This paper studies the anisotropic properties of shale formations in the shale gas blocks of Pengshui in Chongqing city. Uniaxial and triaxial compression tests on specimens of Longmaxi formation in Shizhu county were carried out. The anisotropy of mechanical properties, strength and failure modes were analyzed. The anisotropic failure mechanisms were revealed. The results show that: (1) Significant anisotropy is observed on the specimens. The elastic modulus parallel to bedding planes is the maximum, and the modulus perpendicular to bedding planes is the minimum. The increasing rate of elastic modulus decreases gradually as the confining pressure increases, while the variation trend of Poisson's ratio with bedding orientations of β=0°, 30°, 60° and 90° is opposite. The well-developed pore and microcrack in the bedding planes maybe contribute to these results. (2) The compressive strength of the specimen for β=0° is the maximum, the value for β=90° is a little less, and the minimum is in the orientation of β=30° at the same confining pressure. As the bedding orientation changes, the compressive strength curves present U-shape. The anisotropic compressive strength variations can be better described with the Hoek-Brown failure criterion of different orientations. (3) The anisotropic failure modes are mainly resulted from the anisotropy of failure mechanisms. The strength anisotropy is governed by the anisotropy of failure mechanisms. Under the condition of uniaxial compression, tensile splitting along bedding planes occurs for β=0°, sliding failure along bedding planes occurs for β=30°, composite shear failure across and along bedding planes occurs for β=60°, tensile splitting across bedding planes occurs for β=90°. But under the condition of triaxial compression, conjugate shear failure across bedding planes occurs for β=0°, sliding failure along bedding planes occurs for β=30°, shear failure across bedding planes occurs for β=60° and 90°. The layered sedimentary structure and weak cementing strength of bedding planes are the causes of the anisotropy of failure mechanisms. The results can provide references for the wellbore stability analysis of horizontal wells and hydraulic fracturing design in the shale gas exploitation.

With large scale shaking table tests, the effects of dip direction, strike, vertical direction, slope surface direction, dip angle and direction perpendicular to slope surface on seismic response of inclined and layered site are studied. The research results show that the amplification effect of inclined site in dip direction trends to increase with increasing dip angle of strata. In strike, the amplification effect of inclined site is stronger than that in horizontal layered site when the dip angle is less than 12.5°; in both dip and strike directions, when the dip angle reaches to 12.5°, the site has an amplification influence on the part of T ≤0.1 s period in response spectrum and a weakening influence on the part of T >0.1 s period. In the vertical direction, the amplification effect of inclined and layered site is stronger than that of the horizontal layered site with increasing dip angle. The amplification effect of inclined and layered site in slope surface direction is less than that of horizontal layered site, while the amplification effect in the direction perpendicular to slope surface is stronger than that of horizontal layered site. The research results provide a reference for construction design in inclined and layered sites with small dip angles.

Experimental research on the maximum shear strain fields of sand specimens with different water contents (12.7%-16.5%) under displacement-controlled loading condition (loading rate is 5 mm/min) is carried out with a digital image correlation method based on the particle swarm optimization algorithm. Also, the influence of the size of subset on the maximum shear strains at different positions of sand specimen is studied. It is found that with the increasing of the water content of sand specimen, deformation becomes even uniform, region of maximum shear strain becomes wider, which reflects an increase in the number of shear bands, and a raise in the maximum shear strain prior to microcrack initiating. With increasing the longitudinal strain, the maximum shear strain increases rapidly in a nonlinear form at region with higher strain, while it generally increases linearly at region with lower strain. After shear bands are generated, especially in a later deformational stage, the size of subset significantly affects the maximum shear strain. The evolution of the maximum shear strain with the size of subset is closely related to the position of subset.

There are large amounts of crushed lime stabilized soils after the rebuilding of engineering projects which are constructed with limed soils many years ago. It’s necessary to reuse them to avoid environmental pollution and to save construction investment. But the strength of crushed lime soil would significantly reduce. So, the gel materials are added to enhance the mechanical properties of crushed lime soil. The remolded lime soil is re-stabilized through adding 5% lime or cement. Comparisons of strength and compressibility between the lime re-stabilized soil and cement re-stabilized soil are made. The results show that the mechanical properties of lime re-stabilized soil are better than those of cement re-stabilized soil. Furthermore, it reveals the internal mechanism of superior performance for lime re-stabilized soil with particle size analysis, scanning electron microscope, X-Ray diffraction and thermo gravimetric analysis tests. It is found that the lime and limed-aggregates in lime re-stabilized soil can be cemented up well. But cement fails to form effective cementation with limed-aggregates. The cement re-stabilized soil forms edge-plane and edge-edge contact porous structure. The Calcium hydroxide remained in the remolded lime soil is the major factor which makes the property of cement re-stabilized soil inferior to the lime re-stabilized soil.

Heavy haul railway transportation usually enhances freight volume by increasing axle load of the train. However, this change always produces a considerable cyclic loading on coarse-grained soil filling in subgrade. It may result in excessive plastic deformation or even subgrade destruction. These subgrade defects mostly relate to the dynamic failure rules of coarse-grained soil filling. This paper focuses on the dynamic failure rules of subgrade filling. A series of large-scale dynamic triaxial tests is carried out. The influence of confining pressure and water content on plastic strain increase is analyzed. All the specimens are classified as stability type or failure type according to their features of plastic strain increment. An empirical formula of critical dynamic stress is also established by the classification. Moreover, the possibility of subgrade destroy under different axle loads is discussed. Finally, the rules that dynamic strength changes with confining pressure and water content are investigated. The correlation of static strength and dynamic strength is verified. An empirical formula for estimating dynamic strength according to static strength is proposed by the normalizing data.

Burgers rheological model is used to establish the consolidation equations with the consideration of vertical and radial consolidations, while soil around pile is assumed to be saturated viscoelastic media. According to free-draining or undrained condition, the boundary condition is divided into three categories. Series solutions for dissipation of excess pore water pressure are obtained. The series solutions can provide theoretical basis for inverse calculation of consolidation coefficient from static cone penetration test. On this basis, application program is compiled to analyze the main parameters of Burgers rheological model. The result shows that the consolidation rate reduces with depth within a certain depth under the conditions of ground surface free-draining and pile tip foundation undrained. But beyond a threshold, consolidation rate tends to stabilize. When both of upper and lower boundaries are under free-draining condition, the consolidation rate with depth will decrease at first, followed by stabilizing, and increase again at the end. When both of upper and lower boundaries are under undrained condition, the dissipation rate of pore pressure no longer changes with the variation of depth, which can be considered as a special circumstance only considering vertical consolidation. Also, the rheological property has great influence on the dissipation rate of excess pore water pressure. The excess pore water pressure tends to a non-zero value with the variation of G1/η1, and the value increases with the increasing of G1/η1. When other parameters are invariant, the dissipation rate of pore pressure decreases with the increasing of G1/G2.

Different foundation structure has different types of embankment piping. Previous researches have always focused on two-stratum dike foundation. In fact, the buried depth of fine sand has a significant influence on the piping development of foundations with fine sand. A series of simulated experiments is carried out to study the development process and mechanism of three-stratum dike foundations when the buried depth of fine sand changes. The results of experiments indicate that the burial depth of fine sand has a critical value. When the burial depth of fine sand is small, the critical hydraulic gradient is low and it’s easy to cause piping. After the occurrence of piping, more sand pours out of the embankment, and it leads to faster erosion. The critical hydraulic gradient increases as the buried depth of fine sand increases. While the buried depth is greater than the critical depth, the buried depth has almost no influence on the critical hydraulic gradient; meanwhile, the foundation has a strong ability to resist piping; its development of piping is similar to two-stratum dike foundation.

A calculation model for stress field due to horizontal well staged fracturing is proposed according to stress superposition principle. The model considers the influence of the wellbore pressure, in-situ stress, fracturing fluid seepage, thermal stress, perforation and artificial cracks. It can accurately adapt to the change of stress field around the wellbore in the process of staged fracturing in horizontal wells, and guide the research of the fracture initiation and extension mechanism. The model focuses on the induced stress caused by artificial cracks in the plane around the horizontal wellbore with the method of the displacement discontinuity. The model can also overcome the limitation of ordinary induced stress analytical models which can only calculate the induced stress in the fracture height plane. Results show that the fracture pressure calculated with the proposed model is consistent with the actual fracture pressure, which demonstrates the accuracy of the model. The artificial fractures can cause great impact on stress field around the wellbore. The stress concentration at the crack tips can result in the reduction of stress components and the obvious increasing of the stress components around a given area of fractures. Meanwhile, the more artificial fractures are fractured, the more serious the stress interference is and the more complex the stress distribution around wellbore is. The research has significance in analyzing the crack initiation and propagation mechanism under the influence of crack interference and provides guidance to fracturing design as well.

PCC energy pile is based on one of new type energy pile technology methods developed by Geotechnical Engineering Institute of Hohai University. On the basis of traditional static load test of pile, PCC energy piles are embedded into Nanjing typical sand. Thermal field of model pile is simulated through water circulation in the cyclic pipe. The characteristic and mechanism of bearing capacity of PCC energy pile in operation are studied. The PCC energy pile is firstly loaded to the working load (half of the ultimate load) and then the heating and cooling cycle is applied. After that the model pile is loaded to the ultimate load. The curves of load-displacement and stress-strain of pile shaft under different temperatures are measured. The results show that the heat can easily transfer from pile to soil (summer mode). The displacement of pile top changes obviously during heating and cooling cycles. The change of temperature brings plastic deformation in the soil, which can harm the upper structure. The thermal stress in the PCC pile caused by temperature field is relatively large. The change of thermal stress is different under different constraint conditions. Under cooling cycle, tensile strain even appears on the bottom of pile.

Contact angle is a basic physical variable of the three-phase interface. Unsaturated soil is a typical three-phase matter. The research on contact angle in unsaturated soil is at the beginning stage. In general, contact angle is supposed as a constant or overlooked. Actually the contact angle will change with the external environment. The contact angle of sand will increase with surface modification. The surface property of sand is altered from hydrophilic to hydrophobic. The apparent contact angle of sand increases by mixing the hydrophobic sand into normal sand. The mixture is used for preparation of samples. The suction measurement tests on samples with different contact angles are conducted. The results indicate that the contact angle has important effect on matric suction in unsaturated soil. When the water content at the same value, the matric suction decreases with the increasing of contact angle. When the water content reaches a certain value, matric suction would not be affected by the contact angle of sand (under hydrophilic condition). When the contact angle reaches a threshold value, the matric suction disappears. The negative pore water pressure does not exist in unsaturated soil.

This paper studies the anti-seepage failure of compacted clay layer (CCL) during wetting-drying cycles in a landfills cover system. The permeability and microstructure tests are conducted. The effects of wetting-drying cycles, degree of compaction and specimen size on permeability coefficient of CCL are discussed. The essence of anti-seepage failure is revealed at microscopic level. The research results show that the permeability coefficients of two size specimens are the same before wetting-drying cycles, but the increments of permeability coefficient of CCL with different degrees of compaction and specimen sizes are different after three times of wetting-drying cycles. The high-compacted and low-compacted small-size specimens both show shrinkage but no crack during wetting-drying cycles. For small-size specimens, the microscopic structural damage and the increment of permeability coefficient of high-compacted clay are larger than those of low-compacted clay. Unclosed cracks in large-size specimens result in larger increment of permeability coefficient than those in small-size specimens with the same degree of compaction. The small-size specimens can not reflect the influence of shrinkage cracks on the permeability of CCL. Therefore the permeability results of small-size specimens are not suitable for evaluating long-term seepage capacity of CCL.

This paper studies the meso-damage evolution of the structure of the brittle shale after hydration. Hard brittle shale samples at different soaking times are measured with the nuclear magnetic resonance (NMR) technique. The quality of the sample, transverse relaxation time T2 spectrum distribution and nuclear magnetic resonance imaging of the hard brittle shale samples at different soaking times are obtained. The results show that hydration can produce damage inside the rock. The water absorption of the samples changes a lot in the first eight hours and shows no obvious change after one day. The microcrack propagates rapidly and the surface cracks are formed as the soaking time increases. NMR image shows that the internal microstructure of the sample redistributes under hydration effect. T2 signal amplitude curve changes significantly as the soaking time increases. The hydration damage process is divided into three stages: the development stage of the large size pore cracks, the formation of the small pores and the propagation of the large size pore cracks, the propagation of the small size pores and the formation of the large size pore through cracks. NMR image shows the internal microstructure of the same sample at different soaking times. The hydration damage process of rocks is shown dynamically.

With central cracked circular disk-split Hopkinson pressure bar (CCCD-SHPB) test system, the pure type I loading tests on the marble center cracked specimens are taken under different loading rates. Relationship between loading rate and dynamic rock fracture toughness of materials is determined. The disc specimen in test has a nonideal crack with center incision. Combining with the actual processing of specimens, the paper presents the prefabricated crack with the notch tip shape of small arc and introduces the machining method for specimens. The feasibility of the nonideal crack test specimen is demonstrated with finite element analysis. The results show that it is feasible to use the nonideal crack disc specimens with circular arc crack tip and the crack width of 1 mm to replace the ideal crack disc specimens; the error does not exceed 2.13%. Under the condition of pure type I loading, the fracture toughness of nonideal crack specimen shows obvious correlation with loading rate, and it increases with the loading rate increasing.

The Barton’s shear strength criterion is widely used in engineering practice. However, the estimation of joint surface roughness coefficient (JRC) is subjective and one-sided in this method. Therefore, a method is proposed to estimate JRC with multifractal parameters based on multifractal theory. Firstly, 3D data of joint surface are obtained with digital image processing (DIP) technique. Secondly, the fractal dimension of surface is calculated with the projective covering method (PCM). Particularly the multifractal parameters of fifteen joint surfaces are computed. The results show that the rougher the surface, the larger the parameters of and . Both multifractal parameters and can well describe the morphology of joint surface. At last, nine groups of gypsum specimens are used for direct shear tests under different normal stresses. The relationship between the multifractal parameters and the JRC is examined with the principle of least square method according to the experimental data of shear strength. Thus, the JRC can be estimated accurately using parameters of and . The results provide a new approach to study surface roughness of rock joints. On the basis, the shear strength of rock joints can be accurately estimated.

Domestic and foreign scholars have made a lot of research on the process and mechanism of coal and gas outburst. Briquette was always used to test, but these tests rarely considered the influence of geological structures on outburst, and the data monitoring did not include the coal inside. On the basis of thoughts of the similar stimulation experiment and new ideas of the model test of geological mechanics, the experimental platform of coal and gas outburst for large coal uncovering by cross-cut in the laboratory was built. The geostress, gas pressure and structure of coal were considered. The test platform included test case, counter force frame, hydraulic loading system, sealing system and test monitoring system. Meanwhile, the line charging and plane charging system were designed to simulate the difference of gas in the coal seam. At the same time, the similar simulation test of tectonic soft coal uncovering by cross-cut was conducted in the laboratory. The variation laws of stress and displacement in the process of tectonic soft coal uncovering by cross-cut were studied. The gas pressure and acoustic emission in the process of outburst were also determined. The results show that the obvious stress concentration exists in surrounding rock ahead working face in the process of tunnel excavation. The closer to the tectonic soft coal is, the more obvious the stress concentration is. The displacement mutates near outburst point at the moment of outburst. Acoustic emission signal reduces once before outburst. The stress release of coal and rock in front of heading face provides the conditions for the crack increase and the rapid diffusion of gas.

The fracture permeability of shale gas reservoirs is an important parameter when estimating the shale gas extraction. On the basis of the fracture normal stiffness concept, the effective stress-dependent permeability model for shale gas reservoirs is proposed, which considers fracture-matrix interaction and gas desorption induced volumetric strain during shale formation deformation processes. Then, the models for gas shale under uniaxial strain and constant volume conditions are analyzed. Theoretical analysis indicates that the fracture permeability model under uniaxial strain conditions is consistent with the one under constant volume conditions (the total strains in all directions are equal to zero). The fracture permeability of shale in coal measures is measured with pulse decay permeameter. Permeability decreases from 41.81×10-17 m2 to 5.43×10-17 m2 while effective stress increases from 0.7 MPa to 14.5 MPa. To verify the effective stress-dependent permeability model, first, the effective stress-permeability model is calibrated with fracture permeability data. Results indicate a good match with the permeability of shale while the fracture normal stiffness, the aperture and the initial fracture permeability are 57 922.5 MPa/m, 0.000 17 m, and 50.15×10-17 m2, respectively. Then, the permeability model is calibrated with field measured permeability. Results show a remarkable match with the field permeability when the relationship between the fracture normal stiffness and the fracture aperture conforms to the inverse proportional function. The proposed permeability model is adaptable to uniaxial strain, constant volume and constant confining stress conditions. It can describe the changes of the fracture permeability of shale formation with pore pressure during shale gas extraction. And then, the comparison between the proposed model and other models is made. Results demonstrate that the match results of the permeability model are basically consistent with S&D model, but showing a bad match with P&M model.

On the basis of the discussion on mechanical behavior and the detail analysis of the change of yield surface with loading on natural marine soft clay, the effects of structural yield stress on the deformation and strength characteristics of marine soft clays, are confirmed, i.e. the behavior is similar to that of overconsolidated remolded clay when the confining pressure is lower than the structure yield stress while the behavior is similar to that of normally consolidated remolded clay when the confining pressure is larger than the structure yield stress. To much better describe the above mechanical behaviors of marine soft clay, the overconsolidated remolded model proposed by Yao et al. is introduced to establish the elastoplastic constitutive model for marine soft clays. Moreover, the tensile strength existing in marine soft clay and its evolution law are also taken into consideration. The equation of strength envelope of marine deposit soft clay is further revised in the constitutive model to reflect the strength and deformation characteristics of this marine soft clay. Finally, the comparison of stress-strain-volume strain curves between the measured and predicted results shows that the elastoplastic constitutive model can describe well the mechanical behavior of the strain-hardening/softening and dilatancy characteristics; and the deformation characteristics are dependent on the confining pressure of marine soft clay.

This study aims to improve the fundamental of theory of the flattened Brazilian disk test for determining the tensile strength of rocks. On the basis of the two-dimensional elasticity theory, a mechanical model is proposed with the chordally opposing distributed compressive loads. And the approximate analytical solution of stress components inside the Brazilian disk is obtained with the superposition method of stresses. The theoretical solutions are validated to be rational through comparing with the numerical results from the finite element method. By using the solutions, the effect of flattened loading angles on the value and the concentration degree of stress inside the disk is researched contrastively. The results show that the concentration degree of stress near loading point and the ratio of compressive stress to tensile stress inside the disk quickly decrease, but the tensile stress value and tensile region slightly reduce with the increasing of flattened loading angle. Further, it is found that both too large or too small loading angle is detrimental to the central tensile splitting failure of specimen in the standard Brazilian disk test, and the optimal flattened loading angles are between 20° and 30°. Finally, according to the Griffith strength failure criterion, the formula for tensile strength of rocks is theoretically derived. And the theoretical tensile strength values obtained in this paper are in good agreement with the existing experimental ones.

The reinforcement could increase the shear strength of soil and reduce the deformation of soil. Polyurethane foam adhesive (PFA) is adopted to reinforce rockfill materials. A series of triaxial shear tests on the PFA-reinforced rockfill materials is conducted. The test results show that the PFA-reinforced rockfill materials exhibit a nonlinear deviatoric stress-axial strain behavior. The shear strength increases with increasing the PFA ratio. A parabola formula is used to fit the deviatoric stress-axial strain curve and reflect the strain softening and hardening behaviors of the PFA-reinforced rockfill materials. The initial elastic modulus of the PFA-reinforced rockfill materials increases with increasing the PFA ratio. The mechanical effect of the PFA is to fill the voids among particles and then to bond the particles. As a result, the particle breakage and rearrangement reduce and the feature of volumetric shrinkage decreases. The dilatancy behavior increases with increasing the PFA ratio. Adding PFA into rockfill materials can enhance the cohesion, but it has no obvious effect on the frictional angle. The deformation and stability of a dam are analyzed using the finite element method. It is shown that the PFA-reinforced method can largely reduce the shallow slide of slope, enlarge the depth of the slip circle and increase the stability of rockfill dam.

A series of wetting tests on a weakly expansive soil, taken from Huaian, Jiangsu province, was performed to investigate the swelling and compression deformations. The influences of initial water content and initial dry density were studied under the applied vertical pressures from 25 kPa to 800 kPa. It is shown that the swelling deformation due to wetting is mainly affected by the initial dry density, and little affected by the initial water content. At the same initial water content, the swelling deformation increases with the initial dry density increasing. At the same initial dry density, the swelling deformation decreases little with the initial water content increasing. According to the points of intersection of the compression lines on unsaturated state and the saturated state lines with different initial densities, a state line is obtained. The state line is almost not affected by the initial water content. And it can judge whether the expansive soil will swell or compress due to wetting under different void ratios and vertical pressures. Finally, based on the results of wetting tests, a simple method for predicting the swelling deformation of expansive soils due to wetting is proposed.

This experiment takes the coal samples from coal seam K3 in Songzao Tonghua mine of Chongqing as an object. Triaxial compression tests under different confining pressures and gas pressures are conducted with a self-developed seepage device. In addition, the experiment studies the characteristics of energy dissipation and seepage of the coal samples during compression process with the method of energy accumulation and dissipation. The results show that the coal samples containing gas have the process of energy accumulation and dissipation during the failure of triaxial compression test. And the energy is absorbed and stored in the form of elastic strain energy within the coal samples. When the load reaches the peak, elastic strain energy stored in coal samples releases instantly into the dissipation energy, which becomes the driving force of coal sample damaging. There is a great influence of confining pressure and gas pressure on the dissipation characteristic of the coal. With the increasing of confining pressure, the total energy, the stored elastic strain energy and the dissipation energy of the coal sample would increase. With the increasing of gas pressure, the total energy and dissipation energy of the coal sample would slowly increase, while the stored elastic strain energy would gradually decrease. Confining pressure and gas pressure also have a great influence on the permeability of coal samples. Before the peak stress, the permeability of coal samples would decrease gradually with the increasing of confining pressure and would increases with the increasing of gas pressure. The study results can provide some references for prevention of coal and gas outburst as well as extraction of coal seam gas.

This paper analyzes the correlations between three regions of rheology and numbers of acoustic emission (AE) events with the application of the rheology-AE test for salt rock under the condition of uniaxial compression. On the basis of the relationship between AE events and loading time, which is obtained from Weibull distribution, the function of damage variable with time is proposed. By comparing the fitting results with data obtained from the rheology-AE test and the rheology-ultrasonic test of salt rock, it is found that the function of damage variable with time has an excellent applicability. In addition, this paper conducts the sensitivity analysis of parameters in the function of damage variable with time and reveals the effects of shape parameters and scale parameters on the damage variable of salt rock. The theories of fractional calculus and damage are introduced to build the constitutive model of the variable-viscosity Abel dashpot. By replacing the Newton dashpot in the Nishihara model with the variable-viscosity Abel dashpot, the fractional rheological model of salt rock is proposed. The fitting analysis of uniaxial rheological test curves of salt rock suggests that the fractional rheological model is evidently superior to Nishihara model in describing three regions of rheology, especially the accelerating one. Furthermore, the Nishihara model is proved to be a special case of the fractional rheological model.

This paper ascertains the condition of super-cooling of soil with experiments under different freezing conditions. If the environmental temperature is higher than the lowest super-cooling temperature, the super-cooled state of the soil specimen is stable. If the environmental temperature is lower than the lowest super-cooling temperature, the boundary of the specimen shows super-cooled for a short time while the inside of soil specimen is not in super-cooled state. With lowering the temperature step by step, this paper measures the freezing temperatures and lowest super-cooling temperatures of the silty clay and fine sand with different water contents and the silty clay with different NaCl concentrations. The water content has little influence on the freezing temperature of soil when the water content is equal to or greater than the saturated water content. The freezing temperature of soil lowers with reducing the water content if the water content is less than the saturated water content. The lowest super-cooling temperatures for soils with different water contents are nearly the same. The freezing temperature lowers with increasing the NaCl concentration. The coefficient of freezing temperature lowering is very close to that of the ideal dilute solution. A parameter representing the free water content is given along with the use of the factors such as steady time, freezing temperature, environmental temperature or lowest super-cooling temperature.

An incremental elastoplastic constitutive model describing the softening of soft clays subjected to cyclic loading is proposed by combining the softening exponential relationship with non-isotropic hardening modulus field theory. The evolution rule of hardening modulus field is established with the interpolation of hardening modulus and the mobile mapping center in the deviatoric stress space for the model. The stiffness softening of soft clays with cyclic loading is simulated with a softening coefficient of initial elastoplastic modulus in the elastoplastic modulus interpolation function for the model. Hysteretic loops of stress-strain curves are enhanced with a parameter adjusting hardening modulus for the model. Cyclic accumulative strains of soft clays subjected to cyclic loading are described by introducing a parameter to take into account the rate and the level of accumulative strains for the model. Relation curves of cyclic softening coefficient and the number of stress cycles are fitted with the exponential equation proposed by Idriss. Besides, the relationships among cyclic softening coefficient and static stress level and cyclic stress level are established by introducing a cyclic stress parameter. The methods for determining model parameters are also presented. The predicted results are obtained with the model. Comparing the predicted results with test results, it is verified that the model can describe the softening of soft clay subjected to cyclic loading.

When drilling is executed in the deep rock mass, rock is mainly subjected to loads with medium and low strain rates. However the medium and high strain rates damage constitutive model is still used instead, which doesn’t adapt to the real situation. The dynamic characteristics of rock under medium and low strain rates are analyzed from engineering background and practical experiments. A parallel model of rock, which is made up of Maxwell element, Bingham element and damage element, is proposed. The damage parameter based on degradation of pore and fissure is introduced with Laplace transformation. A new dynamic damage constitutive model of rock is derived. The proposed model is used to fit the stress-strain curves of argillaceous sandstone and granite at strain rates of 87 s-1, 382 s-1 and 673 s-1. By comparing fitting results with the experimental data and literature results, it is shown that the proposed model is suitable for the behavior of rock under medium and low strain rates. With analyzing the fitting parameters, the proposed model can actively adapt to medium and low strain rates. The variations of constitutive curves and damage parameters are in agreement with the practical situation.

Aiming at fully-mechanized top-coal caving face with great mining height in extra-thick coal seam, the coal mass affected by abutment pressure is divided into three zones, the fracture zone, the plastic zone and the elastic zone. A mechanical model of rib spalling affected by abutment pressure is established. With Mohr-Coulomb yield criterion and non-associated elastoplastic analysis, analytical expressions of coal wall horizontal displacement and the fracture zone and the plastic zone radii, are obtained by considering the hydraulic support protecting unit strength. At the same time, the main factors of rib spalling are analyzed. The model is demonstrated by comparing the theoretical results with the results of field measurement, the error is only 15.6%. The results show that with the increasing of abutment pressure concentration factor and cutting height and the decreasing of hydraulic support protecting unit strength, the horizontal displacement of coal wall increases and the extent of rib spalling is worse. Some measures, such as improving support resistance, reducing the pressure of coal wall, controlling the cutting height and increasing the protecting unit strength, are adopted to decrease the rib spalling.

This paper develops an effective approach to evaluate the system reliability of slope with stochastic response surface method. Firstly, the proposed approach selects the representative slip surfaces from a large number of potential slip surfaces. For each representative slip surface, a stochastic response surface (SRS) is constructed to estimate its factor of safety with the Hermite polynomial chaos expansion. Then, the direct Monte Carlo simulation (MCS) is employed to calculate the system probability of slope failure. The minimum factor of safety for each random sample during the MCS is calculated with SRSs of representative slip surfaces. For illustration, the proposed approach is applied to estimate the system reliability of two slopes with multiple soil layers. The results show that the proposed approach can effectively identify the representative slip surfaces of the slope and yield the system probability of slope failure with reasonable accuracy. It can also evaluate the system reliability of slope at small probability levels, and provide an effective tool for system reliability analysis of slope considering correlated nonnormal soil parameters. In addition, the tedious procedure of calculating correlation coefficients between potential slip surfaces to determine the representative slip surfaces is avoided in the proposed approach. There may be multiple failure modes for a slope with multiple soil layers. If only one critical slip surface (e.g. critical deterministic slip surface) or insufficient representative slip surfaces are considered in system reliability analysis, the probability of slope failure would be underestimated.

The JinpingⅠhigh arch dam with a height of 305 m is the highest under-construction dam of the world at present. The overall stability of the dam and foundation is a prominent problem due to the complex geological conditions in the dam site area. There are a variety of weak structural planes including faults, alteration veins, inner layer compressed zones, joint fissures and deep cracks. To make the dam be in much better stress state and meet anti-sliding stability and deformation stability of the skewback, a lot of reinforcement measures are adopted in the project. The main reinforcement measures include the left abutment concrete seating replacement, concrete grid and hole plug replacement, grooving replacement, and shearing resistant hole, etc. The overall stability of the dam abutment and the effects of dam abutment reinforcement are the important issues which must be concerned in practical engineering. The method of 3D geomechanical model test is adopted to carry out damage experiments. Two 3D models of JinpingⅠhigh arch dam are established respectively. One model is for the unreinforced scheme, and the other one for the reinforced scheme. Deformation distribution characteristics of the dam and foundation, failure mechanism and the overall stability safety degree derived from the two models are comparatively analyzed. The results show that, after reinforced, the symmetry of displacement of the dam body and dam abutments are significantly improved and the displacements are greatly reduced; the crack range and the damage extent of dam abutments are reduced under the same overload ratio, the overload coefficients to failure of the dam abutments are increased and the overload capacity is raised. The safety factors of overall stability obtained with comprehensive method are 4.7-5.0 for unreinforced scheme, and 5.2-6.0 for reinforced scheme. The safety degree is obviously improved through reinforcement measures. Comprehensive analysis shows that the main reinforcement measures, including the left abutment concrete seating replacement, concrete grid and hole plug replacement, grooving replacement, shearing resistant hole, applied to JinpingⅠhigh arch dam, are quite effective.

This paper presents improvement in measurement technology and space distribution of earth pressure of high fill in loess gully. The numerical simulation, laboratory calibration test are used to investigate the factors influencing the measuring results of earth pressure with earth pressure cell in high fill. It is found that the depth-span ratio of the hole where earth pressure cell is embedded, compaction degree of the fill materials, as well as gully slope, etc., have more significant impacts on testing earth pressure. Therefore the depth-span ratio λ is better recommended to be larger than 0.6. By analyzing in-situ observations at Lüliang airport test section, two earth pressure empirical formulae for middle and marginal regions of the fill respectively are presented, incorporating fill height, weighted average unit weight, slope angle. Using numerical back-analysis, the spatial distribution rules of earth pressure of the high fill are obtained. Comparatively analyses show that the rules from back-analysis are basically in agreement with the ones from empirical formulae. This study can provide references for underground structure design and foundation deformation calculation in similar high fill engineering in loess gully.

There are many hidden joint planes in columnar jointed rock mass. The failure mode of columnar jointed rock mass is different from that of ordinary rock mass due to the crack of hidden joint plane. Its failure mode is mainly influenced by the extremely developed joint and high geostress. Because of the extremely developed joint in columnar jointed rock mass, the failure mode controlled by rock mass structure is the main part of damage mode, which includes joints plane slip (collapse) under single free face, joint plane slip (collapse) under multiple free faces, joint collapse combined with dislocation interface and fault, etc. The failure mode controlled by geostress is the second part of damage mode, which includes concrete layer cracking at crown of valley side. The failure mode controlled by the combination of geostress and rock mass structure is the third part of damage mode, which includes jointed rock mass caving at the lithologic boundary, etc. The failure mode at the surface of columnar jointed rock mass is tension cracking of the joint between columns and joint inside the column. Shear cracking of the joint between columns mainly happens in the surrounding rock. So the corresponding support of columnar jointed rock mass should mainly include two aspects: the shotcrete with steel fiber is mainly to prevent the tensile cracking at the surface of columnar jointed rock mass, and the anchor system is mainly to control the shear failure inside the columnar jointed rock mass.

A new autoregression curve method based on energy gradient is proposed. It can improve the accuracy of measuring shear wave velocity with single-hole method. Firstly, the time-history curves of shear waves are transformed into a set of spatial energy gradient wave time-history curves. Secondly, short trigger average/long trigger average (STA/LTA) method is used to transform energy gradient wave time-history curves and pick the arrival times of P wave and S wave. Finally, a quadratic autoregression model is proposed to pick the accurate arrival times of P wave and S wave. The model is used to process the energy gradient curves near the arrival time. A comparing experiment is conducted to validate the theory. The shear wave velocities of one field tested with proposed method, cross-correlation function method and manual picking method are analyzed. The results indicate that in comparison with the cross-correlation function method, this method has a better inhibitory effect on noise, and not only can get accurately S shear wave velocity but also can get accurately P shear wave velocity. Meanwhile the proposed method has much higher accuracy and stability in practical test relative to the manual picking analysis. This method enriches the automatic-picking methods of shear wave velocity. On the basis of method proposed in this paper, cross-correlation function method and manual picking method, a shear wave measurement system is designed. It is easy to pick shear wave velocity automatically and produce a test report by this system.

This paper provides the reliable theoretic guidance for parameters selection of surrounding rock stability analysis in Bulungl-Gongur hydropower station underground cavern. The grey relation analysis of deformation sensitivity method is proposed based on probability distribution model of surrounding rock mechanical parameters, while the spatial variability of parameters and the shortcomings of conventional sensitivity analysis are considered. Three-dimensional discrete element calculation program is used. This method regards density, elastic modulus, Poisson’s ratio, cohesion, internal friction angle and joints internal friction angle as factor array. The vault crown settlement is specified as the target array. The influence of each factor changing in defined domain on the vault crown settlement is analyzed. The results show that the density is the most sensitive influential factor among all the factors. The subordinate sensitive influential factors are the elastic modulus, cohesion and Poisson’s ratio. The internal friction angle and joints internal friction angle are the minimum sensitive influential factors. Finally, comparison of results between conventional sensitivity analysis and the proposed method is made. The results indicate that except density, internal friction angle and joints internal friction angle are consistent, the sensitivity of the rest parameters are not consistent. Therefore, this method could evaluate those parameters more accurately and reasonably based on considering the probability distribution of rock mechanical parameters.

In geological engineering, dominant partitioning of discontinuities of rock mass is a fundamental work for mechanical and hydraulic behaviors analysis of rock mass. In common methods, only two characteristic parameters (dip and dip angle) are selected to identify discontinuity sets. Trace length, joint opening and surface morphology of discontinuities also influence the mechanical behaviors of rock mass. Therefore, a novel scheme for discontinuities classification is proposed based on multivariate parameters and artificial bee colony algorithm. The sum of deviations squares of the entire sample data is taken as an objective function. The artificial bee colony algorithm is used to search the optimal solution which makes the objective function achieve the minimum value. The optimal solution is the cluster centers. On this basis, a mathematical model is established. At the same time, the boundaries between different sets are determined automatically. The validation of the novel scheme is proved by results based on artificial data. The calculation precision of the method is satisfactory. Finally, the proposed method is applied to multivariate parameter dominant partitioning of discontinuities of rock mass at Songta dam site on the NuJiang River. The classification result verifies that the method is efficient and practical.

On the basis of analyzing the actual engineering data and the limitation of existing instability models, a new conceptual artesian water model of reservoir bank slope is proposed. The conditions pertinent to artesian water model are given. Theoretical calculation formulae for artesian water pressure at the bottom of the sliding zone and for factor of safety of reservoir bank slope are deduced respectively considering the artesian water. It is verified that the existence of artesian water is reasonable. The influence of rainfall infiltration and water level fluctuation on the stability of bank slope is significant by considering the artesian water. The combined effect of these two factors is greater than the simple superimposed effect of single factor respective action. The stability of artesian water slope is the lowest when the infiltration ratio belongs to the range of (10-5, 10-2). The slope is prone to slide when the factor of safety reaches the minimum value. With the same infiltration ratio, the larger the rainfall infiltration is, the lower the landslide stability is.

Considering connectivity rate and spacing of fractures, volume fractions of pore matrix and fractured material in a representative element volume (REV), a method for determining the equivalent cohesion and internal friction angle is proposed under the condition of thermo-hydro-mechanical-migratory coupling. While the equivalent internal friction angle of the medium is assumed to be a constant, the equivalent cohesion will be a function of inherent cohesion, equivalent plastic strain, suction, solute concentration and temperature. A hypothetical disposal model for nuclear waste located in unsaturated dual-pore-fracture rock mass is analyzed and simulated with the proposed method. The results show that the enhancement for the equivalent cohesion by suction is larger than the weakening effect by equivalent plastic strain and solute concentration. The plastic zones in the surrounding rock mass reduce with the increasing of equivalent cohesion. Thus the distributions and values of rock mass stress, pressure and flow velocity of pore water and fracture water, solute concentration in pore and fracture also change correspondingly.

In rock material, the smooth crack mostly becomes kinked crack during its growth due to the anisotropy of rock material. For the kinked crack, the outer normal direction of the crack surface at the kinked line is not unique, so the continuous element is not feasible to discrete the crack surface near the kinked line. Therefore four types of new discontinuous element are employed for the kinked crack. A dual boundary element method (DBEM) based on the method suited for the smooth crack problem is proposed to deal with the kinked crack problem. The numerical verification shows that the results calculated with the present method are in very good agreement with those with the primary method for the smooth crack problem. Furthermore, the proposed method is used to analyze the kinked crack in transversely isotropic rock material of infinite domain. The stress intensity factor (SIF) is obtained. The rectangular smooth crack in transversely isotropic rock material bends. The crack opening of both crack surfaces at two sides of the kinked line has mutual inhibiting effect due to the crack surface subjected to uniformly-distributed normal load. The dip angle between the crack surface and the isotropy plane changes as the crack surface bends gradually. It is found that the fracture behavior of the kinked crack is also affected by the anisotropy of the rock material.

Discontinuous deformation analysis (DDA) is a dynamic calculation method for solving problem in an implicit pattern. It adds or subtracts stiff springs between block interfaces to satisfy the contact conditions of neither tension nor embedment. It is found that both of time step and spring stiffness directly impact the calculation results in the process of DDA. This paper investigates the role of inertial force during solving process of DDA based on adjustment of time step and spring stiffness during DDA and simplified mechanical conceptual model for block contact problems. Numerical simulation tests are conducted to study some concerned mechanical problems under three mechanical states in free falling model and single block sliding model on incline respectively. By simulating the free falling movement, this paper studies the influence of value selection of time step on calculation result and determines a proper range of time step preliminarily. Further, single bock sliding model is used to analyze the joint effect of time step and spring stiffness. A proper range for spring stiffness corresponding to different time steps is obtained. The results show that the proper ranges of time step and spring stiffness constitute a simply-connected domain. When the values of time step and spring stiffness are both within the proposed domain, the result of DDA is rational.

Carbon capture, utilization and storage (CCUS), as an emerging technology to reduce greenhouse gas emissions, could mitigate climate change. CO2 leakage as one of the potential risks would influence the quality of groundwater and affect the growth of surface flora and fauna, even threaten the safety of human beings living around. In order to monitor this kind of leakage and estimate the influence of leakage on shallow groundwater, it is necessary to sample the shallow groundwater continuously. Thus, a novel CO2 monitoring system in shallow well is developed. Its composition structure, working principle, countermeasures to technical problems and the procedure are introduced in detail. The monitoring system is based on the U-tube: groundwater permeates into the borehole and flows into the U-tube through a check valve; then a nitrogen cylinder pressurizes one end of the U-tube; the sample is obtained from the other leg of the U-tube. Moreover, the monitoring system is able to sample from different formation layers (the number of formation layer depends on the actual situation). It also provides data for the risk warning system in project.

With large sample size and slight disturbance of sample’s original structure, a large scale in-situ direct shear test is an effective method for obtaining the strength parameters of material in geotechnical engineering. After investigating a set of direct shear apparatus for field and laboratory tests, a set of large scale in-situ direct shear apparatus is developed by Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. The apparatus is different from the traditional in-situ direct shear apparatus. It has an upper rigid shear box and a lower one, and is competent to conduct in-situ direct tests on soil sample with size of 50 cm×50 cm×41 cm and the largest grain size of 5 cm. It is convenient for assembly and suitable for complex field test environment. It can collect data automatically with a high precision sensor. This paper introduces the configuration, operation principle and technical advantages of the improved apparatus and describes the usages and problems encountered during testing on site in detail. The apparatus is applied to field tests of two landslides on Xiangjiaba reservoir to obtain the in-situ shear strength parameters of soil. Through analysis of shear strength curves for different samples, the apparatus is verified to have excellent performance.