Because of the complexity of unsaturated soil, traditional three-phase model for unsaturated soil is oversimplified, which is unfit for interphase analysis and determination of stresses in soil. Considering a special structure in unsaturated soil , in this work, soil water system is divided into six phases and its bearing structure, named generalized soil structure, is defined. Then the differences between saturated and unsaturated soils are concluded: the bearing structures and pore liquids are different. Based on the similarity of bearing structures, a set of variables to depict the structural properties of soils is defined as generalized structural properties to describe the properties of the bearing structures of different soils. The rationality of some variables is analyzed by explaining some practical phenomena, e.g. the essence of collapse phenomenon is the weakening of the bearing structure of soil. Two representative interphase interactions are discussed and the physical significance of neutral stress is revealed, and the suction stress is redefined. Finally, it proves that the total skeleton stress in the grain is the “effective stress” for unsaturated soil.

The interlocking effect of calcareous soil due to irregular particle shapes increases the shear strength markedly under shearing. To investigate the interlocking mechanism of calcareous soil, a series of triaxial tests was carried out for different particle sizes under consolidated undrained and consolidated drained conditions. Particle shape analysis was also conducted to reveal the formation mechanism and manifestation of occlusal force of calcareous soil. The test results show that: 1) irregular shape is the prerequisite for the occlusion of calcareous soil particles; 2) the difference in the content of particles for different shapes in calcareous soil with different particle sizes results in different values of occlusal force; 3)the occlusal force of calcareous soil is obviously affected by the stress level. Under low confining pressure, the occlusal action causes dilatancy and increases the internal friction angle. Conversely, under high confining pressure, the occlusal action causes particle breakage, raises cohesion, but reduces the internal friction angle. The occlusion of calcareous soil has obvious enhancement on the strength. Therefore, the occlusion of calcareous soil should be considered in engineering design work of coral reef.

Based on model experiment and UDEC simulation combined analysis method, the deformation characteristics and damage mechanism in the process of load-failure of a new type foamed lightweight soil subgrade were studied. The variation of strain, stress distribution and the law of deformation in the process were obtained. The results show that in the process of load-failure of the lightweight soil subgrade, the inner old roadbed is first to deform. When the load reached 175 kPa, plastic deformation firstly occurs in the middle of the subgrade at the left side. The junction between lightweight soil subgrade and old subgrade is easily affected by the interaction between old subgrade settlement deformation and new subgrade failure deformation, resulting in bending shear failure crack, and finally causing damage. The foamed lightweight soil subgrade load-failure mode is from inside to outside with elastic deformation to plastic yield, finally to shear failure (local damage to overall instability). In the longitudinal direction, the stress transfer of the old roadbed is smaller than that of the lightweight soil roadbed. Within a certain load range (less than 100 kPa), the deformation of the subgrade is inversely proportional to the depth of the subgrade.

The penetration of the bucket foundation is a vital construction procedure. Seepage field is generated in the soil under the suction pressure during the penetration. The seepage has an influence on the friction along the skirt wall and on the resistance of the skirt tip, which leads to the difficulty in predicting penetration resistance. In order to solve this problem, firstly, the methods of experiment and numerical simulation were applied to analyze the seepage characteristics of the bucket foundation during the penetration; moreover the distribution of the excess pore water pressure along the bulkhead and skirt tip was revealed. Thereafter, the analytical results were applied to derive the penetration resistance, and the derived theoretical formulae were verified. The results show that during the penetration of the bucket foundation, the excess pore water pressure of the soil changes linearly along the depth of the skirt, but becomes nonlinearly near the skirt tip. The effect of seepage flow on the penetration resistance is different for different penetration depths; the reduced resistance caused by seepage accounts is for a greater proportion of the penetration resistance with increasing penetration depth. The suction pressure of the test model and practical engineering calculated by the theoretical formulae are in good agreement with the measured values.

The analytical solutions of layered pavement system subjected to temperature loading are derived with the use of analytical layer-element method under unsteady heat conduction. Starting with the basic equations of plane strain problems of thermo-elasticity, the analytical layer-elements of a single layer and the underlying half-plane are obtained with the aid of Laplace-Fourier transform. Following the principle of the finite layer method and considering the boundary conditions, the total stiffness matrix is assembled and solved in the transformed domain, and the actual solutions in the physical domain are acquired by adopting the numerical inversion of Laplace-Fourier transform. Because positive exponential function is not included in the analytical layer-element, the computation overflow and ill-conditioned matrices can be avoided. Numerical results are obtained by corresponding computer procedures and are compared with those obtained by the finite element method, which shows a good agreement. The solutions under the assumption of a finite depth and a half-plane are derived and compared. Finally, the variation of vertical displacement and temperature increment along time factor and the distribution of vertical displacement along z direction are analyzed. The results reveal that the temperature change has a certain effect depth, and the results based on the finite depth assumption are consistent with those based on the half-plane assumption when the depth-of-interest is beyond the effect depth. The effect depth is related to the degree of temperature change, the greater the temperature intensity, the deeper the effect depth.

Ultra-fine tailings have become the main source of filling materials. In order to facilitate mixture ratio design and strength prediction of filling slurry, based on the microstructure of ultra-fine slurry, solid filling rate is used to characterize the structure of filling slurry. 63 sets of proportioning strength tests are carried out on ultrafine tailings of a mine. The results show that the solid filling rate and water cement ratio have exponential and negative power functions relation with the unconfined strength of the filling body respectively. The correlation between the solid filling rate and the water cement ratio is obtained by using the Pearson theory. It is found that the solid filling rate and the water cement ratio are independent of one another. Then on this basis, a double variable strength calculation model of ultra-fine tailings cemented hydraulic fill is developed. The error between the calculated value and the experimental value is less than 7%. Besides, experiments on the strength of ultra-fine tailings cemented body with curing time are carried out. A mathematical model of strength-age and a formula for calculating the strength of three variables are established using the fitting law of the experimental data. The developed model not only predicts the strength of mine filling body accurately, but also guides the preparation of mine filling slurry effectively.

Aiming at the special requirements of the grouting material for the prevention of water inrush hazards in tunnels, the mechanical properties and anti-washout properties of the grout were improved by adding the admixture. The optimum mixing ratio of water to cement was obtained by testing the compressive strength and flexural strength of cement stone under different water to cement ratios, fiber contents and silica fume contents. The anti-washout characteristics and fluidity of the grout under the optimum mixing ratio were tested. It was found that the incorporation of fiber and silica fume with cement could significantly improve the strength of cement stone and had little effect on the fluidity of grout. At the same time, the anti-washout performance of the fiber silica fume cement grout under the low flow velocity was better than that of the pure cement grout, but the anti-washout performance of the fiber silica fume cement grout was still poor when the flow velocity became high. The results showed that the redispersible emulsion powder could significantly improve the anti-washout properties of the grout. Even at high flow velocity (0.6 m/s), the grout retention rate was still more than 60%. The results provide a reference for the prevention and treatment of water inrush hazards in tunnel and the choice of grouting.

Pressure-bearing and concealed karst caves intensively develop in karst areas. A three dimensional test system was developed to study the evolution process and mechanism of water inrush disaster. In addition, new similar materials were developed for fluid-solid coupling test, and innovative preparation methods were proposed for pressure-bearing karst caves. Various tests under different scenarios were carried out with different tunnel excavation schemes and different cave sizes based on the background of Qiyueshan tunnel on Lichuan-Wanzhou expressway. Multivariate parameters (such as displacement, stress and water pressure) were monitored to forecast water inrush. Test results show that water inrush disaster easily occurred under adverse impacts (blasting disturbance and pressure-bearing and concealed karst caves). Firstly, fractures developed intensively under blasting excavation, and displacement was 27% higher than the artificial excavation in the key monitoring position. In addition, the rate of stress relieving reached 23.5%, and the seepage pressure was only 36.7% of the initial pressure. The water inrush occurred when the pressure was maintained at 40 kPa for fifteen minutes. In the same hydraulic loading conditions, the greater the karst cave size, the greater the displacement release rate, but the lower the seepage pressure. Finally, a larger karst cave caused water inrush earlier under the action of stress and seepage. The catastrophic process was divided into three stages: group cracks initiation, the formation of preferential transfixion passageway and complete damage of water insulation rock.

Disturbance induced by the construction of dams, tunnels and other engineering activities occurs in the surrounding rock mass and causes additional water pressure in the water of rock mass fracture. Thus, the unstable rock fracture propagates along the fissured surface under the disturbance load and fissure additional water pressure. Firstly, an analytical expression of fissure additional water pressure caused by the disturbing load is derived based on the inclusion theory, which is verified by numerical analysing. Then variation regularity of fissure additional water pressure is analysed under different rock mechanical properties, fracture shapes and inclination angles. Secondly, considering the influence of fissure additional water pressure, an analytical formula of fracture strength of rock mass is deduced by using the compressive shear fracture criterion. Finally, the effect of fissure additional water pressure on fracture strength is further investigated with an example. The results show that fissure additional water pressure reduces the fracture strength and increases the inclination angle range of fracture failure, which makes the rock mass more prone to hydraulic fracturing along the fissured surface. In addition, rock elastic modulus, fracture shape coefficient and inclination angle can have a significant influence on the additional water pressure. The fracture strength of rock mass increases with the increase of rock elastic modulus and fracture shape coefficient, and its increasing trend is more significant with the increase of fracture inclination angle.

With the increase of excavation depth, the deep rock mass is in high stress and complicated geological environment and the zonal disintegration phenomenon is observed at some projects, which is largely different from failure modes of shallow caverns. Under the action of dynamic unloading, an elastoplastic damage softening dynamic model is put forward based on the strain gradient theory and damage softening model. The dynamical equation, the equilibrium equations, boundary conditions and the failure criterion are deduced by considering the strain gradient. The theoretical solutions of radial displacement, radial stresses and tangential stresses of deep surrounding rock mass at different unloading times are calculated by Runge-Kutta and Matlab. The total displacement and stress fields of surrounding rock are also obtained after excavation. The dynamic formation and development regularity of zonal disintegration in deep caverns are achieved. The radial displacement, radial stresses and tangential stresses of deep surrounding rock mass are exhibited as an oscillating mode. The number and the width of zonal disintegration are in good agreement with the data of model tests. The applicability of the elastoplastic damage softening dynamic model for zonal disintegration in the explanation of zonal disintegration is confirmed. This model can also be used to provide theoretical support for the deformation and failure of surrounding rock in deep underground engineering.

Submarine mud flow is a kind of dilute submarine landslide body which is evolved by complex soil and water exchange after the unstable sliding of submarine slope. It shows the dual characteristics of soil and fluid. However, it is difficult to obtain the continuous changing strength under low shear strain rate by the existing testing methods, and the comprehensive strength characteristics can not be well revealed. The rheological and strength properties of the simulated submarine mud flow at different shear strain rates are investigated by using new full-flow penetrometer and RST rheometer, and the relevance of the undrained shear strength, yield stress and apparent viscosity with moisture content are analyzed according to the experimental results. Based on the shear thinning theory, a piecewise fitting model is developed to describe the rheological relation of submarine mud flow from low to high shear strain rate. Then, the new rheological model shows a good applicability and advantages through the comparison with other conventional models. In addition, an undrained shear strength model of submarine mud flow is established by considering the effect of strength softening, which provides a scientific basis for the numerical simulation and disaster assessment of submarine mud flow movement.

Calcareous sand is often used as filling material in construction of artificial islands in South China Sea. The permeability of calcareous sand has significant influence on the consolidation and settlement of soil mass. The drag force coefficient, which expresses the fluid drag force on particle surface, likewise an important parameter that characterizes the permeability of calcareous sand, is not extensively studied by researchers so far. In this study, a modified three-dimensional shape coefficient is introduced to quantitatively evaluate the shape of calcareous sand. A series of single calcareous sand particle settling tests is carried out in which a high-speed camera is employed to record the settling course and imaging technique is used to obtain the terminal equilibrium settling velocity of the sand particle. By doing so, the drag force coefficient-CD and Reynolds number-Re can be determined. The experimental results show that for the same Reynolds number, the drag force coefficient increases as the shape coefficient increases. Through a comparison with other test results, it is found that the richness of particle surface pores of calcareous sand can reduce the drag force coefficient. Finally, a semi-empirical model of the drag force coefficient for calcareous sand including CD, Re and , is obtained. This model will improve the prediction of permeability of soil mass especially with particles of irregular shapes. This improvement of drag force coefficient model has the significance on the analysis of the consolidation and settlement of foundations or artificial islands filled with calcareous sand in South China Sea.

In deep mining, there are a large number of local high confined water areas in floor aquifers which can easily induce floor water inrush disasters under strong mining disturbances have been confirmed by measured geological data and water control practices. Based on the theory of “lower three zone” and “the key strata”, the key aquiclude in the floor and the local high confined water area were simplified into a cylinder mechanical model, and the yield failure mechanism of the water-resisting key strata under the local high confined water was analysed. Four critical water pressure formulas for yielding in the water-resisting key strata were obtained. By dividing the critical water pressure values into sections and analysing the yielding state of the water-resisting key strata in different sections, the water pressure criterion balance equations for two stages of yielding and breaking of the water-resisting key strata caused by local high confined water were determined. The calculation expression of the remaining water-resisting capacity of the Ordovician top rock layer as water-resisting key strata was obtained. In addition, the formulas for the upper and lower limits of the mining depth were obtained by the inverse derivation. By combining with the deep mining practice of Jiulong mine, the mechanical model was validated and applied. Moreover, the relevant measures were proposed to prevent the local high confined water disaster, which has significant theoretical evidence for realising safe mining of deep coal seam.

Loess is a typical unconsolidated soil with structural strength. Its special structure results in an obvious turning point (where the pressure is called the compressive yield stress of structure) on its compression curve, similar to the curve of over-consolidated soil. To analyze the effect of initial structure on compressive yield of loess, confined compression tests and uniaxial compression strength tests were conducted on loess soils from six sites. The compressive yield stress and the structure index of loess with different water contents were obtained respectively. The results show that the structure index and the compressive yield stress of loess decrease with the increasing of water content. Meanwhile, with the increasing of water content, the variation of structure and variation of compressive yield stress are small. With the same sedimentary period of loess , greater structure index results in greater compressive yield stress. However, the linear relationship between structure index and compressive yield stress is different for the loess in the different sedimentary periods. The expressions of such correlations for Q3 (late pleistocene) loess and Q2 (middle pleistocene) loess are given respectively. Furthermore, the applicability of the correlations is verified by examples. Taking the structure as a bridge, there is a way to calculate compressive yield stress by using simple and easily available physical indexes.

The uplift pressure acting on a bottom of debris flow check dam can counteract partial effective weight and reduce the overturning stability of the dam. To study the distribution laws and influence factors of uplift pressure, a check dam model and an acquisition system of uplift pressure were designed and produced. A series of simulation tests of uplift pressure was conducted based on different gully bed slopes and different accumulations in front of the dam heel. The experimental results show that the uplift pressure linearly decreases from dam heel to dam toe. When placing accumulations in front of the dam, the absolute values of correlation coefficients between the uplift pressure and the distance to dam heel exceed 0.98. The uplift pressure decreases with the increase of gully bed slope and the influence of the bed slop on the pressure at the dam heel is greater than that of the dam toe. The permeabilities of materials placed on gully bed and accumulations in front of the dam all have impacts on uplift pressure. The lower their permeabilities are, the lower the uplift pressure will be. The permeability of accumulation in front of the dam heel also has a marked impact on the distribution laws of uplift pressure; and the lower the permeability is, the more obvious the distribution laws are. These research results will be the basis of further study on process and mechanism of uplift pressure acting on a bottom of check dam.

The strength for frozen silt soil increases with the increase of confining pressure at relatively low pressures, but decreases with the increase of confining pressure at relatively high pressures, which is different from unfrozen geomaterials such as metal, concrete, rock, sand and clay. To investigate the strength criterion for frozen soils and simulate the breaking process under different confining pressures, the strength criterion is derived from the modified slope M* of q-p strength curves in the meridian plane, and the formulation is deduced, which is related to internal friction angle and average normal stress on the basis of the Mohr’s circle and envelope theory. The strength criterion in the deviatoric plane is obtained from the assumption that the deviatoric stress is a combination of Mohr-Coulomb and Von-Mises strength criterion. A series of cryogenic triaxial compressive tests are conducted at three different temperatures, i.e. -6, -10 and -15 ℃, and different confining pressures of 0.3, 1.4, 3.0, 6.0, 10.0 and 15.0 MPa to determine the related strength parameters. Testing results are shown as follows: 1) the modified strength criterion in the meridian plane can simulate the strengthening effect at a relatively low confining pressure and the weakening effect at a high confining pressure; 2) the variation tendency of internal friction angle increases first and then decreases with the increase of normal stress; and 3) with the increase of parameters, the envelope shape of deviatoric stress is transformed from Mohr-Coulomb to Von-Mises criterion in the deviatoric plane, and its value corresponds to yield stress. Finally, the comparison between literature and experimental data demonstrates that the proposed strength criterion has a satisfactory applicability for frozen silt soils.

The studies of pile-anchor supporting structure of deep foundation pits have aroused the attention of scholars, and the interaction between supporting structure and soil still needs to be further researched. We established the static equilibrium equation considering the combined action of soil resistance after the pile and anchor tensile. The pile anchor deformation compatibility condition is modified and compared with the other three algorithms of deformation compatibility condition. The results show that the improved method can reflect the actual situation of the pile anchor supporting structure deformation. The designed pulling force of anchor is larger than other methods of designed pulling force of anchor. To overcome the ignored obliquity of the anchor, the anchors' elongation is increased and the stress states are not considered. FLAC3D is used to simulate the pile body’s internal force. The calculated internal force of pile body by the modified method is consistent, indicating the advantage of the proposed method.

To understand the permeability of shale under osmotic pressure and stress coupling, a servo-controlled triaxial rock testing system was employed to determine the complete strain-stress curves and permeability of shale under different confining pressures and osmotic pressures. The relationships between the deformation stage and permeability of shale samples were analyzed. The relationship between the compression zone and the permeability in the process of shale destruction was discussed. The results show that under different confining pressures, the initial permeability decreases with the increase of confining pressure, and the peak intensity increases with the increase of confining pressure. Under the same confining pressure, the permeability of the samples increases with the increase of the osmotic pressure, but the peak strength decreases to a certain extent. It is found that there is a localised compression zone in the shale, and the compression zone appears to inhibit the increase of permeability. The appearance of the compression zone is not the characteristic of the brittle to the ductile transition critical point, but the characteristics of the initiation, propagation and softening of pores. The shale samples appear hardening under high confining pressure. Under the low confining pressure, the formation of the fracture network in the shale is earlier than the samples under high confining pressure, and the failure mode is mainly dominated by the high-angle shear failure. This study on the permeability of shale under different stress conditions is significant to reveal the percolation mechanism of the process of shale gas development.

Convection heat transfer in a single granite fracture was experimentally investigated in this work. Distilled water was used as working medium for heat transfer in manmade smooth and rough fractures of granite samples. The influence of fracture roughness on heat transfer intensity was analyzed. The evolution of external surface temperatures of rock samples was monitored using resistance temperature detectors during seepage heat transfer to study the local heat transfer characteristics along the seepage path. Subsequently, the heat transfer correlations were summarized on the basis of the experimental results. Main conclusions are as follows: (1) under a given temperature level, the convection heat transfer coefficient features a positive correlation with flow rates. The increase rate of heat transfer coefficient is greater than the flow rates. Under a given flow rate, the convection heat transfer coefficient increases with the increase of experimental temperature. (2) the roughness of rock fracture increases the local heat transfer intensity to a certain extent, but the enlargement is not big. (3) the external surface temperatures exhibit nonlinear characteristic with multiple peaks, the temperature evolution history of rough fracture are more complicated than smooth fracture. For both smooth and rough fracture, the heat transfer intensity decreases with the distance to the inlet. (4) the quotient of Nusselt number and the 1/3 power of Prandtl number is close to a power function of Reynolds number under the experimental conditions in this work. With the increase of experimental temperature, the relationship gradually tends to be linear.

To investigate the propagation of subway vertical vibration in layered soil, an analysis model of layered foundation under a moving load is proposed. The Dirac function and the triplex Fourier transform are used to transform a moving harmonic load in time-space domain to a load in frequency-wavenumber domain based on the analysis model. The analytical solutions of the dynamic response of 3D layered foundation under a moving harmonic load and a moving line harmonic load are deduced by using the thin layer method and the moving coordinate system method. The range of the parameter n in the analytical solution of a moving line harmonic load is given. The influence of load speed on the dynamic response of 3D layered foundation, and the influence of the elastic modulus, Poisson’s ratio, damping ratio and load frequency on the critical speed of soil are analyzed. The results show that the influence scope of the load speed on the dynamic response of different frequency bands is different. The influence of moving speed on the low frequency response is greater than that of the high frequency response, and the elastic modulus has the greatest influence on critical speed of soil compared with Poisson’s ratio and damping ratio. The dynamic response amplitude will increase and the critical speed will decrease when the frequency of the dynamic response is close to the load frequency.

Model tests of the suction anchors with taut mooring systems are conducted under combined average and cyclic loads at the optimal loading point on the side wall of anchors. The deformation instability process of suction anchor subjected to constant and variable amplitude cyclic loads are investigated. It is found that too large cyclic accumulative displacement is the main reason for the failure of anchor. The cyclic accumulative displacement of anchor in the horizontal direction is larger than that in the vertical direction due to application of the vertical additional loads, so the horizontal failure of suction anchors occurs for the constant amplitude cyclic loading tests. The accumulative displacement increases faster with higher cyclic load level at a given average load level, and the number of cycles to failure becomes less. The cyclic displacement does not change obviously with the increase of the number of cycles, but increases with the increase of cyclic load level. The cyclic accumulative displacement and cyclic displacement in each direction at the mooring point increase with the increase of cyclic load level for variable amplitude cyclic loading tests. The accumulative displacements are larger in vertical than in horizontal under different cyclic loading time histories, so the moderate preferring vertical failures of anchors occur. Besides, the previous cyclic loading histories have an obvious influence on the accumulative deformation produced by subsequent loading. Compared with the static loading, the movement direction angle of the anchor under cyclic loading increases, which may be due to the greater accumulation of pore pressure at the bottom of the anchor than that at the side wall. From the view of effective stress, the decrease of effective stress at the bottom is relative obvious than that at the side wall, thus vertical bearing capacity decreases more remarkably, and vertical movement of anchor is more obvious.

Non-linear flow in rough-walled rock fracture is one of significant issues of rock mass seepage properties. Based on viscous pressure drop and local pressure drop, a novel non-linear flow model (MT model) at the low velocity though rough-walled rock fracture is proposed for the assumption of velocity proportional to an aperture in sub-fracture which takes place assumption of equal velocity in Javadi’s T model. Saturated seepage experiments of five rock fracture replicas at the low flow rate are carried out. The results show that MT model is preferable to fit experimental data compared with preceding others, so the MT model is more exact in describing non-linear flow. Furthermore, the MT model is applicable to the case: the fractures with JRC less than or equal to 10 and Reynolds number lower than 1 000. After a thorough study of MT model, it is discovered that there are two flow regimes in rough-walled rock fractures: Darcy flow in small Reynolds number and Forchheimer flow in large Reynolds number, and a critical Reynolds number is defined to differentiate between them. The effects of fracture roughness and aperture on non-linear flow are discussed. The rougher and smaller aperture of fracture is, the smaller critical Reynolds number is, and the stronger non-linear effect is. A formulation of the critical Reynolds number, hydraulic aperture and absolute roughness is developed. In addition, the formulation is reasonable in rough-walled fracture with JRC less than or equal to 10.

The research about spatial form of non-cohesive soil slip surface in passive failure behind the retaining wall in translation was done by the method of model tests. A model test device was designed to carry out 6 passive failure tests for soil behind the retaining wall. The spatial coordinates of the points where the fragile glass strips embedded before break were recorded, in order to determine the location where the soil slide occurred and plot the spatial form of slip surface behind the retaining wall. The test results show that: the 3D effect of the slip surface behind the retaining wall is obvious; in the width of the retaining wall, the slip surface height in longitudinal direction slowly increases in the beginning and then increases in an approximately linear pattern. The initial fracture angle is 9° and the average fracture angle is 26° while the Rankine theory fracture angle is 28°. The maximum length of longitudinal fracture surface was 1.8 times the height of the retaining wall which is generally consistent with the plane assumption of the classical soil pressure theory. The slip surface has a certain horizontal extension, and the principal plane projection extends with initial diffusion angle of about 45°. The form which is the most distant from the retaining wall is a horizontal line with 0.7 time the width of the retaining wall, and the diagonal and horizontal lines are connected with an arc with a radius equal to retaining wall width. The results provide experimental reference for analyzing the spatial form of slip surface in passive failure.

True triaxial tests on clay mixed with gravel were carried out under complex stress state to simulate the loading process of core wall elements under water storage process, and loading was applied from the minor principal stress direction. Under initial state, the major principal stress and the second principal stress were adjusted with constant minor principal stress; initial anisotropic stress state was reached to simulate the stress state of dam elements. The major principal stress and second principal stress were then kept constant. Minor principal stress increment was applied to simulate the stress path that core wall elements go through during the process of water storage. Test results show significant differences compared with the result of conventional triaxial tests and true triaxial tests loading from major principal stress direction. Under different initial stress conditions, the initial tangent modulus and initial Poisson’s ratio of the principal stress direction are very complex, and the stress - strain curve shows obvious anisotropy. In the process of core wall rockfill dam construction and the water storage process, the stress path experienced by the core wall unit is obviously different. The reasonable soil constitutive model should be used to describe the modulus and Poisson’s ratios caused by the different loading paths.

To explore the strain-softening behavior of a deep circular tunnel, the strain softening coefficient is introduced to characterize the degree of strain softening. This coefficient is defined as the ratio of the tangential strain at the boundary of the softening-residual plastic zone to the tangential strain at the boundary of the elasto-softening zone. Then, the displacement equations of the softening plastic zone and the residual plastic zone are deduced. The displacement curves calculated by the deduced method are compared with those calculated by Lee’s method and Cui’s method to verify its accuracy. Finally, using example analysis, the difference of the plastic radius is obtained due to the difference of the selected mechanical model. In addition, the effect of the strain softening coefficient on the ratio of the softening plastic zone to the residual plastic zone and displacement is analyzed. The results show that the confining stress at the elasto-plastic boundary is not related to strain softening coefficient and support force, but the plastic radius is related to the support force. The strain softening coefficient has a direct influence on the ratio of the radius of the residual plastic zone to the radius of the plastic zone. With the increase of strain softening coefficient, the range of softening area increases, leading to the decrease of the residual plastic zone. The displacement surrounding tunnel wall is greatly affected by support force and deceased with the increase of support force.

This study investigated pile-cap-soil system considering different connection details in four pseudo-static seismic tests using a 1.2 m×1.2 m×1.2m mini-soil box. The failure modes, hysteretic performance, stiffness degradation, moment of pile and soil pressure were observed. Effects of the different pile-cap connections on the seismic performance were studied. The research shows that the different connections obviously influence the pattern and degree of failure of the pile head, the energy dissipation of the system, the level of ultimate bearing capacity, and the distribution of pile bending moment. However, the distribution and magnitude of soil pressures on cap sides and pile are not influenced by the connection types. For common connections, it is optimum that pile head is directly embedded in pile cap by 0.5D. When the strengthen ring connection is adopted, the restraint effect of the strengthen ring connection is roughly the same as that of common connections (embedded depth is 1.0D). Obviously, the construction of the strengthen ring connection is complicated, the restraint effect and damage form of the strengthen ring connection are related to the section, the strength of concrete and reinforcement of strengthen ring. The further works will be needed to analyze these parameters.

To investigate the deterioration rule and failure criterion of rock in the acid-based environment, experiments were conducted on sandstone specimens after 1, 5, 10, 15, and 20 times of wetting and drying cycles in the environment of pH=7, 5 and 3, respectively. By analysing uniaxial compressive strength (UCS) and triaxial compressive strength (TCS) after different cycles, the parameters of Mohr-Coulomb failure criterion and Hoek-Brown failure criterion were calculated, and the effect of wetting and drying cycles on these parameters is also analysed. Finally, according to the relationship formula between the deviatoric stress and the strength criterion parameters in the stress space, the failure envelopes changed with cycles in the π-plane were drawn under the action of solutions with pH values of 7, 5, and 3. The results show that the parameters of strength criterion decrease with the increase of cycle time, at the early stage of cycles, the deterioration is more significant, and then the deterioration is relatively low. The lower the pH value is, the more serious the deterioration is, and the degrees of deterioration effect from large to small are as follow UCS, cohesion, material constant and internal friction angle. In the same environment of pH value, when the cycle number is low, the failure envelopes in the π-plane are relatively sparse. However, the greater the number of cycles are, the denser the failure envelope is; in the different immersion environment of pH value is, the lower the pH value is, the smaller the failure plane is. The deviatoric stress is positively correlated with UCS and cohesion, but negatively correlated with the material constant and internal friction angle.

Through the analysis of existed triaxial creep test results of red sandstone under the chemical corrosion, it is known that water-rock chemical interaction can accelerate the development of damage and enhance the creep properties of red sandstones. In this paper, based on the chemical kinetic theory of water-rock chemical interaction, the loss of the soluble cement in red sandstone is the key reason for the deterioration of rock mechanical properties under the interaction of chemical corrosion. The chemical damage factor considering the initial pH value and the time is defined by the chemical reaction rate equation and the change of pH value of solution during the immersion process. Meanwhile，based on the generalized Kelvin model, the rheological damage constitutive model of sandstone considering chemical corrosion is proposed. The parameters of the model are identified and verified by the creep results of red sandstone under chemical corrosion. Results show that the proposed model is valid and reasonable, which can well describe the creep properties of sandstones under chemical corrosion.

The treatment of soft ground deposit is problem in geotechnical engineering. Most treatments drain the water out of the soft soil deposit. Siphon method is simple and free of power, and can be used to dewater the groundwater. To better understand the mechanism of siphon drainage process in soft ground improvement, the analytical analysis are carried out to investigate the ground water level in soft ground and siphon discharge according to the ground water movement theory. An explicit analytical solution of axisymmetric well-flow differential equations in unconfined aquifer is derived to assess the water level and discharge in soft ground based on Theis theory and Boltzmann transformation. The analytical solution is verified by numerical simulation. The results show that the analytical solution agree well with data obtained from experiment. Relative error is 0-15% by comparing analytical solution and classical solution, and it is more simple than classical solution. It is more convenient than classical solution for engineering application.

Horizontal reinforcement solutions are generally used in pavement engineering to prevent or delay the sudden damage of adjacent roads caused by collapse of cavities induced by vehicle loads and ground water, and to provide an early warning. This kind of approach is extensively adopted in many countries, but load transfer mechanisms and characteristics of the interfaces between the geosynthetics and soils are not yet fully understood. This study presents an review of the state of the art for the geosynthetic-reinforced embankment overlying voids. The mechanical mechanisms (e.g. sliding surfaces of the embankment fills, arching theory, membrane effect, soil expansion over the geosynthetics, friction in anchorage areas and reduction of tensions in the transition areas) are mainly introduced. The comparisons and shortcomings of the design methods are also discussed. To improve the design methods, the several mechanical behaviors of prior literatures need to be further investigated: load transfer mechanisms, delayed deformation and collapse due to the geosythetics, settlement calculation, ultimate bearing capacity and stability of the embankment subjected to localized voids. The load distributions have not been revealed, the exiting design methods are overly conservative. A set of recommendations and insights is presented for further researches.

Ground vibration induced by shield construction has become a major environmental vibration problem in urban areas. Based on a sandy pebble formation of a shield construction in Lanzhou, by synchronizing the test tunnel and three-direction vibration acceleration on the surface of the earth, this paper studies the shield construction-induced vibration in the time domain, and frequency domain propagation law within the surface of the 50 m×50 m area. The findings of this study are as follows: 1) the spread of the surface free field acceleration with the distance firstly increases and then sharply attenuates. In X direction, the amplification phenomenon repeatedly appears; 2) the transverse maximum peak of 0.33 m/s2 is harmful to sensitive ancient buildings; 3) within the scope of 50 meters, the surface frequency mainly ranges from 4 to 80 Hz, the vibration spectrum magnitude does not monotonously decrease with the increase of the vibration source distance, but has rebounding phenomenon, which is associated with excellent frequency field soil; 4) the influence of three directions of vibration should be considered in the evaluation of shield induced environmental vibration.

It is challenging to represent the surface deformation characteristics and the rock mass failure modes caused by underground mining, since there are many uncontrolled factors such as variational orebody shapes, complex geological conditions, mostly subcritical excavation, different mining methods, conspicuous tectonic stress and obvious structure effect. In this study, the eastern area of Chengchao iron mine was selected as an example, and monitoring results were achieved by 3D laser scanning and GPS surveying based on the first-hand monitoring data of surface deformation from March 2010 to September 2015. Thus the surface deformation characteristics and rock mass failure mechanisms caused by underground mining were explored. The comparative analysis of surface deformation in the hanging wall and on the footwall of eastern area of Chengchao iron mine showed that: tubular caving continuously developed upwards at the beginning of the mining. Different sizes of funnel-shaped collapse pits appeared on the mined-out area surface after the rock mass caving propagated to the ground. The extension of surface deformation was consistent with the mining advance in the hanging wall. Furthermore, the surface deformation characteristics were mainly affected by horizontal stress which served as a main driving force of rock mass deformation. Additionally, the damage modes of rock mass were changed by the structural plane, which mainly slowed down and accelerated rock mass deformation in the hanging wall and footwall, respectively. Moreover, the total deformation and the vertical deformation rate were much greater in the downward direction due to the slope morphology.

The gateroads on the sides of a longwall panel at Zhenchengdi Coal Mine are driven along the roof and floor, respectively, and thus the gateroad along the floor becomes the gob-side entry under a longwall gob. In this paper, theoretical analysis, physical modelling, numerical modelling and field observation are conducted to investigate structures and stress of surrounding rock mass of this gob-side gateroad. It is found that the gob-side entry is independent of the side and front abutment pressures. The caved rock cushion under the masonry beam structure can dissipate energy and stress for the gob-side entry, which prevents from dynamic and impact loads, providing the stable stress environment much lower than pre-mining stress. The angle of break developed due to strata movement has a significant effect on stress and distribution (especially on gob edge). The lower the angle of break is, the smaller the gob pressure and stress are around the entry, and the larger distance between the gob edge to the location where pre-mining pressure occurs. The angle of break has a dictating and guiding function for the plastic zone development. The stress of surrounding rock mass of gob-side entry is significantly lower than premining stress with the high destress degree. Both the roof to floor and rib to rib convergences are smaller than that of non-gob-side entry, which demonstrates that overall stress environment is improved. The study is of certain drawing significance for highly stressed burst-prone gateroads.

The deformation of surrounding rock tunnelling by tunnel boring machine (TBM) is normally large when the tunnel passes through the deep and weak layer. The TBM shield is squeezed easily by the surrounding rock, which further results in the TBM jamming and influences the operation of TBM. By analyzing the mechanism of TBM shield jamming problems, two important conditions for forecasting TBM jamming are concluded. One is that the deformation of the surrounding rock is greater than the reserved space, and the other is that the rated thrust force cannot overcome the frictional resistance. For monitoring the jamming state of the actual TBM engineering, this study is to propose a scheme of monitoring the deformation of the TBM shield and a method of calculating the pressure of the shield. The extrusion force between the surrounding rock and the shield can be estimated, then the frictional resistance of TBM is calculated, and the state of the TBM jamming can be achieved. According to the relation between TBM frictional resistance force for excavating and the TBM rated thrust, the state of the TBM jamming can be divided into four grades: no jamming, minor jamming, jamming and severe jamming, and the corresponding treatment measures are suggested. At last, the flowchart of warning of the TBM jamming is developed by combining the monitoring scheme with the conditions of TBM jamming. The flowchart and the scheme of monitoring the deformation are successfully applied to Lanzhou water conveyance tunnel engineering, and it is found that the predicted jamming state is nearly the same as the actual state, and thus this method has certain reliability and attaches great importance to TBM tunnelling construction.

In this study, based on the 250 m grade concrete face gravel dam of Dashixia in Xinjiang province, large-scale direct shear tests were conducted to determine friction parameters of the interface, and numerical model considering the contact effect was established. The influence of contact effect on stress and deformation of the dam body, concrete slab, and water stops were studied. Results show that the hyperbolic model can meet the non-linear relationship of the shear stress and the displacement of the interface. If the contact effect is not taken into account, the deformation gradient and the principal stress value of the dam body become low, and the arch effect would be overestimated. The deflection and the slope direction stress of slab are less affected by the contact effect, while the axial displacement and the axial stress are greatly influenced. The deformation of the peripheral joint is strongly affected by the contact effect. Under the high-water pressure, the local dam body slip may occur, which may lead to an increase of the peripheral and vertical joint deformation. The results of this study and in-situ observations of Anchicaya dam reveal that the control of peripheral joint deformation is the key point in constructing concrete-faced rockfill dams in steep valleys.

The geological properties of the soil are poor in soft soil areas, and the ultimate skin friction and tip resistance provided by the foundation soil are also limited in these areas. The material strength of the precast pile shaft can’t be fully mobilized in soft soil areas. Filling sand into the foundation soil in precast pile construction process can improve the properties of the foundation soil and promote the frictional capacity of the pile-soil interface as well. The compressive bearing capacity of pile foundation can then also be enhanced. A group of field tests as well as ABAQUS simulation are used to investigate the bearing capacity of the sand filled nodular pile. The following conclusions can be gained based on the measured and simulation results: the compressive bearing capacity of the sand filled nodular pile is obviously better than the compressive bearing capacity of the conventional pipe pile in soft soil areas; the axial force of the sand filled nodular pile decreases sharply at the nodes along the nodular pile, and the nodes along the nodular pile can promote the shaft bearing capacity of the pile foundation; the shaft bearing capacity of the sand filled nodular pile is much better than that of the conventional pipe pile in soft soil areas, and the enlarged shaft resistance coefficient is about 1.15-1.40.

Foundation pit supporting structure is a temporary retaining facility, how to reduce the engineering cost and improve the construction speed under the precondition of ensuring the safety is a common concern. To satisfy the engineering demand, a new type of foundation pit supporting structure, cross-shaped assembled foundation pit supporting structure, is proposed, which is safe, rapid, low cost, recyclable and environmentally friendly. In this paper, the structure selection and calculation method of the lattice element are introduced. The field test relying on a project in new Wuxiang district, Nanning, Guangxi province, shows that the experimental values are similar to the calculated values. It proves the correctness of the proposed design method. With the support of the foundation pit supporting structure, the stability of foundation pit, deformation of foundation pit and the strength of support structure all can meet the requirements of specification, so it can be applied in similar projects in the future.

The surface roughness of particles may have a strong influence on the mechanical properties of granular assemblies. The assumption made in the classic discrete element method(DEM) that the particle surface is smooth makes it difficult to describe the contact behavior of real granular materials accurately. It is necessary therefore to develop the stochastic discrete element method (SDEM) which could quantitatively consider the surface roughness of particles. To this end, the most popular statistical treatment of rough surface—the Greenwood-Williamson(G-W) model is introduced. Then the defects of incorporating the G-W model into DEM simulation are fully addressed. An extended model which treats the rough surface as the combination of two parts is proposed and the corresponding non-dimensional form for subsequent DEM simulations is presented. The pressure distribution, deformation distribution and total contact force obtained by the G-W model and the extended version are compared. It shows that the extended model can better reflect the influence of the surface roughness on contact between rough particles. Based on the extended model, a new normal interaction law ready to be incorporated into DEM is derived by the curve-fitted empirical formula. A user defined contact model of the new normal interaction law is incorporated into (the particle flow code)PFC3D. Numerical simulations are first conducted to compare the influence of the surface roughness on mechanical properties of particulate system under different loading conditions.

Site effects can generate large ground motion amplification during earthquakes, and it is important to study the wave field characteristics of layered soil. A new model was presented to compute the diffraction of P and SV waves by a valley embedded in multi-layered half-space. Based on the theory of soil-structure-interaction, the response of scattered wave field could be achieved by the response of free wave field. The layered half-space could be decomposed into near field (the generalized structure, composed of the structure itself and its surrounding soil) and far field (the infinite layered half-space with regular boundaries). The near and far fields of multi-layered half-space were modeled by scaled boundary finite element method (SBFEM) and high-accuracy precise integration method (HPIM), respectively. The dynamic flexibility coefficients of the far field were solved in the frequency-wave number domain by using the precise integration method and then the results were transformed by the inverse fast Fourier transform within the frequency-space domain. The dynamic stiffness of near field was solved by a continued-fraction-based high-order transmitting boundary of SBFEM. Numerical examples were provided to validate the accuracy and efficiency of the proposed approach. In order to give perspective on the range of effects caused by the trapezoid valley embedded in the soft interlayer site, some examples were presented as well.

The perilous rock is one of the typical disasters in the Three Gorges reservoir region. Crack propagation of controlling joint under loads is the key process in failure of perilous rock. The extended finite element method (XFEM) is an effective approach for fracture analysis. The governing equation of XFEM for hydraulic fracture modeling is derived by the virtual work principle of the fracture problem considering the water pressure on crack surface. Then the implement method of XFEM for hydraulic fracture modeling is deduced. The Taibaiyan cliff at Wanzhou is a representative case of massive perilous rocks in the area. The hydraulic fracturing process on this site is simulated and analyzed by extended finite element method. The numerical analysis results show that water pressure in controlling joint of perilous rock is sensitive to the rainstorm condition. With the increases of water pressure in control joint, the tensile stress at the crack tip increases rapidly and the stability of perilous rock decreases; type I crack propagation is the main form of crack propagation in perilous rock and the crack propagation is non-steady propagation.

The motion of submarine landslide might generate tsunami, destroy the offshore facilities and threatening the safety of coastal zone. At present, the research on submarine landslide generated tsunami is in the ascendant. Mih granular flow model is adopted to control the movement of sandy landslide with low cohesive. Two-phase model is used to calculate the interaction of soil/water. RNG model is applied to control the dynamic of water. Based on granular flow model, the coupling numerical analysis method of submarine landslide tsunami is established. This full coupling model can be more accurate to characterize the movement of slide, the interaction between the sliding mass and the water, and the following impulse wave process of generation, propagation, and run-up. The case of simple submarine landslide in water tank is used to study the whole process of submarine landslide and the following tsunami. Numerical analysis presents the inhomogeneous dynamic of deformable slide mass, the differentiation flow of density, the hydroplaning mechanism, the impulse wave characterized by trough, and such typical phenomena of submarine landslide and tsunami are generated. These mean the numerical model built is valid. Low and non-cohesive submarine landslide exist in many sea regions (including north of the South Sea, China). Therefore, this numerical method is worth spreading and making further research and improvement.

The dynamic responses of saturated soil are the always concerning problems of soil dynamics. The liquefaction caused by cyclic loadings often increases the pore pressure and decreases the strength of the soil. In addition, for the site with large size saturated soil, large numbers of degrees of freedom often lead to low calculation efficiency, and restrict the development of the numerical method of saturated soil. Therefore, the proposed fully explicit finite element method for the equations of saturated porous medium in u-p formulation is implemented into the OpenSees software. By using the element and constitutive models in OpenSees, the efficient and explicit computation of the dynamic responses of saturated soils can be realized in this paper. In a two-dimensional saturated model, the elastic dynamic responses obtained from the Newmark method are compared with the results obtained from the embedded method. Two results are in good agreement, which verify the embedded algorithm. The proposed algorithm is used to compute the nonlinear free field seismic responses of the seabed soil. This method simulates liquefaction process, failure modes and the lateral deformation of the seabed soil effectively. The proposed algorithm illustrates significant advantages in terms of computational efficiency.

Investigation on tensile properties using ionic soil stabilizer (ISS) contributes to better understanding about the modified mechanism of mechanical behavior such as cohesion. To overcome the defects of existing apparatus, a digital image processing technology-based soil tensile device which comprises displacement controlling module, loading holder module and data detecting module was developed. The soil shape in loading holder was designed as “8” shape to solve the problem about connection between soil and box without any adhesive force. The justification to design the “8” shape loading holder was verified by FLAC3D. In addition, the loading holder had the function of sample preparation box that could avoid soil disturbance when transforming sample from preparation box to loading holder. Image capture device was added to record the process of deformation and failure of soil sample so that these recorded images can be analyzed by digital image processing software named Geo-PIV to study the deformation of soil in the period of tensile test. After finishing the tensile test, comparative trial and investigation on raw montmorillonite and modified montmorillonite by adapting ISS solution with certain concentration were carried out. The results indicate that the soil sample is under tension without stress concentration at the part of sample that contacts the loading holder through the analysis of recorded transformative image based on PIV. Furthermore, tensile strengths and moduli of the modified montmorillonite by ISS are lower than those of raw montmorillonite and the degree of reduction increases with increasing concentration of ISS solution. The data acquisition module is sensitive to the change of stress and strain. Consequently, the developed tensile apparatus is reasonable, reliable and sensitive.

Based on Ganggou tunnel of Jing-hu high-speed connection line road which crossed large fault zones, mechanical characteristics of surrounding rock were studied during the construction process of super-large section tunnels under complex strata. For this purpose, a large-scale three-dimensional assembled geomechanical model test system was designed and developed. The system included stress and strain field monitoring systems based on static data acquisition and a displacement field monitoring system based on raster ranging in order to monitor the mechanical response of surrounding rocks during tunnel excavating. Model tests on mechanics in construction process of super-large section tunnel under complex strata were conducted, and the data of displacement and stress were real-time monitored during testing through the pre-buried monitoring instruments at specific positions in the models. The results indicate that the displacement deformation of both horizontal and subsidence can be divided into three phases: slowly increasing phase, sharply increasing phase and steady state phase. The sharply increasing of horizontal displacement starts earlier than subsidence. Meanwhile, the three phases of stress accumulation, releasing and steady state of stress are also revealed. The research methods and results will guide similar engineering practices.

How to accelerate the seepage rate of water in model test is significant to the study of bank landslide. Based on the principle of electromagnetism, the force of pore water was calculated by applying mutually perpendicular electric and magnetic fields in the landslide model. According to the theory of electroosmotic consolidation, the resultant force of groundwater is calculated, and the relationship between the migration rate and the voltage and magnetic field intensity is deduced, then the time similarity ratio is obtained. The water migration rate of landslide model is improved by controlling the voltage and magnetic field strength applied to the model, and the effect of the electromagnetic field on the soil moisture is verified by experiments. The influence of electromagnetic field significantly affects the water migration velocity, and the voltage has little effect on the stable seepage field of the model. Without changing the parameters of model material, the changes of the magnetic field strength and voltage can determine the seepage velocity of any pore water lays which can be the foundation for studying the evolution mechanism of the landslide under fluctuating reservoir water conditions.