplift pressure in different models are deduced. Furthermore, three kinds of uplift pressure distribution forms are put forward, and then the starting criterion of translational landslide is modified. Finally, based on a case of translational landslide, the law of slope stability under different forms of seepage is discussed.

Similar simulation experiments were carried out to study the chock sudden closure incident of hydraulic supports when the workface crossed the abandoned roadway or accessed to the removal roadway. The failure characteristics of surrounding rock, the abutment pressure and the working resistance of supports were investigated through the experiments, respectively. Results indicate that the advance fracture appeares before the incident when the workface crosses a large section roadway. The advance fracture leads to an increase of the block length, comparing to that in a normal periodic weighting. Meanwhile, the inferior key stratum brokes and then slides down to the main roof. Once the advance fracture occurrs, conventional supports are unable to prevent the block sliding, which indicates that an incident takes place. Therefore, the most important thing is to prevent the occurrence of advance fracture. To investigate the main causes for the advance fracture, bending moment and deflection of the main roof are calculated by the Winkler foundation beam theory. The calculated results comprehensively explain the failure characteristics of surrounding rock, the abutment pressure and the working resistance of supports. Finally, it is revealed that the failure of coal pillar is the reason for advance fracture of the main roof. Hence, it is significant to improve the strength of coal pillar. At last, a roadway filling strategy is put forward to make uniaxial compression of coal pillar into triaxial compression by Shenghua coal mine. In-situ tests verifies that the strength of coal pillar is successfully increased.

To verify the adaptability and effectiveness of inclined digging technology in the rectification of a deviated rooting mine shaft tower in East China, the plastic zone around the inclined hole, the mechanism of the technology, and the influence of various factors on the rectification effect are studied by theoretical analysis, numerical simulation and field measurement. The results show that the radius of the plastic zone is proportional to the diameter of the hole and the stress around circle hole, and it increases with the depth of drilling hole. Drilling can effectively reduce the stress within a certain range of the digging hole, so that the soil around continuously collapses, and then the difference between external load on drilling side and the shaft lining can be reduced, which produces a stress difference with the opposite to promote the shaft tower back to correct. Based on the orthogonal experiment design, we find that the most important factor to influence the deviation is the row width of the drilling, and depth, diameter and the distance between drilling row and shaft centreline. Last, according to the study results, the optimal deviation scheme is designed by long term monitoring of the shaft tower deflection and lining stress, we conclud that this drilling technology is effective in the deviation rectification of rooting mine shaft tower.

The objective of this study is to provide an analytical approach to the dewatering forecast of deep foundation pit under the condition of waterproof curtain. The hydrogeological model is generalized in a case study of deep foundation pit of Wuhan Changjiang Shipping Center. Effectiveness of waterproof curtain is analyzed using field pumping test. A modified non-complete well group formula associated with the mirror method is used to conduct the dewatering forecast. The results are therefore compared with numerical results and measured results respectively. Results show that simplified hydrogeological condition is confined aquifer. The effectiveness waterproof curtain of the eastern side is the worst. The north is better than the south, and the best is on the west side. According to the calculation results of original well spacing plan, there will not be safe in the south of deep foundation pit. Dewatering effect is improved after adding two dewatering wells. The analytic solution is consistent with the numerical results and the measured results.

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The terrain from Sangri to Jiacha is steep with deep-incised valleys and intense tectonic activities. The strong erosion trenching of Yarlung Zangbo River since early Pleistocene has caused release and redistribution of tectonic stress in this region. The stress field here is extremely sophisticated. Geostress field analysis is of great significance to the route selection and construction of railways. This study combines the terrace characteristics alongside the Yarlung Zangbo River to generalize the evolution laws of the river valley and create a 3D geological-mechanical model according to geological conditions. The existing geostress field from Sangri to Jiacha of Lasa-Linzhi railway is then calculated based on the real-tested geostress data and the utilization of the geostress inverting method combining the RBF neural network and the principle of strata denudation. The result shows that the geostress measurements in each testing point are in good consistency with the real-testing values, and the geostress field obtained through this method is reasonable and reliable. On this basis, the stress field features of the river bank slope of Sang-jia canyon section and the major tunnel projects along the valley river bank are analyzed, and the major problems during the tunnel construction are discussed based on the value and direction characteristics of the main stress field at tunnel axis location.

In reliability analysis of geotechnical engineering, the performance function is usually implicit and has strong nonlinearity. However, practical moment methods such as JC method and SORM are mainly applicable to the explicit performance function. In this paper, an improved fourth-moment method for reliability analysis of geotechnical engineering is presented by combining the efficient point estimate method for probability moments with the high order moments method for reliability analysis. Firstly, by introducing independent transformation and linear transformation, the performance function becomes a function of the reference variables, and then an efficient estimate method for the first four moments of performance function is established, which combines the univariate dimension-reduction method for multivariable function with the method for the points and weights of reference variables. Secondly, based on the combination of the estimated probability moments estimation and the cubic normal transformation, an improved fourth-moment method to assess reliability of geotechnical engineering is proposed. Finally, two numerical cases are investigated to verify the proposed point estimate method for probability moments, and results indicate that the proposed estimate method is efficient and accurate, and a classical geotechnical engineering case is used to illustrate the easy-implementation, efficiency and accuracy of the proposed fourth-moment method for reliability analysis of geotechnical engineering.

This paper proposes a new method for modeling the probability distributions of shear strength parameters using maximum entropy principle (MEP). First, the procedure for constructing the probability density functions (PDFs) of shear strength parameters using MEP is presented. Then, Monte Carlo simulations are conducted to validate MEP for modeling the PDFs of shear strength parameters and probability of slope failure. Moreover, the accuracy and robustness of MEP, Akaike Information Criterion (AIC) and kernel density estimation (KDE) are compared. Finally, a dataset of shear strength parameters for residual soil is compiled, and an infinite slope is adopted to demonstrate the application of MEP to the estimation of the probability distributions of shear strength parameters and probability of slope failure. The results indicate that with limited shear strength data, MEP can effectively model the PDFs of shear strength parameters and probability of slope failure. In comparison with AIC and KDE, MEP produces more accurate and robust results for the PDFs of shear strength parameters and probability of slope failure. MEP not only avoids relying too much on the limited shear strength data in KDE, but also overcomes the possibility of excluding the true probability distribution in the set of candidate probability distributions in AIC. Furthermore, there are significant variations in the probability distributions of shear strength parameters and probability of slope failure estimated from limited data.

A reasonable description of soil hysteretic constitutive relation has a significant impact on the evaluation of design ground motion parameters. Based on the 200-meter deep borehole profile in Suzhou region, the 1-D seismic site response analyses were performed by equivalent linear wave propagation analysis (ELA) and nonlinear analysis (NLA) using a multi-degree-of-freedom, lumped mass model in term of the modified Matasovic constitutive model. The effects of bedrock motion characteristics and bedrock interface depth on site response in deep sediment layers were analyzed. The results show that: 1) Surface peak ground acceleration (PGA) calculated by ELA increases monotonically as the PGA of bedrock motion increases. However, surface PGA calculated by NLA first rapidly increases and then gradually decreases or keeps constant. 2) Surface acceleration response spectra (Sa) for short periods computed using ELA and NLA show significant differences. The high-frequency contents of bedrock motions exhibit obvious filtering in ELA, while the high-frequency contents in NLA first magnify and then attenuate as the PGA of bedrock motion increases. 3) Surface Sa values become slightly larger with increasing bedrock surface depth. However, surface Sa values for the periods less than 0.1 s computed by NLA become slightly smaller. 4) For the medium or strong bedrock motions, the surface ground motion duration is closely related to bedrock motion characteristics, site response analysis methods and seismic bedrock surface depth. The influence of bedrock motion intensity and the overburden thickness on the duration prolongation of surface ground motion can be reasonably evaluated by NLA.

In general, limited test data can be collected from geotechnical site investigation. However, it is typically difficult to accurately characterize the spatial variation in soil properties with limited test data. This paper aims to propose a probabilistic back analysis and reliability updating approach considering the spatial variability of soil properties. With this approach, multiple sources of test data including laboratory and in situ test data can be utilized to rationally back analyze the spatially varying soil properties and update the slope reliability. The implementation procedures of the proposed approach are presented step by step. In addition, a non-stationary random field model of undrained shear strength is developed for proper characterization of the prior information of soil property. Finally, a clay slope under undrained conditions is investigated to demonstrate the effectiveness of the proposed approach. The influences of the test data and borehole location on the posterior probability of slope failure are also addressed. The results indicate that the proposed approach can effectively back analyze the spatially varying soil properties and update the slope reliability. By incorporating multiple sources of test data into the Bayesian analysis, the estimated means of soil parameters are consistent with the test data. The uncertainties of soil parameters are greatly reduced and the slope reliability is significantly improved. Due to spatial variation, test data has a stronger effect on the updating of soil parameter statistics with short distances to the borehole locations of measurement, compared with soil parameter statistics with long distances to the borehole locations.

Coal damage by adsorbed gas has been observed and detected in a large number of experiments. Under the action of the adsorbed gas, the adsorption strain of coal is firstly generated, and then coal microstructure is rearranged, which will induce the coal damage and further deteriorate mechanical properties of coal. However, this adsorption-induced damage is usually ignored in the current coal-gas interaction models. Hence, it is necessary to propose a mechanical model for dual porosity medium, considering the adsorption-induced coal damage. In this study, a novel mechanical model was developed to accurately describe coal-gas interactions, including the routine mechanistic effect and the adsorption-induced internal swelling stress. Besides, the additional mechanical damage caused by these two coal mechanic actions was also studied. Research results show adsorption-induced coal damage, mostly in tensile mode, rearranges coal microstructure, and causes significant reductions of coal strength and Young’s module. It is found that the tension damage is the main reason for the gas adsorption-induced damage. In addition, gas with higher adsorption capacity will result in a larger rearrangement of coal microstructure and more significant damage, and it even may cause a new failure pattern. Furthermore, supercritical CO2 with a higher adsorption capacity results in greater damage and causes larger alterations of coal strength and Young’s module.

Smoothed particle hydrodynamics (SPH) is a new meshless method and is gradually developed to the field of landslide analysis due to its advantages in large deformation simulation. However, flow rule and dilatancy angle has an important influence on the motion characteristics of slope after failure, but the analysis of their influence on large deformation slope is rarely reported. In this paper, the procedure of SPH based on elastic-plastic constitutive and D-P yield criterions was implemented in Fortran. Then, through two typical examples, the influence of flow rules and dilatancy angle on landslide analysis were discussed by using associated flow rule and non-associated flow rule (? =0 and ? =1/2? respectively). The results show that: excessive expansion will be produced when using associate flow rule and non-associated flow rule with ? =1/2? , both cases above are not in conformity with the actual situation. However, the non-associated flow rule with ? =0 can obtain the satisfactory result when calculating non-expansive soil, but will cause smaller speed and sliding distance when simulating expansive soil. Non-associated flow rule with appropriate consideration of expansion (? =(0.1～0.2)?) is suggested when calculating post-failure behavior of expansive soil and could obtain satisfactory results.

This study aims to investigate the dynamic stress field during the process of rock failure. Firstly, physical model experiments were conducted to obtain the results of acoustic emission (AE) in the laboratory. According to the measured results, an equation was established for describing characteristics of the rock mesoscale damage based on the energy dissipation theory. Then this equation was implemented to FLAC3D software by using the FISH language. The improved equation can not only automatically search rock units within the damage scope of AE, but also weaken mechanical parameters of meso units. Finally, the relatively true rock fracture dynamic stress field was successfully acquired. The calculated results of rock failure stress field showed good agreement with the experimental results, which verified the rationality of mesoscale damage characterisation method. Simultaneously, the obtained dynamic rock fracturing stress field can not only explain the damage causes from the point view of rock mechanics, but also can predict the location of next rock failure. However, this method still has some limitations, and it needs for further explorations.

The purpose of the study is to improve the simulation of liquefaction of sands and variations in effective stress when using FLAC3D for the dynamic analysis of liquefiable ground and structures. Based on the physics of large post-liquefaction deformation of sand, a bounding surface plasticity model with appropriate mapping rules for plasticity and dilatancy in three-dimensional stress space is developed. A state parameter for compatibility with critical state soil mechanics enables the simulation of sand at various densities and confining pressures with a same set of parameters. According to requirements and procedures of user-defined-model (UDM), the plasticity model is successfully implemented into FLAC3D code in Visual C++ environment. After testing the calculation stability, the implemented schematics allow subzones of the mixed discretization process in FLAC3D share mapping center and simultaneously enter and leave liquefaction status. Using the program, undrained and drained triaxial tests, cyclic triaxial tests, undrained cyclic torsional tests are simulated and a three-dimensional site dynamic response analysis is also performed. The results show that the model and the implemented program have superior and reasonable capability to simulate small and large deformation in pre- to post-liquefaction phase of sand.

A novel hollow cylinder torsional apparatus was developed for rock to investigate the variations of the principal stress and orientation induced by the excavation of rock mass. The improved apparatus can be used to study the strength, deformation and failure mode of rock under complex stress in the laboratory. This study introduced the basic structure, working principle and technical parameters of the apparatus in detail. According to the features of the hollow cylinder sample with top and bottom pressure heads, the technical problem of the torque application was solved by combining the loading axis of the axial force with the torque into one. A new self-balanced loading triaxial cell was employed to load and control four loadings independently, which were from the axial force, torque, inner and outer confining pressures. Through the software integration technology, a load control method for stress and flow was applied to perform the accurate simulation of the principal stress, the stress path of the principal axis rotation and stability control of the loading process. At last, a preliminary test was carried out using the hollow cylinder torsional apparatus with advantages: simple structure, multiple functions and easy operation. Experimental results verified the feasibility and practicability of the apparatus, and indicated that the system realised the rotation of the principal stress axes and the change of the principal stress.