Through researching variation of soft clay microstructure in accelerated creep condition, we can deeply understand internal mechanism of accelerated creep characteristics. According to the micro quantitative technology and triaxial creep test of a variety of conditions of soft clay in Tianjin area, comparison between microstructures of soil samples under static and dynamic loads is made for explaining creep mechanism from microcosm. Research shows that the abundance and complexity of the structure element reduce when the accelerated creep appears, and the shape of the structural unit body becomes oblate and tends to smooth edges. Soil particle has no obvious directional property under natural condition. The particle orientation enhances obviously after the accelerated creep. Vibration loads make the creep degree increase and the soil creep rate be accelerated. It reveals that the accelerated creep of soil mass is actually a self adjusting and reengineering process of the soil internal structure under dynamic loads.

Most of the existed studies of soil-geogrid interaction mainly focus on uniaxial and biaxial geogrids. Nevertheless, the interface behavior between triaxial geogrid and soil has not been fully understood by experimental study. A series of laboratory pull-out tests is conducted on triaxial geogrid considering the effect of two kinds of pullout directions, referred to as TX_0 and TX_90, respectively. The displacements of specimens are measured and recorded at 4 sections along the pullout direction, and then the tensile strain, relative displacement between geogrid and soil, distribution pattern of interface friction, and deformation and failure mode of the geogrid specimens are all analyzed. Based on the peak shear strength and the residual shear strength, the variation laws of the interface behavior between geogrid-soil and apparent friction coefficient are investigated. The experimental results demonstrate that the interlocking of transverse rib increases with the increase of normal stress due to out-of-plane bending in the case TX_0, which leads to a better pullout performance than that in the case TX_90. The interface friction develops in a progressive mode along with constant adjustment of the distribution pattern and an elastoplastic softening characteristic is observed for interface behavior. The interface friction angles in the case TX_0 are significantly larger than that in the case TX_90, while the interface cohesions are just opposite. Higher normal stress can contribute to a better pullout performance in the case TX_0.

In the free state, the phase velocity of the planar Rayleigh waves in layered media is related to the frequency and the material properties of media. Rayleigh waves activated by the surface sources propagate with cylindrical wave-fronts. The phase velocity is related to the travelling distance as well as the frequency. Thus, without taking the spatial behavior into consideration, the theory of the planar Rayleigh waves in layered media can not be appropriately applied to analyzing the propagation behavior of the activated Rayleigh waves. Based on the displacement of Rayleigh waves obtained by the thin layer method for the disk-like vertical surface sources, the phase velocities of the activated Rayleigh waves are derived. The difference between the activated and the normal Rayleigh waves is compared. The spatial behavior of activated modes is analyzed and its mechanism is investigated. The results show that the effect of sources on the spatial behavior of activated modes is confined within the wave field about one wavelength from the sources. The nearer the wave field is, the slower the phase velocity of vertical vibration is. In the wave field with multiple activated modes, the spatial behavior of apparent phase velocity is obvious due to the constructive and destructive interferences of these modes. The study results can provide some guidelines for developing new inverse mathematical models and algorithms which could include both the frequency behavior and the spatial behavior.

The energy pile with embedded steel tube is a new type of ground source heat pump (GSHP) technique in the form of pipe-coupled pile. However, there are few studies focused on thermal response of this new pipe form. Experimental test and numerical simulation were conducted to study the heat transfer from tube to steel tube, to concrete, and to soil of energy piles with single U-shaped embedded steel tube. Temperature variations of surrounding soil and pile shaft under temperature loading of heating-cooling cyclic were measured. The thermal response of the ordinary single U-shaped heat exchanger energy pile with tied tube was also tested for comparative analysis. Finally, the applicability of energy pile with embedded steel tube was analyzed. The results show that the thermal response of energy pile with embedded steel tube is slightly lower than that of energy pile with tied tube. The final temperature of surrounding soil and pile shaft of two types of energy pile varies 23% and 16% in summer, and 14% and 18% in winter.

The nonuniform coefficient and curvature coefficient are very useful coefficients in soil mechanics. However, the precise approach to calculating , , is seldom studied. A modified Van Genuchten (MVG) equation is proposed to fit the particle size distribution curves. Cftool in the scientific programming language MATLAB is applied to fit the function. This paper analyzes the influence of three parameters of , , in MVG model on the particle size distribution curves of the thirty-three types of soils, which including the Qinghai loess, the Qinghai relic soil, the Gansu relic soil and the Xinjiang relic soil and so on. It is shown that the fitted curves of MVG equation perform well in predicting the particle size distribution curves, the square of the correlation coefficients are all bigger than 0.98. The parameter a causes the curves to migrate from the left to the right and vice versa, and can also indicate the maximum particle sizes. The parameter m influences the proportion of every group with the different particle sizes and the parameter n affects the slopes of curves. The proposed MVG equation is a precise approach to calculating , , .

Many experiments are carried out to study strength of expansive soil reinforced by polypropylene fiber with different lengths and weight ratios of fiber to dry soil (0.0%, 0.1%, 0.2%, 0.3% and 0.4%), respectively. The results show that the shear strength of expansive soil is enhanced significantly by adding fiber, and the unconfined compressive strength increases dramatically with the increase of fiber contents. While the fiber content exceeds the optimal content 0.3%, the unconfined compressive strength and the shear strength all decrease. Under the condition of the same fiber content, the strength of expansive soil also increases significantly with the increase of fiber length. Polypropylene fiber can also improve the peak strength and fracture toughness of expansive soil, delay the destruction of expansive soil. The study results provide a useful method for improvement of expansive soil.

Liquid nitrogen fracturing is a technique using liquid nitrogen as a fracturing fluid to stimulate the reservoir. During the treatment of liquid nitrogen fracturing, the cryogenic nitrogen is injected into formation, which leads coal rocks damage and increases coal rocks permeability. To reveal the laws of permeability variation after cryogenic nitrogen injection, the permeability tests are conducted on coal rocks before and after cryogenic treatment with pressure pulse decay method. By comparing the permeability results of dry and saturated coal rocks at different temperatures, it is found that the permeabilities of coal rock are all improved after 30 minutes cryogenic treatment respectively at -10 ℃, -25 ℃, -40 ℃ and liquid nitrogen (-195.8 ℃). Saturated coal rocks have a higher increasing rate of permeability than dry coal rocks. With the decrease of temperature, the permeability of coal rocks increases by a large amplitude. An exponential relation between the increasing rate of coal rock permeability and the temperature is obtained. The test results are analyzed to reveal the principles of coal rocks damage and permeability enhance influenced by low temperature.

Belled wedge piles with enlarged wedge base through grouting or ramming present high material usage ratio, and benefit the side friction and tip resistance comparing to those of traditional equal section piles. However, few studies focused on quantitative analysis of improvement ratio of vertical bearing capacity of the new type pile. The vertical bearing capacities of belled wedge piles, the load-settlement curve, the distributions of side friction and tip resistance, and load share ratio were measured in sandy and clayey soils. The vertical bearing capacities of traditional belled pile with the same concrete volume were compared as control. The results show that the ultimate bearing capacity of belled wedge pile is nearly 1.25 times that of traditional belled pile embedded in sand. The ultimate bearing capacities of belled wedge pile and traditional belled pile increase 11.1% and 66.7% when they are embedded in clay than in sand, respectively.

The complicated construction conditions, the small volume and irregular shape of the frozen wall are the characteristics of freezing reinforcement for shield junction in soft soil stratum. According to a freezing reinforcement project of shield junction in Shanghai, the model test based on similarity theory is conducted. Some conclusions are drawn through analyzing temperature data measured in the test. Firstly, under the condition of constant temperature on the inner surface of shield shell, the average expansion speed of the frozen soil inside the freezing-pipes is about 1.5 times that of outside the freezing-pipes. And the average temperature of the inside frozen wall is about 1.9 times that of the external frozen wall after 28 hours, when the temperature at the interface of shield and soil is about ?20 °C. Secondly, with a superposition of freezing-pipes, little difference appears at the beginning, and then similar variation for the temperature occurs in main plane and interface of the frozen wall during the freezing process. Thirdly, the freezing effect of the inner freezing-pipes on the outside soil is insignificant due to the temperature shielding of outside freezing-pipes, which leads to identical frozen wall thickness in the case of different freezing tube spaces and multiple freezing pipes crossing. Little difference in temperature distribution is found inside the frozen wall. The research results indicate a similar shape of the frozen wall to the layout of the outside freezing pipes during freezing process, and unchanged thickness and average temperature of frozen wall in 28 hours.

It has been gradually recognized that threshold hydraulic gradient of seepage exists in soft clay. However, nonlinear large-strain consolidation of soft clay with threshold gradient, which takes time-dependent load into account, has rarely been reported in the literature so far. By employing the excess pore water pressure as variable, and considering both threshold hydraulic gradient and characteristics of nonlinear compression and permeability, a model for large-strain consolidation is developed in Lagrangian coordinate system. On that basis, the corresponding finite difference solutions for this model are provided. Meanwhile, compared with the semi-analytical solutions of large-strain consolidation under Darcy's law, the numerical solutions for the proposed consolidation model are verified. Finally, the differences in the influence of threshold hydraulic gradient on consolidation behaviors of clay between large- and small-strain conditions are emphatically investigated. The results show that, no matter large- or small-strain condition is considered, both the dissipation rate of excess pore water pressure and the settlement of clay layer become smaller than that under condition of Darcy's law when considering the influence of threshold hydraulic gradient. The excess pore water pressure in clay with threshold hydraulic gradient is not completely dissipated under both large- and small-strain conditions, moreover, the residual value of excess pore water pressure under large-strain condition is smaller than that under small-strain condition, which leads to a larger settlement of clay layer under large-strain condition than that under small-strain condition. Both threshold hydraulic gradient and different deformation conditions have influences on the consolidation behavior, while the influence of threshold hydraulic gradient is more evident. Therefore, the threshold hydraulic gradient of seepage in soft clay cannot be ignored during the consolidation calculation of soft clay layer.

A creeping landslide shows a deformation response of long-term and small-scale, the evolution and stability of which are controlled by the creep response of sliding-zone soil. The Majiagou landslide, a typical creeping landslide in Three Gorges reservoir region, is selected as a case. A series of large-scale triaxial compression tests is conducted on the undisturbed specimens of sliding-zone soil to reveal the creep laws of sliding-zone soil under different confining pressures and stress levels. On this basis, the difference between long-term strength and conventional strength of the soil is determined by the isochronous curves. The results show that the sliding-zone soil of Majiagou landslide has steady creep characteristic, and the creep process can be divided into attenuation creep stage and constant speed creep stage. And the deformation tendency of sliding-zone soil is similar to the macroscopic deformation of the landslide. The absolute creep displacement and the strain rate of constant speed creep stage are positively correlated with the axial stress. While the duration of the attenuation creep stage increases linearly with the shear stress level. The long-term cohesion and the long-term internal frictional angle decrease by 24.8% and 22.4% respectively comparing with the conventional strength parameters.

Excavation of the expansive soil slope results in fissure development due to drying-wetting cycles, and affects the stability. Although the materials of cement panel and geotextile are generally used to deal with the drainage problem successfully, their service lives are short and less ecological friendly. Therefore, a capillary barrier with dual soil structure consisting of a relatively fine soil layer above a relatively coarse soil layer, is introduced in this paper considering both ecological and drainage-seepage controlling functions. The aim of this article is to investigate the effects of particle size and distribution of the coarse soil layer on the capillary seepage flow. Six groups of tests are conducted to monitor the soil water infiltration process under the condition of rainfall using the brilliant blue dyeing tracer. The results show that preferential flow and discontinuous horizontal seepage field appear in coarse soil with larger particle size and worse particle distribution, and worse capillary barrier effect. The measured vertical and horizontal drainage volumes indicate that the dual structure presents good drainage control. The parameter of steady drainage efficiency and the total drainage efficiency are used to evaluate the effect of capillary barrier. The steady drainage efficiency between 80% and 100% is small firstly and then increases with smaller grain size and better particle distribution of the coarse soil layer. The variation of total drainage efficiency between 43% and 79% is just opposite compared to the former. In summary, the dual structure of the fourth scheme is suggested to apply the South-to-North Water Transfer Project, according to the optimal seepage control efficiency and the lower cost of coarse material. The research results can be directly applied to the seepage control of expansive soil slopes in other projects.

To simulate the deformation behavior of rocks under cyclic loading and unloading, a cyclic loading-unloading model is developed based on Drucker-Prager (D-P) yield criterion and the subloading surface theory. Tensile strength and stress angle effect are considered in this model. By introducing the corner model into the traditional D-P yield criterion, and referring the D-P-Y yield criterion proposed by Yin Youquan, a modified D-P yield criterion is put forward on the basis of strength characteristics of rocks under triaxial compression and tension. According to the modified yield criterion and the subloading surface theory, a subloading surface model for rock under cyclic loading and unloading is proposed. Numerical verification of this model is conducted by programing. The results show that the subloading surface model can be used to represent the Mansingh reaction and the ratchet effect of rock. As the tensile strength decreases, the deformation of rock increases, and the rate of increase is gradually improved, which demonstrates that the modified model can be used to well reflect the effect of tensile strength on the deformation of rock under cyclic loading and unloading.

Acoustics tests are conducted on deep tight sandstone reservoir samples in Tazhong area. A new method is developed for quantitatively evaluating the microcrack stress sensitivity of tight sandstone reservoir using inversion of acoustic data. The fracture density and the aspect ratio are inversed by using the Biot consistent model and the DEM model, and the variations of and are discussed under different confining pressures. The stress sensitivity of microfractures are also evaluated. The results show that, with the increase of confining pressure, decreases and increases, mainly due to the closing of the microfracture. According to the reducing amplitude of under different confining pressures, the percentage of fractures that close or open can be determined. Samples with a larger under high confining pressure represent low stress sensitivity. Otherwise, the stress sensitivity is higher. This paper defines the point, where the pore-fracture in the rock changes greatly, as the turning point. The values of corresponding to the turning points of different samples are similar. This phenomenon can be seen as the common characteristics of tight sandstone reservoir fractures, and it can also act as the contrast indicator of the fracture development degree. The correlations of (with a confining pressure of 65 MPa) and turning pressure with rock porosity are discussed, which shows that they both have a very good positive correlation. For the deep low permeability sandstone reservoir in this region, the favorable fracture that has weak stress sensitivity is influenced mostly by physical properties of rock.

To study the influence of water-soil chemical interaction on cohesive force under different conditions, montmorillonite- quartz remolded soil is prepared and soaked in ultrapure water (normal water), pH=3 HNO3 (acid rain) and pH=13.5 NaOH (alkaline waste liquid). The results show that, under the condition of ultrapure water, the cohesive force rises firstly and then declines and then rises again; under the acid condition, the cohesive force declines firstly and then rises and then declines again; under the alkaline condition, the cohesive force declines firstly and then rises and then declines again, at last rebounds. Temperature promotes the chemical reactions at different degrees. The X-ray diffraction analysis results show that acid causes corrosion to montmorillonite mineral. None of new material generated in montmorillonite sample during the soaking process leads to a decline in cohesive force. The reason for cohesive force rise in the middle stage of acid soaking is not clear. Under the alkaline condition, calcium silicate hydrate (CSH) is generated. Under the condition of ultrapure water, both CSH and CaCO3 are generated. The bond strength, connecting the unit cells through chemical bonds for the new ionic cements, is far greater than the strength of binding force connecting two adjacent montmorillonite layers. The presence of new cements cause rise of cohesive force under ultrapure water and alkaline conditions. Chemolysis and ion exchange are the main reasons for descent of cohesive force. Furthermore, combined with the vertical pressure of soil landslide and the internal friction angle, the shear strength variation of soil under the influence of water-soil chemical interaction is analyzed. Under the ultrapure water condition, the shear strength changes slightly in general; under the acid condition, the shear strength changes in accordance with the cohesive force; and under the alkaline condition, the shear strength increases in general.

The distribution and value of lateral earth pressure are closely related to the displacement mode of retaining wall. The critical depth of plastic zone behind the retaining wall should be considered during design when the backfill is in active earth pressure state. Based on the upper bound method of limit analysis, the infinitesimal backfill body under elastic overburden and adjacent wall are studied to determine the external work rate and internal energy dissipation rate. The equations are obtained to calculate the critical depth of plastic zone under sliding mode, considering the effect of displacement direction of the retaining wall. The results show that Rankine and other theories are special cases of the recommended method. The critical depth of plastic zone increases with the increase of the angle between the displacement direction of wall and the horizontal plane, and with the increase of the values of cohesion and friction angle of wall-soil interface and the values of cohesion and friction angle of backfill. However, when the wall displaces horizontally, the critical depth of plastic zone becomes constant regardless of the change of friction angle of wall-soil interface.

The deformation characteristics of soft foundation subjected to long-term cyclic loading is significant. Various models have been developed for predicting cumulative plastic strain in clay under repeated loading. The most commonly used is empirical model, but it has some limitations. Based on the dynamic deformation curve of typical structured clay, an improved model is proposed to describe the cumulative deformations of clay subjected to cyclic loading, by adding exponential function of to the exponential hyperbola model of . This model applies to both stable strain curve with the strain limit and destructive strain curve under different stress levels. As for brittle failure of strong structured clay, the model has obvious advantages, and it also shows good universality of dynamic deformations of different structured clays under different stress levels. What is more, the improved model can be used to calculate the critical dynamic stress approximately. Since the behavior of structured clay is damaged promptly under dynamic loads when cumulative plastic strain is relatively small, the inflection point of strain-cyclic number curve is proposed to determine the failure criteria of strain.

Time-dependent behavior of viscosity of quick setting slurry and double liquid grouting mode lead to spatial uneven distribution of viscosity in diffusion region. The influence of spatial uneven distribution of viscosity should be considered in permeation grouting diffusion model of quick setting slurry. By regarding quick setting slurry as a Bingham liquid of time-dependent behaviour, an even capillary group model is used to describe porous flow process. A theoretical model of one-dimensional permeation grouting is developed under constant grouting rate. A visual permeation grouting simulation test system is designed to obtain the permeation rates of different media and the relationship between grouting pressure and grouting time for cement-sodium silicate (C-S) slurry. Results show that: when the spatial uneven distribution of viscosity is considered, the calculated value of grouting pressure is 1.2-1.4 times the test value and the calculated value of grouting distance is 0.9-1.1 times the test value. The theoretical and experimental results are in good agreement. The proposed model can well describe the process of one-dimensional permeation grouting of quick setting slurry. When the spatial uneven distribution of viscosity is not considered, the calculated value of grouting pressure is 3.5-4.1 times the test value and the calculated value of grouting distance is 0.5-0.7 times the test value. So the grouting pressure is overestimated significantly and the grouting distance is underestimated. The spatial uneven distribution of viscosity should be considered carefully in grouting design.

To study the impact of different construction procedures for cut slope protection of expansive soils and to prevent disasters triggered by rainfall infiltration, in-situ borehole shear tests (BST) were conducted under different normal stress levels and soaking conditions. Strength characteristics of expansive soils cut slope in Nanyang were obtained with various loading paths and soaking conditions. Results show that the relationship between shear stress and displacement from BST presents weak hardening as the shear strain increases. A max drop of 56.9% in shear strength, and a decrease of 18.1 kPa in cohesion are observed. Preloading inhibits softening but fails when it increases to some threshold. The cohesion has a positive linear relationship with the preloading stress, while the internal friction angle has a negative linear relationship with the preloading stress, but internal friction angle rarely varies. In engineering practices, effect of rainfall infiltration on strength parameters should be considered. Meanwhile, the linear relationship between parameters of shear strength and preloading stress should be used to back-calculate the preloading needed according to the safety factor that the project should satisfy. The study results provide technical reference for site evaluation, parameters selection and disaster assessment of the similar sites of expansive soils.

A large-scale shaking table model test is designed to study the dynamic behaviors of slope reinforced by multi-frame foundation beam with anchor cable and double-row anti-slide piles under seismic loading. Several critical parameters are monitored during the test, including axial force of pre-stressed anchor cable, earth pressure on piles, acceleration of slope body and displacement-time relationship of slope surface. Experimental results show that the pre-stressing of anchor cable varies with input seismic wave, and its maximum value of pre-stress loss reaches 23% when input wave is El Centro seismic wave with an amplitude of 0.15g. The test results suggest that the applied pre-stress value should be risen up to 1.2 to 1.3 times of the designed value for reinforced slope with strict deflection limit. The axial forces of anchor cables installed at different altitudes reach the maximum almost simultaneously, but the increase proportion of peak axial force demonstrates non-uniformity in space, so the aseismic design of anchor cable should be divided into upper and lower sections with anti-slide piles installed in the middle section of the slope. The earth pressure increases with the amplitude of input seismic waves. As the amplitude increases, the distribution of active earth pressure changes from ‘upper small-lower big shape’ to ‘upper big-lower small shape’. The demarcation line between the passive earth pressure zones I and II shifts to the bottom of pile. Anchor cables and anti-slide piles should perform as a collaborative structure under earthquake, so the effect of earthquake on the sliding force sharing ratio between pile and anchor cable should be carefully considered. The results can provide references for the design of anchor cable frame beam and anti-slide pile supporting structure in earthquake zone.

A new kind of test equipment was designed and manufactured to testify the principle of heavy cover replacement technique for foundation treatment of coarse sulphate saline soil. Indoor tests examined the effects of temperature, salt content and water content, minimum void ratio on expensive behaviour of coarse sulphate saline soil and validated the heavy cover replacement technique. The study shows that the deformation of coarse sulphate saline soil is temperature sensitive in the range of 0 ℃ to 2.5 ℃, and the expansibility of sample is subtle during the cooling process below -5 ℃. The swelling phenomenon is found less prominent as the void ratio decreases. Both water content and salt concentration affect on expansion of saline sample. The rate of swelling pressure change decreases as the expansive strain increases. The expansive stress and vertical strain show a linear relationship. The linear coefficient depends on the depth of replaced soil. The exploratory testing equipment and method provide engineering implications for the practical design.

At present, CH4 is replaced by CO2 in physical simulation test of coal and gas outburst, which causes a large deviation of the results. In order to ensure the similarity of simulation test while avoiding the risk of CH4, a concept of similar gas which is close to CH4 is put forward in the physical simulation experiment. Based on the mechanism of gas in outburst and similarity criterion, several similarity indices including gas content, initial velocity of gas emission, initial gas expansion energy, mechanical properties of coal containing gas are presented by combination with the coal and gas outburst prevention provisions. The mixture of CO2 and N2 is used as the original similar gas, CO2 volume fraction of which are 20%, 40%, 60% and 80%. According to the relevant specifications, the similarity indices of CH4 and the similar gases are measured respectively. The mixed gases, whose volume fraction of CO2 are 60%, 35%, 45% and 54% respectively, are similar to CH4 in the gas content, the initial velocity of gas emission, the initial gas expansion energy, the mechanical properties of coal containing gas. Correlation analysis results show that the four mixed gases are highly relational to CH4, and can be used as undetermined gases of similar gas. Simulation tests on the undetermined gases and CH4 are carried out. It is found that the phenomenon and the critical value of mixed gas with a CO2 volume fraction of 45% are the closest to those of CH4.

Compacted bentonite is widely applied in many countries as a suitable barrier material for the geological disposal of radioactive waste. However, cracks occur in compacted bentonite during shrinkage process. Whether the crack coalesces with other crack or not is a basic issue of the safe geological disposal of radioactive waste. In order to evaluate the influence of cracks on the performance of bentonite barrier, penetration test is carried out on compacted bentonite with a single longitudinal crack. The permeability coefficient, normal stress and water content are measured to indicate the impacts of cracks on the permeability and mechanical property of samples. The results show that the permeability coefficient decrease and the normal stress increases with time elapsing, and both of them finally reach a stable level after 85 days. At that time, the values of permeability coefficient and normal stress are about 4.64 m/s and 2.5 MPa respectively, which are the same level with that of integral bentonite. It means that the bentonite is saturated and homogeneous. It also can be concluded that the cracks have no obvious influence on the permeability coefficient and stress of bentonite. The compacted bentonite has a better self-healing ability. Not only the basic knowledge for bentonite as backfill material is acquired, but also a novel evaluation method is established in this study.

Laser speckle image of transparent soil, which is a novel method for studying the soil mechanics problems, can be used to measure the displacement field inside the soil mass through digital image cross correlation (DIC) method. Tests are conducted on fused quartz particles with four different grain sizes, i.e. fine quartz (0.1-0.3 mm), medium quartz (0.3-0.5 mm), coarse quartz (0.5-2.0 mm), and fine gravel quartz (2-5 mm). This paper reveals the influences of grain sizes of fused quartz on the quality of laser speckle image, the selection of appropriate query window size and the displacement measurement accuracy of transparent soil. The results show that the gray histograms and the speckle patterns are different for transparent soils of different grain sizes. With the same incident laser light, the quality of image for smaller sizes is better than that of the larger sizes. The histograms of obtained displacement error indicate that the displacement error is dependent on the query window size and grain size. By adjusting the query window size with the average gray level gradient, the transparent soil models of different grain sizes can provide the equivalent measurement accuracy. Digital and physical translation tests show that the transparent soil models of smaller sizes tend to give higher measurement accuracy.

Based on the distribution of normal stresses over three-dimensional (3D) slip surface, a method satisfying four equilibrium conditions is proposed to calculate reinforcing forces of 3D sliding mass for any shape of slip surfaces. A hypothetical model of forces among slices is established based on the classical soil pressure theory analogy and Spencer slices method. The distribution functions of normal stresses over the 3D slip surface are calculated under the equilibrium condition of classical slices, involving three undetermined parameters. The reinforcing force coefficient can be calculated by solving a set of linear equations established with three undetermined parameters and one reinforcing force coefficient, according to the main four equilibrium conditions of the sliding mass. This new method features simple computation process and high precision due to satisfaction of four equilibrium conditions. The method has been successfully applied to the design of reinforcing the potential 3D sliding mass on the left abutment of the Yinpan gravity dam on Wujiang river and is valuable to engineering applications.

The geological and topographical asymmetries of high arch dam foundations are essential problems which threaten the arch dam safety. Based on Baihetan arch dam engineering, a geomechanical model test is conducted to particularly evaluate the characteristics of the high arch dam with an asymmetrical foundation, from the respects of states of stress and deformation of the dam and its failure modes. Three-dimensional numerical simulations are built on both original and improved design schemes, based on which elastic-plastic finite element analysis is conducted. A comparison is then made between two sets of results in terms of dam deformation, stress distribution in dam abutment, local and global stabilities of the structure. The actual effect and reinforcement mechanism of the design optimization and reinforcement measures, adjusted to those existed asymmetries of dam foundations, are evaluated by combining with experimental results. It is shown that the optimization of dam shape and foundation reinforcement act synergistically to improve the dam deformation, state of stress and transmission of force in dam abutment area, and global stability of the dam-foundation system. The research of Baihetan arch dam asymmetry problem is significant to deepen the comprehension of optimization design and engineering reinforcement especially for high arch dams.

The commonly used approximation for evaluating the correlation coefficients between failure modes has a certain degree of error. This paper uses Pearson correlation coefficient to characterize the correlation between different slope failure mechanisms. Based on the correlation coefficients calculated from two different methods, this paper studies the effect of soil spatial variability on correlation coefficients between failure modes, the number of failure modes of a slope and the bimodal bounds of system failure probability. A brief introduction to risk aggregation method aiming at selecting representative slip surfaces, and Ditlevsen’s formulas for calculating bimodal bounds of system failure probability is presented. A single-layered and a two-layered slopes are studied to evaluate applicability of the approximation correlation coefficients. The results show that the commonly used approximation correlation coefficients cannot reflect the effect of soil spatial variability on correlation between failure modes, whereas the Pearson correlation coefficients can. When the spatial variability of soil properties is weak, there is large discrepancy between approximation correlation coefficients and Pearson correlation coefficients. Too many representative slip surfaces are selected and the representative failure modes cannot be reflected effectively based on approximate correlation coefficients. Furthermore, the upper-bound limit of system failure probability calculated by approximation correlation coefficients is probably greater than 1, and the bimodal bounds of system failure probability are too wide, all of these make system failure probability become meaningless. By contrast, the calculated bimodal bounds of system failure probability based on Pearson correlation coefficients are narrower, showing the changes of system failure probability effectively.

Description of rock morphology is of great significance to better understand the shear behavior of the discontinuities. Firstly, from the shear directional characteristics of the discontinuities, a new index SC (shear coefficient) describing discontinuities morphology is proposed based on some pivotal role on shear behavior of its morphology in the shear direction. The index describes undulation characteristics, statistical distribution of undulation and height characteristics of two-dimensional discontinuities morphology in the shear direction, and can also characterize directionality of the morphology. Moreover, the relationship between SC and JRC (joint roughness coefficient) is established based on 10 digitized JRC standard curves. Then, with the help of point cloud data of rock discontinuities obtained by three-dimensional (3D) white scanner, the shear coefficient SC is extended to 3D to better characterize 3D morphology characteristics of discontinuities. Finally, the three-dimensional shear coefficient (SC3D) is used to quantify morphology of natural rock discontinuities in different directions. It is shown that SC can well represent anisotropic morphology characteristics of discontinuities.

The prediction for post-construction settlement of building foundation or roadbed is an important basis for its safety assessment and the determination of maintenance strategy. Therefore, firstly, a methodology of combination prediction is introduced in this paper. By considering the effect of new or old degree of the measured settlement data on the prediction of post-construction settlement, an analytical model is developed by introducing a fresh-degree function, which can reflect the effect of the new or old degree of measured settlement data on prediction. Secondly, using parallel-modification, a method of the adjustment of value interval for combination prediction is proposed through analyzing the variations of the possible combination prediction, to improve the precision of the prediction. And then, on the basis, an improved model for combination prediction of post-construction settlement is established, which can simultaneously describe the effect of new or old degree of the measured data and the effect of adjustment of value interval for combination prediction on settlement prediction. Finally, the proposed method is used to analyze the practical engineering examples, which demonstrates that the method is feasible and reasonable.

To overcome the theoretical deficiency of the segmented Knothe time function, and to enlarge its range of application and improve its prediction accuracy, this paper conducts further study of the existing problems of the segmented Knothe time function through theoretical analysis and comparative study. The corresponding improvement method is given. And a new segmented Knothe time function is established, which has a broader applicable scope and higher prediction precision in the practical engineering. The results show that the established model successfully solves the problem of the function value differs from the theoretical value in the place of subsection point, and the problem of the time function value cannot eventually converge to 1. The new model of time function does not rely on certain restrictions of the parameter selection. The applicability of the new time function to dynamic prediction for different geological and mining conditions is enhanced. Through the prediction comparison between the new segmented time function and the original time function, it is shown that the prediction accuracy is improved significantly while using the new time function. In addition, the final prediction value of surface subsidence will stabilize and no longer change with the extension of prediction time.

Based on the underground powerhouse of Dagangshan Hydropower Station, the characteristic angles according to the geometric relationship between the principal stress direction and the cavern space position are defined, in order to describe the rotation of the principal axes of stresses. The research shows that different degrees of stress release and principal axis rotation are induced in the arch and the side wall during the excavation. The principal stresses in surrounding rock unload intensely in the current excavation, while the direction of principal stresses rotates violently in the current and subsequent excavation stages. Furthermore, the principal stress direction adjustment has certain similarities in the arch and the side wall. The final direction of the minimum principal stress is approximately perpendicular to the cavern free surface, and the directions of the maximum principal stress and intermediate principal stress are adjusted almost parallel to the excavation surface plane. On this basis, considering the effect of principal stress rotation, the stress disturbance index (SDI) is defined as a mechanical characterization quantity, and using it to describe the disturbance degree of stress field in the surrounding rock. SDI is applied to study the time evolution, along with the space distribution characteristics of stress field disturbance in the underground powerhouse of Dagangshan Hydropower Station. The strong stress disturbance zone obtained by numerical simulation is compared with the excavation damaged zone by field test, and the related understanding and conclusions are of certain theoretical and engineering significances.

In-situ soaking tests were implemented on undisturbed and remolded soils in the Ili region to study the regularities of soaking infiltration and settlement of Ili loess. Surface settlement and water content were also monitored. The results show that transient saturated zone exists in the soil depending on temporary mechanical equilibrium among pore water pressure, air entry value and pore air pressure of the closed compressed gas. Undisturbed loess presents multistage settlement, which can be described by piecewise function, due to soil structure and stratum structure. On the contrary, there is no obviously multistage settlement for remolded soil due to the structural damage. The wetting front reaches 8.8 m in the 21st day of soaking test. At the same time, the settlement of the remolded soil (S4) is 120 cm, 35% larger than 78 cm of the undisturbed soil (S5). Due to the effect of stress concentration, unsaturated soil below the wetting front does not deform before the saturated soil near the wetting front reaches stable deformation. Therefore, the settlement of S5, less than the calculated value (85 cm) of the dead weight collapsibility volume, is not stable settlement deformation of saturated soil above wetting front. The results provide a basis for the understanding of mechanism of soaking infiltration and calculation of wetting deformation of Ili loess.

There is a complex nonlinear relationship between rock joint roughness coefficient (JRC) and the statistical parameters. And JRC value calculated using single statistical parameter is not reliable, since the description is one-sided on the morphology of discontinuity surface. Four parameters, average inclination angle , average relative amplitude , standard deviation of inclination angle and standard deviation of amplitude , are selected to describe the morphology of discontinuity surface. The training samples containing 102 profiles with available experimental back-calculated JRC values are chosen to establish the nonlinear relationship between JRC and the selected statistical parameters, then a JRC support vector regression (SVR) prediction model is established. The SVR model is proved to be reliable by comparing the predicted and experimental back-calculated JRC of Barton standard profiles. The discontinuities of Majiagou landslide in Zigui county, Three Gorges Reservoir Region are selected as a case. Three-dimensional laser scanning test is conducted to obtain the morphology data of discontinuity surface and a 3D model of discontinuity surface morphology is developed. Direct shear test is carried out to back calculate its JRC. The results show that JRC predicted by the SVR model and experimental back-calculated value have good consistency, and the relative error is only 4.5%. The JRC estimation results by different regression equations based on statistical parameters for the same profile have larger variation, which indicates that the JRC predicted by SVR model based on the chosen statistical parameters is more reliable. The results may also provide a new approach to quantitatively determine JRC.

Freezing-thawing cycle in seasonal frozen soil region frequently damages the slope protected by soil nailing structure and threatens the slope retaining structure. In this paper, a finite element model was established using the thermal-fluid-structural coupling module in the nonlinear finite element software ADINA as case study of a project in Lanzhou. A constitutive model was developed to solve freeze-heave and thaw-subside. The program was verified by measured results. The structural characteristic response of soil nailing structure under freezing-thawing cycles was analyzed by the software secondary development. The results show that the increment of axial force of soil nail in each layer reaches a maximum at the nail head and decreases gradually along the axial direction under freezing-thawing cycles. The relative increment of axial force increases with the slope height. The horizontal displacement and ground settlement increase due to melted frozen soil. These conclusions provide significant references for design and construction of slope retaining structures in seasonal frozen soil region.

As is well-known, rock-fall is one of the most common geo-hazards and always causes serious damage to both lives and properties. There are many triggering factors that give rise to the occurrence of rock-fall disaster and earthquake is one of the main triggers, while often leading to a greater loss than other factors. As one of the methods to carry out researches of rock-fall, numerical simulation plays an important role in the study of movement characteristics. A conceptual rock-fall model with four cases, one without seismic loading and three with different seismic loading input modes, is used to simulate the effect of seismic loadings on the mobility characteristics by discontinuous deformation analysis (DDA). The simulation results show that the seismic loading prompts the collapse of potential rock-fall and different seismic loading input modes have different significant influences on the mobility characteristics of the collapse block. Another important conclusion is the vertical component of seismic loading has more significant influence on the movement distance of collapse block than the horizontal component, which differs from the traditional knowledge about the earthquake-induced rock-fall. Thus the vertical seismic loading should be given enough attention in the future prevention design of earthquake-induced rock-fall.

Chebyshev spectral element model is applied to one-dimensional wave propagation analysis of horizontal layered soil. A time-domain analysis is developed with high-order numerical scheme for the simulation of seismic response of soil site. The bedrock and upper soil are discretized by spectral elements, and the wave motion equation is applied to the domain of each element. Simultaneously, transmitting artificial boundary condition is introduced in the bedrock to simulate the influence of bottom infinite district on the interior wave motion. The Chebyshev orthogonal polynomials are used for constructing the displacement mode of the high-order elements, then a spatial discretization procedure is accomplished and the motion equation of all the computation nodes is obtained. A stable time-domain integration scheme is derived using the central difference theory and the numerical formulae of artificial boundary. Two soil sites seismic response problems are solved to compare the results using traditional methods. The proposed method provides remarkably enhanced computation efficiency for site seismic response analysis with high accuracy on small quantity of computing nodes .

Using Nishihara model to describe the rheological characteristics of dual-pore-fracture media, a method is theoretically presented to determine the rheological parameters and strength indices of the media. The plane finite element scheme for solving the transient elastic-viscoelastic-viscoplastic problems is built, and the corresponding calculation program is developed. Aiming at the two conditions of surrounding rock mass from a rectangular underground cavern, in which the first rock mass is fractured by two sets of joints (a dual medium) and the second one is intact (a single medium); the displacements, stresses and plastic zones in the surrounding rock masses are analysed and compared numerically. The results show that when compared with the case of single medium, the deformation modulus, cohesion and internal friction angle of the dual medium decrease, so the corresponding displacements and plastic zones in the surrounding rock mass develop with time elapsing obviously. And there is a greater difference between the stress distributions of these two cases, especially the difference between the maximum principal stress and the minor principal stress in the surrounding rock mass, which is larger for the case of dual medium. Therefore, the possibility of rock mass failure is increased.

A fundamental equation of state-based peridynamic theory is derived firstly from equating the traditional strain energy density to peridynamic ones and using the peridynamic fundamental equation. This paper introduces the damage theory to the fundamental equation of state-based peridynamic theory, and discretizes the fundamental equation, and then develops a corresponding peridynamic numerical program. Then classical fracture process of a single side tensional plate with a circle hole and the propagation and coalescence of cracks in rock under biaxial tensile stress are simulated using the theory. Numerical results from state-based peridynamic theory are in good agreement with those from RFPA2D. The results indicate that the state-based peridynamic theory not only breaks through the limitation of constant Poisson’s ratio on bond-based peridynamic theory, but also efficiently simulates the propagation and coalescence of cracks without any external fracture criterion. Therefore, the state-based peridynamic theory has great advantage over other numerical methods, and it can also provide a better understanding of propagation and coalescence of cracks.