Slabbing failure with regularity of surrounding rock is a typical failure phenomenon in deep hard and brittle rock mass due to excavation activity, which poses a serious challenge to safely construct the underground tunnels. There are two critical problems in the research of slabbing failure, i.e. the formation mechanism of slabbing failure and its influencing factors, and the relationship between slabbing failure and rockburst. Remarkable achievements have been made in the slabbing failure by theoretical analysis, field tests, laboratory experiments and numerical simulation over the past decades. By summarizing the research progress related to these two critical problems, it is believed that the formation mechanism of slabbing failure is a complex problem involving various influencing factors. Based on the meso-mechanism of the slabbing failure, the key point to explore its formation mechanism is to establish different types of mechanical criterion and model. Slabbing failure and rockburst have strong correlation and essential connection. To further reveal characteristics of slabbing failure and the involved precursor information of rockburst is a critical and difficult problem to study the relationship between slabbing failure and rockburst.

Because large construction ships cannot enter the shallow sea, traditional configuration foundations, such as gravity-type foundation and pile foundation, are not suited for offshore wind power project in shallow seas. Therefore, a new type of foundation—segmentally-tapered bucket foundation is proposed. Based on the limit equilibrium method, a systematic method is proposed to calculate the horizontal bearing capacity of the segmentally-tapered bucket foundation. The influences of obliquity of wall, foundation height, top diameter of bucket and soil parameters on the horizontal bearing capacity of the segmentally-tapered bucket foundation are analyzed. It is found that the horizontal bearing capacity increases with the increase of the wall obliquity, soil resistance, top diameter of bucket and foundation height, while decreases with the increase of the depth of seabed. Based on the concept of volume compression ratio, the bucket foundation with inclined upper section wall and vertical lower section wall is recommended and demonstrated. An accurate method is proposed to determine the proportional coefficient of soil resistance. The results are helpful in the optimization design of traditional bucket foundation.

Clay-based materials are widely used in practice of contaminant control. Diffusion coefficient is one of the most important parameters of clay. It is usually determined by fitting the data of one-dimensional convection-diffusion soil column tests. Zero concentration boundary, zero concentration-gradient boundary and semi-infinite boundary are discussed. A unified boundary condition is proposed. By transforming and introducing auxiliary problems, unified convection-diffusion-adsorption analytical solutions for three boundary conditions are acquired. Both difference between these analytical solutions and data-fitting errors are investigated. The results show that different boundaries should correspond to different conditions in the bottom of a column test. Cauchy boundary can be regarded as an unified form of all these boundaries. The calculated results corresponding to these boundaries are equivalent before breakthrough, however, the results become quite different in the bottom of the column after breakthrough. The concentration decreases as Cauchy parameter increases. The bigger the Cauchy parameter is, the more dominant role the diffusion effect plays in the solute transport process, at the same time, the bigger the concentration gradient at the bottom is. Fitting the data of a semi-infinite boundary test using analytical solutions of zero concentration boundary and zero concentration-gradient boundary will overestimate 15% and underestimate 9% of the result, respectively. It is essential for data fitting to choose an analytical solution according to convection-diffusion proportion and concentration-gradient at the bottom of a soil column.

The dynamic shear modulus Gd and the damping ratio D are two main parameters in geomaterials seismic response analysis and the initial condition is one of the principal factors affecting the dynamic parameters. This paper studies the effects of initial stress ratio and moisture condition on dynamic shear modulus Gd and damping ratio D of loose deposit with large-scale dynamic triaxial tests. The experimental results show that the stress ratio Kc has important effect on the maximum dynamic shear modulus Gdmax of loose deposits. In a certain range of Kc=1-3, the stress ratio is larger, the maximum dynamic shear modulus is greater. Based on Hardin’s equation, an improved empirical equation considering the effect of stress ratio is proposed. By comparing the two Gd/Gdmax-?dn curves of saturated and air-dried loose deposits, the curve under air-dried condition is found to shows more obvious nonlinearity than the one under saturated condition. Moreover, the damping ratio under air-dried condition is slightly greater than the one under saturated condition. The proposed improved empirical equation of Gdmax and the nonlinear relationships of Gd/Gdmax-?dn are used to analyze the ground response spectrum of loose deposits. The calculation results show that the stress ratio and moisture condition influence the ground response spectrum obviously.

By injecting Pasteur bacillus suspension and CaCl2-urea solution, the coral sand was solidified through the microbially-induced precipitation of calcium carbonate. Then a series of experiments including the permeability, strength and microstructure tests was conducted on the solidified soil. It is shown that the bacteria activity of Pasteur bacillus decreases slowly with time elapsing, which satisfies the requirement of the improving coral sand. Due to the bio-mediated improvement, the permeability of coral sand pillars decreases by 1 to 2 orders in magnitude. The stress-strain curve of improved coral sand pillars can be divided into 3 stages: stress increasing slowly with strain, stress increasing fast with strain and stress suddenly falling with strain. The unconfined compressive strength of specimen is up to 14 MPa before specimens being compressed into brittle failure. The compressive strength increases with the increase of dry density and the decrease of permeability. Unlike the silica sand improved by microbe, the coral sand improved by the current technology has a structure that the calcium carbonate precipitates wholly around coral sand particles. Hence the bonding between two particles by calcium carbonate is relatively weak, which properly explains the insignificant decrease of permeability.

When the composite pile foundation is loaded, the laterally constraint pile will displace horizontally, and composite foundation with lateral constraint and vertical strengthen pile will become instable and failed. The horizontal deformation of the laterally constraint pile during the reloading and repetitive unloading of the composite pile foundation was studied by experiment. The results show that: (1) During loading, the horizontal deformation of lateral constraint pile increases first and then decreases, showing a peak along the depth. The peak value increases with the increase of loading. Position of the peak value is at the depth of 0.4 times pile length from the ground. With the increase of loading, the proportional coefficient between the peak displacement and the displacement of pile top or ground increases, the length of pile moving laterally also increases. (2) During reloading and repetitive unloading, with the increase of the pile spacing, the horizontal displacement of lateral constraint pile top increases, the elastic deformation of pile decreases. The lateral displacement of middle pile is larger than that of side pile. With the increase of reloading times, the increase rate of lateral displacement for pile top decreases. When the loading becomes larger than the maximum of the first loading, the loading and lateral displacement curve will merge into extension line of the first curve, showing memory effect. The (i+1)-th and the i-th curves between unloading and lateral displacement are parallel to each other. In the beginning and the medium term of unloading, the lateral displacement of pile remains constant, and begins to diminish only in the last 1-2 stages, and the permanent plastic deformation occurs finally. The horizontal rebound curve of pile top has a shape similar to the vertical rebound curve for rock or soil subjected to vertical loading and unloading.

A new slice block force-displacement method for slope stability analysis is established on the basis of current research on slice method. In the traditional slice method, mechanical parameters of the limit equilibrium state are applied to describe behaviors of the sliding surface of slope, which means the sliding plane of each slice block reaches the limit equilibrium stress state, and it is suitable for the residual stress state. An ideal elastic-plastic model and a new constitutive model are employed to characterize mechanical properties of the slip face of slice block. Taking the unbalance thrust method as an example of model application, a new method is proposed for determining critical state slice block. The possible failure types of slope are explored. The methods to determine stress and displacement of slice block are presented during the progressive failure progresses. The corresponding stability coefficients are obtained by traditional strength deduction method, comprehensive sliding-resistance method (CSRM), main thrust method (MTM), comprehensive displacement method (CDM) and surplus displacement method (SDM). It is found that, when mechanical parameters have not been changed, the ideal elastoplastic model is hard to describe the processes of progressive failure of slope, but the newly proposed constitutive model is capable of predicting mechanical behavior of each slice block. The proposed slice block force-displacement method can be used to calculate the stability factors under various loading and displacement conditions, to acquire the thrust force and the movement of sliding surface, and furthermore to forecast the stresses, displacements and stability of slope.

An elastic-plastic load-transfer model (t-z model), which can consider the Poisson's effect, is proposed. The model can reflect both the difference in compressive bearing capacity between the piles of different materials embedded in the same soil and the difference between the compressive friction and the tensile friction for the same pile embedded in the same soil. In addition, the model can also take into account the hysteretic characteristics of t-z curve under the cyclic load. A Matlab program, which can simulate the pile responses under both the compressive load and the tensile load, is developed based on the displacement coordination algorithm. The applicability of the model is demonstrated by comparing the measured results and the calculated results with the program. Finally, the influence of the elastic modulus of pile material on the ratio of the ultimate tensile friction to the ultimate compressive friction is studied. It is shown that the ratio decreases with the decrease of elastic modulus. The ratio is between 0.6 and 0.8 for the concrete pile, which is very close to the value proposed by the standard.

To study characteristics of rock mass with non-persistent joints under loading in engineering structures, two conceptions are put forward, which are mesoscopic damage of loading and macroscopic damage with joints. The initial damage state of intact rock is defined as a basic state. A compound damage variable is deduced on the basis of the Lemaitre strain equivalence hypothesis, which considers the existence of macroscopic defect with joints, the damage propagation of mesoscopic defects, micro cracks, and the coupling actions of macro and meso-defects under loading. A new calculation formula of the macroscopic damage variable is derived simultaneously in terms of the specimen size, geometrical size of joints and mechanical properties of joints. Then, a damage constitutive model for rock mass with non-persistent joints is established based on coupling macroscopic and mesoscopic defects. This paper describes the evolution of mesoscopic damage and the behavior of macroscopic damage of rock mass with non-persistent joints under loading. The calculated results are in good agreement with the actual failure of rock mass. The results show that: (1) The stress-strain behaviors of fractured and intact rock samples show a significant difference prior to the peak strength. The difference gradually decreases after the peak strength. Finally, the residual stress tends to be equal. (2) The strength of fractured rock mass increases with the joint connectivity rate, and exhibits obvious anisotropy with the variation of joint inclination angle, and also is relevant to the internal friction angle of joints. (3) The peak strength of fractured rock samples is the highest at the joint inclination angle of 90°. While the peak strength is the lowest at the joint inclination angle of 45°for open-type fractured rock samples. (4) The mechanical properties of rock mass under loading in engineering structures are determined by the mesoscopic damage of loading, macroscopic damage with joints and their coupling effects. The coupling macroscopic and mesoscopic based compound damage variable may well characterize mechanical properties of rock mass with non-persistent joints.

To investigate the problems such as the failure of compacted clay liners as the anti-seepage structure in the landfills cover system under the action of drying-wetting cycles, experiments under the simulated climatic environment of landfills have been conducted to determine the mechanical properties of compacted clay and its microstructure characteristics during the drying-wetting cycles and hence to reveals the intrinsic nature of the damage of compacted clay from the micro level. The experimental results show that as the number of drying-wetting cycle increases, all the secant moduli of low-, medium- and high-compacted clays increase at initial stage, while they decrease significantly at later stage, and the magnitude of secant modulus variation increases with the increase of initial compactness. Meanwhile, the shear strengths of above-mentioned three compacted clays decrease, and the magnitude of variation decreases with the increase of initial compactness or confining pressure. After three drying-wetting cycles, the total pore volume of compacted clay shows irreversible shrinkage, resulting in the increase of initial tangent modulus and shear strength. The shrinkage ratio decreases with the increase of compactness, and the shrinkage ratios of low- and high-compacted clays are 20.5% and 11.5%, respectively. The large pore volumes of low- and high-compacted clays increase 25.7% and 53.9% and the microcrack volumes increase 3.1% and 41.7%, respectively, resulting in a decrease in the shear strength and tangent modulus at later stage. The effect of drying-wetting cycles on the mechanical property of compacted clay with different compactness is controlled by two factors, i.e. the decrease of total pore volume and the increase of big-pore and microcracks.

Seasonally frozen soil is distributed widely in the Northeast China. The prevention measures against the frost heave of graded crushed rock, which is used as the filler of surface layer in subgrade, are crucial to high-speed railway constructed in seasonally frozen soil region due to the strict requirements of subgrade deformation. In order to study the frost heave characteristics of graded crushed rock under different conditions, water content, fine content, cooling temperature and compaction are chosen as influential factors of frost heave characteristics. The closed system laboratory frost heave experiments have been performed based on the orthogonal design, showing that different frost heave amounts appear in different combinations of factors and levels. The frost heave ratio of most graded crushed rock samples is small when water content is 5%, and it exceeds 1% when water content is above 7%. The temperature field, frozen depth, frost heave deformation process and water content distribution in sample after freezing are analyzed. It is found that the water content is greater than the initial water content at the cold side, and is lower than initial water content at the warm side. Using the frost heave ratio as a reference sequence and other factors as comparison sequences, the correlation degrees among water content, fine content, compaction, temperature at cold side and frost heave ratio are analyzed with the gray correlation method. The results from this analysis indicate that water content produces the most significant effect on the frost heave ratio of graded crushed rock. The water content of graded crushed rock should be maintained below 5% in order to prevent frost heave development in the cold regions.

The soil-water characteristic curve (SWCC) of a low-plasticity clay over a wide range of suction was determined based on the pressure plate and vapor equilibrium techniques. The soil samples were prepared by saturating the low-plasticity clay with NaCl solutions with different concentrations. The effect of pore solution concentration on the SWCC was analyzed. The experimental results show that the effect of salt content has little influence on the matric suction, and has great influence on the total suction, the reason for this is that the saline solution induces the osmosis suction. In the vapor equilibrium experiments, it is found that the solution concentration increases with the decrease of water content, and correspondingly the osmosis suction increases. With the decrease of water content, however, the matric suction increases rapidly, while the contribution of osmosis suction decreases gradually. In unsaturated soils, the total suction (the negative value of pore water potential) includes the matric suction and the osmosis suction, where the matric suction has two contributions, i.e. capillary and adsorption, and the osmosis suction depends on the concentrations of pore solution. When the water content of the sample is low, the adsorption effect is dominant. Based on the experimental results, the interaction between adsorption water film and the soil particles is analyzed, and the influence of the solute on the intermolecular forces is also investigated. According to the surface chemistry theory, a relationship between intermolecular forces and adsorbed water film is proposed to describe the soil-water characteristics at low water potential.

This paper studies the joint effect of seepage force and axial stress on the stress and displacement of circular tunnel. The circular tunnel is simplified as an axisymmetric model and the seepage field is simplified as volumetric force in the stress field. The excavation cross-section of surrounding rock is assumed as a plane as well, and an axial stress perpendicular to the plane is further introduced. Nonlinear solutions for the stress and displacement of circular tunnel are deduced considering the joint effect of axial stress and seepage force, based on the generalized Hoek-Brown failure criterion and the non-associated flow rule in elastic-brittle-plastic rock mass. Numerical simulations are also employed to analyze the distribution of stress field and displacement field in plastic zone of a circular tunnel under the joint effect of axial stress and seepage force. The calculated results show that the displacement in plastic zone increases significantly with the gradient increment of the seepage pressure, compared with the situation without seepage force. The radius and stress of surrounding rock in plastic zone increase when axial stress is the intermediate principal stress, while the radius and stress have less change when axial stress is the major or minor principal stress. It can be concluded that the seepage force has negative effects on the stability of circular tunnel, and the axial stress significantly influences the stress and displacement of the circular tunnel, especially in water-rich areas. Therefore, it is necessary to consider the joint effects of axial stress and seepage force to ensure the stability of circular tunnel in water-rich area.

A series of flume model tests was conducted to study the process and mechanism of piping in a three-stratum dike foundation, which was composed of weak permeable clay layer, sand layer and strong permeable sand gravel layer. To observe the process clearly, fine sand layers of different colors were laid on the gravel layer according to the color sequence. The thickness of colored sand was changed to investigate the effect of thickness on the process and mechanism of piping. The experimental results indicate that the different thicknesses of color sand results in the different critical hydraulic gradients, eroded masses and developing speeds of piping channel, which are quite different from those in two-stratum dike foundation. The critical hydraulic gradient depends on a number of factors including the properties and integrity of the damaged soil. The sand layer makes the flux insensitive to the erosion at the early stage of seepage deformation. Furthermore, it is also found that several times of intermittent erosion occur at the same upstream hydraulic head. One of the reasons for this is that the particles are clogged in the process of movement, and the other reason is that the stress release of the soil near the boundary of piping channel after the erosion of soil at the frontend, resulting in a decrease in the soil resistance over time.

The problem of environmental pollution results in the accumulation of heavy metal ion in soil, which not only influences the engineering properties of soil, but also threatens the health of human beings. Currently the cement solidification technology (S/S method) is adopted to treat heavy metal-contaminated soils. However, with the increase of concentration of corrosive salt in the groundwater, the solidified heavy metal-contaminated soil can be influenced by the corrosive salt ions, resulting in the deterioration of the strength of soil and leaching-out of the heavy metal ions. A series of systematic laboratory tests is conducted to investigate the strength and leaching characteristics of chromium polluted soil solidified with cement after soaking in NaCl solution. The experimental results show that the unconfined compressive strength of chromium polluted soil solidified with cement decreases with the increase of the concentration of NaCl solution, and decreases at first and then increases with soaking time, and the minimum strength is determined after 7 d soaking. The results of the toxicity characteristics leaching procedure (TCLP) show that the concentration of Cr3+ in leachate increases with the increase of NaCl concentration, and decreases with the increase of soaking time. The pH value of leachate decreases with the increase of NaCl concentration, and decreases at first and then increases with soaking time, and the minimum concentration of Cr3+ is got when soaking 7 d. when the pH value of leachate is within the range of 4.0 to 5.5, the leaching quantity of Cr3+ decreases with the increase of pH value.

With the rapid development of urbanization, the heavy metal pollution of industrialization becomes increasingly serious. Zinc pollution is one of the common industrial pollutants in China. Currently, research efforts about soil pollution are mainly paid to change a single feature of contaminated soil, and few researches have been done on the correlations among different characteristics of contaminated soil. The contaminated soil samples of specified pollution concentrations were prepared using the unique Yangtze River floodplain silty clay of Nanjing. The variations of basic physical properties such as liquid and plastic limits, pH value and particle size with zinc pollution concentration are determined. The effect of curing time is also analyzed. It is shown that with the increase of zinc concentration, the liquid and plastic limits, silt content and pH value of the contaminated soil decrease, while the clay content and plasticity index of the soil tend to increase. In addition, the variations of physical indices with the curing time are obtained. The improved round four-electrode Miller Soil Box is used to determine the electrical resistivity of soil sample. The correlations among electrical resistivity and moisture content, void ratio, saturation degree, pollution concentration, and other state parameters are analyzed, and the change of electrical resistivity with the curing time is discussed. Based on the contamination-induced changes of soil physical properties, the correlations among electrical resistivity, liquid limit, plasticity limit, pH value and soil composition are established.

The layering phenomenon in filling is very common in the process of stepwise or subsequent backfilling. Different cemented filling specimens are prepared with four concentrations (65%, 70%, 72% and 75%) and backfilling times of 1, 2, 3 and 4, separately. Uniaxial compression tests are conducted to study mechanical properties and failure modes of specimens. The research demonstrates that: (1) When the concentrations of different filling specimens are the same, the weakening effect of the uniaxial compressive strength (UCS) increases with increasing the filling time. When the concentrations vary from 65% to 75%, the corresponding strength reduction coefficients are in the range from 0.592 to 0.967. (2) The relationship between UCS of the specimen and the filling time fits the quadratic function, whereas the relationship between UCS and concentration fits the logarithmic function. (3) Main failure modes of different filling specimens are characterized by conjugated shear failure and tensile failure along the layer plane. Low-strength interlayer may result in decreasing the strength of layered cemented filling specimens, which can also be considered as theoretical reference for designing the strength of mine backfilling.

This paper investigates the effects of simulated acid rain on the strength and dissolution characteristics of lead contaminated clay, which is stabilized by GGBS-MgO (ground granulated blast furnace slag-magnesium oxide). Semi-dynamic leaching tests are conducted to measure the soil pH value, needle penetration depth, unconfined compressive strength and concentrations of lead, calcium and magnesium in leachate. Thus the effects of the initial pH of leachant, content of GGBS-MgO and lead contamination on the strength characteristics of GGBS-MgO stabilized clay are analyzed, and their effects on the cumulative mass of leached lead, calcium and magnesium and effective diffusion coefficient of lead are further determined. The results demonstrate that the unconfined compressive strength of clay using the semi-dynamic leaching tests is 2%-53% less, compared with the value under standard curing conditions for 39 days. Moreover, the highest impact on the strength of soil is found with an initial pH 2 of the leachant. Under the same content of GGBS-MgO and initial pH of leachant, the strength of the GGBS-MgO stabilized clay is approximately 12%-43% higher than that of the cement solidified clay. When the content of GGBS-MgO is 18%, the strength of clay stabilized by GGBS-MgO is almost 1.3-1.8 times of that of clay stabilized by cement. When the initial pH of leachant is 2, the pH at the specimen subsurface is approximately 50% of that when the pH values of leachant are from 3 to 7. The needle penetration depth decreases with increasing initial pH of leachant, qu and internal pH of clay. Furthermore, the relationship between needle penetration resistance and unconfined compressive strength fits unique power. In addition, the cumulative mass of leached lead, calcium and magnesium decreases with the increase of initial pH of leachant and the content of GGBS-MgO. When initial pH of leachant equals to 2, the cumulative mass of leached lead, calcium and magnesium is approximately 29-222, 1.7-4.4, 12.0-80.3 times of that when initial pH values of leachant are 3, 4, 5 and 7, respectively. Besides, when the content of GGBS-MgO is 12%, the cumulative mass is 1.1-2.0 times of that when the content is 18%. In addition, the effective diffusion coefficient of lead De decreases with the increase of the initial pH of leachant. When pH of leachant is 2, the De is 3-5 orders of magnitude higher than that of the pH values of leachant are 3, 4, 5 and 7. It is found that the De of lead contaminated clay stabilized by GGBS-MgO is lower than that of cement stabilized clay. Particularly, when the pH of leachant is 7, the De of the former one is 1-2 orders of magnitude lower than that of the later one.

Cracking is one of important structural characteristics of expansive soils. The cracking damage has significant impact on the deformation, strength and stability of an expansive soil. In developing a damage model for soils, it is crucial to choose proper variable to describe the soil damage. To evaluate the applicability of several existing methods for characterizing the damage variables, a series of CT-triaxial tests was conducted on the expansive soil sampled from the site at the middle part of the South-to-North Water Transfer Project in Taocha, China. Damage variable characterization methods based on the loaded area, mean ME and variance SD of CT numbers are quantitatively examined by means of CT-triaxial shear tests under 100 kPa net confining stress and 50 kPa suction respectively. It is shown that the strength and the deviatoric stress-axial strain curves are almost the same for the soil samples with the same damage areas and different damage positions. It is appropriate for the damage variables to be defined using the damage area and the SD. However, the ME is not suited for defining the damage variable of expansive soil, though it performs well in characterizing the damage of rock. The results can provide a starting point for defining damage variable, strength and the constitutive model of expansive soil.

The standard sand and ordinary Portland cement were selected as the experimental materials to prepare the samples of zinc contaminated soil solidified by cement. A series of tests was conducted to determine the unconfined compressive strength and electrical resistivity of the prepared samples. From these experiments, the effect of the current frequency on the electrical resistivity is investigated, and the influence of zinc ion concentration and curing time is also discussed on the delayed coagulation of cement, the electrical resistivity, unconfined compressive strength, the electrical resistivity and unconfined compressive strength. The results show that the electrical resistivity decreases significantly with the increase of current frequency, especially when current frequency is lower than 50 kHz. With the delayed coagulation influence of zinc ion content on cemented soil, the strength always grows slowly with the increase of zinc ion content but when the zinc ion content is up to 500 mg/kg, the delayed coagulation is abnormal. Both the electrical resistivity and strength increase with the increase of curing time, and fluctuate with the increase of zinc ion content. The electrical resistivity reaches a minimum and a maximum respectively at the zinc ion contents of 50 mg/kg and 500 mg/kg, and strength reaches a minimum and a maximum respectively at the zinc ion content of 100 mg/kg and 500 mg/kg. There exists a good linear relationship between electrical resistivity and unconfined compressive strength in different curing times.

The aim of this study is to investigate the responses of dynamic elastic modulus of rock on stress amplitude and stress level. Stepwise cyclic loading tests are conducted on sandstone, conglomerate and sandy conglomerate using a WDT-1500 reactive material testing machine. The variations of dynamic elastic modulus and dissipated energy with stress amplitude, stress level and moisture content are determined. The results show that the dynamic elastic modulus gradually decreases with the increase of energy dissipated. It is observed that the higher the stress level, the greater the dynamic elastic modulus and dissipated energy; the greater the moisture content and stress amplitude, the lower the dynamic elastic modulus, but the greater the dissipated energy. Ducan-Chang model is capable of describing the stress-strain relationship of rock under stepwise cyclic loading. Thus, a dynamic elastic modulus evolution model is proposed by taking into account the stress amplitude, stress level and moisture, and the methods to determine parameters of the model are discussed. Then, based on an empirical rule of energy dissipation, a dissipated energy evolution model is developed. The results show that the proposed models are able to describe correctly the characteristic of energy dissipation of rocks under stepwise cyclic loading.

To investigate the stability of the expressway embankment on soft ground, the whole arc method is used to deduce a limit equilibrium equation with coupling variables of internal friction angle and cohesion .The effect of internal friction angle on the tangential direction of slip surface is then assumed equivalent to cohesion effect, and the concept of equivalent cohesion is proposed. Based on the limit equilibrium equation and the equivalent cohesion, a procedure to calculate the optimal section size of loading berm is developed. The proposed procedure is used to design the section size of the loading berm and to determine the safety factor for a expressway embankment, and the calculated results are compared with the method from the code. The results show that because the combining effect of internal friction angle and cohesion is considered, the proposed procedure has a greater advantage in acquiring the optimal section size of loading berm than the method recommended by the code, in which only cohesion is considered. The safety factor calculated by the proposed method is 1.05, which agrees well with the results obtained with the method from the code. The proposed method can avoid the shortcomings of traditional methods that require experience in determining the size of berm.

This paper performs a series of model tests to explore the law of ground settlement induced by moving rigid wall with various movement modes, i. e. translating mode (T mode), rotating around toe mode (RB mode) or rotating around top mode (RT mode). The different ground settlement curves have been achieved with respect to three basic movement modes. It has been found that T mode movement tends to cause a spoon-type settlement profile with the maximum surface settlement at the wall back, and RB mode produces a triangle profile with the maximum surface settlement at the wall back, and RT mode movement results in a parabolic type settlement profile with the maximum surface settlement at a certain distance away from the wall back. For RB and RT modes, their ground settlement curves almost share the same area if their maximum movements of retaining wall are equal to each other. It is also found that for RB and RT modes, the sum of ground settlement of two modes is approximately equal to that for T mode. In addition, the wall movement-induced displacement area is almost equal to that of ground settlement. The experimental observed surface settlement agrees with the existing analytical solutions.

To investigate the influence of drilling method on the bearing characteristics of pile foundation in loess areas, statically loading tests on four tested piles were carried out on two sites of the Yongshou-Xianyang Expressway project, and the loading transfer behavior of pile foundation with different drilling hole methods is analyzed. The experimental results show that the drilling method has significant influence on the bearing characteristics of pile foundation. The bearing capacity of bored pile by churning is much higher than that of circulation bored pile with slurry protection wall in loess area. The reason is that the borehole wall needs protecting during drilling, the formed mud cake significantly weakens the exertion of pile shaft resistance. This can result in a minor ultimate friction resistance and a larger tip resistance accounting for a larger percentage of the load on pile top. Loess structure is destroyed after immersion in water, so that the bearing capacity of pile decreases compared with the test pile in original state. Due to the fact that the collapse settlement of overlying loess is small, negative skin friction is not produced by the soils in immersion state at pile side

Passive pile is a kind of pile deformed due to horizontal movement of soil. To study the deformation behavior of passive pile in both indoor experiment and numerical calculation, a horizontal displacement is normally applied on the model boundary (as a displacement boundary condition) to form a displacement field of soil. However, various distances between the position where horizontal displacement applied (usually the model boundary) and the location of passive pile are chosen by different researchers. According to an embankment field case, the loading position of horizontal displacement is analyzed using one univariate parameter in finite element method. The results show that the deformation of the pile decreases with increasing the distance between loading position and the location of passive pile, which indicates that stress dispersion occurs obviously in the soil after applying the displacement boundary condition. When the distance is less than 5.5 times of the pile diameter, there is much more stress required to achieve the same level of displacement at the model boundary. The distance from loading position to the pile location is also discussed, and it is found that the reasonable distance is in the range of 5-8 times of pile diameter.

Based on typical scour shape, the lateral bearing capacity tests are conducted on typical nine-pile group foundation to simulate different local scour effects by changing scour depth, and parallel contrast tests on single pile foundation with the same parameters are also carried out. The load-displacement behavior, distribution of bending moment along pile shaft, efficiency coefficient of pile group and load sharing ratio of piles are analyzed in detail. The results show that as the scour depth increases, the lateral bearing capacities of single pile foundation and nine-pile group foundation are both weakened, the lateral efficiency coefficient of nine-pile group foundation increases gradually, the cap constraint effect becomes much more notable, the maximum bending moment along pile shaft increases, the maximum moment point of pile shaft comes down to the pile bottom, and the load sharing ratio of the front piles increases, while load sharing ratios of the rear and middle piles decrease. The front corner pile is severely affected by the scour depth and lateral load, so effective measures should be adopted to enhance the front corner pile in design.

As scouring can induce soil loss around pile foundations, it is important to investigate the scouring effect on laterally loaded piles. The strain wedge method is an effective method to predict the p-y curve and to analyze the deformation characteristics of laterally-loaded piles, which can only be applied to the case of horizontal ground surface. An equivalent-strain wedge method considering scouring effect is proposed based on the equivalent depth of the strain wedge above the bottom of scour hole. The validity of the method is confirmed by comparing it with those in the literatures. It is found that the lateral responses of a pile decrease with the increase of scouring depth and scouring width at the bottom of a scour hole, and also with the decrease of scour slope angle. Compared to the simplified method, in which only the ultimate lateral pile resistance is affected by scouring, the present method yields a smaller maximum bending moment on pile. Removing the whole soil layers above the scour bottom would result in a conservative result due to omitting the effect of soil layers located in the range of scouring depth.

The hydraulic head distribution of seepage field is the basis of seepage discharge and seepage hydraulic gradient calculation. Calculating the hydraulic head distribution of seepage field accurately and effectively is the key link in the calculation of seepage. According to the flow equation of unidimensional steady flow in homogeneous unsaturated soil and the functional relationship between hydraulic conductivity and matric suction, an analytical general formulation of seepage field is obtained with mathematical transformation. In addition, based on the Gardner model, the analytical solution of unidimensional steady flow hydraulic head vertical distribution in unsaturated soil is derived. The general formulation indicates that the unidimensional steady flow hydraulic head vertical distribution is mainly controlled by such three factors as surface water head, depth and rate of flow. Under the condition of unidimensional steady evaporation, the hydraulic head distributions of two typical soils in vertical direction, namely silt and clay, are calculated respectively. The result shows that under the steady evaporation condition, the laws of hydraulic head distribution of silt and clay in vertical direction are similar. With the increase of depth, the characteristic of hydraulic head distribution shows an accelerating degressive tendency from surface to groundwater level. The hydraulic head in clay is higher than that in silt under the same evaporation condition. For the same soil, the faster the evaporation, the higher the hydraulic head. Conversely, the hydraulic head is lower.

The interval non-probabilistic reliability analysis method may lead to conservative design under some conditions, and increase the project cost. To resolve the issue related to the applicability of interval non-probabilistic reliability method, the probability theory and Monte Carlo method are introduced, and the evaluation index for applicability is determined. Then the study method is proposed for application of the interval non-probabilistic reliability analysis method. Based on the analysis of practical problems, the applicability problem of interval non-probabilistic reliability analysis method is discussed, and the applicability of interval non-probabilistic reliability analysis method is investigated for different changing ranges of interval independent variables, number of interval independent variables and function types. The results show that when the changing range is relatively large and the number of interval independent variables is large, the applicability for interval non-probabilistic reliability analysis method is lacking. This study can provide a reference for the application of interval non-probabilistic reliability analysis methods.

On the basis of the experiences from some pipelines transporting oil and gas in permafrost regions, this paper investigates the formation process, influential factors, causing mechanisms of frost hazards and their impacts on the pipeline according to the results from the field surveys and ground penetrating radar (GPR) detections along the Mohe-Daqing line of China-Russia crude oil pipeline (CRCOP). In addition, some mitigative measures and research needs are proposed. Investigations show that the CRCOP has being encountered with some frost hazards including thaw settlement, frost mounds, icings, permafrost slopes, ice gouging and frost heave, which may cause damages to pipeline in the future. The monitored oil temperatures at three pumping stations show the lowest and highest oil temperatures are 0.42 ℃ and 16.2 ℃, respectively, during the period from 2011 to 2012. This year-round positive oil temperature becomes the predominant factor causing the current thaw settlement of permafrost surrounding the CRCOP in some sections. In the winter, the frost mounds, icings and floating ices potentially threaten the pipeline in some sections. The results can provide important references and bases for construction, design, operation and maintenance of the second CRCOP, the China-Russia gas pipeline, the Golmud-Lhasa and other pipelines in permafrost regions.

The aim of this paper is to further investigate the influencing factors on outburst intensity of coal and gas due to the limited studies of its mechanisms. An expression of elastic potential energy released by coal is derived by establishing a three-dimensional outburst model and calculating the volume of irregular outburst pore. Based on analyzing gas internal energy and the energy after outburst, we propose an energy conditional model for the occurrence of coal and gas outburst and a forecast model of outburst intensity. These two models are applied to calculate the energy changes prior and after outburst, according to the statistical analysis of ten times of coal and gas outbursts. It is noted that the energies are almost the same between prior outburst and after outburst, and even the predicted values of outburst intensity are basically equal to the statistic ones. Therefore, the proposed models are verified to be valid, which provide a quantitative approach for analyzing the coal and gas outburst in terms of energy. Furthermore, the proposed procedures are successfully used to analyze the factors influencing outburst intensity of Zhongliangshan colliery and Huachu colliery. The results show that the outburst intensity is mainly dominated by the geostress of coal seam and gas content, and trivially affected by sturdiness coefficient and footage; the sensitivity of outburst intensity to gas content is higher than that of geostress.

The designing and calculating methods for compressive bearing capacity of a single pile can be divided into two types, i.e. characteristic value method and ultimate value method, in the Chinese codes related to pile foundations. The bearing capacity of a single pile is obtained by directly summarizing the skin friction and the tip resistance. These methods have some conceptual and theoretical disadvantages, since the skin friction and tip resistance cannot be simultaneously mobilized due to different mechanical responses and deformation requirements at the pile skin and the pile tip. The ultimate value method is more direct, reliable, accurate and clear in concept, and is more ready to be used in parallel to international standards. Hence it is suggested here that this method is preferred in the standards. A contradiction may occur in determining the uplift bearing capacity of a single pile according to the results of pull-out tests using the different standards. Because of this, the natural unit weight of pile should be used in calculation, instead of the buoyant unit weight of pile. Further research should be conducted to explore the following two phenomena in revising the relevant codes: one is that the unit skin friction decreases when exceeding the effective length of the pile, and the other is that tension coefficients for pull-out pile in some engineering is far less than the recommended values in the relevant codes, especially when pile length is longer.

Winkler model based p-y curve method has been widely used in the design of laterally loaded pile. This semi-empirical method was originally proposed for the offshore oil/gas platform and developed from field lateral loading test results mainly on flexible piles with diameters not greater than 1.2 m and ratios of pile embedded length to outer diameter larger than 20. In the past decade, the boom in the wind energy industry, especially for offshore, has increased the dimensions of piles out of the range for derivation of current p-y models. To date, it is generally agreed that, for the design of a laterally loaded pile with a large diameter, such as diameter 6 m, the reliability of current p-y models is not clear and should be further investigated. According to the test results of two laterally loaded piles, a detailed case study was conducted to investigate the p-y model recommended by the API code and other researchers’ refinement. The results show that the negligible error is shown in bending moment predicted by different p-y models. The pile head deformation is mainly dependent on the initial stiffness of subgrade reaction and the expressions of p-y models. Not only the internal friction angle and relative density of sands, but also the geological history of ground should be considered for determining constant of subgrade reaction stiffness. Finally, future study is highlighted.

A contact model considering rolling resistance is introduced and implemented into the distinct element method (DEM) for analyzing the earth pressure at critical state against a rigid wall. The variation of earth pressure coefficient and the shear band formation in the backfill material are analyzed, when the passive earth pressure varies with displacement for the retaining wall with different densities and different displacement modes (passive T mode, RB mode, RT mode). The DEM simulation results are compared with those of other researches. It is shown that earth pressure coefficient is greatly affected by different void ratios and wall displacement modes. The -displacement relation switches from hardening to softening when the void ratio decreases or the relative density increases. In contrast, the -displacement relation demonstrates either hardening or softening feature for the medium dense backfills even they exhibit a strain softening response in the biaxial compression tests. As the retaining wall moves to soil behind the wall, the shear strain increases and the strain localization occurs, i.e. shear band forms in the soil behind the wall. Similar to the shear strain field from laboratory experiment, the distributions of the shear band in the critical state are better simulated by DEM. Meanwhile, the surface of the backfill is no long a smooth surface rather than an upheaval surface, the value of upheaval increases significantly with the increase of the displacements of retaining wall, and finally the soil body behind the wall damages.

The contaminants, such as filtrate of waste landfill, intrusion seawater, nuclear waste, production sewage and living sewage, would threaten human survival when they migrate into groundwater system. Randomness of groundwater seepage makes the problem of solute transport more complicated. According to the characteristics of flow net, implicit difference scheme of the solution of unit solute concentration based on the principle of mass conservation with the stream tube element is solved by the streamline and equipotential lines. Based on the velocity distribution patterns of porous media, the Monte Carlo method is used to establish the flow rate field for simulating the process of migration of solute. The accuracy of the numerical simulation method is proved by the comparison of the simulation and model tests. In the numerical model the convection and diffusion have effect on the substance exchange along the direction of stream tube. However, only solute diffusion exists between stream tubes. In this model, the feasibility of dispersion coefficient and the limitation of feasibility are overcome. The method for determining flow rate with randomness can provide a new idea for research of advantage migration of contaminants in heterogeneous flow field.

Determination of the freezing pressure in deep alluvium is crucial in designing the outer shaft lining. Using the UMAT of ABAQUS subroutine, the modified Nishihara model for creep of frozen soil is implemented into ABAQUS. With considering the effect of thermo-mechanical coupling during freezing, the freezing pressure distribution of frozen soil before excavation is obtained. Based on these results, the variation of freezing pressure on the outer shaft lining is determined by analyzing the process of deep frozen shaft construction. The results show that the values of freezing pressure are related to the soil depth, soil frost heave ratio and the temperature of the frozen wall. The freezing pressure increases 21% when the depth increases from 400 m to 500 m, and decreases 10% when the average temperature of frozen wall decreases from -16 ℃ to -18℃, and increases 3.8% when the frost heave ratio increases from 2% to 3%. The freezing pressure increases with the increase of depth and frost heave ratio of soil. The lower temperature of the frozen wall benefits the stabilization of the frozen wall. The error between numerical and measured results is less than 15%, showing that the proposed method can reasonably predict freezing pressure of deep shaft in practice.

The time-dependent deformation experiments on different types of loesses, which are sampled from the test section of loess-high filling 80 meters thick at Lüliang Airport, are carried out. A modified Burgers (M-B) model is established for depicting time-dependent behaviors of loess. The developed model is introduced to the software FLAC3D to analyze the sensitivity of post-construction settlement of loess-high filling due to such factors as compaction degree, control standard of water content and foundation treatment methods. Based on the in-situ monitoring data, the numerical back analysis and prediction are conducted to further study the difference between experiment parameters and generalized layer’s parameters of high filling. The results show that reinforcement treatment of original foundation is the first critical factor for controlling the post-construction settlement, and the water content selection is also important for designing the compaction degree of high filling. The generalized layer’s parameters of M-B model are one to four times bigger than the experiment ones. The stability duration time for post-construction settlement of the thick loess foundation needs 3 or 4 years. It is suggested that the construction of airport infrastructure should be carried out 1.5 or 2.0 years after the completion of the high filling.

Due to the rapid development of modern construction activities, the landslide disaster induced by artificial disturbance is increasing gradually. Therefore, landslide monitoring is becoming more and more important to ensure the safety of human and stability of engineering structures. An improved system is introduced to monitor and to pre-warn the whole process of large deformation landslide disaster. This system based on two-way communication platform includes Beidou satellite and general packet radio service (GPRS). The zigbee technology is applied to build a wireless multi-hop self-organizing sensor network. The new anchor cable with constant resistance and large deformation functions, which can absorb energy, is used to replace the common anchor cable as the transmission device. Thus two-meter deformation of slope rock mass is allowed without tensile failure of energy absorption anchor cable. In addition, four level warning criteria are established according to four color grades (i.e. red, orange, yellow and blue). 3D automatic searching and processing software system is also developed. Vector maps, such as topography remote sensing map, geologic profile map and distribution map of monitoring points, are embedded in the monitoring area. Therefore, this new system has benefits in: searching area automatically, processing data intelligently, displaying monitoring curve automatically, and querying monitoring information quickly. The system has been used in Nanfen open pit iron mine. According to the warning criteria, the warning information of the landslide on October 5, 2011 was sent out 5 days in advance. Combined with the monitoring data of rainfall and the cumulative amount of mining, it is proved that sliding force is the only effective parameter for landslide pre-warning, which results from the coupling analysis of the evolution of the various parameters before and after the landslide. The successful application of this system provides theoretical and practical basis for monitoring and pre-warning other similar slopes.