Under applied loadings, particle aggregate produces complex effect of contact force chain between particles. In order to elaborate the formation and development of force chains and to describe the distribution and configuration of the force chains，based on the principle of optical stripes in photoelastic material under loading, an experimental equipment is developed that performs photoelastic test on particle aggregates under biaxially loading and bilaterally flowing conditions. Through case studies for different combinations of loading and particle flow conditions, the effect of force chain of particle aggregates in variety of form and distribution has been generally recognized. After the flowing of particle aggregates, an arch structure forms upon the flowing gate, which can support the upper particle aggregates to maintain the stability of the upper structure. The presented work provides a fundamental experiment method for studying force chain structure of particle flow and mesomechanical behavior of particle aggregates under different backgrounds, particularly, the special design which allows particles to flow out from both the bottom and side gates provides convenience for the practical application.

A series of model tests is conducted to explore the load transfer behavior of batter piles embedded in sand under vertical loads. The effects of inclined angle of pile and ratio of pile length to its diameter (L/D) on pile shaft axial force, bending moment, shear force, skin friction and the ratio of tip resistance to the pile head load are analyzed. The results show that: the axial force of batter pile subjected to vertical load is less than that of vertical pile; the greater the pile inclination and the ratio of L/D are, the faster the axial force attenuates along the depth. The maximum bending moment of batter pile increases with the increasing of inclined angle as well as the ratio of L/D; but the depth at which the maximum bending moment occurs is only associated with the ratio of L/D. No matter what the magnitudes of the inclined angle and the ratio of L/D are, the maximum shear force always occurs at the pile top; and the maximum shear force increases with the increasing of the pile shaft inclined angle. The larger the pile inclination and the L/D are, the greater the maximum frictional resistance is, the smaller the maximum frictional resistance of the batter pile is; the maximum frictional resistance of the batter pile always occurs at a depth of 1/4-1/5 pile length below the pile head. The end resistance ratio of batter piles increases with the increase of vertical load of the pile, and decreases with the increase of inclination angle and the L/D.

It has been shown that reactive MgO-stabilized soils carbonated by CO2 after a few hours have almost the same or even more strength of 28-day curing cemented soils. The predominant products of the carbonated reactive MgO-stabilized soils are the hydrated magnesium carbonates, which can significantly reduce the water content and porosity of stabilized soils, and increase the binding strength between soil particles. The sulfate resistance of carbonated reactive MgO-stabilized soils is further studied through laboratory tests. The sodium and magnesium sulfate solutions are selected respectively for soaking the carbonated soil samples and contrasting to cemented soil samples. After soaking different days, the unconfined compressive strength of these samples are measured, and then the microstructure characteristics are analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Mercury intrusion porosimetry (MIP) tests. The results show that the unconfined compressive strength of the MgO-stabilized soils can reach about 5 MPa after the carbonation of 3 hours. It remains almost the same strength and mass after the sulfate attack of 28 days, while the strength of the cemented soil decreases greatly after sulfate attack with its mass significantly increasing, though it increases slightly at the shorter attacking time (7 days). The microstructure analysis reveals that the hydrated magnesium carbonates generated by carbonation and its pore structure do not change significantly after the sulfate attack, thus ensuring its stable strength. Therefore, it can be concluded that the carbonated reactive MgO-stabilized soil has better resistance to the sulfate attack compared to the cemented soil.

Mudmat is commonly used as the foundation of subsea wellhead, pipeline manifold and umbilical cable. In practice, it suffers severe V-H strong coupling nonlinear loads. A new type of slope-skirted mudmat foundation is developed, which can not only reduce the current scour to empty and erode the bottom soil of foundation, but also adjust envelops in V-H loading space by changing the angle ? to match different engineering design requirements. The bearing capacity of the new type of mudmat foundation is studied in combination with the engineering design examples. The results show that the ultimate bearing capacity of the new type of mudmat foundation increases linearly with the increase of soil strength heterogeneity index ?. Effect of the contact properties between mudmat and soil on the horizontal bearing capacity is more significant than that on the vertical direction. The normalized envelope of V-H load space of mudmat foundation can generally applies to the case that the index ? varies from 0 to 10, and the Hanson equation overestimates the bearing capacity of mudmat foundation when the normalized vertical load ranges from 0.5 to 0.8.

For surcharge preloading method used in land reclamation, the effect of ground treatment is usually evaluated by subsequent deformation, which depends largely upon the overload ratio and unload controlling time. This research focuses on the double-layer soft clay foundation with the upper soft layer and lower hard layer in coastal area in Tianjin. The appropriate overload ratio and the best time of overload are determined by consolidation experiment used a modified oedometer under various overload ratios and unload controlling times. The results show that when overload ratio is larger than 0.375 and overload time is longer than the primary consolidation time, the foundation deformation is mainly resilient deformation after overload removed. At the same time, the post-construction settlement decreases significantly by up to 70 percent. Secondary consolidation coefficient significantly reduces after removing the overload, and the longer the overload time and the overload ratio are, the smaller secondary consolidation coefficient is. Unlike the homogeneous foundation and the upper hard and lower soft double-layer foundation, the post-construction settlement of upper soft and lower hard double-layer foundation mainly comes from the upper soft soil layer, accounting for more than 73% of the total settlement. According to deformation curves under different overload ratios and overload times, it is suggested that the suitable surcharge ratio is 0.5 or less and the best overload time is controlled within 1 to 3 times the primary consolidation time for the layer soft clay foundation by land reclamation in coastal area in Tianjin,

To explore the failure mechanism of deep-buried hard rock, a series of experiments was performed, including conventional triaxial tests and the compression tests by decreasing the confining pressure under constant or variable axial stress. The crack volumetric strain is selected as the key analysis variable, and using volumetric strain, crack volume strain and equivalent plastic strain, the rock failure process is analyzed under different stress paths. The phenomena and characteristics of rock failure process are clarified by using the volume strain-axial strain curve of the cracks, the equivalent plastic strain-axial strain curve and the axial stress-strain curve. It is shown that the crack volumetric strain can be used to reflect the extent of rock initial damage, the crack closure has an important influence on the calculation of elastic modulus of rock, and to obtain accurate modulus, the crack closure needs to be divided into appropriate stages to eliminate the influence of the crack closure stage on the elastic modulus calculation. In addition, at the moment that the confining pressure decreases, the cracks of rock sample are closed suddenly, leading to a mutation of the volumetric strain-axial strain curves of the cracks. There exists hysteresis in the crack growth during the unloading failure of rock. The above results can help understand the process of rock failure, while providing a theoretical basis for preventing the failure of hard rock under high stress conditions.

To explain the differences between matric suction measurements under natural environment and axis translation conditions, the influences of surface tension coefficient and micropores, which are hard to be saturated on water content under the same suction, are studied. It is found that while the axis translation technique can depress water content since the surface tension coefficient decreases slightly with pressure increase, it increases the water content due to the existence of closed micropores which can hold some amount of water at high pressure. As a result, the water content in axis translation conditions may be larger or smaller than that in natural environments at certain matric suction depending on the competition of the above two mechanisms. The capillary rise test and the study of one-end closed pore model show that the influence of the closed micropores on the soil-water characteristic curve (SWCC) is far greater than that of the surface tension coefficient. Based on the experimental results of quartz sand, sand and clay, it is shown that as the soil particles become finer, the effect of axis translation technique on SWCC becomes more and more obvious. Hence, it is clear that the difference of SWCC, measured by axis translation technique, is owing to the micropore closed at one end.

Clay mixed with gravel is becoming widely used as a core material of high earth and rockfill dams. Its tensile fracture characteristics are crucial to the safety of the core wall. Clay mixed with gravel is considered as a four-phase composite material and a mesoscopic numerical model is constructed via image processing and random packing to consider the real shape and distribution of gravels. With this model, whose effectiveness is validated by physical tests, the macroscopic and mesoscopic tensile fracture characteristics of clay mixed with gravel are analyzed. The nonlinear behavior on macro scale is due to mesoscopic heterogeneity. The addition of gravel greatly decreases the tensile strength but increases the post-peak tensile resistance. Soil-rock interfaces are the source of microcracks and tensile fracture is a process where microcracks initiate, propagate and coalesce to macrocrack. Tensile fracture occurs in a region, i.e. the fracture process zone, and the formation of this zone is related to the random distribution of gravels. Through numerical experiments, the influence of the random packing and content of gravel on the macroscopic and mesoscopic behaviors of clay mixed with gravel is analyzed.

Water saturation has an appreciable effect on deformation and strength feature of sandstone. The aim of this paper is to understand micro- and meso-mechanical properties of water-saturated sandstone under complex stress path by considering real occurrence environment of rock mass. A series of unloading tests is conducted on the water-sandstone samples after cyclic loading to examine the fatigue damage feature under different influence factors by using the rock mechanical testing system RMT-150C and scanning electron microscopy(SEM). The effects of loading frequency and upper limit stress on unloading deformation, strength and meso-damage are analyzed emphatically. The study results indicate that the stress-strain curves of water-saturated sandstone can be roughly divided into five stages according to the design scheme of the experiment. Thereinto, under the same stress condition, the axial irreversible strain rate in constant velocity stage rapidly increases with the loading frequency increasing during fatigue damage stage, which implies that “threshold value” of the upper limit stress is likely to be variable, and to be closely related with loading frequency and cycles. Meanwhile, during the unloading confining pressure in deformation failure stage, both the total strain and unloading capacity of confining pressure about water-saturated sandstone decrease with increasing the loading frequency or upper limit stress, which is consistent with the variation law of the duration of this stage with the loading frequency (or the upper limit stress). Moreover, it is found that the meso-damage characteristics under the action of loading frequency and upper limit stress are significant by analyzing meso-characteristics of failure surface, and the proportion of the microcrack area in the failure surface decreases with the increase of loading frequency, and the upper limit stress is just the opposite.

A series of cyclic shear test on remolded unsaturated sandy soil with different water contents was performed using the cyclic simple shear test apparatus WFI25735. The effect of water content variation on dynamic properties of unsaturated sandy soil is examined at different shear strains. The experimental results show that there exists a critical moisture content of 11.2% corresponding to the normalized value of dynamic shear modulus Gd/Gdmax-? at large strain. When the water content is lower than critical moisture content, the value of Gd/Gdmax increases with the water content, and when the water content becomes higher than the critical moisture content, it decreases gradually with the increase of water content. The same critical water content can be found on the skeleton curve. When the water content is lower than the critical water content, the skeleton curve goes up slowly, and reaches a peak value at 11.2% water content. The skeleton curve decreases sharply with the increase of the water content when the water content is higher than the critical water content, and the strain softening appears, which can further explain the scatter diagram changing trend of Gd/Gdmax-?. At relatively high stress, the normalized damping ratio D/Dmax increases as the shear strain increases. The hysteretic energy dissipation of unsaturated sandy soil increases with the increase of the shear strain. As the water content increases, there exists a critical water content. The hysteretic energy curve shows a trend of first increasing and then decreasing and the critical water content can shift as the normal stress increases.

Shale gas reservoirs have low porosity and low permeability characteristics. One of the best ways to produce gas from shale gas reservoir efficiently is using hydraulic fracturing to create complicated fracture networks. Displacement discontinuity method is employed to set up a mathematical model of two-dimensional induced stress field distribution based on the assumption that the formation is homogeneous and elastic. Through the horizontal stress difference coefficient, fracture spacing has been researched. The results show that the horizontal stress difference coefficient is affected by fracture net pressure, fracture length and in-situ stress field etc. The greater the net stress is, the longer the fracture length is, the smaller the difference coefficient of horizontal stress is. With the increase of fracture spacing, the horizontal stress difference coefficient firstly decreases and then increases. Therefore, there is a best fracture spacing for subsequent fracture to form complicated fracture network. The fracture spacing of consecutive multi-stage hydraulic fracturing should not be too large and subsequent fracture spacing should be suitably reduced. When the fracture spacing of alternate multi-stage hydraulic fracturing is optimal, the horizontal stress difference coefficient between the first two fractures is the minimum, and it provides the most advantages for the third fracture to form more complex fracture networks in the altered stress region.

A smeared crack model of hydraulic fracturing numerical calculation is proposed based on the complete liquid-solid coupled elastoplastic theory. In this model, the elastic part of the material uses the linear elastic constitutive relations; the plastic part adopts the Mohr-Coulomb failure criterion and hardening criterion. To simulate the fluid flow in the crack, the permeability is modified according to the current state of effective stress. The relation between the permeability and the effective mean stress is assumed to be a hyperbolic tangent function. The onset of crack is determined by the mean effective stress. Using the user defined subroutines provided by ABAQUS software, the smeared crack model is added. According to section photo of the in-situ rock sample, a finite element model of heterogeneous material with hard inclusions distributed is generated. The progress of hydraulic fracturing under the loading condition of centered injection is well simulated and the results show the characteristics of fracture zone, stress path located at typical location and range of fracture propagation. Numerical tests on the rock with hard inclusions distributed are carried out under different conditions. The paper concludes the influences of elastic modules, cohesion, permeability, and injection rate on the maximum injection pore pressure, average injection pore pressure and fracture aperture.

To provide better description for the volume deformation of rock, a lateral-axial strain fractional dashpot is presented on the basis of the Abel dashpot with a constant viscosity coefficient and a variable viscosity coefficient. A new model of volume-axial strain relationship is proposed based on fractional order calculus. The analytical solution for the model of volume-axial strain relationship is given theoretically. The new models have the advantages of solving volumetric strain of rock. Moreover, a multifunctional material testing setup is employed to measure volume-axial strain of various rock samples under the condition of triaxial compression, stress relaxation and uniaxial creep compression. The parameters of the volume-axial strain model are determined by regressing the experimental results of volume-axial strain of rock. In addition, a sensitivity study of the analytical solution of the volume-axial strain model is carried out, which shows the effects of confining pressure, fracture angle, fractional derivative order and model coefficient on volumetric strain of rock samples. It is found that the new models can describe not only the volumetric strain phenomenon of negative and positive dilatancy but also the stress relaxation and creep deformation characteristics in rock.

The granites are taken from Beishan area in Gansu province which is selected as a potential high-level radioactive waste disposal repository in China. The sparsely irregularly fractured rock model of 750 mm ×300 mm ×1 000 mm (width × thickness × height) consists of 18 granite rocks with vertical and oblique fractures with thermal sensors, pressure sensors and square strain rosettes installed in the interior, and a heater is placed on one side to study the influence of the heat source temperature and the crack velocity on the temperature and stress of the rock. The test results reveal that: vertical fracture water flow is mainly from the top inlet to the bottom outlet vertically, and oblique fracture water flow is mainly from the side inlet to outlet obliquely, with weak interchange flows at the intersections of the vertical and oblique fractures. Heat conduction and oblique fracture water flow control the temperature distributions in the model because a heater is put between the two oblique fracture intakes and oblique fracture length is less than the vertical fracture, while the vertical fracture water flow hinders heat conduction to the far side of the heat source. Heat transfer paths are mainly from left to right in the upper rock layer and from top to bottom in the middle rock layer and the low rock layer, due to the irregularities of heat conduction and water flow and heat transfer. The temperature gradients are smaller and thus contraction of rock is affected by tensile stress in the upper and lower rock layers, whereas the temperature gradients are larger and expansion of rock is affected by compressive stress in the middle rock layer. The major principal stress direction is being approximately orthogonal to the intersections of the oblique fracture planes and the vertical fracture planes, and the stress increment increases with the increasing of temperature gradients in the oblique planar direction. The higher the heat source temperature is, the lower the fracture water flow velocity is, the higher the rock temperature is, the greater the rock stress is, and the system requires longer time to reach steady state.

The failure of bedrock laminar slope mostly happens due to heavy rainfall; and it causes huge losses to people’s lives and property. To explore the process of rainfall infiltration into bedrock laminar slope under heavy rainfall, a new rainfall infiltration model for this slope is built and then a formula of calculating infiltration rate and wetting front depth about slope is obtained for different stages based on Green-Ampt infiltration model. The geometric characteristics of slope and the seepage of saturation zone are considered in this new model. Based on the rainfall infiltration model and limit equilibrium method, an analytical expression of safety factor is developed for bedrock laminar slope under different rainfall durations by considering the seepage of saturation zone. The expression is used to analyze the variation of the surface of bedrock and the surface of wetting front. It is shown that the calculated results have a high consistency with that of slope model test. Moreover, the proposed procedure and the traditional method are employed to analyze the process of rainfall infiltration and the regularity of stability of Zhangjiawan landslide under the rainfall intensity of 30 mm/h. The variations of wetting front depth and safety factors with the increase of rainfall duration are obtained. The results show that, the proposed procedure is superior to traditional method in analyzing the stability of bedrock laminar slope.

Equivalent hydraulic aperture and hydraulic gradient are two important factors that significantly affect the permeability of rock mass fracture networks. A test model of fracture network is made and a high accuracy seepage testing system is established. The Navier-Stokes equations are solved to simulate the flow state of the fluid in the fracture network; and the influences of equivalent hydraulic aperture and hydraulic gradient on nonlinear seepage characteristics are studied. The results show that when the hydraulic gradient is smaller, the equivalent permeability holds constants, indicating that fluid flow is in the Darcy’s flow region; the flow and the pressure have linear relationship and the cubic law can be selected as the governing equation of fluid flow. In contrast, when the hydraulic gradient is higher, the equivalent permeability decreases dramatically with the increment of hydraulic gradient, and fluid flow is in the strong inertia region; the flow and pressure have a strong nonlinear relationship, which can be calculated by the Forchheimer equation. As the equivalent fracture aperture increases, the critical hydraulic gradient, which is utilized to characterize the onset of nonlinear flow in fractures, will decrease following a power law function. When the hydraulic gradient is smaller than the critical hydraulic gradient, the cubic law is selected as governing equation; when the hydraulic gradient is greater than the critical hydraulic gradient, the Forchheimer equation is selected as control equation; the parameters of a and b can be calculated according to the empirical formula. This study can propose useful suggestions to the determination of critical hydraulic gradient and the selection of governing equations when calculating fluid flow in fracture networks.

Rock mass exists often with a combined fractured-vuggy-porous void in nature. This work focused primarily on the seepage behaviour of a combined fractured-vuggy-porous geological media. On the basis of brief analysis for the Darcy’s law applied to the porous media, the Poiseuille’s law suitable for the fracture flow and the Darcy-Weibach theory used in the pipe flow, this paper derived the equivalent seepage coefficient KE which could describe the seepage nature of different combinations of fractured-vuggy-porous voids in geological medium and analyze the main factors for different combinations. In addition, laboratory seepage tests were used for two combinations to validate the theoretical equations derived, and available porous brick was chosen to simulate the rock matrix during testing. Comparison of the values of KE obtained from testing and computing respectively shows that KE is in the same order of magnitude and the error is very small as well.

The permeability of debris flow deposit, if served as a foundation of check dam, is vital to forming uplift pressure on dam base. Current researches on soil permeability are focused on cohesionless coarse-grained soils and few on wide graded gravelly soils, such as debris flow deposits. The upper limit particle size of the fine particle affecting the permeability of wide graded gravelly soil is determined by the permeability test on the debris flow deposit in Beichuan county, Sichuan Province of China. The relationships between fine-grained soil content and permeability coefficient are also obtained. The results show the coarse particles only play a skeleton role, and the fine particles dominate the permeability of debris flow deposits. The upper limit particle size of 0.1 mm has significant influence on the permeability of wide graded gravelly soil. The content of fine particles (<0.1 mm) has a negative exponential relationship with the permeability coefficient, and the permeability of debris flow deposits tends to be stable when the fine particle content is more than 20%.

In order to investigate the analytical calculation method of T-stress for the central cracked Brazilian disk (CCBD) subjected to the compression, a weight function method is used to derive the explicit expressions of the T-stress for CCBD under concentrated loading and the distributed force loading. Compared with the boundary coordination method, the advantage of the explicit expression is that the T-stress for arbitrary relative crack length and any loading angle can be obtained explicitly and easily. Further analysing results show that the deviation of the T-stress under the distributed force and the concentrated force increases with increasing load distributed angle. At a fixed relative crack length, the T-stress increases with the increasing of loading angle under concentrated force. In most cases, T- stress is negative when the central cracked Brazilian disk is under pure mode I and pure mode II fracture tests. The value of T-stress for CCBD affects the fracture toughness testing, and it is difficult for CCBD to eliminate the influence by reducing the T-stress to zero.

To explore the hydraulic conductivity of lacustrine peaty soil in plateau areas, the permeability coefficients of 20 groups of soil samples from 6 sites were measured under one-dimensional compression conditions through oedometer tests. The effects of loading time, stress level, loss-on-ignition and residual fiber contents on the permeability coefficients are analyzed. The experimental results show that under the conditions of separately loading, permeability coefficient decreases with the elapsing time and tends to be stabilized in about ten days; under the conditions of stepwise loading, the permeability coefficient decreases nonlinearly with increasing consolidation pressure, and the curves of - resemble a reverse “S”. A permeability model for lacustrine peaty soil in plateau areas can be represented by expression e- , and the relations between the permeability index ( ) and initial void ratio can be described by 0.25 . The relationships among initial permeability coefficient and loss-on-ignition , residual fiber content and are more discrete, and there clearly exits a positive correlation among , , and the initial water content . Through scanning electron microscope, the mechanism of the peaty soil permeability is discussed from the pore characteristics of soil.

Soil-water characteristic curves (SWCCs) can be used to predict the properties of unsaturated soils, including unsaturated permeability coefficient, shear strength and thermal property. However, the measurement of SWCCs is time-consuming and expensive. To solve this problem, considerable research efforts have been made to developing the procedures to directly estimate the SWCCs from basic geotechnical properties. Two types of MK models (fitted equations and prediction equations) are used for the SWCCs models, and the cftool in the scientific programming language Matlab is applied to fit the MK models, based on which four types of soils are analyzed, i.e. Xining loess, silty sand, red silty clay, moraine soil. The effects and differences of fitting equations and prediction equations are compared with regard to their capability of describing SWCCs of fine-grained soils. A calculation formulation is developed for parametric analysis based on MK model. It is shown that both the fitted equations and predicted equations of MK model perform well in describing SWCCs of the 4 types of fine-grained soils, though the former is better than the latter; it is also shown that soil texture and clay content influence . The sensitivity analysis shows that the degree of saturation is more sensitive to parameter a than to parameter m.

International Society for Rock Mechanics has suggested four methods for measuring Mode-I fracture toughness (KIC) of rocks. By combining the suggested semi-circular bend specimen and cracked chevron notched Brazilian disc, the cracked chevron notched semi-circular bend (CCNSCB) specimen is produced, which inherits many merits from previous methods. The CCNSCB method has recently received much attention by researchers for testing KIC of rocks, but has not been numerically assessed. Thus，the method is numerically studied and the progressive fracture process is presented via meso-damage mechanical analysis. Considering different span to diameter ratios , the results show that the real fracture is more aligned with the measuring principle while β is greater. Therefore, β=0.8 is suggested. The minimum dimensionless stress intensity factor , which is critical to determine the KIC value, is calibrated by finite element method (FEM) with a sub-modelling technique for diversified CCNSCB geometries in terms of β=0.8. The calibrated values are conveniently obtained for other relevant researches. The critical crack corresponding to the peak load simulated by microscopic damage mechanics is quite consistent with that corresponding to the calibrated via FEM. It is indicated that the CCNSCB method is appropriate to measure KIC of rocks and the numerical simulations as well as the calibration of values are effective.

The aim of the paper is to investigate the effect of groundwater flow on Gaomiaozi bentonite(GMZ). The expansion-permeameter and turbidity meter are used to measure the turbidity of erosion liquid and the expansibility of bentonite samples. The influence of such factors as the dry density of bentonite, pH value and flow direction of erosion solution, type & concentration of solution, and crack amount of surrounding rocks is analyzed. It can be concluded that: the expansibility of bentonite increases dramatically during the first several days and remains stable then; the higher dry density of the bentonite, the weaker erosion presents on bentonite; pH value has a great influence on the erosion of bentonite, and the erosion is weaker under a higher alkaline conditions and vice versa; radial seepage of water flow has a greater effect on the erosion of bentonite than vertical seepage; and the erosion of bentonite becomes more intensive if the crack amount increases; the erosion of bentonite firstly increases and then decreases as NaCl concentration in erosion solution increases; the influence of CaCl2 concentration on bentonite is similar to that of NaCl, but the effect of CaCl2 is less significant.

Argillaceous sandstone from a slope in Three Gorges Reservoir is investigated. A series of tests including triaxial compression test under four confining pressures, scanning electron microscope (SEM) is conducted on the sandstone samples subjected to cyclic wetting-drying in different pH conditions(pH=3, pH=7). The area ratio of skeleton and fractal dimension of images obtained by SEM under different pH conditions and different times of dry-wet cycle is obtained by MATLAB. The study shows that when samples suffer the same times of dry-wet cycle, the fractal dimension in acidic conditions (pH=3) is bigger than that in neutral conditions (pH=7). Also, it is indicated that the fractal dimension is proportion to water absorption rate and inversely proportion to skeleton area and cohesion. And the critical area ratio of skeleton of argillaceous sandstone subjected to alternation of wetting and drying is calculated to be 0.55. A concept of erosion degree is defined for argillaceous sandstone subjected to dry-wet cycles. Then a relation curve between the erosion degree of argillaceous sandstone and times of dry-wet cycle is obtained by fitting. Damage variable formula of cohesive force is derived. The study results provide theoretical basis for erosion of argillaceous sandstone in different pH conditions.

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In Shanghai, the foundations of three super-tall buildings, 88-story Jinmao Tower, 101-story Shanghai World Financial Center (SWFC) and 121-story Shanghai Center Tower (SCT), are compensated piled raft (box) foundations with deep embedment. It is worth discussing how to make use of advantages of compensated foundation during foundation design and to estimate the wind resistance of deep embedment of foundation. Based on the analysis of the interaction of high-rise building and ground foundation, the pile raft foundations of the three buildings are analyzed using the statistical empirical formula. A considerable amount of piles can be saved after analyzing, and their bearing capacities and deformations of the foundations can still meet the design requirements. Meanwhile, the capability of optimizing design is further discussed, and the diaphragm wall is proven to be able to share a considerable amount of load. The re-analysis of the relevant cases puts forward suggestions for further improving the design theory of the deep buried pile raft foundation, which can save a lot of investment for China.

Small-strain shear modulus plays a crucial role in numerical analyses of underground geotechnical Engineering issues such as excavations and tunnels. The research on small strain shear modulus of typical clay layers has rarely been reported, despite the fact that many large-scale underground construction projects have been ongoing in Shanghai. In this study, the initial shear moduli of typical clay layers at small strains in Shanghai have been investigated on spot by the field acoustic wave measurement and indoor bending element test. The experimental results show that the initial shear modulus obtained from the bending element test is consistent with that obtained from the in-situ wave velocity test if the soil disturbance is minimized and the soil stress state adopted in the indoor experiment is equivalent to the in-situ soil. It is shown that the proposed empirical formulation with considering the stress state and the void ratio of the soil can reasonably describe the variation of the initial shear modulus of the typical clay layer in Shanghai, and the empirical parameters of each soil layer are given. The experimental results can provide reference for calculating and analyzing the shear modulus of soft clay at small to medium strain.

In the modern foundation pit engineering, pits-in-pits is becoming more and more popular. It needs special analysis according to the structural design requirements of retaining walls. There exists mutual influence between the outer retaining walls and the inner retaining walls; so the stress analysis of the retaining walls is more complicated. For the complex stress condition of the outer and the inner retaining walls in pits-in-pits, a combined bars FEM system based on the flexibility fulcrum method is developed. By solving the spring stiffness of the finite soil mass between the inner and outer retaining walls, the model can be used to solve the problem of calculating the internal force and deformation of the retaining wall. The pits-in-pits case study shows that the deformation and internal force of the retaining structure calculated by flexibility fulcrum method are quite consistent with the engineering practice. The research results have certain theoretical and engineering practical significance.

Surrounding rock of tunnel is cut into blocks by structural planes. Tunnel excavation breaks the mechanical balance of the blocks in the natural state. Dynamic loads may promote the slip of a block toward a free surface, which will cause the failure of surrounding rock. However, most applications of block theory only consider the effect of gravity without taking blasting vibration load and seismic load into account. Blasting vibration load and seismic load are transformed into equivalent static loads, and the most unfavorable direction of dynamic load is calculated where the safety factor of block is the lowest. The vector analysis method of block theory is applied to analyze the stability of surrounding rock mass in tunnel considering the effect of dynamic load as well as gravity. The calculated results for Changgang tunnel show that the safety factor of block under dynamic load is obviously lower than that only considering the effect of gravity. Under the action of dynamic load, the original stable block can be turned into a key block and leads to surrounding rock failure, which is consistent with the actual destruction phenomenon recorded in Changgang tunnel.

For the problem of pressure burst disaster in step region of unequal length working face in Yangcheng coal, based on the special arrangement mode of working face and overlying strata characteristics, the theoretical analysis, numerical simulation and field measurement are adopted to analyze the dynamic evolution process of surrounding rock stresses and the movement characteristics of overlying, and the mechanism of pressure burst in step region has been investigated. The results show that: the overlying strata in step region experiences a complex evolution of “OX-S-C”, when it is converted from OX to S, large area of roof rock is breaking and sinking, in large area of roof rock, and the higher the height is, the greater the length of cantilever beam over step region is. Influenced by the overlying rock movement and the mining stress field, the coal and rock mass form a high stress concentration area. The coal-rock mass is suddenly destroyed with releasing elastic strain energy under the action of dynamic load of roof rock, and the pressure burst occurs. The strain energy distribution characteristics are investigated by using software COMSOL under different drilling parameters, and the parameters of drillhole pressure relief are optimized. According to the simulation results, with the increases of borehole diameter, depth and decreasing spacing, the pressure relief effect is more obvious. Considering the engineering application, diameter of 150 mm, depth of 30 m and spacing of 1 m are regarded as the reasonable drilling parameters. This method is applied to the prevention of pressure burst in step region of working face 1302 in Yangcheng coal, and good prevention results have been achieved.

Disturbance cracks or fractures are generated in the surrounding rock mass of mining face in the process of coal mining. Among these cracks or fractures, some experience the opening process. Due to the fact that there is no substance in these opened cracks or fractures to transmit force, the stresses in the zone near to these cracks or fractures will decrease to a small value from their initial gravity-induced large stress values but not necessarily reach 0. After these cracks or fractures are generated, the stresses in the zone near to them would adjust and cause vibration due to stress redistribution. Accordingly, these cracks or fractures would be closed again, they could even bear great shear stresses. Based on the described phenomenon that the stress in the zone near to disturbance cracks or fractures have experienced the process of stress unloading from large to small values, a method referred to as “dynamic stress tracing method” is developed to identify the range and height of disturbance factures/cracks zone. The No.3 coal seam mining of Shizuishan in Ningxia province is given as a case. The discrete element software package UDEC is applied to determine the stress distribution during the process of coal mining. Based on the proposed dynamic stress tracing method, the range and height of the disturbance fractures/cracks zones are estimated using the post-processing package TecPlot. It is indicated that the proposed dynamic stress tracing method for identifying the height of coal mining disturbance fractured/cracks zone is feasible, and owns good suitability.

Rock stress sensitivity is a reflection of the development of microcracks in the rock, which plays an important role in the evaluation of the physical properties and the fracture forming ability of tight reservoirs. Due to the high modulus of the matrix and relatively weak sensitivity to stress of shale，a new test method of high sensitivity is required. Coda wave interferometry is a measurement method for monitoring weak variation based on scattered wave of media, and it has a high sensitivity to the change of rock stress. In this paper, coda wave interferometry tests are conducted on the Lower Cambrain Lujiaping Formation shale from Chengkou, Chongqing using GCTS RTR-1500 high temperature and pressure triaxial testing system, the development and response to stress of coda are studied, and the stress sensitivity of shale is analyzed under different confining pressures. The results show that the shale stress sensitivity to coda wave is greater than to the direct wave; S-wave stress sensitivity is greater than P-wave. The relative variation ratio of the coda wave velocity varied with the stress can reflect the generating of internal fissures, and it has a good relationship with the corresponding expansion point; confining pressure leads part of the fractures to close and natural fracture density to decrease, which results in a reduction in sensitivity coefficient of shale stress. Coda wave interferometry is available as evaluation of shale stress sensitivity and fracturability.

The scalable parallel computation of finite element models with hundreds of millions of elements is discussed. The software and hardware solutions for the preprocessing, parallel computing method, software algorithms, and postprocessing are proposed. A finite element model of one hundred million elements is generated by grid encryption method. And the dual-primal finite element tearing and interconnecting method (FETI-DP) is utilized to solve the finite element system of equations. The topological connections among sub-domains are set up based on graph theories. Point to point communications are built to accelerate data exchange among sub-domains and to avoid the time-consuming global communications. Some modules are written based on an in-house code using object-oriented programming technique and message passing interface (MPI). A numerical example with more than one hundred million number of elements is carried out using 5000 cores at the same time; and super-linear speedup is obtained. The postprocessing is performed on a graphical workstation; and the interactive operations respond quickly. The study shows two big improvements: one is that the numerical model has more than one hundred million numbers of elements; the second is that 5 000 cores are used at the same time and high efficiency is obtained. The research results show that the high resolution numerical simulations provide an efficient tool for large size and complex geological conditions simulations in geotechnical engineering.

Deformation and stability of the seawall on soft clay are the key problems for reclamation engineering. Centrifugal model test is carried out to obtain the soft clay settlements, where the variable acceleration method and constant acceleration method are applied to simulate the construction process and operating phase, respectively. Particle image velocimetry (PIV) technique is also introduced to capture the potential failure mode of seawall. Further, based on the total stress and effective stress analysis methods, the changes of global stability with time are analyzed by using GeoStudio software in both the construction process and operating phrase. Physical and numerical simulation results show that the centrifugal model test is able to reflect the deformation and stability behaviors of the seawall to a certain extent; and its data is in good agreement with that obtained by numerical simulation. The sliding surface of the seawall passes through the soft clay, leading to an immediate settlement of more than 1 m. In addition, the safety factor of global stability increases gradually with time after the seawall construction due to the dissipation of excess pore pressure. The maximum vertical and horizontal displacements are located at the axis and the toe of the seawall, respectively.

Through centrifugal model tests, the failure characteristics of the shield tunnel excavation face and the limit support pressure in dry and saturated silty sands are studied. By means of remote control of soil displacement, the relationships between the support pressure and the displacement of the excavation face are obtained, and the failure mode of the excavation face to the active limit equilibrium state is revealed. Two sets of dry silty sand centrifuge model test results show that when the ratio of tunnel depth to the tunnel diameter is from 0.5 to 1, the failure mode of the excavation face is changed from the whole collapse to funnel shape, but the change of of the limit support pressure is small. The test in saturated silty sand shows that the destruction extent in the horizontal direction of the excavation face is more than that at the same buried depth in dry sand, and the limit of the support pressure increases significantly. Three-dimensional elastoplastic finite element method is used to simulate the failure process of excavation face, and then the limit support pressure and failure mechanism of the excavation face are obtained. The numerical simulations are in good agreement with the experimental results. Additionally, the influence of the soil strength parameters, tunnel depth and seepage on the limit support pressure is further analyzed through the numerical simulation, it is shown that the damage area and the limit support pressure of the excavation face are larger than that of the nonseepage condition; the limit support pressure decreases with the increase of the internal frictional angle, and decreases with the increase of the tunnel depth.

Catastrophic failure of slopes often results from cyclic softening, i.e. onset of significant strains or strength loss in soils during earthquakes. Therefore, it is necessary to study the nonlinear dynamic constitutive model considering cyclic softening in order to analyze the stability of seismic slope under complex conditions. On the basis of existing nonlinear dynamic constitutive models, a method to deal with the cyclic softening is proposed. A secondary development of the constitutive model is implemented into the FLAC3D platform, and the proposed procedure is verified by the theoretical formulation and the experimental data available in the references. It is shown that the calculated backbone curve is consistent with the theoretical formula, and the calculated dynamic shear modulus ratio and damping ratio are in good agreement with the experimental data. When the shear strain is larger than >0.01%, the modified model describes better the damping ratio-shear strain relationship than Hardin-Drnevich model and Davidenkov model. If the cyclic softening is taken into account, the calculated shear strength is significantly reduced, and the convergence of the model is improved when the shear stress of the backbone curve can be continuously transferred to the softening main curve. The developed constitutive model can provide support for the seismic disaster assessment of soft soil site and slope under large strain condition.

Cyclic simple shear test (CSST) is one of the most appreciative methods for studying the dynamic characteristics of soil in earthquake site. To minimize the size effect in the experiment and to monitor the dynamic properties of fiber-reinforced and coarse-grained soils, a testing system called large-scale CSST apparatus is developed. In the developed equipment, the vertical loading plate at the top of the specimen is constrained by a series of vertical linear guides so that it can translate vertically, the horizontal loading plate at the bottom of the specimen is constrained by a series of horizontal linear guides so that it can only translate horizontally, and the shearing box containing specimen is formed by laminated steel rings which are interlayered at four discrete bearing ears with rubber membrane. These features of the equipment ensure proper boundary conditions of the soil specimen during testing similar with soil element in seismic site. The developed CSST equipment is used to perform experiments on geo-cell reinforced rubber sand mixtures. It is shown that the relationship between the dynamic stress and dynamic strain of the specimen exhibits typical hysteresis, nonlinearity and ratchet characteristics, and the - curves and - curves gained from large- scale CSST show similar characteristics as those gained from normal size CSST, implying that the device works well; the differences of the dynamic shear modulus properties between results of large-scale and normal size CSSTs coincide with size effects of CSST; no obvious regularity of size effect on damping ratio is observed from the tests.