Structural characteristic is a basic property of loess, and there is a connection between loess collapsibility and its structure. This paper aims at studying how freeze-thaw action affects loess collapsibility with different structural characteristics. A series of collapsibility experiments was performed on artificially structured loess, undisturbed loess and remolded loess, with the use of cement as connection medium among soil particles to prepare artificially structured loess samples. Experimental results show that the collapsibility coefficient of artificially structured loess is less than that of the undisturbed loess and remolded loess before and after freezing-thawing process. The collapsibility coefficient decreases with the increase of cement content. After freezing-thawing, the collapsibility coefficients of most loess samples increase. Especially, for remolded loess and artificially structured loess with low cement content, the increase of collapsibility coefficient is more evident when the water content is close to the optimum water content. Moreover, the increase of collapsibility coefficient is also closely related to the initial structure, water content, dry density and vertical load. Regarding undisturbed loess and remolded loess, a significant negative linear correlation is found between the collapsibility coefficient and unit weight under standard load, 200 kPa. However, for artificially structured loess, it is not the case. Furthermore, for remolded loess and artificially structured loess with 5% cement content, there is a good logarithmic relationship between the collapsibility coefficient and number of freeze-thaw circle under a load of 50 kPa. Also, further research is needed to study whether the original loess can be replaced by artificially structured loess mixed with cement to reflect the collapsibility of structural loess.

The traditional humidity stress field theory cannot perfectly describe the time-dependent relationship between the swelling state and humidity state when simulating the swelling process of anhydrite rock mass. Based on this theory, the swelling tests on anhydrite rock mass were designed to investigate the swelling with different initial humidities and soaking time. In addition, tensile strength tests were carried out after swelling. The testing results showed that with the increase of initial humidity, the duration time of swelling, the maximal axial swelling strain, and the maximal lateral swelling stress increased. The water absorption rate and crystallisation water rate of anhydrite increased at the end of the test, while the free water rate was close to zero. Under the same initial humidity, with the increase of soaking time, the water absorption rate exhibited a rapid increase first and then slowly grew. The crystallisation water rate gradually increased to the water absorption rate, while the free water rate decreased to close to zero. With the increase of water absorption rate, the maximum axial swelling strain, the maximum lateral swelling stress and the tensile strength increased. Therefore, this study proposed the time-dependent humidity state equations and the time-dependent swelling constitutive model according to the testing results.

In this study, uniaxial cyclic loading tests were carried out on granite specimens to study the relationship between acoustic emission (AE) characteristics and non-uniform deformation of rock materials during the cyclic loading process. The AE signals and the deformation images of the specimen surfaces were collected by using the AE system and CCD camera in the deformation and failure process, respectively. Combined with the digital speckle correlation method, the AE characteristics of specimens were investigated during the evolution process of non-uniform deformation. The research results showed that the minimum point of non-uniform deformation corresponded to the lowest point of unloading stress during each cyclic loading process. However, after the startup of the localisation band, the maximum point of non-uniform deformation lagged behind the vertex of loading stress in each cyclic loading process. There was a good correspondence between the non-uniform deformation evolution and the AE signal. During the cyclic loading process, the first turning and increasing point of non-uniform deformation is the starting point of the increase of AE signal, whereas the maximum point of non-uniform deformation is the starting point of the quiet period of the AE signal. With the increase of cyclic number, the degree of non-uniform deformation is negatively correlated with the Felicity ratio, that is, the greater the non-uniform deformation is, the greater the damage degree is, and the smaller the Felicity ratio is.

Pulsating grouting has been widely used in seepage prevention and reinforcement grouting and engineering, but the mechanism of infiltration grouting is not clear, which impairs theory development and current theory could not guide engineering practice. Based on the Bingham fluid rheological equation, the seepage equation, and the particle deposition theory, the infiltration grouting theory of Bingham fluid under pulsating pressure is deduced. Also, the effect of pulsating grouting parameters on slurry diffusion range is analyzed, and it is verified by the self-made indoor experimental device. The results show that there is an error between the calculated value based on the theory and the value measured in the test, but it can meet engineering requirements and can be used to guide project construction. The slurry diffusion range increases with the increase of grouting time and the initial porosity of the formation, and the slurry diffusion range decreases with the increase of grouting interval time and the decrease of the initial porosity of the formation. Therefore, it is necessary to adjust pulsation grouting parameters according to initial porosity of the formation to ensure the effective slurry diffusion range in grouting engineering. The research results can provide references for the study of theory and guidance for practical construction.

Uniaxial compressive tests were carried out to investigate the dilatation behaviour of phyllite samples under different loading azimuths. There were four types of samples taken from the Chengdu-Lanzhou railway. The results showed that the samples generally expanded before the peak stress reached, and the dilatation behaviour was influenced by the loading azimuth and degree of anisotropy. The vertical strain rate was greater than the horizontal one before the dilatation occurred, and vice versa after expansion. When the volumetric strain of phyllite samples converted from a positive value to a negative one, three conditions existed: pre-peak stress, post-peak stress and not-converted. Besides, the probability of the conversion was related to the participation degree, the form, and the failure mode of the original cracks during the loading process. The maximum dilatation rate appeared at the moment when the axial strain reached its maximum value, and the high azimuth angle was more sensitive to the dilatation capacity. The initiation stress of the dilatation was usually low, and the difference between the loading azimuth and lithology was large. The deformation and failure process of phyllite under loading was significantly reflected by the elastic modulus and Poisson ratio which were greatly affected by the dilatancy.

Under the influence of natural forces and human activities, earthen heritage sites in arid and semi-arid regions like Great Wall, Jiaohe Ruinsy, Beiting Ruins were hanged in the air largely by sapping at the base of the wall even causing partial collapse. In this study, rammed heritage sites with serious basal sapping were consolidated by rammed roof-propping, which conformed with basic conservation principles of cultural heritage sites protection and followed the requirement to conserve original material and technology, and also had good reinforcement effect. However, large-sized rammed roof-propping body produced big crack in 1-3 mm width from the original wall under the effect of consolidation and dehydration. Control and reduction of shrinking cracks between roof-propping body and original wall were the key to realize reliability and effectiveness of large-sized ramming repair. Based on the theory of consolidation and dehydration, this study conducted consolidation test with different density and gradation samples indoor, and collected the data of dehydration shrinkage of samples with different shapes. This study made a comparative analysis of the regulation of consolidation deformation and dehydration deformation in the condition of different densities and different clay particle gradations, and analyzed threshold value of consolidation and dehydration deformation for roof-propping body, according to traditional rammed technology and laboratory empirical formula. The empirical formula to control large-sized vertical deformation was preliminarily proposed, which can provide theoretical references for controlling shrinkage settlement of large-sized rammed roof-propping body.

Reinforced soil retaining walls are widely used in the civil engineering because of their excellent seismic performance. The study on the seismic design method of reinforced soil retaining walls is particularly important. To analyze the effect of arrangement and tensile strength of reinforcement on the yield acceleration, the equation of coefficient of yield acceleration is derived based on limit analysis theory assuming a two-wedge form of the failure mode. Compared with the values calculated by the design codes, the results obtained by the proposed method are closer to the experimental test and the numerical simulation. Meanwhile, the proposed method can reflect the real failure mode of the models. Parametric analysis shows that: the yield acceleration increases gradually with the increase of the tensile strength of the reinforcement, especially when the reinforcement is longer; the yield acceleration decreases with the increase of vertical spacing of the reinforcement; the width of the panel facing barely affect the yield acceleration; compared with the width of the panel facing, the tensile strength and the vertical spacing of the reinforcement impact significantly on the failure shape.

In order to investigate the effect of fine content (FC) on liquefaction resistance (CRR) of saturated sandy soils with different densities, three cases are categorized: 1) at a constant relative density 50%; 2) at a constant void ratio e = 0.90; 3) at a constant skeleton void ratio 1.20. A series of undrained cyclic triaxial tests were performed on sandy soils with different FC and density state ( , e and ). The test results show that an increase in FC causes a decrease in CRR of sandy soils at a constant or e. and the CRR of sandy soils at a constant will increase with the increase of FC. There is no clear correlation between , e or and CRR for saturated sandy soils with different FC. Moreover, the test data in this study reveal that the CRR of sandy soils with different FC and density decease with the increase of the . A power relationship between a decrease in CRR and an increase in indicates that the fraction of the fines contributes to the formation sustaining the loads can be used as an index to uniquely evaluate the CRR of different kinds of sandy soils. By comparing the published results of the other sandy soils, it is found that the sand grain is an important factor affecting the CRR of sandy soils, and the overall CRR of the sandy soils will increasing as grain shape changing from spherical to angular.

Membrane penetration is the most important factor influencing the measurement of volume change in triaxial consolidated-drained shear test. It has proved that the effective pressure, average particle diameter, thickness of membrane elastic modulus of membrane, contact area between membrane and soil particle and initial void ratio are the major factors influencing membrane penetration. According to the deformation model given by Kramer et al. the analytic solution of the membrane penetration considering the initial void ratio is deduced using the energy conservation law based on the basic equations from theory of plates and shells as well as the elastic mechanics. Membrane penetration volumes are deduced from isotropic consolidation tests by the method of embedding different diameters of iron rods in the triaxial samples. The differences between the analytic solution and test result are analyzed. In general, the results from the analytic solution are considerably agree well with the test data.

The principal stress axis rotation will accelerate the accumulation of pore pressure and plastic strain and influence the mechanical properties of soil. The cyclic triaxial test and cyclic torsional shear tests were carried out by using GDS-HCA test system. The influence of continuous cyclic rotation of principal stress on the accumulative plastic strain and pore pressure of saturated silty clay under consolidation were investigated. The amplitude of the dynamic shear stress, the area surrounded by the stress path of the heart, the amplitude of the cyclic stress amplitude increase with the increase of the cyclic shear stress ratio and cyclic stress ratio. The pore pressure ratio increases as vibration load cycles increasing before specimen damaged. The pore pressure dissipates rapidly after the specimen failure, and then the pores pressure ratio declines sharply. The axial cumulative plastic strain which produced by cyclic torsion shear tests is always greater than the cyclic triaxial tests. This indicates that the axial cyclic rotation of the principal stress axis will accelerate the accumulation of the axial strain of the specimen. The cumulative plastic strain increases with the increase of cyclic shear stress ratio and cyclic stress ratio. Large cyclic stress ratio results in significant cumulative plastic strain caused by the rotation of the shaft. The accumulated plastic strain of saturated silty clay under consolidation and the cyclic rotation conditions of principal stress is established basing on the Monismith power function model. The reliability of the model is analyzed and verified.

The self-developed stress relaxation-dynamic disturbance test apparatus was used to measure the axial stress, axial strain and acoustic emission of rock subjected to loading and stress relaxation, dynamic disturbance. From the experimental results, it was found that the stress of rock specimen declined and its strain increased after the dynamic disturbance. In addition, the characteristics of sandstone were more obvious than that of granite. The preliminary study suggests that one reason for this phenomenon is likely related to the irreversible damage in the rock during the stress relaxation-disturbance process. Another reason is related to residual strain induced by the dynamic disturbance. During initial compaction and elastic phase, it is found that AE hits seldom occurs, while in the peak near the peak stress, AE hits instantly increases; during stress relaxation phase, the AE hits decrease, and it may increase instantly when triggered by dynamic loading. Clearly, the acoustic emission signal is induced by the damage evolution of rock, thus the AE data may reflect that the induced rock damage is one reason for the phenomenon of stress decline and strain increase. In addition, the quasi-static cycling loading and unloading test is conducted to quantify the residual strain of rock under the different loading levels. The residual strain in sandstone specimen is much larger than that in granite specimen, which corresponds well with the obvious phenomenon of stress decline and strain increase. In addition, the residual deformation increases with the rising initial unloading deformation both in stress relaxation-disturbance testing and quasi-static cycling loading and unloading test. Also, it should be mentioned that, the damage in rock is closely associated with residual strain, thus the both the rock and residual deformation may contribute to the phenomenon of stress decline and strain increase of rock specimen during stress relaxation-dynamic disturbance test of rock.

The contour and size of the rib on the thread steel have significant effects on the anchoring strength of resin bolt in the coal mine. To analyse the effects of ribs on load transfer of thread steel bolt, theoretical analysis and numerical simulation methods were used for solving the load distribution of the bolt. By simplifying the mechanical model of the bolt as an axisymmetric model under the pull-out condition, the second-order variable coefficient differential equation has been derived for the shear displacement, in which the variable coefficient function is periodic and discontinuous. Based on MATLAB, this differential equation is solved by Fourier transforming the periodic, discontinuous and variable coefficient function into a continuous function. Thus, the shear stress distribution is obtained and then compares with that of the round steel bolt. Furthermore, a numerical simulation of the bolt has been conducted by ABAQUS to verify the correctness of theoretical solutions. Moreover, based on the results of theoretical analysis and numerical simulation, the rib stress concentration coefficient F is defined to discuss the range and degree influenced by the rib. The results show that the shear stress is a zigzag decreasing distribution along the long axis of the bolt. The rib stress concentration coefficient F is in a range of 1.875 and 2.156 in the effective bearing zone of the bolt. For pull-out force of 300 MPa, the shear stress peak value reaches 36 MPa, which indicates that the initial damage and failure zone commonly occurred near the rib in the anchoring system.

To study the effect of mechanical property of freezing-thawing interface on slope stability, we carried out a series of direct shear tests of soils and ice-soil interfaces for saturated or nearly saturated gravel soil, silt, and clay under different normal stresses. Results show that the shear stress-deformation behaviors of gravel soil and corresponding thawing-freezing interface are all elastic deformation with clear peak shear stress. Silt, clay and corresponding thawing-freezing interfaces have plastic deformation within a small range, and there is no peak shear stress. Moisture content has little effect on shear strength of gravel soil in active layer, with little decreasing of the friction angles of gravel soil and ice-gravel soil interface with the increasing of moisture content. But for silt clay and clay soil, the effect of moisture on strength shows great decreasing of the cohesive force with the increasing of moisture content. We find that slope instability occurred more likely in the fine particle soil slope. Compared to silt soil, the corresponding thawing-freezing interface has a stronger resisting shear deformation ability, and the sliding slope will be in thawing soil layer above the interface, but the opposite the case for the clay soil. At the same time, the fine-grained soil slope tends to slide before reaching its maximum thawing depth. The higher the slope gradient, the earlier the time of instability. The main reason of slope failures in permafrost regions contributes to the lower cohesive force of sliding surface resulted from the higher moisture contents in active layers and the pore water pressure can affect the slope stability, and the influence of depth of water layer need to be taken into account.

One of the major functions of buffering or backfill material is to conduct and dissipate the heat generated by the high-level radioactive waste to the host rock. Sand, graphite and crushed granite rock can improve the thermal property of bentonite with relatively high thermal conductivity. In this paper, mixtures of crushed Beishan granite and GMZ01 bentonite with different dry densities and water contents were compacted, and Hot Disk TPS2500s Thermal Constants Analyzer was used to measure thermal conductivity of the mixtures. The experimental results were analyzed to observe the effects of granite content, dry density, degree of saturation on the thermal conductivity. Various theoretical models were adopted to predict the thermal conductivity of bentonite/crushed Beishan granite mixtures. It is found that the thermal conductivity of GMZ01 bentonite can be effectively improved by the addition of crushed Beishan granite. Linear correlations are observed between the thermal conductivity of bentonite/crushed Beishan granite mixtures and degree of saturation, and volumetric fraction of air, respectively. Maxwell’s equation provides the most satisfactory prediction for the thermal conductivity of bentonite/crushed Beishan granite mixtures.

Dynamic deformations of unsaturated silt have been tested using a suction controllable dynamic triaxial testing apparatus. The skeleton curve, dynamic elastic modulus, damping ratio were obtained at different net confining pressures and suction paths. The effect of drying and wetting cycle on dynamic deformation characteristics of unsaturated silt was studied. Test results show that at the same net confining pressure and suction, the skeleton curve and dynamic elastic modulus of silty specimens subjected to drying and then wetting are higher than that of the specimens subjected to drying path only. but the damping ratio of specimens under drying and then wetting is lower under drying path only. With increasing the maximum suction experienced, the skeleton curve and dynamic elastic modulus of unsaturated silt increase, and oppositely the damping ratio decreases. The test results can be explained by the average skeleton stress and the effect of surface tension of meniscus water, which are together used to predict the maximum shear modulus of unsaturated soil.

Under the punching shear failure mode, the experiments were conducted on the karst cave roof to study the bearing capacity under different roof thicknesses and load eccentricities in the laboratory. The failure mode of karst cave under eccentric loading was assumed to be axisymmetric according to the experimental results. Based on the upper bound limit analysis method and Griffith strength criterion, a new method was proposed for calculating the ultimate bearing capacity of karst cave roof both under axial symmetrical and eccentric loading. Besides, a method was given for estimating the range of the punching failure area. The experimental results show that at the same eccentric distance, the ultimate bearing capacity of the roof increases linearly with the increase of the roof thickness before reaching the ultimate bearing capacity of the bedrock. When the roof thickness is constant, the ultimate bearing capacity increases nonlinearly with the increase of eccentricity. In addition, the eccentricity e tends to be gentle and reaches the ultimate bearing capacity of the bedrock at the outside the range of punching shear failure. The theoretical calculation results are in good agreement with the experimental results.

The original natural stress balance of the rock structure is destroyed by human engineering activities of excavation and construction, and the geological environment safety is deteriorated further by the existence of weak structural plane. Therefore, it is necessary to analyze the stress state and strength characteristics of rock structure under engineering disturbance to effectively control the occurrence of geological disasters such as collapse and landslide. In this paper, the disturbance process of the rock structure was quantified in the form of stress. The propagation of the stress wave in weak structure plane was analyzed and its attenuation characteristics were quantified. Also, the quantification expression of stress was given and the stress analysis model was established. Based on this, the criterion of strength analysis of rock structure under stress disturbance was deduced by the Coulomb-Navier criterion. At the same time, the damage effect of stress disturbance on the strength of rock structure was realized and the reduction coefficient was used to quantitatively describe it. The realization of this process provides a theoretical basis for effective prevention and control of geological disasters caused by engineering disturbance, and a new idea to analyze the induced mechanism of geological disasters under engineering disturbance is given.

Series of model tests are performed in calcareous sand retrieved from the Nansha Islands to investigate the axial tension response of monopile. The effects of the relative density of the ground soil and the embedment length of the monopile on the tension response of monopile are studied in detail. The results show that, the pull-out capacity of the model monopile is improved, as expected, by increasing the relative density of the ground soil and the embedment length of the model monopile. Reducing the relative density or embedment length not only reduces its pull-out capacity, but also increases its displacement under a same tension load as on a pile with a larger embedded depth or in a denser ground. As the depth increases, the axial force developed in the model monopile decreases gradually from the maximum value at the top of monopile to zero at the monopile tip. The increase of relative density affects both the magnitude and the distribution of the ultimate frictional resistance between the model monopile and around soil. 0.1 times the diameter of the monopile can be regarded as the critical displacement for the failure of the tension monopile.

Adopting the hypotheses that the variation of compressibility is proportional to permeability, and based on - and - relationships, analytical solutions are derived for one-dimensional nonlinear consolidation of saturated soft layered soils. The average degrees of consolidation of each layer and whole layered soils are defined in terms of settlement and effective stress respectively. A relevant computational program is developed by Fortran in this paper, and the solutions are verified by comparing with the existing analytical solutions for the one-dimensional nonlinear consolidation of double-layered soils. It is shown that in the process of the nonlinear consolidation of layered soils, the influence of the permeability is complex. The influence of permeability on the excess pore water pressure in the upper and the lower layers is different. The larger compressibility is, the greater the excess pore water pressure is, and the slower the rate of dissipation of the excess pore water pressure and greater the value of loading generate slow dissipation of the excess pore water pressure, and the slow consolidation process. The rate of dissipation of the excess pore water pressure depends not only on the layers thickness, but also the relative value of permeability of each layer soil.

This study aims to investigate the energy and deformation characteristics of rock joints under multi-stage shear loading-creep-unloading conditions. The experiments were conducted on jointed marble specimens using a GCTS (RDS?200) servo-controlled testing machine. The results showed that the area of the hysteresis loop had linear or exponential relationships with cycling numbers, when the normal stress was lower than 6.5 MPa or higher than 7.8 MPa, respectively. The total deformation energy and the elastic deformation energy were positively related to the normal stress and exponentially related to the cyclic number, respectively. However, the plastic deformation energy was positively correlated with cycle number and normal load. At the ends of different levels of shear stress loading, the outer envelope of the shear displacement curve had the same trend as the direct shear displacement-shear stress curve. It could be divided into three stages: accelerated growth, linearly increasing segment and linearly decreasing segment. The accumulated plastic displacement increased with increasing loading cycles, but the increasing rates decreased gradually. Each shear loading or shear unloading curve can be divided into two stages according to the shear sliding point. Before the shear failure of rock joint, the normal displacement-shear curve became lower than the later ones under shear loading and unloading conditions. The accumulated normal displacement changed from increasing to decreasing at the ends of cyclic shear loading and creeping at each stress level.

The design and construction of the diversion tunnel are very difficult in the soft rock strata of the Northern Xinjiang, which is caused by the complexity of geographical, climatic conditions and engineering geology. The large deformation and even collapse hazards of surrounding rock are very easily to be encountered, due to its bad self-stability, strong permeability and water-softening characteristics. Hence, the uniaxial, triaxial compression tests and uniaxial creep tests were conducted to further study the physical and mechanical properties, water-softening characteristics and energy damage evolution mechanism of the Jurassic and Cretaceous argillaceous sandstones of Northern Xinjiang. Compared with the results of these two kinds of soft rocks both with rich clay minerals, the particle size distribution of the Cretaceous argillaceous sandstone was more uniform, but its cementation degree was lower. As a result, the strength, stability and the wave velocities of strata in the Cretaceous argillaceous sandstone were lower than those in Jurassic argillaceous sandstone. Under the condition of low confining pressure, two kinds of rock deformation were mainly circumferential deformation and volume expansion. With the increase of confining pressure, the failure mode changed from volume expansion to volume compression type. High confining pressure loading can cause internal damage of rock structure, resulting in the reduction of compressive strength. When these two kinds of rocks were saturated, the ductility and strain softening characteristics were significantly enhanced. The water-softening characteristic of the Cretaceous argillaceous sandstone was much more obvious. Cretaceous argillaceous sandstone had more significant creep characteristics, and their long-term strengths were both close to their damage stress values in uniaxial compression tests. The energy damage evolution processes of two kinds of argillaceous sandstones both showed the S-shaped evolution law. The energy-hardening characteristic of Jurassic argillaceous sandstone was more significant, but the Cretaceous argillaceous sandstone was earlier to enter energy-hardening and energy-softening stages.

To research the effect of seepage on mesostructural change of soil-rock mixtures, a laboratory seepage test was applied on soil-rock mixtures with the ratio of 7:3. Nuclear magnetic resonance (NMR) analysis system was applied to monitor the mesostructure change of soil-rock mixtures under different hydraulic gradients and different time periods, such as pore distribution, movable fluid porosity, etc. According to NMR results, it was found that: 1) Seepage pressure caused change of soil-rock mixture properties such as pore distribution, pore size and pore connectivity, which can damage structural characteristics of soil-rock mixtures. 2) With the increase of hydraulic gradient and time, porosity, mobile fluid porosity and NMR permeability all increase, and the NMR permeability growth rate is increased. Besides, mobile fluid porosity has a more significant contribution to permeability than irreducible porosity. 3) Under low hydraulic gradient, the coefficients of Kua and Kca have small change, which reveals low erosion scales and low degree of seepage failure. Under high hydraulic gradient, the coefficients of Kua and Kca have significant change and erosion scales become higher. The soil-rock mixtures form seepage channel and seepage failure.

Consolidated and drained triaxial shear tests were conducted on Yanji swelling rock to investigate the effects of wetting-drying, freezing-thawing and wetting-drying-freezing-thawing cycles on the stress-strain behaviour, volumetric strain and shear strength of Yanji swelling rock samples. The test results indicate that the stress-strain behaviour of samples before cyclic treatments appears to be strain-hardening, while the samples after cyclic treatments show strain-softening behaviour and more evident shear dilation. Additionally, the effects induced by cyclic treatments are more pronounced with increasing number of cycles and decreasing confining pressure. As the number of cycles increases, the cohesion of samples significantly decrease but the internal friction angle slightly increases. It can also be seen that the samples subjected to wetting-drying-freezing-thawing cycles suffer greater alterations in mechanical properties compared with those subject to separate wetting-drying and freezing-thawing cycles. Subsequently, a stress-strain formula considering the effect of wetting-drying-freezing-thawing cycles and confining pressure is presented based on Konder hyperbolic function, which can describe both strain-hardening and strain-softening behaviours. A comparison between the predicted and measured values verifies that this model can well predict aforementioned stress-strain behaviours.

Uniaxial and triaxial compression tests have been carried out on pure salt rock to study the relationship between damage variable and fractal dimension of salt rock in the deformation and failure process. The damage variable and fractal dimension in the deformation and failure process of salt rock have been studied by using the damage model based on acoustic emission ringing count and fractal dimension calculation based on the spatial distribution of acoustic emission event. The results showed that the fractal dimension of salt rock gradually reduced and the damage variable slowly increased in the deformation and failure process of salt rock. Moreover, each stage of the declined fractal dimension were corresponding to each stage of the increased damage variable. Before the failure of salt rock, the fractal dimension of salt rock was not significantly reduced and was different under different stress states. With the increase of confining pressure, the fractal dimension of salt rock gradually reduced. Under stress states of uniaxial compression and triaxial compression, the fractal dimension of specimen below to 2.42, 2.31 and 2.20 respectively indicated that the internal damage of specimen gathered together to form a macroscopic fracture surface, leading to the specimen deformation and failure. The confining pressure had obvious inhibitory effect on acoustic emission activities. With the increase of confining pressure, there were less acoustic emission activities in the deformation and failure process of salt rock. When the stress state of rock changed from the uniaxial compression process to triaxial compression process, it was found that in the initial loading period, the percentage of stress gradually increased when the fractal dimension of salt rock decreased rapidly. However, in the late loading period, the percentage of stress gradually increased when the fractal dimension of salt rock reduced slightly. In addition, the damage variable was small and energy releasing was less at the early loading time of the deformation and failure process of salt rock. While the damage variable fast increased and energy quickly released before the failure of salt rock.

The pile anchors are used widely as supporting structure. But in excavation, the stability of foundation with the prestressed anchors and displacement hasn't been solved yet. Additional stress caused by prestressed anchors influences on the stability and displacement of foundation, the expression between prestress and the stability of the pile anchor supporting structure, and the equation of horizontal displacement and structure stability are formulated. In a typical foundation pit, comparisons of the calculation results by general design software show that: 1) The prestress is considered as additional stress to calculate the overall stability safety factor of foundation pit, and the safety factor increases with increasing prestess; there exists a non-linear relationship between the safety factor and prestess; 2) Similarly, the displacement of the pile anchor supporting structure can be calculated by the forementioned way; and horizontal displacement of retaining structure decreases as prestress increases, which presents a non-linear relationship; 3) The expression of relationship between the stability safety coefficient of supporting structure and the horizontal displacement of retaining structure is given, which is more suitable for theory and engineering practice; 4) Compared with the calculation method for stability and displacement of the foundation pit considering prestress, the existing design of the pile anchor supporting structure is conservative and still needs to be validated and corrected according to a large number of engineering practices. 5) We first study the relationship of stability of pile anchor supporting structure and horizontal displacement considering additional stress, which can provide theoretical foundation for dynamic stability evaluation of foundation pit in the process of excavation.

The settlement of foundation in stable goaf site is analyzed to evaluated its suitability. One calculation method of load influence depth for goaf ground is proposed. The residual deformation of goaf ground is predicted by the probability integral method, and the settlement calculation method of building ground on goaf is put forward considering the activated deformation, the residual deformation and the additional deformation. Research results show that: 1) The less the coefficient of standard (0.10 (self-weight stress of ground), 0.08 , 0.07 , 0.05 ) under the same building load, the greater the influence depth. The larger the building load under the same coefficient, the influence depth is increased non-linearly. 2) The standard of (additional stress of ground) = 0.10 should be used to determine the influence depth for normal goaf ground, and the standard of 0.05 for complicated goaf ground. 3) The influence depth is determined by the conventional standard ( 0.20 ), and the 1.4 and 1.8 can be used as goaf building design for the normal goaf and complicated goaf. 4) The residual deformation of goaf ground is very small and can be negligible under the maximum building load without the activated deformation, and the settlement deformation of building ground is mainly the additional compression deformation. 5) Numerical results show that the ground settlement at the edge of goaf is large, and its uneven settlement is obvious, so the edge of goaf is not suitable as construction sites; however, the ground settlement at the central of goaf is small, and there is no obvious uneven settlement, so the central of goaf is suitable as construction sites.

Deformation of filled embankment and its stability are common engineering problems of the western mountains area construction. A typical slope of one expressway in Chongqing slides along the weak stratum on the bedrock after stacking fill, under the condition of continuous heavy rain. To study the failure mechanism of the landslide, physical simulation is adopted to study the rainfall influence on slope deformation. We also analyze pore water pressure change with the rainfall time and its relationship with the deformation and failure. The results show that the landslide deformation and failure is due to large amount of stack at trailing edge, changing the slope stress condition greatly. Secondly, the construction changes the original hydrological environment, and continuous heavy rains cause a lot of rain infiltration into the slope. Pore water pressure in the process of the landslide plays a key role. Embankment has a mass of debris and argillaceous, which can be carried to the slide zone with rainwater. And argillaceous of slide is the same. These substances can block the dissipate of groundwater. This phenomenon is the accumulation of slope deformation and pore water pressure. Deformation suddenly increase and pore water pressure decrease. The landslide can divide four phases: rainfall infiltration, slide with full water softening, trailing edge cracks, crack through whole sliding. The final landslide deformation failure mode is creeping-cracking.

The grout migration height has a remarkable influence on the calculation of bearing capacity for post-grouting pile. Based on the time-dependent behaviors of power-law cement grout, a theoretical expression to calculate upward grout migration along the pile side was proposed with consideration of time-dependent behavior of viscosity. The methods to determine the parameters and to iteratively determine the grout migration height in the layered soils were presented, respectively. Moreover, based on post-grouting project of the connecting engineering of Taizhou Bay Bridge in Zhejiang Province, the reinforcement effect of post-grouting piles was analyzed by means of electromagnetic wave CT. The results show that the predicted results of grout migration height on the basis of fitting value of pressure loss along the grouting pipeline and time-dependent behaviors of viscosity are consistent with measured results, which verifies the rationality of proposed expression for grout migration height. However, an overestimated bearing capacity of post-grouting piles may be obtained when ignoring the influence of time-dependent behaviors of viscosity, which has an unfavorable influence on pile design. Additionally, the electromagnetic wave CT can detect the distribution pattern of the pile, injected grout and soil, and can also deduce the diffusion range of cement grout at pile tip, as well as the grout migration height along the pile shaft, which can be applied to assess the grouting effect of grouted pile. The research results can provide reference and guidance for design and effect detection of post-grouting piles.

Effect of size on crushing strength of rockfill grains is studied using the particle flow code. Firstly, a discrete model of rockfill grains is developed using secondary development method with FISH language, in which particle shape and breakage behavior of rockfill grains are replicated reasonably. Then an equivalent simulation method is proposed to investigate the effect of size on crushing strength of rockfill grains in various particle sizes. A negative power formula is presented to describe the relationship between crushing strength of rockfill grains and its particle sizes. The meso bond strengths of contacts inside an aggregate model of rockfill grain are dependent on the size of the aggregate itself. Then, one dimensional compression tests of rockfill grains in lab are replicated based on the proposed numerical method to verify its accuracy and validity. At the end, influence of shape of rockfill grains on distribution of crushing strength is studied. Several basic conclusions are obtained: 1) Size effect on crushing strength of rockfill grains due to microcracks can be simu-lated equivalently by the way that meso strength of contact in the numerical model of rockfill grains decreases while the size of rockfill grains increases; 2) Crushing mechanical of rockfill grains is influenced by the particle shape, and square grains are usually crushed in compression-shear mode, while irregular and round grains fail in tension-shear or splitting mode. As a result, crushing strength of square grain is usually much higher than that of irregular and round grain; 3) When fail in tension-shear or splitting mode, dispersion of crushing strength of rockfill grains is dependent on shape of rockfill grains. The regular particle shape presents higher Weibull modulus, indicating smaller divergence for the crushing strengths. The breakage behavior of rockfill grains with different sizes under load pro-vides a reasonable method to predict the evolution of particle size distribution of rockfill assembly.

The anisotropy of horizontal permeability coefficient causes an elliptical contour of the water level drop when pumping, which further results in an elliptical land subsidence funnel. The phenomenon of this elliptical land subsidence funnel exists widely. For homogeneous isotropic aquifers, circlular land subsidence contours are round, and subsidence and distance coincides with the rules of linear s- relation. The relationship of linear s- is suitable for homogeneous anisotropic aquifers too. While land subsidence contours are elliptical for homogeneous anisotropic aquifers. In equation of , and are coefficients. For each radial line of subsidence contours, the relation between coefficients , and angle θ of radial line is founded applying groundwater hydraulics. The coefficients , are in proportion to square of or square of . The formula is proved by monitoring data from 6 regional land subsidence located in China, American and Indian. These monitoring data have great agreement with the new formula of , and . One correlation coefficient between , and is 0.871 9, the other 11 correlation coefficient are all greater than 0.9. The character of elliptical land subsidence due to horizontal anisotropic permeability is represented. The formula of , and has simple form. So it is easy to apply in engineering. The formula can be used to predict the vertical displacement for land subsidence.

Study on searching methods of slip surface plays a crucial role in slope stability analysis to assess the safety factor of slopes. The potential failure surface under ultimate stress state can be found by limit equilibrium method (LEM) and strength reduction method (SRM). The objective of this paper is to present a new slip surface searching method, which considers the distribution of local safety factor and displacement under current stress state. The statistical concept, K-means clustering, is introduced to distinguish the points with similar characters in slope into potential failure set and stable set. Then the boundary of the potential failure set is regarded as the potential slip surface under current stress state and the safety factor of potential slip surface is calculated using vector sum method (VSM). Afterward, three examples were calculated using the presented method to compare with results from LEM and SRM. Results show that 1) Slope stability evaluation by clustering analysis has been proved to be reliable and effective; 2) If the slope is near the limit state, the potential surface obtained from the proposed method is consistent with the slip surfaces obtained from LEM and SRM. If the slope is stable, the potential slip surface under current stress state is deeper and larger but is with higher safety factor. If there is a weak layer in the slope, the potential slip surface is steeper, and the safety factor calculated from VSM is lower than that calculated from LEM and SRM.

Geocell geosynthetics can effectively reduce the deformation of embankments on soft subgrade and enhance its stability, but there are few researches on critical height of geocell-supported embankments. In this study, the limit equilibrium method was employed, and circular sliding failure mode presented in the foundation under the embankment load was assumed firstly. Geocell and its filled soil were regarded as composite material considering its vertical stress dispersion effects and lateral confinement effects. An analytical model about critical height of the embankments was then proposed and its results were compared with that of the finite difference model which was calculated using FLAC. Finally, the effects of geocell height, angle of stress dispersion and friction coefficient between geocell layer and foundation on the critical height of embankments were discussed based on the analytical model. It turned out that the results between theoretical analysis and numerical calculation were well coincident with each other. The critical height of geocell-reinforced embankments was obviously greater than the critical height of unreinforced ones. Increasing the three influencing factors can improve its critical height, and strengthening the lateral confinement of geocell layer was more in favor of the stability of embankments than improving the geocell height and angle of stress dispersion.

To effectively tackle system reliability problems of rock slopes involving multiple correlated potential failure modes at small probability levels, this paper aims to propose a subset simulation-based approach for system reliability analysis of rock slopes. The expressions for system failure probability calculation of typical slope systems are derived. To account for the correlations among multiple failure modes, the “max” and “min” functions are utilized to construct the system performance functions. A benchmark rock slope with two sliding blocks and the left abutment slope of Jinping I slope with multiple correlated failure modes are investigated to demonstrate the effectiveness of the proposed approach. The results indicate that the proposed approach is much more efficient than the Monte-Carlo simulation (MCS) and more accurate than the first order approximation, N-dimensional equivalent method and Ditlevsen’s bounds method when solving the system reliability problems of rock slopes with small probabilities. In summary, it provides an effective means for tackling system reliability problems of complex rock slopes at small probability levels. In addition, the correlations among different failure modes can be effectively quantified with the aid of the “max” and “min” functions, which greatly facilitates the system reliability analysis of rock slopes.

The fracture of the rock bridge is a discontinuous deformation phenomenon. Strength reduction method, although it is the mainstream approach for progressive failure process simulation, it can not describe the discontinuous deformation phenomenon. The connectivity rate reduction method and the stiffness reduction method are proposed to simulate the progressive failure process of the rock block bounded by the coplanar non-persistent joints, and a block stability analysis method considering the progressive failure process is established. Firstly, the Goodman element is introduced to describe the rock bridge part and the fracture part of the coplanar non-persistent joint. The stress of the rock bridge element and the fracture element in the slip surface is solved by the equation of static equilibrium. Secondly, Griffith criterion is used to judge the failure for rock bridge element, and the connectivity rate reduction method is used to describe its rupture. The MC criterion is used the to judge the failure for fracture element, and the stiffness reduction method is used to describe its yield. By cyclic iteration, rupture process of the rock bridge element and the stress redistribution process of the fracture element to realize the simulation of the progressive failure process of the whole slip surface. Then, the limit state of the slip surface is redefined considering the progressive failure process, and the slip surface is pushed to the limit state by the weight overload method. Based on the theoretical framework of the limit state design, the safety factor of the block stability is calculated. The results of the engineering examples show that the simulation results of the progressive failure process are consistent with the field survey results. The simulation of the progressive failure process is helpful to the analysis of the deformation mechanism of the rock slope from the qualitative analysis stage to the quantitative analysis stage.

With the development of the construction technique of pile sleeves driven by high frequency vibratory hammers, the cast-in-place piles have been widely used in construction engineering. However, the studies on the penetration speed of sleeves for cast-in-place piles driven by high frequency vibratory hammers are still not complete. Assuming rigid body for the sleeve, the soils around the sleeve were divided into several concentric circular cylinders. Considering the soil plugging effect during vibratory sleeve driving, the shear between the soil elements outside the sleeve and the vertical stress at the sleeve bottom were calculated by using the Gudehus-Bauer hypoplasticity constitutive model. The penetration speed was obtained by modelling of the high-frequency vibratory driving of the cast-in-place pile sleeve into sand. To validate the calculation model, the penetration speed obtained by the calculation model was compared with those by the experiment and the finite element simulation. The influence of the void ratio of foundation soil, the vibration frequency and sleeve diameter on the penetration speed of sleeve is analyzed through parametric analysis. The calculation model provides a reliable way for practical engineering to quickly and accurately predict the penetration speed of sleeve.

According to the bearing capacity of bridge pile in steep slope, a finite bar element method of calculating internal force and displacement of pile is presented to consider the effect of pile-soil nonlinear interaction. Firstly, based on the result of bar element division, equivalent nodal load vector is obtained according to the distribution of lateral friction force and residual sliding force of slope. Secondly, with the introduction of p-y curve, nonlinear analysis of soil resistance is carried out using line elastic foundation reaction method. Then element stiffness matrix correction method is employed after cooperating with the calculating method of P-? effect (P is the axial load of pile top, and ? is the horizontal displacement of pile top). A finite bar element method using nonlinear analysis of pile internal force and displacement is proposed and relevant MATLAB program is edited. Finally, the calculated results are compared with measured values and theoretical values of other papers for an engineering example. The results show that method of considering pile-soil nonlinear interaction in this paper is reasonable and the influence of pile P-? effect on pile internal force and displacement is so large that cannot be ignored in the actual engineering design.

Based on the two-dimensional particle flow software (PFC2D), this paper studied the failure modes and dynamic response laws of rock slope with non-persistent joints by the combination of different dip angles of rock bridge and joint spacing under earthquake. The results showed that the bedding non-persistent jointed rock slope with single potential sliding surface present the sliding-block toppling mixed failure under the action of seismic dynamics. While the bedding non-persistent jointed rock slope with multi-potential sliding surfaces mainly present the block toppling failure. The dynamic stability of the slope was mainly controlled by the potential sliding surface composed of non-persistent joints and alternate connections of rock. Under the action of seismic dynamics, the wing crack at the rock section closest to the foot of the slope was first generated, resulting in the released tensile stress. Successively, each joint started to crack and expand, which eventually led to the step-like instability. Crack propagation was controlled by bedding non-persistent joints. Cracks are dominated by tensile cracks, and the number of cracks was synchronous with the acceleration of the input seismic waves. The existence of the joint surface had a significant impact on the dynamic response of the slope. The peak velocity and displacement along the slope surface and the horizontal direction increased with the increase of the inclination angle of the rock bridge and the decrease of the joint spacing. Meanwhile, the effects of joint spacing and rock bridge inclination on the PGA amplification factor were mainly on the slope surface and shoulder. Along the vertical direction, the peak displacement decreased with the inclination of the rock bridge and the joint spacing, and the curve of the PGA amplification factor exhibited U-shaped distribution with the elevation change.

The ?800 mm model EPB shield machine was used to study the deformation and failure model of earth pressure balance (EPB) shield tunnel in sandy cobble ground. Meanwhile, three dimensional discrete element method (DEM) simulations were conducted to assess the face stability and the influence of buried depth, which couldn’t be observed in laboratory test. Results show that, after tunnel losing stability, the ground settlement surface is “round funnel” shaped with a gradual contraction from top to bottom in sandy cobble ground. The influenced zone is smaller than that of sand. The dynamic soil-cutting process greatly destroys the initial soil fabric, and the face stability is weakened, thus the limit support pressure increases. The limit support pressure increases linearly as buried depth increases, while the ratio of limit support pressure to initial support pressure decreases with increasing buried depth. The face failure mechanism can be divided into three modes according to buried depth. The whole dynamic construction process considered in this paper is close to real constructions, and can serve as guideline for guaranteeing EPB shield tunnel stability in sandy cobble ground.

The conventional analysis methods for face stability of shield tunnels always assume that the soil is homogeneous, isotropic medium, and ignore its heterogeneity. Therefore, the influence of spatial variability of shear strength on face stability in sand is investigated in this paper. Based on random field theory, three dimensional random fields of friction angle are generated using the covariance matrix decomposition method. The performance of the coefficient of variation and the auto-correlation distance of friction angle is analyzed to explore the influence of that on the failure mechanism and the critical support pressure. Meantime, the selection of the characteristics value of critical support stress is discussed by probabilistic analysis approach. Results show that the spatial variability of friction angle does have significant influence on the stability of tunnel face. The critical support stress scatters as the coefficient of variation of friction angle increases. The failure mechanism is closely related to the auto-correlation distance. When the auto-correlation distance is close to the tunnel diameter, the local failure may happen. The concept of characteristics value of critical support stress is proposed and defined preliminary based on the probability of failure.

The hydraulic fracture of the gravity dam was analysed by considering the advantages of the numerical manifold method in the non-continuum field and the basic principle of fracture mechanics. Besides, this study realised the whole process of dam crack initiation, propagation and progressive failure. With the respective advantages of the Mohr-Coulomb failure criterion with tensile strength and the stress intensity factor discriminant criterion, the fracture and its propagating direction were determined according to different conditions, and no pre-notched model was required. One example under two different conditions was selected to analyse the hydraulic fracture of the gravity dam with or without considering the inner water pressure on crack. The results showed that for the hydraulic fracture of gravity dam without considering inner water pressure on crack, the crack of dam site propagated toward the direction of downstream and depth, and the crack propagation at the upstream slope belonged to the compression-shear failure. However, when considering the inner water pressure on crack, the crack of the dam site was extended in the direction of depth, and the crack propagation of slope point belonged to the tension-shear failure. Furthermore, the required time steps for the dam failure were reduced, resulting in the decrease of the safety factor of the dam. This study has deepened the understanding of hydraulic fracture of the gravity dam and has great practical application value.

In the saturated soil-pile foundation-superstructure system, different controlling equations and temporal integrator methods of pile foundation, superstructure and saturated soil lead to inconvenient calculation by using the finite element method. An interactive computational method for the saturated soil-structure interaction problem is developed using on the Client-Server technique. In this method, the dynamic responses of the saturated soil subsystem and pile foundation-superstructure subsystem are calculated in two subroutines respectively. The forces and displacements are transferred by common nodes of the two subsystems. The completed explicit temporal integrator method is introduced to determine the u-p relationship of the saturated soil subsystem. It significantly improves the computational efficiency. In numerical example, the proposed method is compared with the Newmark method. And the proposed method is demonstrated as an effective tool to solve the seismic responses of the saturated soil site-pile foundation-superstructure system.

In this paper, the large apparatus to measure static lateral pressure coefficient was introduced. The value of dry sand was tested by using the apparatus. The dry-sand test result was used to compare with the test of the water-bag type oedometer. The friction of the sidewall produced during the experiment was amended, and the deviation caused by lateral expansion were also analyzed. The accuracy and effectiveness of the apparatus was validated. Coarse granular soil was tested by this apparatus. And the change of under various stress conditions was tested, which verified the applicability of the apparatus to coarse granular soil. It is convenient in operation, stable in performance, and precise in accuracy. It can be used to test the static lateral pressure coefficient of large practical size coarse grained soil, which is hard to get with the traditional instrument.

The experiment of hydro-mechanical coupling rheological damage is an important means to reveal the catastrophic mechanism of soft rock. However, the limitations of this experiment are in the lack of large-scale experimental apparatus that can simulate the actual engineering environmental conditions and its multi-scale measurement technology for accurately tracking the entire process. Hence, a pressure chamber was designed by applying high-strength transparent materials, according to the principles of mechanical control and intelligent optimisation. Combining with servo control, non-contact 3D measurement and synergetic integration technology, a multi-scale mechanical testing system was developed for studying the hydro-mechanical coupling rheological damage of soft rock. This system mainly includes the full transparent chamber with high dynamic/static water pressure, the multi-phase synchronous-loading triaxial system, a real-time measurement system embedded the fiber optic sensing technology under high confining pressure, a multi-scale three-dimensional imaging system for the observation of internal and external rheological damage and a synchronous and rapid system for processing the spatial measurement data. Thus, a prototype machine was successfully developed using the integration of hardware and software. This system can simulate the whole process of hydro-mechanical coupling soften damage of soft rock under the conditions of high pressure dynamic/static water and other working fluids. Besides, it also can carry out a variety of soft rock rheological damage tests with different solutions, pressures and rheological stages. Thus, both high-precision non-destructive measurement and multi-scale observation were achieved in the same period. The stress-strain curves, internal damage evolution, surface strain changes and surface damage evolution of soft rock were obtained through application. Internal and external damage evolution processes were reconstructed, and their reconstructed images were further compared with the changes of actual rock samples. The results indicate that the reliability of the testing system was verified. This study provides experimental technical support for the capture of the whole process and in-depth study of soft rock disaster.

Soil-rock mixture landslides present obvious features such as wide distribution, high frequency of occurrence and poor regularity, which have become one of the most common geological disaster types in the western mountainous area and its key construction projects. The complex internal soil-rock structure is the critical factor leading to the difficulty of preventing and controlling the landslides. Hence, a new method by combining the geophysical prospecting and trenching was proposed to acquire the nearly realistic geological structure of soil-rock mixture landslides. The prospecting geological structure was conducted by high-resolution geophysical exploration techniques and supplemented using digital image processing of trench section. Thus, the precise geological structure of soil-rock mixture deposit was obtained, and the integration of macroscopic and mesoscopic geological structure was preliminarily achieved by the method. The proposed combination method was applied to investigate the precise detection of geological structure within the soil-rock mixture landslide in Baidian township of Nanyue district in Hunan province, and then the nearly realistic geological structure was obtained. This study provides a basis for revealing the structural control mechanism of the formation and evolution of landslides and makes the prediction and prevention of landslides more reasonably and scientifically.

Shenhua carbon capture and storage (CCS) project is China's first complete process coal-based CO2 capture and multi-layer injection CO2 storage demonstration project in deep saline aquifer with low porosity and low permeability. With Shenhua CCS project as an example, the time-lapse vertical seismic profile (VSP) technology is presented and monitoring results of CO2 storage is obtained. By means of 3 VSP observations before and after gas injection, high quality time-lapse VSP data are obtained. High-quality time-lapse VSP images are achieved by developing consistency processing, vector wave-field separation and multi-component imaging. The seismic response characteristics of VSP before and after gas injection are analyzed by depth domain calibration and multiple attribute interpretation. The range of CO2 underground migration is predicted to reach the expected monitoring target of the CCS project. This case study shows that the VSP monitoring technology is an effective method to monitor carbon dioxide geological storage and migration.