To evaluate the air tightness of lined cavern for compressed air energy storage, a kind of unsteady seepage equation considering the influence of air leakage and porosity of concrete lining in the cavern is derived based on seepage flow theory of porous media, and an approximate analytical solution for approximate calculation of air pressure in the cavern is given. To solve this kind of nonlinear parabolic equation accurately, an unconditional stable implicit difference scheme with second order accuracy is constructed by using finite difference method. The results show that, compared with the traditional air leakage estimation formula based on the steady seepage theory, the air leakage calculated considering unsteady flow process of air is slightly smaller. When the permeability of concrete lining with a thickness of 0.5 m is less than 6×10?20 m2, the percentage of air leakage within 24 hours in a compressed air energy storage cycle is less than 1%, ordinary impermeable concrete cannot meet the requirements of air leakage control, and special sealing measures are thus needed. The air leakage percentage of compressed air energy storage cavern is related to lining permeability, air storage pressure, lining thickness. The lower the permeability is, the larger the gas storage pressure is, the larger the lining thickness is, the smaller the air leakage percentage is, and the control effect of lining thickness on gas leakage decreases with the increase of lining thickness.

As an excellent backfill material of the joints and gaps in high-level radioactive waste disposal repository, granular bentonites have a great application prospect. The thermal conductivity of granular GMZ bentonite was studied compared with compacted powder bentonite, using a thermal probe method under variable parameters including temperature, dry density and water content. The test results show that at the same condition, the thermal conductivity of compacted powder bentonite is higher than that of granular bentonite. With increasing the dry density, such difference in the thermal conductivity has decreased at constant water content. Temperature effect on the thermal conductivity of granular bentonite has increased with the increasing temperature and water content, as well as decreasing dry density. One possible explanation is that the size of inter-aggregate pores of compacted powder bentonite specimens is larger than those of compacted granular bentonite specimens at the same dry density, which causes it more conducive to the heat transfer within the compacted powder bentonite specimen, consequently its thermal conductivity is larger than that of granular bentonite specimen. As the dry density increases, the inter-aggregate pores of granular bentonites decrease, which weakens the influence of the latent heat transfer of vapor and thus reduces the temperature effect.

In order to investigate the stress, deformation, and stratigraphic effects of surrounding rock between the supported and unsupported TBM tunnels in deep mixed strata, an experimental investigation was conducted by a self-developed biaxial plane strain similarity model test system. The stress-strain measurement devices and the self-developed refinement digital photogrammetric measurement system named PhotoInfor were applied in this study. The results show that the stress distribution and failure mode are distinctly different between the upper-soft and lower-hard strata, showing an obvious non-uniformity stratigraphic effect. The stress in hard rock is larger than that in soft rock. As the confining pressure increases, the internal stress of surrounding rock firstly increases and then decreases along the radial direction for both supported and unsupported tunnels; under the unsupported condition, the evolution of the deformation and failure process and the broken rock zone of the surrounding rock have been fully investigated. The upper-soft rock is dominated by collapse, while the lower-hard rock is dominated by fracture. The development stages of radial displacement for surrounding rock is also summarized; the supporting structures effectively improve the stress redistribution and the integrity of surrounding rock, slow down the unloading speed and enhance the self-bearing capacity of surrounding rock.

The reinforced retaining wall with composite full-height rigid facing is a new reinforced retaining wall developed in recent years. The wall facing is composed of precast concrete slab and cast-in-place concrete. Based on the test section of Chengdu-Kunming railway, the in-situ tests of the reinforced retaining wall were carried out, and the corresponding design principle was proposed according to its structural characteristics. During the construction, sensors were installed in different parts of the retaining wall for long-term monitoring. The evolutions of vertical stress on basement, earth pressure on wall back, geogrid strain, settlements of basement and wall top, facing horizontal displacement during and after construction were analyzed. Two earthquakes occurred after the completion of the wall facing. The changes of the retaining wall before and after the earthquake were monitored, and the influence of the earthquakes on the structural behavior of the retaining wall was studied. The results show that: with the increase of filling, the vertical stress on basement and the earth pressure on wall back gradually change from linear distribution to nonlinear distribution. The shape of peak geogrid strain surface along the wall height is similar to the “0.3H (wall height) method” fracture surface. After the earthquake, the vertical stress of basement, settlements of basement and wall top, facing horizontal displacement increase, while the earth pressure on wall back and geogrid strain increase firstly and then decrease.

The integral abutment jointless bridge (IAJB) has lots of advantages, so it has been widely used in western countries. The pile foundation of IAJB requires higher horizontal deformation capacity. H-beam steel piles are often used to construct integral bridges in the west, while RC piles are mainly adopted in China. Lots of studies and engineering examples show that the application of RC piles can meet the deformation requirements of IAJBs, but the influence of the earth pressure behind abutment on RC piles is not clear. Therefore, based on a practical IAJB in China as an engineering background, with certain RC pile reinforcement ratio and the shape of the section as parameter, four integral abutment-RC pile test models were designed. The reciprocating low-cycle pseudo-static test on interaction of integral abutment-H-shaped pile-soil was carried out to study the hysteretic behavior, lateral deformation law and interactive mechanism. The test results show that under the reciprocating displacement loading, the soil behind the abutment will be emptied, and the failure positions of the specimens are mainly concentrated at the connection between the bottom of the abutment and the top of the pile. Increasing the reinforcement ratio of RC piles or using rectangular section RC piles can lower the failure positions and improve their mechanical properties. The hysteretic curve of the integral abutment-RC pile-soil system is full in the first quadrant, indicating better energy dissipation capacity, while the third quadrant hysteretic curve has a smaller covering area. The experimental results also show that the abutment movement can be regarded as a rigid displacement with rotation, and under the action of reciprocating displacement beyond the limit of elastic deformation, the abutment and the pile appear obvious cumulative deformation. Besides, the relative angle between abutment and pile head increases as the damage degree increases. Accordingly, by increasing the reinforcement ratio of RC piles or adopting rectangular section RC piles, 1) the energy dissipation capacity of the whole bridge-RC pile-soil system can be increased; 2)the elastic cracking displacement of RC piles can also be increased, which leads to its later yield and failure and increases the bearing capacity of the whole system; 3) the stiffness degradation rate and degradation amplitude of the system are significantly reduced; 4) the failure of bridge abutment and pile joint, along with the accumulated deformation, can be effectively reduced.

Cone penetration test (CPT) is an in-situ test method to obtain common geotechnical parameters accurately, but CPT data cannot be directly converted into macro constitutive model parameters (i.e., a type of fine geotechnical parameters). The principal reason is that there is insufficient research on the macro and micro penetration mechanism. Based on the Mohr-Coulomb failure criterion of cylindrical (cone) cavity expansion theory, a macro and micro coupling numerical calculation method for the CPT process is established. Firstly, based on the cavity expansion theory, the limit pressure in expansion is solved, and the relationship between the cone resistance, sleeve friction and the limit expansion stress are derived. Secondly, taking the ②1 silty clay of the shallow bearing layer as the research object in Shanghai, through the same scale triaxial compression tests, the conversion formula of the geotechnical parameters in the macro finite element with micro discrete element coupling calculation is established, the formula is calibrated by ②1 silty and ⑤1-1 gray clay. Finally, taking the ②1 silty clay as the research object, the error of the theoretical solution, numerical solution and measurements of cone resistance, sleeve friction and limit pressure in expansion of cylindrical cavity are analyzed from a macro perspective. Soil particle deformation and contact force chain are analyzed from the micro perspective. The errors of the limit pressure of expansion, cone resistance and sleeve friction calculated using the theoretical method are 1.30%, 0.45% and 0.77%, respectively. The errors of the limit pressure in expansion, cone resistance, sleeve friction and pore water pressure calculated by the macro and micro coupling method are 9.68%, 2.99%, 9.19% and 8.42%, respectively. The results of the macro and micro coupling numerical calculation are not only close to the results of the cylindrical (cone) cavity expansion theory, but also considering the effect of pore water pressure. Above research provides a macro and micro coupling numerical method for simulating the CPT mechanism and obtaining the parameters of the specific constitutive model.

Based on Barron’s equal strain consolidation theory, the consolidation governing equation of sand-drained foundation under vacuum combined surcharge preloading is derived and a general analytical solution is obtained, which considers the vacuum loading process, the time-dependent surcharge loading, the characteristics of the vacuum pressure decreasing along the depth and radial direction, and the well resistance of vertical drains and the vertical flow. The correctness of the analytical solution proposed in this paper is verified by comparing the degenerate analytical solution with the existing analytical solution and the finite difference solution. Based on the analytical solution, the consolidation behaviors of sand-drained foundation are analyzed. The analysis shows that the consolidation rate of sand-drained foundation is accelerated with the increase of vacuum loading factor ?. However, when ? increases to a certain extent, the influence of vacuum loading process on the consolidation rate of sand-drained foundation can be ignored. The consolidation rate of sand-drained foundation decreases with the increase of vacuum pressure attenuation coefficient k1 and k2. The consolidation rate of sand-drained foundation decreases with the increase of vacuum pressure p0 and increases with the increase of final surcharge loading qu. With the increase of loading time Th1, the consolidation rate of sand-drained foundation decreases gradually, and the consolidation rate is the largest under instantaneous surcharge loading.

A model experiment of passive soil with limited width behind a rigid retaining wall was carried out using non-cohesive coarse sand, with the soil images during the experiment collected through a high-speed camera. In addition, the soil deformation and shear strain were analyzed based on the digital image correlation method to reveal the slip surface characteristics in 3 movement modes: translational mode (T mode), rotate-about-top mode (RT mode), rotate-about-base mode (RB mode). The results show that: the boundary value of width to height ratio (B/H) of soil with finite passive width is, B/H≤2.0 for T mode, B/H≤1.6 for RT mode and B/H≤1.1 for RB mode. In T mode, when 1.6≤B/H≤2.0, the passive slip surface is composed of two discontinuous fracture surfaces, the lower and upper fracture surfaces start from the heel of the moving retaining wall and the top of the fixed retaining wall respectively; when 1.10≤B/H≤1.35, the slip surface is a curved surface, the starting point and the end point are the heel of the moving retaining wall and the top of the fixed retaining wall respectively; when B/H≤0.75, the slip surface is a "reflective broken line" composed of multiple straight lines, and the horizontal angle between the sliding line starting from the moving retaining wall and the fixed retaining wall is obviously different. In RT mode, the passive slip surface is a curved surface which passes through the H/4 point, the heel of the moving retaining wall and the top of the fixed retaining wall; in RB mode, the passive slip surface starts from the top of the fixed retaining wall and extends to the middle of the moving retaining wall, and the height of extension point gradually increases with the decrease of B/H.

Subject to geological processes, natural rock fractures can be dislocated to some extent, and the normal deformation behavior of such dislocated fractures has not been quantitatively estimated, and the applicability of classic deformation models has not been verified against experiments and numerical simulations. The deformation and failure behavior of dislocated sandstone fractures were studied via compression tests and elastic-plastic contact simulations. The obtained stress-displacement curves were fitted by a hyperbolic model, an exponential model and a logarithmic model, respectively and the coefficients involved in these models were estimated. The results show that the experimentally and numerically obtained stress-displacement curves agree well with each other, and the surface damage areas are also consistent, which verified the reliability of the elastic-plastic contact model. The hyperbolic and logarithmic models do not fit the curves well under relatively low stress levels, while the exponential model well accommodates the simulation results in the whole loading process by introducing a coefficient n. The maximum closure Vmax is positively correlated with the maximum local aperture, the initial normal stiffness Kni is positively correlated with the elastic modulus and negatively correlated with the fracture roughness and dislocating ratio, and n is positively correlated with the fracture roughness and dislocating ratio. A model was established to predict the three coefficients, and the prediction values agree well with the experimental results.

Interfaces with different strengths are usually existed in rock mass, the shear strength of these interfaces plays a critical role on the stability of rock mass, and it is thus highly important to accurately evaluate their shear strength. With the help of 3D-printed resin molds, the soft-hard jointed cement specimens with different joint roughness coefficients (JRC) and joint wall compressive strengths (JCS) were fabricated to conduct laboratory tests and numerical simulation of direct shear under constant normal stress. The test curves of shear stress-displacement agree with those by numerical simulation. Based on the test results, a coefficient of proportionality T was proposed to characterize combined compressive strength CCS of soft-hard joint, and meanwhile an influence factor ? was proposed to characterize the effects of JRC, JCS and normal stress ?n on the peak shear strength of soft-hard joint by calculation and statistics method , thus a method for estimating the peak shear strength for soft-hard join surface was derived. The residual shear strength of soft-hard joint is mainly controlled by the soft joint side, and this control effect increases with the increase of JRC. The shear stress-displacement curves of soft-hard joint with smaller CCS earlier reach the peak and enter the residual stage. The study indicates that the proposed model may be used to evaluate the peak shear strength of soft-hard joint by integrating the influence mechanism of joint surface morphology, joint compressive strength and normal stress.

Aiming at the durability problem of post grouted piles in the marine environment, micro cone penetration (MCPT), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and unconfined compressive strength (UCS) tests were conducted to study the strength change of cement stabilized calcareous sand with different curing times and cement ratios in the marine environment. The relationship between unconfined compressive strength and penetration resistance of cement stabilized calcareous sand was obtained and compared with the experimental results of cement stabilized siliceous sand, the micro-erosion mechanism of cement stabilized calcareous sand was revealed. The results show that according to the distribution characteristics of penetration resistance, the stabilized cement in seawater environment can be divided into eroded layer and non-eroded layer, and the erosion depth increases with the increase of curing time and the decrease of cement ratio. Compared with the non-eroded layer, with the increase of curing time, the porosity of the eroded layer increases, and the amount of hydration products decreases. At the same time, the Ca contents significantly decrease. In addition, according to the distribution laws of the temporal and spatial variation in the strength, the microstructure and the phase composition of the cement stabilized sand, it can be found that the strength change of the cement stabilized sand in seawater erosion environment is a common result of the strengthening effect of hydration reaction on the strength of cement stabilized soil and the weakening effect of erosion reaction on the strength of the cement stabilized sand. The research results can provide a reference for evaluating the durability and long-term stability of post grouted pile in calcareous sand.

The soil-freezing characteristic curve (SFCC) is significantly affected by the specific surface area of soil particles. The existing studies about the relationship between the SFCC and the specific surface area so far have mainly taken natural soils as research objects, which cannot avoid the interference of other factors such as dry density and total water content, and the test data obtained are discrete. In the present study, Qinghai-Tibet silty clay and bentonite are mixed in different proportions to prepare artificial soils with various specific surface areas. The temperature-controlled nuclear magnetic resonance (NMR) test and the freezing temperature test are conducted on these artificial mixtures. The test results indicate that: (1) In comparison with the classical three-stage SFCC, the SFCC of the mixtures consists of four stages, i.e., the super-cooling stage, the rapid-drop stage, the slow-drop stage, and the stable stage. As the specific surface area increases, the changing range of the unfrozen water content (wu) in the rapid-drop stage narrows, correspondingly the changing rate of wu in the slow-drop stage and wu in the stable stage both increase. (2) As for the temperature-time relationship curve obtained from the freezing temperature test, the duration of its isothermal stage decreases with the rise of specific surface area, while its corresponding freezing temperature decreases. (3) According to the evolution of transverse relaxation time distribution curve with temperature, it is found that the mixture with a larger specific surface area has a higher content of bound water. Bound water is strongly constrained around soil particles and exhibits lower freezing temperature, making the mixture with the larger specific surface area more difficult frozen, which is the rudimentary reason that the specific surface area influences the SFCC.

The decrease of rock stability is caused by the possible deterioration of rock mechanical properties under high temperature environment. Therefore, the study of the constitutive behavior of rocks under high temperature is of great significance. Based on the recent researches of statistical rock damage constitutive model, the statistical damage constitutive model of rock after high temperature is established by adopting M-C criterion with the thermal damage variable and Weibull distribution function and the parameter expression is determined. The model is compared with the theoretical curve to verify its rationality. Finally, the model is verified by the uniaxial compression test results of sandstone under different temperature conditions (e.g., 25℃, 80℃, 100℃, 150℃). The results show that the theoretical curve of statistical damage constitutive model of the high-temperature rock established in this paper has the same trend as the theoretical curve in the literature, proving that the established constitutive model is reasonable. The theoretical curve of the model is in good agreement with the curve obtained in the experiments, implying that it can represent the stress-strain characteristics of sandstone failure under the condition of uniaxial test. This model does not contain unconventional mechanical parameters, and the physical meaning is clear. The research results can provide theoretical support for related calculations and numerical simulations of rock mechanics after high-temperature treatment.

Most of the constitutive model for liquefaction analysis cannot simulate the large post-liquefaction deformation of saturated sand, and there is little research on the nonlinear time-domain large deformation constitutive relationships suitable for seismic response analysis of saturated sand sites. In this paper, a feasible, simple and applicable large deformation constitutive model for time domain analysis is proposed through experimental analysis and theoretical research. The post-liquefaction stress-strain relationships of liquefied sand are obtained based on the undrained cyclic triaxial test data, then loading-reloading rules of large post-liquefaction deformation are proposed. Combined with the effective stress constitutive model based on logarithmic skeleton curve, a constitutive model that can quantitatively describe the large deformation of saturated sand liquefaction is proposed. According to the test results, the constitutive model can simulate small to large deformations from the pre-to post-liquefaction regime of sand. This constitutive model is also implemented to the program Soilresp1D for the dynamic response analysis of liquefiable soil sites. The results show that the time domain nonlinear large deformation unified constitutive model based on the logarithmic dynamic skeleton curve, effective stress-modified logarithmic dynamic skeleton constitutive model and liquefaction large deformation constitutive model can be directly applied to the dynamic response analysis of saturated sand.

Constant resistance and large deformation bolt has the excellent characteristics of high constant resistance force, large deformation and high energy absorption, and is thus widely used in the reinforcement and monitoring of roadway, tunnel and slope engineering. A nonlinear mechanical model of constant resistance and large deformation bolt is established based on the analysis of the characteristics of constant resistance anchor. The model could unify the rising section and the stick slip section of constant resistance force, and can more completely describe the mechanical behavior of the constant resistance and large deformation bolt. Moreover, the dimensionless method is used to analyze the four parameters ?, ?, ?d and f, which affect the mechanical behavior of the constant resistance and large deformation bolt, and the influence characteristics of each parameter on the mean value of constant resistance force, amplitude, vibration period and main vibration frequency of the system in the stick-slip phase are obtained. Finally, the nonlinear model is verified based on the finite element numerical simulation method, and the accuracy of this nonlinear mechanical model is proved. Meanwhile, the influence characteristics of the constant resistance body bulk modulus, casing bulk modulus and tensile speed on the constant resistance stick slip behavior of the constant resistance and large deformation bolt are researched. The results could provide a theoretical basis for the subsequent optimization design and engineering application of the constant resistance and large deformation bolt.

In order to characterize the rheological properties of surrounding rocks after the excavation of circular tunnel, theoretical solutions of radius, stress and displacement of the plastic zone for surrounding rocks after the excavation of circular tunnel are derived by using the Drucker-Prager yield criterion and considering the viscosity and dilatancy characteristics of plastic zone, assuming the constitutive model of surrounding rocks as the Nishihara model. When the dilatancy angle is 0, the solutions change into viscoelastic-viscoplastic solutions based on the Nishihara model and Mohr-Coulomb criterion under the assumption of constant volume. The effects of dilatancy angle on the radius of plastic zone, tunnel-wall displacement and stress field are analyzed. The solutions for viscoelastic-viscoplastic displacement and viscoelastic-plastic displacement are compared and analyzed. The results show that before the surrounding rock reaches the steady state, the effects of dilatancy angle on the stress field and the radium of plastic zone are relatively smaller while the effects of dilatancy angle on the tunnel-wall displacement is relatively larger. The stress field and the radium of plastic zone for stable surrounding rocks are independent of the value of dilatancy angle, however, the tunnel-wall displacement of steady-state rock increases obviously with the dilatancy angle. When the dilatancy angle is large, the viscosity of plastic zone should be considered; otherwise the tunnel-wall displacement of steady-state surrounding rocks will be underestimated. The research results are of certain reference value for practical engineering.

In order to study the response of granite residual soil slope with cracks under different number of drying-wetting cycles (D-W cycles), model test was carried out and the crack width expansion index was quantified by investigating the crack images. Based on the direct shear test, the calculation formulas of soil strength degradation and crack depth were developed. Then, the model test and the numerical simulation results were compared to analyze the response of the residual soil slope considering crack extension. The results showed that the fractures width expansion in residual soil under D-W cycles followed the Logistic model, and there was a quantitative relationship between fracture depth and strength degradation. The fracture depth tended to be stable with the increase of D-W cycles. When the number of D-W cycles was small, the change of moisture content at the bottom of the slope lags significantly behind that at the top and the middle of the slope, however, the change of moisture content at each position of the slope tended to be the same with the increase of D-W cycles. The deformation at the bottom and the middle of the slope with the crack expansion tended to be the same compared to the slope without cracks, however, the deformation at the top area was larger, which led to the increase of the deformation gap between the top and bottom of the cracked slope.

Helical pile is widely applied in engineering, such as solar photovoltaic panel, transmission tower, etc. However, the research focused on the vertical or horizontal bearing capacities of helical piles is relatively limited. Especially, the bearing capacity and the bearing mechanism of inclined pile group are still unclear. The comparative model tests of vertical and inclined helical pile groups embedded in sand are carried out. The pile top load-displacement curves and the distribution of soil pressure on the plate of the helical pile group (vertical pile group and 15° inclined pile group) under vertical uplift or lateral load are measured. The ultimate bearing capacity, the load distribution ratio of the plate, and the group effect of inclined helical pile group under vertical uplift or lateral load are comparatively discussed. The results show that the ultimate uplift or lateral bearing capacity of the inclined helical pile group are larger than those of the vertical pile group in the model test conditions, respectively; the peak value of the plate load distribution ratio of the inclined pile group (15°) under the vertical uplift load is smaller than that of the vertical pile group; the maximum lateral earth pressure in the front and behind row of the inclined pile group is both larger than that at the same position of vertical one.

The large scale construction of both military and civil infrastructures located in Nansha reefs and offshore marine areas, South China Sea, has raised the seismic safety a challenging issue for the projects in the region. The influences of fines content (FC) on the liquefaction characteristics of saturated terrestrial quartz sands have been extensively studied, but the corresponding research on saturated coral sands in reclaimed coral islands is less involved. Using the GDS hollow cylinder torsion shear apparatus, a series of isotropically consolidated undrained cyclic tests has been performed on saturated coral sand sampled from the Nansha Islands, South China Sea. The samples are prescribed with the stress path formed under the 90° jump rotation of principal stress with various cyclic loading directions. The influences of the inclination angle (?d) of the major principal stress and fines content FC on the liquefaction characteristics of saturated coral sand are investigated. It has been discovered that, regarding the zero effective stress state as initial liquefaction criterion, the liquefaction resistance of saturated coral sand decreases with the increase of ?d for 0°≤?d≤45° and FC for 0%≤FC≤30%. The correlation among the generalized shear strain amplitude (?ga), the fines content FC, and the revolution of residual excess pore water pressure of saturated coral soil has been clearified. By introducing a unit cyclic stress ratio USR as a new index for liquefaction resistance and based on binary medium theory, the expression between the unit cyclic stress ratio USR15, inducing initial liquefaction in 15 cycles, and the equivalent skeleton void ratio for the saturated sands is established for the test. The theory is validated by the experimental data in the literature.

Permeable pipe piles are set in the soft soil foundation to accelerate the dissipation rate of excess pore water pressure induced by pile driving and then to accelerate the consolidation of soil around the pile. At present, there are many studies, including model tests and numerical simulation, on the bearing capacity and permeability performance of permeable pipe piles. However, few field tests have been conducted to deeply study the time effect of bearing capacity and load transfer law of permeable pipe piles. Based on the fiber Bragg grating (FBG) technology, the static load tests were carried out to study the strain distribution and internal force transfer of the permeable pipe pile in soft soil foundation. Meanwhile, the relationship between the variation of excess pore water pressure of the pile-soil interface with time at different positions of the pile body and the time effect of bearing capacity of the permeable pipe pile was analyzed. The test results showed that at the early stage of pile driving, the growth rate of bearing capacity of a single permeable pipe pile under increased vertical loads was higher, and then gradually decreased with time. Under the test site conditions, the improvement of the bearing capacity of the permeable pipe pile within 10 days was mainly attributed to the pile side friction, whereas the pile tip resistance made more contribution to the improvement of bearing capacity within 10-24 days. The excess pore water pressure of the pile-soil interface increased along with the depth of the pile. With the rapid dissipation of excess pore water pressure near the pile tip, the effective stress of soil gradually increased, and the pile side friction and pile tip resistance also increased. This study provides an improved insight into the design and construction of permeable pipe piles in soft soil foundation.

To determine seismic permanent displacement of a new type of assembled multi-step cantilever retaining walls, based on overall rotation-sliding failure mode of the wall-slope system with potential slip surface passing by the bottom edge of the heel plate of the lowest wall member, the seismic yield acceleration coefficient of the wall-slope system is proposed by the upper bound limit analysis and pseudo-static method. Moreover, according to Newmark’s block method, calculation formulas of seismic horizontal permanent displacement at the top of each step of the wall including two, three, and four steps are derived via angular displacement of the wall-slope system determined by quadratic integration of the rotational angular acceleration. Compared with shaking table tests and numerical simulations of the wall models with two and three steps, the horizontal permanent displacements under two-step and three-step walls calculated by the proposed analysis method are 10-40% and 10-30% larger than those by the tests, respectively. However, the theoretical results are relatively close to the numerical simulation results. Analysis results of the practical example show that the proposed method is generally more conservative than the numerical simulation method. Internal friction angle and cohesion of the backfill have greatly positive correlation with the horizontal yield acceleration of the wall-slope system, while the height of a wall member has obvious negative correlation with the horizontal yield acceleration of the wall-slope system. However, width of the bench between vertically adjacent wall members, length and thickness of bottom plate of a wall member have little effect on it. In addition, the total number of the vertically assembled walls has nonlinear and positive correlation with the horizontal yield acceleration, and the seismic horizontal permanent displacement of the system is decreasing as the filling soil particle size decreases gradually.

To solve the problems of preventing and controlling water for vertical shaft in ultra thick dissolved porous dolomite aquifer in southwest China, a grout-water two-phase radial diffusion model is proposed to study the diffusion laws of the grout in the porous stratum based on Darcy’s law. The fractional-flow equation of grout is derived and the advancing distance of the grout saturation along the radial direction is obtained. According to the distribution of the grout saturation along the radial distance, the diffusion area could be divided into grout area, grout-water mixing area and water area. The shock saturation front is the interface between the grout-water mixing area and the water area. The grout saturation face moves forward with the grout injection, and the effective diffusion distance of the grout to meet the requirement of water prevention is significantly smaller than the diffusion distance of the shock front. Moreover, the technical parameters of surface pre-grouting for sealing the dissolved porous dolomite aquifer in ventilation shaft of the Laohudong phosphate mine are studied by field test combining with numerical simulation. The optimal borehole spacing and effective diffusion distance are obtained. Consequently, the engineering design of surface pre-grouting for the ventilation shaft is proposed based on these technical parameters. Finally, after the completion of grouting, the sealing efficiency of the grouting for the ventilation shaft could reach up to 98.04% obtained from the water pressure test. The research results of the present paper could provide technical reference for water sealing by grouting for similar porous aquifer.

Mechanical analysis of laterally-loaded piles embedded in multi-layered soils is a critical step in design. Traditional finite-element method may have deficiency in accuracy and efficiency when applied to analyze this problem. An efficient finite-element method is proposed in this paper. A “pile element” that adopts the distributed “soil springs” along the element length to reflect the nonlinear behaviors of the pile-soil interactions is developed in this method. The dominant feature of the pile element is the direct integration of soil properties into the element formulation, namely, a pile element comprises both the pile and soil properties. The pile element formulation in multi-layered soils is derived, and the Gauss-Legendre method is introduced to simplify the total potential energy summation process. The element stiffness matrix is derived and applied to Newton-Raphson incremental iterative numerical process, and the secant relations are used to minimize the cumulative errors during the numerical iteration process. Besides, the updated Lagrangian method is employed to account for the large deformation issue. Results show that: 1) the proposed method can provide predictions that match well with both the theoretical solutions and field test data; 2) using the pile element model can substantially reduce the number of elements and calculation time compared with those of the discrete element model, and thus significantly improve the calculation efficiency.

The cast-in-place pile is one of the most common forms of pile foundation. It is very important to conduct the measurement of pile deformation of the cast-in-place pile, which is of great use for understanding the bearing characteristics and quality of the pile. In this paper, optical frequency domain reflectometer (OFDR) is introduced as the most advanced technology in the world to carry out the field test on the high-precision measurement of deformation of the cast-in-place pile. During the test, the pile deformation, pile axial force and pile side friction distribution are obtained in the loading and unloading process. Simultaneously, the pile deformation characteristics and load transfer law are analyzed. The test results show that the strain of pile measured by the optical fiber sensor increases with the loading during the loading phase and decreases during the unloading phase, the pile has a certain residual stress after the unloading, however. Besides, through comparison of the pile force distribution curve in the loading and unloading process, it is found that the pile force has a time lag effect after unloading; the results prove that OFDR technology can achieve the high-precision measurement of pile deformation of the cast-in-place pile, which can be applied to investigate the pile deformation characteristics.

There are differences between explicit and implicit solution methods in design expression, definition of slip resistance etc., resulting in disputes between the two methods in terms of stability factor (safety factor) K and slip resistance of the proposed project. In view of the above problems, the specific differences between the obvious solution and the implicit solution are firstly illustrated through the comparison of examples. Secondly, the method of reliability is introduced to calculate the slope reliability index, the reason for the difference between the two methods is analyzed through the corresponding relation with the safety factor. The results show that under the same safety factor, the slip resistance of the proposed project obtained by the implicit solution is amplified, resulting in a great difference of the anti-sliding structure designed by the two methods. Under the same design parameters, the stability factor (safety factor) K of the explicit solution is not equivalent to the implicit solution, thus their corresponding reliability indexes are different. The stability factor (safety factor) between the two methods can’t be unified. The research can be used to guide the engineering design and related standards.

In order to make the frequency independent hysteresis damping in site seismic response analysis equivalent to the viscous damping for time domain analysis, an optimization method is proposed to optimize the conversion frequency of hysteresis damping, and on this basis, the optimization method of equivalent Rayleigh damping calculation is constructed. Firstly, the objective function is constructed by minimizing the cumulative acceleration error of the equivalent viscous damping system of the single degree of freedom hysteretic damping system, and the optimization algorithm of the hysteretic damping conversion frequency is established. Then, taking 21 seismic waves as input, the effects of natural frequency, hysteresis damping ratio and dominant frequency on the hysteresis damping conversion frequency are analyzed statistically. The results show that the optimal conversion frequency of hysteretic damping is mainly affected by the natural frequency, while the influences of hysteretic damping ratio and dominant frequency are very small. On this basis, taking the minimum ground acceleration response error as the objective function, the constrained optimization equation for solving Rayleigh damping coefficient is established. Finally, taking the seismic response of a valley site as an example, the computational accuracy of the proposed method and the traditional Rayleigh damping structure method are analyzed and compared, and the accuracy and effectiveness of the proposed method are verified.

Site investigations on the decay characteristics of the soil shear modulus have so far been very limited. Meanwhile, for the laboratory experiments, which may need sampling, transportation and other procedures, soil samples are normally disturbed to some extent. However, accurate descriptions of the soil modulus are important for the site evaluations as well as the structure designs. Therefore, a series of self-boring pressuremeter based in-situ tests with a maximum depth of 33m has been carried out in the lacustrine clay of Taihu tunnel area, China. Total stress-strain curves of the different soils were obtained, and on basis of that, the shear modulus decay characteristics of the soils were analyzed in detail. Shear modulus distribution along the depth was discussed under different shear strains, where a common conclusion could be obtained for different soils is that strong degradation characteristics are shown for the small strains, and then would become stable gradually as the strain increases. A correlation law between shear modulus as well as its decay characteristics and plasticity index was established. Results show that the plasticity index can be used as a reliable index to evaluate the shear modulus decay characteristics of soils.