The shear strength and compressive volumetric strain are two key parameters which control the mechanical behaviors of the frozen soil-structure interface. A large-scale multifunctional direct shear apparatus is first designed and manufactured, and then used to determine the mechanical properties of the frozen soil-structure interface. Based on the experimental results, the principles of continuum damage mechanics are employed to develop a shear strength and compression damage model, which can be used to describe the mechanical behavior of frozen soil-structure interface. In the proposed model, the conditions of uniform strain, vanishing elastic zone and uncoupled elastic strain are assumed, and the ratio of irreversible volumetric strain to the maximum irreversible strain is used as a damage factor. Comparison of simulated and experimental results shows that the proposed model yields good results.

Clay-based cutoff walls have been widely used as in situ barriers for contaminant isolation and controlling migration of the contaminated groundwater in landfills and site remediation engineering. With the interaction between CaCl2 solution and cutoff walls formed by mixing stratum of clays, what would happen to the permeability? To explore this problem, the Fujian standard sand is used to simulate sandy stratum and four different clays are selected as addition material, and the specimens are consolidated after mixing and pouring. Then the permeability coefficient and moisture characteristic curves of specimens are measured by the improved flexible-wall permeameters and the centrifuge test. The results indicate that at the 10% adding level of clay, all the final permeability coefficients are increased after the four sand-clay mixtures are permeated with 0.2 mol/L CaCl2 solution. Compared with the tap water, and the increases of permeability coefficients are less than 10 times their original values. In addition, the porosities of four mixtures decrease only slightly. The experimental results imply that calcium ions may substitute those monovalent cations on the surface of clay mineral particles, leading to a decreases in the thickness of diffuse double layer and bound water, and hence the increase of effective porosity.

Based on the self-stable phenomena of surrounding rock deformation and failure in the soft rock roadway, the numerical simulation method is adopted to reveal the relationships among the roof, two ribs and floor of the roadway. It is found that the unstable zone of roadway surrounding rock is ellipse around roadway. According to the Protodyakonov’s theory and the interactions among the roof, two ribs and floor, a new theory of self-stable ring is put forward and its elliptic curve equation is given. This research clearly confirms that the rock mass within the ring is the supporting subject and the main purpose of support is to control the stability of rock mass within the ring. This research shows that the “floor - two ribs – roof” constitute the overall system of roadway stability system. The size of self-stable arch in the roadway roof increases with the increase of the plastic zone of ribs, while the plastic zone of ribs increases with the deformation of floor. Hence, the height of ring in the roof will be greatly reduced by strengthening the floor and two ribs. Therefore, the roadway control principle is put forward which can be described as “control roof must control ribs first, and control ribs must control floor first”, and it has been verified in practice by years. This theory provides a new basis for soft rock roadway control.

According to the present researches, the strength of natural clay shows significant anisotropic properties, but its objective laws haven't been verified by rigorous tests. Based on the Hangzhou intact soft clay tests that are finished by hollow cylinder apparatus (HCA), a formula of the anisotropic clay strength for any principal stress directions is proposed to modify the Casagrande formula in this paper. Assuming that the soil slip failure mode follows the Prandtl mechanism, the upper bound solution of stability against basal heave of excavation is presented. Furthermore, the influences on stability against basal heave of excavation caused by the factors such as the anisotropy ratio of soil, the embedded depth of the retaining wall, the thickness of soft clay layer between the foundation base and the underlying hard stratum as well as the wall roughness are discussed. The method proposed in this paper is verified by a case study in Hangzhou basal soil after failure. It is also shown that it would overestimate the safety against basal heave if the anisotropy of strength is ignored or the Casagrande anisotropic strength formula is adopted.

In this paper, dual integral equations are presented to solve the interaction problem between the strip foundation under wall and transversely isotropic layered soils. Starting with the governing equations of plane strain problem in rectangular coordinates, the transfer matrix solution of layered soils can be obtained through the Fourier transform and the continuity conditions between two adjacent layers. Based on the transfer matrix solution of layered soils and the mixed boundary conditions of the contact problem, a pair of dual integral equations of subgrade reactions and the deflection of the footing is derived. The deflection is solved by elastic thin plate theory in the case that the strip foundation is subjected to vertical concentrated load. Dual integral equations are further converted to linear equations by means of the Jacobi orthogonal polynomials and series expansions. The results of numerical calculation carried out by the corresponding computer program are compared and agree well with those by FEM software ABAQUS, which proves the correctness of the method in this paper. Further numerical examples prove that the plate-soil stiffness ratio and the stratification of soils have a significant effect on subgrade reactions, surface settlement and vertical normal stress along the z - axial.

Since engineering rock mass is under high stress conditions, it has strong time-dependent effect due to continuously high ground stress after excavation and rupture. The study of creep properties after its post-peak is significant in both theory and practice. Firstly, the uniaxial pre-peak yield and post-peak rupture unloading tests are conducted on the intact rock samples using RMT-150B rock mechanics test system. Then the rock samples with different damage degrees are prepared under conditions of pre-peak yield and post-peak rupture. Lastly, uniaxial creep tests on the prepared rock samples are conducted to obtain uniaxial creep mechanical properties by using RLW-2000 microcomputer servo rock triaxial rheology testing system. From experimental results, velocities of all damaged rock samples show different degrees of reduction by comparing with the velocities of intact rock samples. Under each stress level, instantaneous dependent variable of the damaged rock samples gradually increases with the increase of the stress level, and there is linear relationship between the instantaneous dependent variable and stress level. It is found that the instantaneous dependent variable of post-peak damaged and rupture rock sample is significantly greater than that of pre-peak yield and damaged rock sample under the same stress level. Generally, each creep deformation gradually increases with the increase of the stress level under all stress levels, which meets exponential function relationship. The creep deformation of post-peak damaged and rupture rock sample is substantially greater than the pre-peak yield and damaged rock sample under the same stress level, Moreover, the difference of the creep deformation between post-peak damaged rock sample and pre-peak yield and damaged rock sample increases with increasing the load. The instantaneous deformation modulus of damaged rock sample steadily improved with the increase of stress level, furthermore, the instantaneous modulus changes linearly with the stress level. The instantaneous modulus of deformation at each stress level is obviously different, the higher the degree of rock damage, the lower the instantaneous modulus of deformation. For the damaged rock samples under all levels, the improved Nishihara model can be used to simulate uniaxial creep characteristics.

As a classic elastoplastic constitutive model, the Cam Clay model can precisely describe the stress-strain relationship of remolded and normally consolidated clay. While soil stress experiences unloading or cyclic loading, the soil may become overconsolidated. An overconsolidated soil shows different mechanical behavior compared to its normally consolidated counterpart. To investigate the mechanical properties of overconsolidated soil, a subloading-surface Cam Clay model, which takes overconsolidation factor into account, is introduced. Then a comparative analysis is carried out for the triaxial compression tests and shear tests of overconsolidated soil, and the stress-strain relationship and OCR variation of the soil under cyclic loading are also studied in detail. The results show that overconsolidation factor can significantly influence the mechanical properties of soil, and the soil has higher yield strength than its normally consolidated counterpart. In addition, the dynamic response of free field under earthquake incidence is analyzed, showing that the influence of overconsolidation factor plays a very important role in the seismic response of soil ground, especially under high-magnitude earthquake incidence. Based on the results of the free-field analysis, the nonlinear dynamic response of a typical pile-soil coupled system under earthquake incidence is analyzed. The results show that the high-frequency component of structure is significantly suppressed by the influence of soil nonlinearity. Because the soil quickly turns into overconsolidated state under cyclic loading, its strength increases significantly, if the subloading-surface Cam Clay model is adopted, when the overconsolidation factor is taken into account, especially under the incidence of high-magnitude earthquake. Therefore, to guarantee the accuracy and reliability of the simulation for pile supported structure under earthquake incidence, it is necessary to account for the overconsolidation effect.

A Y-shape pile is a newly-developed abnormal pile with a reversed-arch surface. The tip resistance distribution along the pile bottom section is non-uniform. Although the calculated additional stresses, due to the assumed uniformly distributed tip resistance, is more close to the actual values compared to those due to the assumed concentrated tip resistance, the former still has some error. Based on the numerical simulation, the nonuniform distribution model of tip resistance for a Y-shape pile is developed, and used to calculate the additional stresses. By means of the integral function NIntegrate of Mathematica software and Geddes’s stress solution, the numerical calculation method is introduced to estimate the vertical additional stress coefficient at any point in foundation under the action of tip resistance of Y-shape pile with considering the effect of abnormality. Assuming the major factors as variables, including the outside circle radius R, template radian ?, open arc spacing s, and angle radian ?, the variation of additional stress is comparatively studied for two distribution patterns of tip resistance of the Y-section pile, i.e, the uniform distribution and the nonuniform distribution with considering abnormality effect, respectively, and the method for calculating the additional stress due to tip resistance is used for estimating the settlement with considering abnormality effect. Based on the field static load tests, it is found that the calculated settlements agree well with the measured results using the proposed method.

To study the mud spillover problem in remediating the VOCs (volatile organic compounds) contaminated site, a series of laboratory tests was carried out on two typical types of VOCs contaminated slurry. The treatment effects of solidification/stabilization of 4 kinds of binding agents are studied. The results indicate that all the binding agents have strong water-reducing capacity and agent A (5% cement) performs best in slurry II with a water reducing rate of 37% after 28-day curing, while slurry I possesses a higher water reducing rate of about 45% for all the agents. The electrical conductivities of pore water solutions increase firstly and reach the maximum on the third day or seventh day, then decrease with the increase of curing time, and the pH value of slurry II is clearly higher than that of slurry I. The unconfined compressive strength qu of soil samples quickly increases with the curing time, and the qu of slurry I is much higher than that of slurry II. It is also shown that agents A and C have a significantly better reinforcing effect, and the qu values for slurry I and II treated by agent C can reach 233 and 48 kPa, respectively, after 28-day curing. Besides that, the addition of attapulgite-based agents B and D can reduce the total organic concentration of TCLP (toxicity characteristic leaching procedure) leachate and improve the environmental safety dramatically. There is also good correlation among the values of EC, pH and qu of stabilized soil, which can reflect the strength growth.

Based on the analysis of physical and normal deformation characteristics, it is considered that the mechanical properties of clastic rock in dam foundation in hydropower station are extremely complex. Therefore, triaxial creep tests are conducted to investigate the creep behaviors of clastic rock by using an automatic triaxial servo-instrument. Firstly, the axial, lateral and volume creep properties and strain rate are discussed. Secondly, the effects of creep properties on the stress-strain curve are analyzed, and then the scanning electron microscope (SEM) tests are performed on the fractured rock specimens. Finally, the long-term strength is determined by isochronous curves. Based on the volumetric expansion of specimen, a new method is proposed to determine long-term strength by assuming that the fast creep failure occurs at the critical point where lateral volumetric expansion rate exceeds the axial compression rate. The results show that the clastic rock has a significant creep property, and the creep curve generally have two stages including transient creep and steady creep. However, the creep accelerates after applying the last level of stress. Thus the creep behavior aggravates until the specimen finally shows the characteristics of large axial compression, obvious volumetric expansion and large steady creep rate. In addition, the relationship between creep rate and the deviatoric stress can be described by an exponential function. The long-term strength of clastic rock, which is 54% to 80% of conventional strength, is basically the same as the intersection of the steady-state creep rate and the stress threshold of volumetric dilation. Therefore, the experimental results in this study provide dependable reference for the establishment of rock creep model and analysis of long-term stability.

To investigate the gas permeability performance of unsaturated fine sandy soil, a series of samples with different moisture contents and different dry densities is prepared and air permeability tests are conducted. Based on the porous media permeation theory, the effects of inlet pressure, void ratio, saturation on the air permeability of samples are analyzed, and an empirical formulation of air permeability is proposed. The experimental results demonstrate that air permeability tends to a stable value with the increase of the inlet pressure. The effect of inlet pressure on air permeability is far more obvious for samples with high moisture content than for samples with low moisture content. The increases of moisture content or degree of saturation can result in a decrease in air permeability of sample. When the moisture content is lower than the optimum moisture content, the variation of the air permeability is negligible; however, a rapid decrease in air permeability is observed when the moisture content is higher than the optimum moisture content. The difference of soil microstructure (flocculation structure and dispersion structure) accounts for the air permeability mutation at the two sides of the optimum moisture content. Air void ratio can effectively represent the influence of void ratio and saturation on air permeability. A power function relationship well adapts the relationship of air permeability with air void ratio. Test dates from the literatures also demonstrate the effectiveness of proposed empirical formulation.

To investigate the effects of pore structure and hydrodynamic forces on the particle transport and deposition, the penetration processes of a typical silica powder (suspended particles) and fluorescein (as the dissolved tracer) in saturated porous media is studied through a series of column tests. Two kinds of porous media (i.e.,quartz sand and glass beads) and 5 seepage velocities (i.e., 0.033, 0.066, 0.132, 0.199, 0.265 cm/s) are considered, and twenty breakthrough curves are obtained. Based on the experimental results, the influence of pore structure and seepage velocity on the hydrodynamic mechanism, dispersion effects and accelerated effects are analyzed during deposition and migration processes of suspended particles in saturated porous media. It is shown that, the breakthrough curves (BTCs) are well described by an analytical solution of the advective-dispersive equation with a first-order deposition kinetics. In contrast with the effect of pore structure, the effect of hydrodynamics processes on particle transport increases significantly with the increase of seepage velocity. There exists a critical seepage velocity, beyond which suspended particles travel faster than the dissolved tracer, and the critical velocity is different for glass beads and quartz. In addition, the mean diameter of the recovered particles, the longitudinal dispersivity and recovery rate increase with the seepage velocity, and a decrease of the deposition rate of particles beyond the critical seepage velocity is also observed in two porous media. Furthermore, the recovery rate of suspended particles is higher in the glass beads even if the porosities are similar. Overall, the study highlights the effect of pore structure and seepage velocity on the transport of particles in saturated porous media, and the pore structure even plays a greater role in high seepage velocity conditions.

The stability and safety of the solidified sludge pile will be threatened when the engineering properties change due to freezing and thawing cycles (FTC). Laboratory FTC tests are conducted on the solidified municipal dewatered sludge in the closed system. Unconfined compressive strength and permeability coefficient of the solidified sludge are tested after each FTC. According to the results of tests, some samples subjected to cyclic freezing and thawing are selected to perform mercury intrusion porosimetry (MIP) tests and to analyze with the scanning electron microscope (SEM). The results show that the 1st FTC results in a decrease in the strength by 30% and an increase in the permeability by 80% of the the solidified sludge. Whereafter the change range gradually decreases. The strength decreases by 50% and the permeability coefficient increases by about one order of magnitude after about 6 FTC, thereafter they both almost keep constant. The variation of the permeability coefficient lags slightly behind that of the unconfined compressive strength. The pore volume and the permeability coefficient gradually increase while the strength decreases little by little with the increase of FTC. In the closed system, the total swelling volume induced by the frozen water in the solidified body is constant and the internal moisture is uniformly distributed, so the pore volume doesn’t continue increasing any more while just the pores mix together and redistribute when reaching an certain number of FTC, then each parameter becomes constant. The investigation provides parameters and guiding for safe landfilling of the solidified sludge in the cold regions.

A constitutive model of soil based on the generalized potential theory is rigorously developed, so that the deficiencies of traditional constitutive theories can be overcome, while the traditional theories can be regarded as its special cases. Hence the generalized potential theory provides an alternative approach to developing the constitutive model of soils. Duncan-Chang model based on the generalized Hooke’s law is one of the most widely used models at present, in which the constitutive parameters can be determined conveniently and have clear physical meanings. However, this model cannot describe well the soil dilatancy, which is the most undesirable feature of Duncan-Chang model. In addition, the hyperbolic hypothesis is adopted to fit the experimental results using Duncan-Chang model, which is also one of the disadvantages of the model. To utilize the advantages of Duncan-Chang model and avoid its disadvantages, a numerical elastoplastic model based on the generalized potential theory is developed, in which the parameters can be determined as conveniently as those of Duncan-Chang model. Meanwhile, the proposed model is not subjected to the limitation of the generalized Hooke’s law, and the soil dilatancy of soils can be well described. In addition, because the proposed model adopt a numerical method to fit the experimental results, it excludes the disadvantage of hyperbola hypothesis in Duncan-Chang model, resulting in a more adaptability of the proposed model. The performance of the proposed model is illustrated through simulating the triaxial testing results, showing that the proposed model yields good results, which describes well the soil dilatancy.

Based on one-dimensional freezing test at five different top cooling temperatures in an open system, the freezing behaviors of the saturated Qinghai-Tibet silty clay are studied experimentally. Combining with digital image acquisition technology and routine data measure system in laboratory, the temperature distribution and development, cryostructure profile development, frost heave development, water supplement process and water content profile are analyzed during one-dimensional freezing of soil sample. Some conclusions are drawn as follows. Firstly, the freezing front in sample reaches a stable state after 26 hours. After that, the longitudinal cryostructure of soil samples can be divided into four belts, including tiny thin layer structural belt, thin layer structural belt, thick layer structural belt and overall structure belt from the cold end to warm end. The frost heave development contains three stages, i. e. fast frost heave stage, stable frost heave stage and linear frost heave stage. The ice lens segregation at the bottom of thin layer structural belt and thick layer structural belt are the main source of frost heave. After tests, the water content profiles of the soil sample indicate that the water content increases in frozen part and decreases in unfrozen part. Meanwhile, the layers in which having the highest water content are located at the location of thick ice lenses. Because of the consolidation of the unfrozen part and water migration from unfrozen part to freezing front and frozen part, the water content of the unfrozen part has decreased and induced a drying phenomenon. The conclusions have provided the dynamic processes of the development of cryostructure and frost heave of the Qinghai-Tibet silty clay under one-dimensional freezing. It is expected that this study will provide a test basis for future study of more reasonable frost heave models.

The digital image measurement method based on sub-pixel accurate corner locator is able to record the displacement of corner of squares on the surface of samples to acquire the partial strain and strain field on the surface of samples at any time. With the change of partial lateral strain of different parts of samples during shearing, the feature values of stress and strain of loose and dense sand samples with different initial water contents at different characteristic times are analyzed. With the axial strain fields, the whole process of progressive failure, including the beginning and growth of strain localization then the final forming of shear band, is analyzed. The characteristic values of maximal partial axial strain when shear band formed are summarized. Different growth rates of axial strain inside and outside the shear band in the process of progressive failure are analyzed qualitatively. The experimental results show that the strain localization is apparent in strain field, by which the characteristic points of the beginning of strain localization and the forming of shear band are determined; for loose sand samples with an initial water content of 0% and dense sand samples, the stress reaches peak just after strain localization appears, stress has decreased when shear band forms, entering the stage of strain softening; for loose sand samples with 6% and 12% of initial water contents, shear band has formed when stress reaches peak; the increase of partial lateral strain inside the shear band is much more larger than that outside shear band. The increase of overall axial strain is mainly due to relatively large axial strain resulted from shear failure inside the shear band.

On account of the complex terrain in the west region of China, the underground mining could break the stability of slope and lead to the slope failure easily. Under the superposed influences of underground mining and landslides pressure, the surface subsidence in valley bottom areas is obviously smaller than that in the flat areas with the similar geological and mining conditions. To accurately predict the surface subsidence in valley bottom areas, a simply supported beam and probability density function (PDF) are employed to update the prediction model. The physical meanings and computing methods of parameters of the updated prediction model are confirmed. The fitness function is built based on the principle that the sum of squares of the difference between the measured value and the predicted value should be the minimum. A new method of parameter inversion is proposed based on the simulated annealing particle swarm optimization (SAPSO), and the corresponding parameters inversion program is developed with MATLAB language. Finally, the research results are applied to a mine in Shanxi province, and the error of mean squares of prediction values is 73 mm which is basically in accordance with the measured values in valley bottom area.

To overcome the limitation of the existing three-dimensional swelling constitutive model, the swelling tests under lateral restraint condition are conducted on the swelling rock sampled from a water-rich argillaceous slate tunnel. On the basis of the experimental results, the relationship between the axial swelling ratio under lateral restraint and the water absorption time is revised, and a one-dimensional constitutive equation for swelling is developed. Based on the Kinnick conditions, the overall swelling process is described with considering the contribution of the maximum and minimum swelling stress to the swelling behavior. With the time of the maximum volume swelling rate being the critical time, a time-dependent 3-D swelling constitutive model of argillaceous slate is developed, which can be expressed stage by stage. The results show that the relationship of axial stress and axial swelling rate can be expressed as a negative logarithmic function. When the water absorption time is less than or equal to the critical time, the relationship between the lateral restraint swelling ratio and the water absorption time follows an exponential law, and the volume swelling rate obeys the three-dimensional swelling constitutive model with considering the time effect. When the water absorption time exceeds the critical time, the axial swelling ratio under lateral restraints no longer changes with time, but remains to be the final axial swelling rate under lateral restraint. Moreover, the volume swelling rate no longer obeys the constitutive model, but becomes the constant value (the maximum volume expansion rate). These results can provide a theoretical reference for solving the surrounding rock swelling problem of water-rich soft rock tunnel.

The deformation characteristics of subgrade graded gravel can be impaired by the variation of water content due to rainwater infiltration so that the traffic safety is adversely affected. However, there is a paucity of the research that addresses the influence of the water content on the deformation characteristics of subgrade graded gravel. To investigate its deformation characteristics at different water contents, a series of large-scale static and dynamic triaxial tests is carried out. The effect of the water content on the stress-strain relationship and shear strength of graded gravel is explored, and the influence of dynamic stress level on the accumulative strain of the soil is studied based on the results of dynamic triaxial tests. Also, an analytical model which accounts for the influences of water content, dynamic stress level, and cyclic number is proposed. Using parameters obtained by fitting the tests for water contents of 5% and 7.3%, the proposed model is validated by calibrating the tests for water content of 8.6%. Comparison of the proposed model and Gidel model shows that the proposed calculation approach yields better results for various dynamic stress levels and loading cycles. The proposed model can not only avoid the scattering of calculated accumulative strain, but also directly reflect the influence of water content on the accumulative strain.

Based on a mud method of preparation sample, some uniaxial compressive tests are conducted on the frozen silty sand samples prepared with the mud sample preparation method. The failure strain and linear elastic modulus characteristics of frozen silty sand under uniaxial compression are investigated systemically in a wide range of strain rate and water content. The experimental results show that with rise of strain rate, failure strain increases gradually when water content is 12.0%; failure strain firstly increases and then decreases with growth of stain rate when water content is between 16.7% and 24.0%; when water content is greater than or equal to 30.6%, with increasing strain rate, failure strain decreases gradually; for the above three cases, the failure strain always tends gradually to be stable in the end. With increasing water content, failure strain firstly increases to a maximum sharply and then decreases dramatically. The failure strain tends to the failure strain of ice after water content is beyond 41.5%. Linear elastic modulus increases nonlinearly to a peak with increasing water content and then further rise of water content makes it lower, which can be described by a quadratic polynomial model. At 2.0 ℃, when strain rate less than 4.67×10-3 s-1, with increase of water content, linear elastic modulus increases nonlinearly and then tends to the linear elastic modulus of ice; when strain rate greater than or equal to 4.67×10-3 s-1, linear elastic modulus firstly increases to a maximum and then decreases to the linear elastic modulus of ice with increase of water content. When temperature is at 5.0 ℃, the similar critical value of strain rate to 4.67×10-3 s-1 is 1.00×10-2 s-1.

In order to evaluate the influence of intermediate principal stress and major principal stress direction on the drainage-induced deformation of natural soft clay, a series of drained directional shear tests is carried out on Wenzhou natural soft clay with different intermediate principal stress coefficients and different major principal stress directional angles, using a GDS hollow cylinder torsional shear apparatus. During the tests, the shear stress is increased gradually until the specimens failed, while the major principal stress direction and the intermediate principal stress coefficient remain unchanged. The influences of intermediate principal stress coefficient and major principal stress direction are discussed on the relationship between the deviator stress and major principal strain, and the relationships between the major principal strain and the intermediate principal strain, minor principal strain and volumetric strain. It is found that the anisotropy expressed by the stress-strain relationship is affected by different intermediate principal stress coefficient and major principal stress direction. When the intermediate principal stress coefficient remains as 0.00 and 1.00, the influence of major principal stress direction on stress-strain relationship is insignificant. However, when the intermediate principal stress coefficient reaches 0.50, the secant modulus in stress-strain relationship is significantly influenced by major principal stress direction. When the major principal stress direction angle is 30°, the intermediate principal strain changes from compressive state to tensile state as the intermediate principal stress coefficient increase from 0.00 to 0.50. When the major principal stress direction angle is 45°, the intermediate principal strain changes from compressive state to tensile state when the intermediate principal stress coefficient increases from 0.00 to 1.00.

It is known that Jinping-I arch dam is the highest arch dam in the world with a height of 305 m. However, the dam foundation lithology is quite poor due to f5, f8 and other faults exposed on the construction base layer. In addition, the foundation is highly asymmetric. Hence, the evaluation of the ultimate bearing capacity of Jinping-I arch dam cannot reach an agreement due to the geological complexity. Based on the deformation reinforcement theory and 3D nonlinear FEM program T-FINE, the concrete elastic modulus and dam foundation deformation modulus during impounding period are inverted using a direct method and values of the forward inverted plumb monitoring stations. Moreover, the validity and feasibility of the inversion parameters are verified in the impoundment period prediction and the ultimate bearing capacity analysis. The stress and displacement of dam body under normal conditions are simulated with the inversion parameters. Based on project analogy method, the ultimate bearing capacity of Jinping-I arch dam is evaluated completely, considering the yield zones, unbalanced force, plastic complementary energy norm, safety factors and other indexes. The reliability of design parameters is also verified by comparing the calculated results of inversion parameters and design parameters. The results show that K1 (the safety factor when crack initiating) of Jinping–I arch dam is double overload while K3 (the safety factor for ultimate load) is 8 times overload. Hence, it is confirmed that Jinping–I arch dam has a higher ultimate bearing capacity than other arch dams in 300 m height and thus the whole stability is guaranteed.

A complete 3D numerical simulation, by using FLAC3D, is developed to investigate the influence of longitudinal displacement profile (LDP) relaxation on ground deformation and contact force acted on the shield in squeezing ground excavated by a double shield tunneling boring machine (TBM). The shapes of LDP curves using the stress relaxation are well controlled and the defect of control method by time step is represented in comparison with the stress method. The model is based on the real geometry and considers the nonuniform gap between the shield and ground. The characteristics of the LDP curves, the contact force and the plastic zone on the cross-section of tunnel are studied. Some useful conclusions are drawn as follows: 1) The sensitivity of LDP curves to the stress relaxation is not uniform for various rock mass parameters. 2) The contact pressure and frictional resistance acted on the shield increase gradually with the increasing stress release rate, and the corresponding behavior of LDP curve of ground and the contact area on the shield are also different. 3) The shape of plastic zone outside the shield is closely related to the stress release rate and the non-uniform gap between shield and ground. The plastic zone will gradually reduce from top to bottom when the stress release rate reaches a relatively large value.

In this paper, an anchorage scheme against the imminent failure of slope in practice has been proposed by considering on-site monitoring data and 3D numerical modeling. From the results, the position, time interval and initial time of internal shear slip plane are observed, according to the continuous monitoring data of the slope. Therefore, the position and shape of a potential slide plane can be predicted. Since the influence of the section morphology on slope stability and deformation is considered in this study, the results obtained by 3D numerical modeling are more reasonable. By fitting the external deformation and sliding surface with the numerical modeling and the measured data, the equivalent mechanical parameters of slope in any state are determined, according to the limit equilibrium condition of the imminent failure slope. From the equivalent mechanical parameters, the ultimate shape and position of the potential sliding surface are obtained by 3D simulation. The length and density of the reinforcement anchor cable can be further decided properly. The performance of this case study demonstrates that the proposed reinforcement scheme is reliable.

A proper spatial effect approach of excavation face is the premise to make full use of the self-bearing capacity of rock mass. In this study, two representative spatial effect approaches of excavation face, i.e., the support stress coefficient approach of T-N (09) and the displacement release coefficient approach of V-D (09), are compared qualitatively and quantitatively about their sources, influencing factors, scopes of application, performances of spatial effect and differences of convergence-confinement and so on. It is found that the two spatial effect approaches of excavation face are both readily combined with ground response curve to practical engineering applications and have good consistency in some range of parameters; the support stress coefficient approach of T-N (09) is only suitable for elastic-perfectly plastic rock, which leads to a smaller support pressure and a larger stable deformation of rock mass, and thus the related material models and parameter ranges should be properly improved. The displacement release coefficient approach of V-D (09) can be applied to various elastoplastic rocks, directly reflecting the changes and influence ranges of spatial effect of excavation face, and thus it has a wide range of engineering applications.

To avoid support crushing again under the similar conditions of working face No. 1202(3) by improving upper limit in Gubei Coal Mine of Huainan, based on fracture characteristics of overlying strata, a structural mechanics model of overlying strata with the natural arch is established. The theoretical formula of the arch rise for both the low the high caving arches are deduced. Firstly, the influence of fracture location of the roof on the support load is studied. Then, the overlying strata loads under conditions of loose aquifer inside and outside the natural arch are calculated. Moreover, the criteria of support crushing for sliding instability and squash instability are determined. This study shows that it is easy to form the structure of high caving arch when the working face of improving upper limit is influenced by the water of loose aquifer. The volume weight of loose aquifer inside the high caving arch increases, and the contact forces between hinged rocks decrease. Additionally, the key layer is influenced by the water pressure of loose aquifer, which increase loads on the supports sharply. Therefore, the working face of improving upper limit easily leads to support crushing. However, the influencing factors of support crushing belong to both geological factors and mining technology factor. It should be mentioned that the blindly increasing working resistance of supports is not necessary to reduce the risk of support crushing, but the support cost is inevitable to increase rapidly. Based on the above analysis, the dimensionless sensitivity index is defined, and then the sensitivity of influencing factors of support crushing is analyzed. It aims at investigating the influencing factors of high sensitivity and preventing countermeasures of support crushing, such as controlling an appropriate mining height, forced caving for the roof of open-off cut, preventing an immediate roof suspending, hydrophobic step-down before mining, strengthening the rib of working face, improving support force, selecting reasonable equipment, and guaranteeing reasonable advance speed of working face. These measures provide some theoretical guidance for safe mining under the similar conditions of working face No. 1202(3).

The west part of Chengchao Iron Mine is metal mine characterized by steep structure plane. In this study, the monitored data of the ground deformation and macroscopic damage features of the mining area are analyzed. The strata movement in mining area can divided into two stages. The first stage is that the failure of the roof rock masses extends to the ground surface and then cause subsidence, while the second stage is that surrounding rock mass around goaf topples to mined-out area. Through the investigation of toppling-sliding area, it is found that the horizontal displacement mainly occurs in this area, which is greater than the vertical displacement; the ground deformation firstly increases slowly, then enters a rapid deformation phase, there exists a significant turning point; the superimposition stress induced by mining subsidence and terrain characteristics increases the ground deformation in the downhill areas, especially the horizontal displacement. Meanwhile, the distribution characteristics of angle of ground movement are revealed in the mine. The angle of ground movement in the south part of mine is greater than that in the north part, and the reason is that the north part is affected by the NNW, NNE structure planes, where the toppling failure is quite serious. The research results may be applied to the similar metal mines.

Generally, presplitting blasting parameters are obtained by the engineering analogy method, which is according to the empirical formulations. However, this method lacks theoretical basis. Therefore, it s necessary to propose new formulations on the presplitting blasting parameters in consideration of some important blasting influence factors such as rock initial damage. Two theories of rock blasting-induced damage and the interaction between stress wave and donation gas are introduced. For practical project, the presplitting blasting tests are conducted to obtain blasting parameters in field by the present method. The results of the linear charge density calculated both by some representative empirical formulations and the proposed theoretical formulations are compared, and then the effects of presplitting blasting tests are analyzed. Experimental results show that the effects of presplitting blasting tests perform well, and the presplitting blasting parameters by the developed method is more rational than that obtained with the engineering analogy one. Finally, some useful suggestions are given to determine presplitting blasting parameters in practical project based on the theoretical method.

Based on the advanced geology forecast by seismic reflection method at Tingzhou Tunnel in Ganzhou-Longyan Railway, fifty-seven selected seismic records are used for investigation. Within the segments of excited seismic wave in the surrounding rock, the differences of the shear wave velocity in horizontal and vertical directions are analyzed statistically, separately. Additionally, the anisotropy of surrounding rock is also considered. It can be seen from the results that when the shear wave velocities in horizontal direction vary from in vertical direction, shear wave anisotropy presences in different degrees in the surrounding rock. Vertical shear wave velocities are generally higher than the horizontal ones, and the most of shear wave anisotropy coefficients are within ±10%. It is found that the anisotropy coefficients of dynamic elastic modulus, dynamic shear modulus and dynamic Poisson ratio are in the ranges from -15% to 15%, from -20% to 20%, from -20% to 15%, respectively. The anisotropy degree of surrounding rock depends on the grade of surrounding rock, seismic longitudinal wave velocity and the buried depth of tunnel. The anisotropy coefficient of shear wave and its discrete degree are relatively higher, when the seismic longitudinal wave velocities are between 3 800 and 5 000 meters per second or when the buried depth of tunnel is between 60 and 100 meters. Among the tests conducted on the surrounding rock of grades Ⅱ-Ⅴ, it is noted that the shear wave anisotropy and its discrete degree is the highest in surrounding rock of grade Ⅳ, but is the lowest in the surrounding rock of gradeⅡ.

Due to the existence of structure bodies in the scope of stope, the work safety in underground mine is seriously influenced.. Hence, it is significant to analyze the mobility of structure bodies in stope under different stoping sequences. Based on the block theory, the general nesting modes of structure bodies in stope are analyzed, combined with the spatial attributes of stope mined with the open stope mining method. In this study, a stope structure model is established by using GeneralBlock code and then the elements of the structure bodies such as type, size and location are deconstructed. The structure mobility in different stope mining sequences is further analyzed by using the vector method. In addition, the mining mobility of the vector immovable structure bodies is investigated by mechanics method when rock bridge destructing and a formula for structure bodies is derived under the conditions of the bodies destroyed and rock bridge moved. The ore block No.1 of the zinc-polymetallic deposits in Tongkeng mine is selected as an example to analyze the mobility of the structure bodies under real stoping conditions. The results show that when the retreating mining sequence is from one end to the other, four structure bodies tend to slide. However, seven structure bodies tend to slide and even one structure body tends to slide after the rock bridge is destroyed, when the retreating mining sequence is from the middle to two ends. When the mining sequence is turned into hierarchical level up, four structure bodies tend to slide and two structure bodies fall in the meanwhile. Therefore, this study can provide a technical guidance for the selection of mining sequence properly and management of stope safely when cracked rocks in underground mine is mined by the open stope mining method.

In order to predict the deformation characteristics of retaining structure in deep foundation pit excavation, we study the design method of subway station excavation retaining structure in soft soil foundation pit from a retaining structure’ system stiffness point of view. A new concept of system stiffness, i.e. multiple variables system stiffness (MVSS) is proposed in view of the defects of Clough composite stiffness model. In addition to the stiffness of the retaining wall and the vertical spacing between the supports, as included in the original Clough model, several important parameters are introduced in the proposed MVSS model, including the depth of the foundation pit, the bracing stiffness, the horizontal spacing between the supports, basement reinforcement. Finite element method is employed to calculate the maximal lateral displacement of the retaining structure. The results show that the proposed MVSS model can describe excellently the deformation of the retaining structure. The measured displacement data from several foundation pits also validates the applicability of proposed method. Therefore, the proposed model is a liable and valuable way to determine the system stiffness of the deep foundation pit of subway in different strata. There exists a negative correlation between retaining structure of foundation pit and maximum lateral deformation, excavation MVSS comprehensive stiffness, but when the MVSS comprehensive stiffness increases up to a certain degree, the continued increase of MVSS comprehensive stiffness has an insignificant effect on controlling further the deformation of the retaining structure of foundation pit.

In engineering practice, a layered soil with sand overlying clay is often witnessed in naturally deposited or artificially backfilled grounds. However, limit insight has been gained into the failure mechanism and bearing capacity of two-layer soil. A numerical model on the basis of a finite difference method is developed for studying the influences of the footing roughness, dilation angle and surcharge on the failure mode and ultimate bearing capacity of the soil foundation. Based on the numerical results, the existing practical methods are evaluated, including the weighted average method, the load spreading method and the punching shear method. Our results indicate that the influence of the footing roughness on the bearing capacity decreases with the increase of the friction angle of soil. The dilation angle has remarkable effect on ultimate load when the dilation angle is small. Besides, the influence of surcharge becomes significant for low-strength clay. The weighted average method overestimates the bearing capacity, since it overestimates the weight of the strength of sand due to a conservative prediction of the depth of the failure slip. The load spreading method is considered to underestimate the bearing capacity when the depth of sand is large due to neglecting the shearing resistance of sand. The punching shear method, in which the vertical side sand block is utilized and shearing resistance of sand is taken into account, gives a reasonable solution for small sand depth and low-strength clay. In addition, the accuracy of the calculation can be improved if the local shear failure in the clay subgrade is taken into account.

The wind turbine is a high-rise structure, which is subjected to both the vertical loading due to structural weight and the horizontal loading and moment due to blade-induced or tower-induced loading. In designing offshore platforms, it is crucial to evaluate the overall stability and the failure mechanisms of the single-pile composite bucket foundation of the wind turbine under combined loading conditions. Based on the Swipe test loading method and the fixed displacement ratio loading method, this paper investigates the failure envelopes of the single-pile composite bucket foundation on the soft soil ground under undrained conditions in the V-H, V-M, H-M and V-H-M spaces by using the finite element method. It is shown that the failure envelopes in V-H and V-M space are symmetrical, while the failure envelope in H-M space is asymmetrical. Moment load affects the shape of failure envelope in V-H-M space, the failure envelopes of V-H space recedes as the moment load increases. By using the relationship between the actual combined loading and the computed failure envelopes, the stability of single-pile composite bucket foundation can be evaluated in engineering practice.

Mesoscopic seepage field of real soil is simulated based on lattice Boltzmann method. In this simulation, the basic model D2Q9 is used; and the inlet and outlet boundaries are constructed by setting the non-equilibrium extrapolation format. The soil particles boundary as well as left and right waterproof boundaries are set by the bounce-back format. At first, the data denoted by physical units from experiments are transformed into lattice units. According to data structure generated by CT scanned slices, the corresponding calculation program is applied to simulate mesoscopic seepage field of real soil. Finally, the results of lattice units are transform into physical units once again. The variation of seepage velocity is analyzed; and the whole and partial distributions of seepage field are obtained. The results show that: 1) Seepage velocity U finally reaches a relatively stable figure in pore channels over time. Accurate time T is obtained from the beginning of seepage to the steady-state of seepage. 2) The average seepage velocity gradually decreases along with the negative direction of y axis from the inlet boundary; and it is less than the average seepage velocity in inlet boundary. 3) The quantity of seepage is dominated by the connectivity and pore size of channels. The maximum seepage velocity is concentrated in a narrow channel. The velocity in closed pore channel and pore is zero. Lattice Boltzmann method is effective in simulating two dimensional CT scanned slice and can be used to research the mechanism of real seepage field quantitatively and accurately.

In this study, the implicit cylindric anchor bar element is adopted to simulate the bonding rock bolt in the large underground caverns. Then an additional stiffness model of the anchor bolt attached to the surrounding rock is established. According to the neutral point theory, the differential equation of load transfer relating to the interaction between the surrounding rock and the bolt is deduced, by assuming the shear slip model on the interface of anchorage bolt body. Based on the discrete displacement of surrounding rock obtained by 3D elastoplastic finite element incremental method, the continuous displacement of surrounding rock which causes the deformation of bolt is acquired by using the interpolation and curve fitting. Furthermore, the distribution functions of the axial load and the shear stress on the interface between the bolt and surrounding rock are obtained by solving the differential equation. The shear stress is transformed into the equivalent additional stress acting on the rock mass, and thus the supporting effect of the bolts can be reflected. This case analysis shows that the new algorithm can be well used to simulate the supporting effect of bolts. It is also found that the anchorage stress distribution obeys the neutral point theory. As a result, the function of shear stress on the interface between the bolt and surrounding rock can be divided into positive part and negative part by the neutral point, and the axial load distribution of bolt is a unimodal curve. In addition, the calculated values by the new method show good agreement with the measured values.

With the further study of the extended finite element theory, the extended finite element method (XFEM) has been widely used to simulate hydraulic fracturing. In comparison with the conventional FEM, the XFEM method has substantial advantages, such as high precision and low computational complexity. However, there are still many difficult challenges including how to simulate the perforation and the interaction between fluid and rock and to analyze propagation law of hydraulic fracturing. In this paper, to study the propagation law of hydraulic fracturing, the stress equilibrium equation of rock porous medium, fluid continuity equation and boundary conditions are established. Through finite element discretization method, the coupling equation matrix is treated. The initial fracture (or propagation) is defined through enrichment functions, and the maximum principal stress and damage variable D are selected respectively as the criterion of fracture initiation and propagation. Hydraulic fracturing propagation process is simulated by using the level set method. Numerical results show that the increase of perforation azimuth, fracture fluid displacement and the reduction of the horizontal stress difference cause the increase of the fracture initiation pressure, and the viscosity has no obvious effect on the fracture initiation pressure. It helps to widen the fracture width by increasing the perforation azimuth, the fracturing fluid displacement, the fracturing fluid viscosity and decreasing the horizontal stress difference. Increasing the horizontal stress difference, fracturing fluid displacement and decreasing the perforation azimuth and the viscosity of fracturing fluid can help to increase the fracture length and vice versa. Different well types and parameters of reservoir and fracturing operation are analyzed by hydraulic fracture XFEM based on ABAQUS platform. The fracture shape is lifelike and the image of degree of concave-convex on the fracture surface is clear. In consequence the result is accurate. As a simple and effective research method for studying the criterion of hydraulic fracturing propagation, this study provides the reference for hydraulic fracturing design and operation in oil field.