The impermeability of compacted buffer block is a key parameter to ensure the sealing of high-level radioactive waste (HLW) repository. It is importance of testing and evaluating the uniformity and anisotropy of the permeability of the buffer material blocks to the design of buffer barrier because the blocks are compressed under uniaxial loading with a large size. In this work, full-sized blocks of bentonite-sand mixture were compacted into different dry densities, cut with electric saw to get smaller pieces at various positions and directions, and tested by both rigid-wall and flexible wall permeameter to evaluate the overall hydraulic conductivity of the blocks. Test results show that the hydraulic conductivity decreases with the increase in block density, and all blocks fall into the order of 10?10 cm/s along the directions of z, ? and r of the blocks. This proves that the compacted blocks possess satisfactory homogeneity and marginal anisotropy in permeability, and meet the low requirements of the buffer barrier for HLW repository. With respect to both permeameters, specimens in flexible wall permeameter expanded 10%?20% than those in rigid-wall permeameter, leading to a slight increase in the hydraulic conductivity than the rigid one. Before and after permeation, CT test was introduced to investigate the microstructure evolution of the blocks. After permeation, the density distribution of the specimen as indicated by CT value transformed uniformly than before, and the micro crack was healed to become unobservable.

Soils are often in an over-consolidated state due to complex stress paths such as unloading and reloading in practical engineering and the existing models for the cavity expansion problem fail to reflect the dilatancy and softening characteristics of over-consolidated soils. To this end, a semi-analytical solution for cavity undrained expansion in over-consolidated soils based on UH model was solved by using similarity solving technique in combination with associated flow rule and large strain theory. The response of stress and excess pore-water pressure caused by compaction effect was analyzed and the applicability of UH model was discussed by analyzing the variation of soil stress path with different over-consolidation ratios (OCR). The results, including the stress distributions curves, the expansion-pressure curves, effective stress path and yield locus variation curves and the evolution of the potential strength during cavity expansion, shows that: (1) For the lightly over-consolidated, the excess pore-water pressure decreases monotonously along the radial direction in the plastic zone in which the pressure curve presents a "S" shaped trend and decreases gradually around the cavity, particularly negative pore pressure appears around the pore wall, with the increase of OCR. (2) With the increase of OCR, the convergence of pressure-expansion curves becomes slower. (3) In the process of the cavity expansion, the normally consolidated soil is always in the stage of contraction and hardening. While for the over-consolidated, it goes through critical state to dilatancy and hardening stage to critical state to shear contraction and hardening one. This paper not only enriches the application of similarity solving technique, but also provides a reference for calculation of bearing capacity of pile foundation in over-consolidated soil, prediction for surrounding rock deformation of tunnels and determination of in-situ test parameters.

High-performance concrete (ECC and UHPC) pile foundations have the advantages of excellent crack resistance and high bearing capacity, which can better meet the longitudinal deformation of piles in integral abutment jointless bridges (IAJBs). Low-cycle reciprocating pseudo-static tests were carried out on interaction of high-performance concrete pile-soil. The failure characteristics, crack resistance and bearing capacity of the pile were obtained. The distribution laws of pile strain, pile deformation and pile side soil resistance were analyzed and compared with the reinforced concrete (RC) pile. Meanwhile, the usability of commonly used codes were discussed. Some findings were as follows. ECC and UHPC materials can significantly reduce the damage of the pile foundation, increase the horizontal bearing capacity and crack resistance compared to RC. The damage position of the high-performance concrete pile is deeper, the effective pile length of the pile is longer, and the seismic performance is better. In special, the ECC pile has the strongest anti-cracking ability, its cracking displacement and cracking load can reach 15 mm and 5.8 kN, respectively. The deformation of high-performance concrete piles continuously reduces along the buried depth, and approaches zero at 15 m and deeper. The soil resistance of pile side increases first and then decreases, the resistance and deformation of the pile bottom soil are both 0; the strain of the pile shaft is symmetrically distributed with an “olive” shape, and there is larger strain in the interval of 4D to 6D buried depth. Furthermore, both the “m” method and the new API standard method can estimate the high-performance concrete pile displacement better when the displacement of pile top is within 10 mm. When the displacement exceeds 10 mm, the “m” method is no longer applicable. Neither the “m” method nor the new API standard method can predict the bending moment of the high-performance concrete pile well, indicating poor applicability. The new API standard method is recommended for estimating soil resistance of pile side.

In order to prevent the anchor cable from shearing and breaking in the surrounding rock of the roadway, and to further improve the shear strength of the anchor cable, we independently developed the anchor cables combined with the c-shaped tube (ACC), which can improve the shear strength and stability of the surrounding rock. The design is mainly composed of c-shaped tube and anchor cables. We first introduce the ACC support structure in detail. In order to better study the mechanical properties of ACC, the indoor mechanical properties tests of ACC and pure anchor cables have been carried out with different types, different prestresses and different cable diameters, with the help of the self-developed new type of anchor able with c-shaped tube tension-shear testing system. We compare and analyze the test results based on the characteristics of the force-shear displacement plot, the effects of the supporting member type, and the failure mode of the supporting structure. The results show that the anchor cable and its combined structure with c-shaped tube undergo three stages in the shearing process, which includes the free deformation of the bore-wall rock, the compression of the c-shaped steel tube by the bore-wall rock, and the joint deformation of the c-shaped tube wrapped with the anchor cable. The shear fracture of ACC is manifested as tensile fracture and tensile-shear composite fracture. Its peak shear force is negatively correlated with the pretension force. Compared with the pure anchor cable, the axial distance of the shear plastic hinge of ACC is larger. The maximum shear force, the maximum axial force and the overall structural deformation capacity of ACC have been improved by 26.8%, 3.5%, and 7%, respectively. The test results show that the use of ACC can effectively improve the overall shear resistance of the joint surface. When the surrounding rock is deformed and damaged, the combined structure of the anchor cable and the c-shaped steel cube can not only increase the shear strength of the entire supporting system, but also increase the tensile strength of the anchor cable at the same time. Therefore, the supporting effect of the anchor cable plus the c-shaped tube can achieve the fact where 1+1>2. The combination of two forms an effective surrounding rock bearing circle around the roadway, and the stability can be guaranteed for the surrounding rock of the roadway.

In order to study the damage and fracture process between particles meso-contact, the tensile damage variable and shear damage variable were introduced into parallel bond model to characterize the deformation, strength and energy evolution characteristics of particle bonding contact based on the Particle Flow Code(PFC3D). According to the maximum stress criterion, the bond damage initiation criterion was determined, and the contact model was redeveloped by C++ language. The results of tensile, shear, bending and torsion tests of single contact were compared with the theoretical results, and the accuracy of the parallel bond contact model considering damage was verified. A three-dimensional meso discrete element model was established to simulate the uniaxial compression test of sandstone and triaxial compression test of granite, showing the applicability and accuracy of the model. Based on this study, the results show that the damage evolution coefficient has a noticeable effect on the elastic range, peak stress and softening rate of the whole stress-strain curve; the evolution process of bond damage, crack germination, propagation and coalescence in different stages of the stress-strain curve was comparatively studied; the evolution law of elastic strain energy and dissipative energy was further studied, and dissipated energy was introduced. It was explained that the larger the damage evolution coefficient is, the faster the decreasing of stress-strain curve is after reaching the peak stress.

The emergence of rock breaking technology combined with high-pressure water jet and mechanical disc cutter has changed the operation mode of traditional tunnel boring machine (TBM). The research object is the rock-breaking mechanism of the high pressure water jet cutting grooves into the rock mass on both sides of the disc cutter. We carry out tests and numerical simulations of white sandstone slab samples with constant cross-section indenters penetrating into different pre-cutting groove depths. We use the DIC method to analyze the post-fracture images. The results show that: (1) The existence of the cutting groove blocks the expansion of the penetration crack of the indenter, so that the energy can be more concentrated on the local rock block, which is conducive to the formation of the splayed cracks and promotes the fracture of the rock. (2) With the increase of groove depth, the stress state and mechanical response zones inside the rock under the indenter are changed gradually. When the groove is deep, the mechanical response zone under the indenter further presents a failure transition zone, which locates between the original crack propagation zone and the elastic zone. In this area, micro-cracks are compacted, and the sample shows obvious deformation, but no obvious failures. (3) The use of grooving changes the rock failure mechanism under the indenter. Without grooving, the mechanism shows the radial crack growth dominated by extrusion shear of the complete specimen, whereas after grooving, it shows the main crack propagation that dominated by tensile shear controlled by both the indenter and the grooves.

Based on the granular micromechanical approach and energy conservation principle, an anisotropic micromorphic constitutive relationship has been obtained for granular materials. It is noted that the particle displacement induced by particle rotation has been ignored. Furthermore, the expressions of anisotropic constitutive tensors are derived through a recursive formula of the unit contact direction integral. On this basis, according to Hamilton’s principle, the motion balance equation and boundary conditions of the anisotropic granular material are derived, and the dispersion relationship of the plane wave can be obtained for the anisotropic granular material. Finally, a detailed parameter analysis is carried out on the dispersion relationship and the frequency band gap. The research shows that: (1) The proposed model predicts that there are three types of waves in the granular materials, which consists of three kinds of longitudinal waves, six kinds of transverse waves and three kinds of in-plane transverse shear waves. For the transverse isotropic condition, the larger the value of the anisotropic parameter a20 is, the higher the frequency of the longitudinal wave and the transverse wave are, and the lower the frequency of the in-plane transverse shear wave is. For the orthogonal anisotropy conditions, with the increase of the anisotropic parameter a22, the frequency of transverse waves corresponding to the kinematics related to the 2-direction increases, whereas the frequency of transverse waves corresponding to the kinematics related to the 3-direction decreases. However, the coefficient a22 has minor effects on the longitudinal wave. (2) The degree of fabric anisotropy has minor effects on the bandwidth of the transverse wave, but it has a greater effect on the bandwidth of the longitudinal wave: the increase of a20 reduces the bandwidth between acousto-optical waves, whereas the bandwidth between optical waves increases. When a20 is greater than 0.84, the band gap between acousto-optical waves disappears. In contrast, the increase of a22 increases the bandwidth between acoustic and optical waves, whereas the bandwidth between optical waves decreases. When simplified to consider the isotropic condition, the dispersion curves of the three types of waves predicted by the proposed model show a good agreement with other benchmark theories.

It is of great significance for the safe construction of shale gas tunnels to deeply understand the evolution law of permeability of laminated shale with macro fractures under cyclic disturbance. The permeability evolution of shale specimens containing axial beddings and axial macro fractures under cyclic axial stress and cyclic confining pressure was experimentally studied using the GCTS rock mechanics testing system. The results show that the permeability of shale specimens containing axial beddings did not change significantly during the loading and unloading of axial stress, but it decreased in a negatively exponential form with the increasing confining pressure and increased exponentially with the decreasing confining pressure. The permeability of shale samples containing macroscopic fractures decreased linearly with the increasing axial stress and increased linearly with the decreasing axial stress, while it decreased in a negatively exponential form with increasing confining pressure and increased exponentially with the increasing confining pressure. The permeability of shale specimens containing axial fractures is significantly higher than that of shale specimens with axial beddings, about 9 times the later one. The sensitivity of shale specimens to confining pressure is about 26 times that to axial stress. The permeability of the specimen almost keeps constant regardless of the number of axial stress loadings and unloadings, but decreases in a negatively exponential form with the increasing confining pressure cycles, and the major reduction occurs in the first cycle. The findings can somewhat provide theoretical support for the safe construction of shale gas tunnels.

Water is one of the main factors that induce mine disasters. Monitoring methods for disasters caused by mine water can be extended by studying the charge induction signal of rock deformation and failure under the interaction between water and rock. In order to study the effect of water content on the charge induced signal in the process of rock deformation and failure, we derive an electrostatic-mechanical coupling model based on the damage theory, and obtain the theoretical relationship among the amount of induced charge, the rock mechanical damage and the water-induced damage. Using the self-developed charge-induced signal acquisition system, we carried out the uniaxial compressional charge-induced signal monitoring on the rock samples with different water contents. We analyze the effects of water on the mechanical properties of rock, as well as on the charge induced signal in each stage of rock failure process, and discuss the mechanism by which water content affects the generation of induced charges. The results show that: (1) The charge induced signal in the process of rock deformation and failure is related to the damage degree of rock. The ratio of the cumulative induced charge to the total induced charge can indicate the damage level of the rock under the action of water and force. The higher the content of water is, the easier the samples that can generate a large number of charge-induced signals under lower stress. (2) The macroscopic failure characteristics of rock samples are obviously different with different water content. With the increase of water content, the compressive strength of rock samples decrease, the cracks develop, and the failure mode of the rock samples changes from single shear failure to tension and shear mixed failure. (3) In terms of the distribution of the charge-induced signal, the increase of water content increases the number of high-amplitude charge clusters, and makes them developed into the elastic stage. The high-amplitude charge-induced signals are mainly distributed in the late elastic stage and the plastic stage. (4) Considering the amount of induced charge, with the increase of water content, the proportion of induced charge released in the elastic stage gradually increases, whereas the proportion gradually decreases in the plastic stage. The amount of induced charge in the elastic and plastic stages accounts for more than 90% of the total amount of induced charge generated in the rock deformation and failure process. (5) Water weakens the rock particles and osmotic pressure, through which it makes the rock produce or expand cracks under low stress, and therefore the induced charge signals can be more abundant.

During the uplift process of suction caisson foundation, the soil at the bottom of caisson is in an axial unloading state. But there are few studies on the mechanism of the unloading creep of soft clay. Therefore, the axial unloading triaxial creep test on saturated soft clay was carried out to obtain the variation law of axial strain with time and deformation mechanism of soft clay under different confining pressures. At the same time, the long-term uplift test on suction caisson foundation was carried out to analyze the long-term uplift bearing characteristics of suction caisson foundation. The unloading creep test results show that under the condition of the low deviator stress, the unloading creep deformation of soil can be ignored. The unloading deviator stress is higher, the unloading creep deformation is greater and the nonlinear creep characteristics become more obvious. Therefore, by introducing the creep model and considering the influence of the deviator stress, the stress-dependent creep model is proposed to describe the unloading creep of soft clay. Then, the stress-dependent creep model is extended to a three-dimension constitutive model, and a finite element subroutine is developed to establish a finite element analysis method for analyzing the long-term uplift capacity of suction caisson foundations and validated with the long-term uplift bearing capacity results of caisson model.

The shear test of saturated clay with different temperatures and different heating paths was performed with the precise temperature-controlled dynamic triaxial test system. Effect of temperature on the undrained shear characteristics of saturated soft clay is explored, and the influence of different heating and consolidation methods on the pore pressure development, volume change, strength and modulus of saturated soft clay is analyzed. The results show that the undrained shear strength of saturated soft clay decreases when the ambient temperature increases from 4 ℃ to 76 ℃, but the increase in temperature has a significant effect on the increase of the soil modulus, and the relationship between them can be well fitted with the function of ET = 26.92T0.3. The excess pore water pressure of the normal consolidated clay increases with the increase of temperature, and the shear strength of the soil increases obviously after thermal consolidation, and the increase of the shear strength of the soil under the condition of drainage is less than that after the completion of thermal consolidation. When the soil mass increases from 26 ℃ by 20 and 40 ℃, the heating induced excess pore water pressure ratio is 0.41 and 0.61, and the shear peak strength increases by 8.23% and 22.37%, respectively . Studies reveal that the increase of heating amplitude will increase the degree of reconsolidation of the soil perturbation, and the more the thermal consolidation grading is, the more sufficient thermal consolidation is, and the corresponding volume change and strength growth rate are larger. At the same time, the final temperature and thermal consolidation path have an impact on the shear phase transition characteristics. The higher the temperature is, the more the thermal consolidation path is, and the more obvious the dilatancy is. However, the temperature range, consolidation classification and thermal consolidation path generally have little influence on the development of pore water pressure in general.

Ground improvement using a joint technology of combined in-situ shadow solidification and pipe-pile-reinforced foundation is one of effective methods used for deep soft clay treatment under infrastructure embankments. Based on the load transfer theory of the composite foundation, this paper analyzes the embankment filling, solidified layer, pile, soil between piles and underlying layer as a whole, and establishes the calculation method of stress and settlement of composite foundation considering the continuity of stress and settlement deformation. The deformations of pipe piles, the surrounding soil, and the overlying solidified layer are compatible by applying the stress continuity and volume deformation continuity at the bottom of the solidified layer. This paper discusses the influence of the in-situ shadow solidification on the pile-soil stress ratio and settlement of the composite foundation. The established method has been verified via comparisons with field tests data about the joint technology and traditional pipe pile-reinforced foundation. It shows that the pile-soil stress ratio in composite foundation increases linearly with the modulus of the solidified layer (with 1.6 MPa?1). The position of the neutral point of pile moves up with the increase of the solidified layer modulus (between 0.12 and 0.45). Considering the performance and reinforcement effect of curing agents, it is more appropriate to select the curing agent with cement content no more than 11%.

Richards’ equation is often used in unsaturated flow problems, and has a wide range of applications. In the numerical solution, the Richards equation is linearized first, and then the finite difference method is used for numerical discretization and iterative calculation. The traditional iterative methods such as Jacobi iteration, Gauss-Seidel iteration (GS) and SOR iteration have a slower convergence rate, especially when the discrete space step size is small and the discrete time step size is large. Therefore, we adopt the integral correction method and the multistep preconditioner to improve the traditional iterative methods, and propose a improved Gauss-Seidel iterative method with multistep preconditioner based on the integral correction method (ICMP(m)-GS) to solve the linear equations derived from Richards equation. Through examples of unsaturated seepage flow, convergence rate and acceleration effect of the proposed algorithm are validated by comparing the traditional methods and analytical solutions. The results show that the proposed ICMP(m)-GS can greatly improve the ill-condition of linear equations. Compared with the conventional methods GS, SOR and a single improvement method, ICMP(m)-GS has faster convergence rate, higher calculation efficiency and calculation accuracy. This method can serve as a reference for numerical simulation of unsaturated flow.

Pisha sandstone is a kind of special rock widely distributed in the middle and upper reaches of the Yellow River, which is composed of sand shale and argillaceous sandstone. Due to the low diagenetic degree, the poor cementation between sand grains, the low structural strength, and containing a large number of clay minerals, its anti-weathering ability is weak. Pisha sandstone becomes sand when encountering wind and becomes mud when encountering water, which is an important source of "sediment delivery into the Yellow River". Based on microbially induced carbonate precipitation (MICP) technology, the weathered Pisha sandstone soil was improved and reinforced. Aiming to obtain good strength of improved soil samples and combine with the analysis of physical properties and pore structure, the optimal scheme design of improvement for the soils containing many fine-grained soils was carried out. Under 12 working conditions, the artificial control with crystal forms, crystal morphology, and crystal size were carried out through three experimental control factors: the concentration of the bacterial solution, the dosage ratio of bacterial solution to calcium source solution, and the molar ratio of calcium to urea. The results show that when the urea consumption was 0.4 mol, using the test scheme that the bacterial solution concentration OD600 was 1.2, the ratio of bacterial solution to calcium source solution was 1:20, and the ratio of calcium to urea was 1:1, it is found that the calcium carbonate crystal induced by microorganisms was deposited in the form of "20?30 μm calcite-vaterite aggregates". These aggregates were filled in the pores of the weathered Pisha sandstone soil to increase the soil compactness, and therefore the sample porosity was reduced by 62.4%, enhancing the corrosion resistance. The improved soil also showed good strength characteristics with 1 MPa of unconfined compressive strength. Due to the filling and cementation of this calcium carbonate crystal, the strength remained 43.6% after being saturated with water, which solved the problem of the soil collapsing in water. The research results expand the application of MICP technology in the reinforcement of mixed soil with a large amount of fine-grained soil and provide a theoretical and experimental basis for the engineering application of the improvement of weathered Pisha sandstone soil.

Aiming at the site boundary effects on the hypergravity shaking table, with the benefits of a newly developed flexible laminar container, we design and carry out comparison tests between the dry sand and the water centrifugal model. We introduce the metrics including the acceleration peak error EPGA, the normalized mean square error NMSE, and the peak frequency error EF, to evaluate the shear efficiency and boundary effects of the laminar container. The results show that compared with the center accelerations of the soil, the maximum values of EPGA, NMSE and EF for the laminar beams can be 21.50%, 21.36% and 3.1%, respectively, with the dry sand model, indicating the shear efficiency of the laminar container. Under the same dynamic load conditions, the peak acceleration and the peak frequency of each laminar beam in the dry sand model are 2.37 and 2.23 times of those of the water model, indicating that the response of the laminar beams in the dry sand model is controlled by the response of the soil, which further verifies the excellent shear efficiency of the laminar container. The shear modulus and the damping ratio are similar between the laminar beams and the center of the soil in the dry sand model, with the relative differences of 3% and 18%, respectively; the shear modulus of laminar beams in the water model is 1/3 of that in the dry sand model, which is only 9.22 MPa; but the damping ratio is relatively large, which is 34.8%. Taking 5% of the acceleration peak error as the threshold of the boundary effect, the test results are valid and reliable in the range of about 90 cm×26 cm at the center of the laminar container. The proposed methods and conclusions should have important guiding significance and application value for evaluating the boundary effect of the laminar container of the hypergravity shaking table.

The direct measurement of unsaturated permeability coefficient is costly and the accuracy cannot be fully guaranteed. Therefore, the establishment of a simple and practical prediction model for saturated/unsaturated permeability coefficient based on Darcy’s law has important theoretical and practical significance. In this paper, a self-made unsaturated permeability device was used to test the unsaturated permeability coefficient of Yan’an compacted loess with different dry densities, and the pore size distribution curve was determined by nuclear magnetic resonance technology. Based on the characteristics of pore distribution, Darcy’s theorem is differentiated, and the relationship model between pore ratio and saturated/unsaturated permeability coefficient is established. The research results show that the parameters (D and B) in the prediction model can be determined by the slope and intercept of the cumulative pore volume at two points (peak point and half-width point) on the pore size distribution curve and the pore size in a straight line in double logarithmic coordinates; the porosity ratio and the dominant pore diameter have a linear relationship in the double logarithmic coordinates, and the model parameters can be expressed by the porosity ratio; the predicted results of the model are basically consistent with the measured values, which suggests that the proposed model is simple, reliable and practical.

According to the structural evolution behaviors of undisturbed loess with different initial water contents, and based on the theory of critical-state soil mechanics, a critical-state constitutive model is proposed to describe the structural evolution and softening characteristics of undisturbed loess. The model involves stress, initial water content and strain as basic variables. By comparing the isotropic compression curves of remolded and undisturbed loess with different initial water content, the structural parameters and evolution equations of undisturbed loess with different initial water contents have been established. The model adopts the uncorrelated flow rule for plastic strain solver in terms of dilatancy equation. Nine parameters are introduced in the model, which can be calibrated from compression test and conventional triaxial shear test. Compared against the existing experimental data, it is found that this model can not only describe the influence of initial water content on the strength, deformation characteristics and failure mechanism of undisturbed loess structure, but also reasonably predict the hardening and softening characteristics of undisturbed loess. The critical state model of structural loess established in this paper provides a solution for further study of mechanical properties of loess and a theoretical basis for adequate calculation of the collapsibility and deformation of loess foundation.

In order to explore the failure precursors of layered slate, uniaxial compression tests of five groups of slate with different bedding angles (? = 0o, 30o, 45o, 60o, 90o) were carried out. The failure modes, acoustic emission (AE) parameters and multifractal characteristics were analyzed, and the relationship between multifractal spectrum width (Δ?) and damage evolution was discussed. In addition, the precursor and warning time of final failure based on multifractal were determined. The results show that when the ? increases from 0o to 90o, the failure modes of slate change from tension-splitting failure to splitting-shear, then to shear slip, and finally to tension-splitting. Moreover, the abrupt increase of AE counts and the continuous increase of low-frequency (LF) and high-amplitude (HA) signals can be identified as precursors. And the proportion of LF-HA signals in the crack coalescence stage decreases first and then increases with the increase of ?. The sudden decrease and the following increase of Δ? can also be the precursor. Furthermore, the sudden increase time of Δ? is ahead of the damage mutation. Specifically, with the ? increasing, the early warning time of Δ? increases first, then decreases and then rebounds. The slate with ? = 30o has the longest early warning time.

A 3D reconstruction of complex-shaped particles based on the multi-view 2D image is processed. The complex-shaped calcareous sand particles are taken as samples, and the typical complex-shaped particles such as block, strip, and dendrite are reconstructed. The final reconstruction accuracy is characterized by convexity, circularity, aspect ratio, and other shape indicators. In the reconstruction process, the initial projection surface of the particles is rotated around an axis to obtain a series of 2D projection images of the particles, and the boundary coordinates are extracted. Then, a 3D point cloud is used to match the coordinates of the obtained 2D image contours, and the set of points located outside the 2D image contours is deleted so that all points are located within the obtained series of 2D image contours. The point cloud is further materialized and constructed to obtain the 3D solid on this basis. By reconstructing 150 particles of different shapes, it is found that the reconstruction error of more than 90% of the particles is within 10%, among which, the largest error range is dendritic particles with the maximum error of 10.84% and the minimum error is less than 1%. The method is simple and it can effectively construct 3D models of complex-shaped particles with high accuracy.

The slurry produced by sand-washing engineering of excavated soil has the problems of poor dewatering property and instability, which are closely related to the dewatering performance of slurry. In this study, sand-washing slurry samples with different dewatering performances were obtained by simulating the field sand-washing process, then the modified filtration loss test and simulated pressure filtration test were carried out to study the influence of sand-washing process on the dewatering performance of sand-washing slurries, so as to find an index for rapid characterization of the dewatering performance of slurries, which can be used to guide the optimization of the sand-washing process. The results show that the dewatering performance of sand-washing slurry was significantly affected by the mesh size and the amount of water added. The filtration loss and hydraulic conductivity indicated a good correlation with the dewatering performance. In particular, the filtration loss at 30 minutes was nicely correlated with the final filtration loss and the final water content of filter cake, which can accurately reflect the dewatering performance. The results of simulated pressure filtration test further verify that the filtration loss at 30 minutes can be used as an index to quickly characterize the dewatering performance of slurries. Based on the above results, a method is put forward for rapid detection of sand-washing slurry dewatering and optimization of field sand-washing process. The method can provide guidance for the adjustment of sand-washing process parameters in time to obtain the sand-washing slurry with better dewatering performance, which can effectively improve and stabilize the dewatering effect.

Offshore wind energy is one of the most important clean energy sources developing in China in recent years. As a new type of offshore wind turbine foundation, the wide-shallow bucket foundation with large diameter has a good ability to withstand moments. It is thus suitable for offshore region in China with soft clay deposits. Moreover, this type of foundation has advantages of onshore prefabrication, foundation-tower-turbine integrated floating transportation and suction installation, resulting in a good benefit for cost reduction. To better understand the bearing capacity of the wide-shallow bucket foundation in clay, numerical analyses are conducted to study the monotonic ultimate bearing behavior. The horizontal and moment ultimate bearing capacities and corresponding failure mechanisms are obtained. By building the velocity field based on the failure mechanisms of the bucket foundations, combined with the virtual work equation and the internal energy loss rate function, the upper bound solutions for the horizontal and moment ultimate bearing capacities of the bucket foundations are established and programmed using mathematical software. The results of the upper bound limit analysis have a good agreement with the calculation of the numerical analysis.

In the simulation of rainfall infiltration, current studies cannot realize the real-time conversion between the flow boundary and pressure boundary so as to accurately capture the groundwater movement characteristics under complicated rainfall conditions. Based on the saturated-unsaturated seepage theory, the difference between the rainfall recharge flow and actual infiltration flow on the boundary was used as a new judgment condition to distinguish the flow and pressure boundaries. The governing equation of dynamic transformation for the rainfall boundary in the single permeability medium was modified. Furthermore, the treatment method and governing equation were proposed to deal with the rainfall boundary in double permeability media. Numerical experiments and field application were conducted to verify and demonstrate the robustness of the newly proposed approaches. The simulation results suggest that the improved governing equation of dynamic transformation regarding rainfall boundary overcomes the limitations of traditional rainfall boundary processing methods, and can accurately realize the dynamic and real-time conversion between flow boundary and pressure boundary. The simulation results of rainfall infiltration on an in-situ slope illustrate the correctness and engineering applicability of the improved rainfall boundary.

With the continuous development of the underground road construction in various cities in China, accidents including damage or even collapse of the surrounding structures can often happen due to the underground excavation. Therefore, it is very importannt to predict reasonably the ground settlement for the protection of ground buildings and structures. We combine the ground settlement velocity coefficiennt with the three-dimensional imaging method, and establish a new calculation method for the tunnel surface settlement considering the time effect. We take a subway tunnel in Shenzhen as an example, and demonstrate the rationality of the method by comparing it with the on-site monitorinng data. This method is then used to further analyze the variation of the ground lateral and longitudinal settlement with time during the tunnel shutdown, and the time dependencies of the ground settlement and the settlement velocity are studied through a parameter analysis. The results show that the ground settlement and the maximum slope of the longitudinal settlement increase gradually with the increase of shutdown time and eventually tend to be stable. The maximum ground settlement velocity increases following a logarithmic function with the increase of the excavation speed and the settlement velocity coefficient. In contrast, the final ground settlement is less affected by those two factors. The final ground settlement and the maximum ground settlement velocity both increase linearly with the increase of the ground loss. The time at which the ground settlement velocity reaches its maximum has nothing to do with the amount of the ground loss.

Compared with traditional small deformation bolt materials, the negative Poisson's ratio (NPR) bolt/cable material has excellent mechanical properties such as large elongation, high strength, high toughness, high constant resistance, and energy absorption. Based on the research and application of macro-NPR bolts/cables, He Manchao developed a new type of micro-NPR steel material and a new type of micro-NPR bolt. At present, there are few studies on the static characteristics of the micro-NPR steel, and the applicability of the micro-NPR anchor in urban underground tunnel engineering needs to be verified by field tests. The mechanical properties of the micro-NPR steel were studied by the static tensile test in laboratory. The results show that the average elongation ratio of this batch of micro-NPR steel is 34.68%, and the constant resistance range is 203.9～240.7 kN. The tensile deformation is uniform in the whole process, and there is no yielding platform and no obvious necking when breaking. Through theoretical derivation, the elastoplastic incremental constitutive model of the micro-NPR bolt under micro-static tensile condition was established. Taking the air duct section of a subway station as the engineering background, this paper introduced the construction technology of the micro-NPR bolt, and tested the ultimate pull-out force, elongation ratio, and axial force on site. The results show that the micro-NPR bolt has the advantages of high constant resistance and large elongation. The application test of the bolt supporting was carried out in the tunnel with the large-deformation surrounding rock, and the large deformation control effects of the surrounding rock were verified.

The deep buried tunnels are the fundamental and dominating projects in the implementation of transportation routes, they have been developing rapidly and vigorously in the last decade. At present, the failure criterion of rock mass adopted in the elasto-plastic analysis of a circular opening is the Hoek–Brown strength criterion, in which only the maximum and minimum principal stress are considered. Obviously, the Hoek-Brown strength criterion is not compatible with the rock mass of a deep buried tunnel which bears high-level three-dimensional geostresses. On the basis of numerical procedure proposed by Lee and Pietruszczak, the deformation and stresses considering the generalized Zhang-Zhu strength criterion(GZZ) of rock mass around a circular opening are analyzed in this paper. It is found that the tunnel wall displacement and plastic radius are reduced, and both of the radical stress and hoop stress in the plastic zone are increased. It is also proved that a greater intermediate principal stress coefficient leads to higher stresses. Compared to another approach, theoretical solutions considering the effect of out-of-plane stress, the tunnel wall displacement calculated by GZZ strength criterion is reduced by 26.6% and the plastic radii are approximately the same. Finally, the GZZ strength criterion is applied as a practical approach to estimate the critical tunnel wall displacements of Jianping tunnel, then the triple bench cut method is modified to improve the advance rates of type Ⅳ and type Ⅴ rock mass, the safe and efficient cut of Jianping tunnel is achieved with outstanding engineering performance.

In view of the uneven deformation of the operating subway line caused by the short-distance upward crossing construction of the new subway shield tunnel, the shield segments of the existing line are regarded as a series of short elastic beams connected by the tension spring, compression spring, and shear spring on the Pasternak foundation. The rotation effect and shear effect between segments and the interaction between segments and soil are considered, and a method is developed for calculating the additional stress caused by the construction of new shield tunnel based on Mindlin theory, and the longitudinal deformation of the existing tunnel based on the principle of minimum potential energy. The applicability of this method is verified by comparing with the measured data and the existing methods. According to the engineering example, the proposed method is used to analyze the influence of the segment connection, soil mechanical parameters, relative position parameters between the new line and the existing line and the reinforcement effect on the longitudinal deformation of metro shield tunnel. The results show that the friction force f and grouting pressure p heavily affect the deformation of the existing tunnel when a new tunnel is constructed to the upper crossing part, and that the longitudinal deformation is mainly affected by the unloading additional stress F when the new tunnel passes through the existing tunnel. With increasing shear stiffness ks and tensile stiffness kT, the uplift deformation of the existing line decreases, and ks has a relatively greater influence. The tunnel deformation can be controlled by enhancing the values of ks and kT, and the ring support reinforcement measures can effectively control the longitudinal deformation of the existing line, and the ring spacing of 1.5 m and 3?5 rings around the intersection point can achieve good results.

Microseismic locating method is an important part of microseismic monitoring technology, the key of which is to locate the hypocenter. We analyze the two-dimensional and three-dimensional spatial distributions of microseismic locating objective functions by using spatial gridding and calculating the objective function values of grid intersections. Accordingly, we find that the objective function is continuous and the minimum value is unique, the convergence range of single axis decreases gradually, and the convergence range of each axis varies. Using the above findings and the advantages and disadvantages of pattern search method and grid search method, we propose the variable step size accelerated search method based on continuous comparison module, the variable step size module and the acceleration module. Through the comparison of four indexes between the simulation example and the engineering data: the convergence stability, the accuracy of the results, the speed of calculation and the degree of influence of initial values of parameters, we get the results that: in the simulation example, compared with that of simulated annealing algorithm and genetic algorithm, standard deviations of objective function value, locating error and wave velocity error of the variable step size accelerated search method are all 0; the average locating error of the variable step size accelerated search method is 0.7% and 1.9% of that of other two algorithm, respectively; the average calculation time of this algorithm is 6.9% and 33.2% of that of the other two algorithm, respectively. The influence of the algorithm changing each parameter individually on the locating error is between 0.005 m and 0.025 m; reducing the lower limit of the step size for search can effectively improve the accuracy of the results but increase calculation time. When the initial arrival time, objective function model and coordinates of the geophone position are specified, the search algorithm has no substantial impact on the locating accuracy.