An ooze seam in a plain river network area generally has a large thickness and a low strength. In such an area, when some ports are built or expanded, the soft soil layers should be dug out and backfilled, leading to a high construction cost. Then the unloading-type sheet pile has be adopted to resolve the above issues owing to its lower construction expense. But the earth pressure for this structure has yet to be effectively evaluated. By drawing lessons from the earth pressure calculation of covered sheet pile wharf, a method for calculating earth pressure for this new structure is proposed. In this method, the whole structure is first divided into many parts, and then the earth pressures on sheet piles facing river and bored piles oriented to land are calculated based on the non-limit state earth pressure theory, meanwhile the earth pressures of sheet pile landside and bored pile riverside are also determined with considering the effect of soil arching and unloading. By comparing the analytical results with the results obtained from centrifuge model tests and finite element method, the applicability and reliability of the proposed method is demonstrated.

To investigate the mechanisms of the prestressed anchor bolts in controlling the slabbing failure of rock mass, laboratory physical model experiments on slabbing failure are conducted and the forming process of slabbing failure in plane strain condition is simulated by using the FLAC simulation technology. On the basis of above work, numerical experiments based on three different applying schemes of prestressed anchor bolts are conducted to reveal the mechanisms of the prestressed anchor bolts in controlling the slabbing failure process. The results show that the effect of the prestressed anchor bolts manifest in weakening the concentration effect of stress near crack tip, restraining the crack propagation, coalescence and the slabbing failure process; when applied on the edge of slabbing failure zone, prestressed anchor bolts can not only effectively restrain the formation of slabbing failure but also control the scope of slabbing failure to some extent; when applied in the slabbing zone, prestressed anchor bolts have significant effect in restricting the displacements of the free surface of rock sample, improving the overall stiffness of the slabbing rock. The research results of this paper are of significant importance in understanding the formation mechanisms of slabbing failure, reasonable support control measures of slabbing failure and also rockburst prevention in deep tunnels.

To study damage deformation behaviour of low permeability soft coal rock subjected to the triaxial compression and pulsed pore water pressures, a series of experiments is conducted under different axial compressions and confining pressures using the RLW-2000 coal/rock rheometer. The results show that the general trend of stress-strain curve exhibits characteristically from sparse to dense and then back to sparse. In addition, both the cumulative and residual strains decrease with increasing confining pressure, however it is opposite with the increase of axial pressure. Meanwhile, the average dissipated energy of a cycle declines with the increase of confining pressure when the axial pressure is constant, but it increases with the increase of axial pressure when the confining pressure is constant. Moreover, the relationship between the average dissipated energy of a cycle and the confining pressure or axial pressure fits the exponential function. Finally, the overall trend of damage in the process of coal failure is calculated on the basis of the relationship between accumulated energy dissipation and damage, and the inverse function of Logistic equation is applied to fit the damage trend. Then the damage evolution model is obtained, which provides the basis for predicting the damage cycle of coal. The present results provide a theoretical evidence for the pulsed hydraulic fracturing on the low permeability soft coal seams under different ground stresses.

To study the unloading characteristic of marble with different initial damages, conventional triaxial loading-unloading tests were conducted under the same initial confining pressure but different axial pressures. Moreover, the rock samples subjected to loading-unloading conditions were performed to investigate the nuclear magnetic resonance (NMR) behaviour. The rock porosity, strain, nuclear magnetic resonance image (NMRI) and crosswise relaxation time T2 distribution were obtained. The results showed that: (1) the rock porosity increased during the unloading process. When the initial axial pressure was at 90% of the triaxial compressive strength (TCS), the unloading process was more steady than at either 70% or 80% TCS. (2) The initial damage advanced the increase of strain, in particular the hoop expansion, which in turn accelerated the growth of microcracks. (3) When the initial damage was low, the deformation of rock sample changed from elastic to plastic. Spectral peaks of the small microcracks moved from left to right, while spectral peaks of the large microcracks continuously extended to right, which indicated that small microcracks were generated at the initial stage of unloading, and both small and large microcracks propagated and coalesced at the last stage. When the initial damage was sufficiently high, T2 spectrum curves just moved towards right, which meant that the propagation of large microcracks played a vital role and the rock had undergone only the plastic deformation. (4) When the initial damage was increased, both the intensity and area of NMRI white spot and the rock porosity were increased at the same unloading confining pressure ratio.

Experiments are conducted on raw coal and reshaped coal samples at varied conditions using a self-developed hydraulic fracturing experimental equipment. The characteristic of strain of borehole wall is analyzed. The results show that the strain of borehole is obvious during the process of increasing water pressure, and the strain is difficult to be recovered while the water pressure is unloaded. There are two types of strains in the borehole, i.e. tensile strain and the compressive strain. There are two types of strain region during the hydraulic fracturing process. The compressive strain occurred in compression region is recovered sufficiently when the water pressure is unloaded. The hydraulic fracturing process is divided into three stages by strain curves, i.e. the water and gas induced micro-damage stage, the local damaged zones stage, and the unstable failure stage. At micro-damage stage, the initial damage stage is caused by the formation of gas stream channels within the borehole wall. At the next stages, the tensile and compressive regions are generated on the borehole wall. The tensile failure zone increases continually until the collapse of the borehole, while the compressive deformation zone has been recovered to some extent due to the rotational direction of the applied force. Therefore, the residual tensile strain is obvious when the borehole has fractured, but the residual compressive strain is unapparent. The study results are of interest in the field of crack initiation and energy evolution mechanism of borehole.

Diffusion law of dynamic grouting has directive significance to the grouting design and construction. Simulation tests of crack dynamic grouting with cement-silicate (C-S) slurry are carried out. The asymmetric ellipse (AE) law is revealed to describe the C-S slurry diffusion process under laboratory conditions. The concept of “speed ratio of slurry to water” is proposed to fit the AE parameters-time curve. How the speed ratio of slurry to water affects grouting diffusion range is analyzed. The transient equations describing slurry diffusion trace is established. The results show that: the slurry diffusion trace could be described with asymmetric ellipse which varies with time. The speed ratio of slurry to water is positively correlated with diffusion distance against flow direction and lateral diffusion distance. The speed ratio is negative correlated with diffusion distance along flow direction. Based on the results above, suggestions for grouting design are proposed.

The backfill of mixed slurry consisting of alkali wastes with saturated brine into abandoned salt cavern can simultaneously resolve the problems of alkali treatment and the potential geology disaster of abandoned salt caverns. The strength of the backfilled alkali wastes is a key parameter which affects the filling effect. In order to improve the strength of the backfilled alkali wastes, fly ash is used to make compound alkali. A series of mineral analysis, strength experiments and mesoscale testing have been conducted to determine the properties of the compound alkali wastes, showing that: (1) The mixing of fly ash can effectively reinforce the alkali wastes, resulting in the increases in the cohesion, the internal frictional angle and the shear strength; (2) The larger the mixing ratio of the fly ash, the stronger the reinforcing effect is; whereas, the strength increases nonlinearly with the increment of mixing ratio. For cohesion, its maximum increasing speed locates in the mixing ratio range of 0-20%; for internal frictional angle, it is in the mixing ratio range of 20-30%; and for shear strength, the maximum increasing speed locates in the mixing ratio range of 0-20%; (3) The mixing of fly ash can significantly improve the compression consolidation properties, inducing an increase in consolidation coefficient, thus the project time of backfill will greatly be reduced; the mixing ratio of 0-10% is most suited to the improvement of consolidation; (4) By mineralogical analysis, it is shown that the mixing of fly ash can change the components of the alkali wastes, significantly reducing the content of the hydrophilia minerals and changing the sedimentary properties. The meso-scale analysis shows that, owing to fly ash mixed into alkali wastes, the flocculation structure of initial alkali wastes changes into the filling structure where the fly ash acts as main skeleton, in this structure the supporting and connecting effects between particles are also more obvious. Comprehensive analysis shows that the mixing ratio of 20% is the optimal ratio in terms of the improving strength, enhancing consolidation effect, shortening project period as well as saving cost. A value less than 20% is recommended for the practical mixing ratio in practice. The research results provide a good reference for revealing reinforcing mechanism of alkali wastes, as well as optimizing technologies for salt cavern backfill.

A viscoelastic displacement discontinuity model is proposed, in which the rock mass is viewed as a three-parameter standard linear solid. The recurrence formulations of particle velocity, stresses and strains at joint are developed based on the characteristic line method for the 1D viscoelastic wave. The dynamic stress-strain relationship of the sand layer is first determined by the split Hopkinson pressure bar (SHPB), which can be converted to the normal stiffness of joint. Then the three parameters for the standard linear solid are evaluated through the velocity formulation and the high frequency attenuation coefficient along with the arbitrary frequency attenuation coefficient of 1D strong discontinuity viscoelastic wave. Finally, by using two rock bars with a length of 1 000 mm and a diameter of 68.50 m as the incident and reflected bars, respectively, the propagation of 1D stress wave in jointed rock mass is analyzed based on a homemade pendulum by using 3 mm sand layer as the alternative joint. Good agreement between the experimental and numerical results are demonstrated, showing the reliability of the proposed method.

To study the effect of temperature and loading rate on mechanical properties and failure modes of rock materials, experiments on granite were conducted under uniaxial compression at different loading rates and real-time high temperatures in the range of of 25-1 000 ℃ by the servo-controlled testing machine MTS810. The results show that: (1) Stress-strain curves of granite at real-time high temperature have the compaction, elasticity, yield and failure stages. Post-peak curves present stepped and segmented drop shape at loading rates from 0.001 to 0.01 mm/s, but present smooth and steeped continuous phenomena at loading rates from 0. 01 to 0.1mm/s. (2) The peak strength and elastic modulus are divided into four stages with increasing temperature, which is the slowly rising stage from 25 to 200 ℃, rapidly declining stage from 200 to 600 ℃, slowly rising stage from 600 to 800 ℃, and slowly declining stage from 800 to 1 000 ℃. The peak strength and elastic modulus at 1 000 ℃ decreases by 53.47% and 64.34% respectively, compared with that at 25 ℃. The peak strain presents cubic polynomial relationship with the temperature. (3) Both the peak strength and elastic modulus show a quadratic polynomial increased relationship with the logarithm of loading rates, the value of which increased by 38.82% and 37.22% respective at the loading rate of 0.1 mm/s to compare with that at 0.001 mm/s. The peak strain presents unobvious relationship with loading rates. (4) As the temperature increases under uniaxial compression state, the forms of deformation and failure of rock samples transfer from the tensile shear rupture to the cone fracture with fragmentation of liquidity; and the instability mode transfers from sudden instability to progressive failure. The fracture modes of rock sample are independent on the loading rate, but the instability patterns depends on loading rate.

Control of soil deformation induced by tunnelling is one of the major objectives of fracturing grouting. Prediction accuracy of tunnel deformation depends mainly on the equivalent elastic parameters of composite soils with fracture grouting. Firstly, according to equivalent grouting area and the existing model of fracturing grouting, a simplified 2D model for equivalent unit cell is developed for composite soils with fracturing grouting, and the analytical solutions of the equivalent elastic parameters of this model are derived based on deformation compatibility principle and homogenization theory. Secondly, finite element method is employed to calculate and analyze the equivalent elastic parameters of the simplified model and existing model, respectively; meanwhile, the comparisons are made between the finite element and analytical results of the simplified model. Lastly, the influence of grouting volume ratio, soil elastic parameters, and grouting concretion elastic parameters on equivalent elastic parameters are analyzed by means of the analytical solution. The results indicate: (1) the equivalent grouting area method is feasible, and the simplified model can be applied to theoretical analysis in the elastic deformation stage; (2) the analytical results are in good agreement with the finite element results, and hence the analytical results are reasonable; (3) the equivalent elastic modulus and equivalent Poisson’s ratio of composite soils are mainly influenced by the grout volume ratio and modulus of grouting concretion body; the Poisson’s ratio of grouting concretion has slight influence on the equivalent elastic modulus of composite soils.

An one-dimensional soil layer model is employed to analyze the site effects of the designing ground motion in five kinds of non-hard rock sites, including firm rock site, soft rock site, upper bound soft-to-medium soil site, soft-to-medium soil site and soft soil site, for designing the foundation of AP1000 nuclear island (NI) structure. In this study, the shear wave velocity in the bedrock of the computational model is selected as 700, 1 100 or 2 438 m/s. The input motion of the bedrock is taken as RG1.60, AP1000 and HAD101 spectra (with 5 damping ratios) matching with the synthetic acceleration time histories of ground motion provided in the relative technical documents and standards, respectively. Analytical results indicate that non-hard rock sites induce the significant changes of the peak ground acceleration and response spectrum of the ground motion, which is enhanced further by a softer site. The effects of non-hard rock sites, except the soft sites, amplify the peak ground acceleration and response spectrum. However, the effect of the soft site increases the peak ground acceleration and response spectrum in a lower frequency range, and it is opposite in a higher frequency range. The peak ground acceleration and response spectrum of the site ground motion are significantly influenced by the changes of the bedrock and its shear wave velocity of all non-hard rock sites. Moreover, the effect is proportional to the shear wave velocity of the bedrock, and the ground motion decreases obviously with the increase of shear wave velocity. The ground motion is unaffected by the shear wave velocity as the site changes from hard to soft. Considering the great effects of the site type and the bedrock selection on ground motion, it is thus necessary to analyze the applicability of the sites by using the AP1000 standard design in the nuclear power plant construction in China.

Soil structure is one of the physical properties of the soil, which represents the spatial arrangement of soil particles and the type of inter-granular cementation, and it plays an important role in influencing the mechanical properties of collapsible loess. As it is closely linked with density, particle and moisture, the soil structural can reflect the change of the mechanical properties such as strength and deformation. The structural variations induced by either the passively wetting or the positively loading are investigated, with adopting the stress ratio structural index that accounts for the overall structural potential of the soil. Firstly, the structural evolution of loess is determined under compression, shearing and wetting conditions; then the effect of structure on the soil behavior is characterized by establishing a correlation among the stress-strain behavior, yielding and failure behaviors and the soil structures; finally, the structural constitutive relationship of loess under wetting and loading conditions is developed. The proposed model is validated by comparing the numerical results with the experimental data and the results of the modified Cam Clay model.

The dissolution of a soluble salt in the inshore saline soil may cause a reduction in strength and an increase in deformation of the soil, which will seriously deteriorate the performances of immature soil material. The acrylamide (AM) polymerization technique is used to improve the saline soil, and the effects of AM and curing conditions on the mechanical properties of saline is analyzed. The results show that when the temperature rises up to 70 ℃, the drying time is 6 hours, the dosage of acrylamide monomer is 3% of saline soil mass, and initiator dosage is 3% of AM mass; furthermore, when the crosslinking agent is not added, the improved saline soil has higher compressive and flexural strengths of the improved saline soil, while the dosages of the various agents are economical; the flexural strength of the soil can reach 2.265, 3.603, 5.255 MPa, and the compressive strength is 5.6, 13.7, 16.2 MPa when the curing age is 7, 14 and 28 d, respectively. Compared with plain saline soil adobe, the compressive and flexural strengths (28 d) of modification saline soil adobe increase 4-5 times respectively, much higher than those of the traditional masonry mortar. At the same time, water resistance and shrinkage are improved significantly. The microscopic mechanism of strength improvement is analyzed using the scanning electron microscope (SEM) and X-ray diffraction spectrum (XRD), it is found that the porosity decreases significantly but mineral structure of solidified soil remains unchanged. AM polymerized solidification of saline soil can be considered as a kind of new environment friendly building materials used in construction projects.

Based on the basic concepts and principles of the theory of probability, the transfer of additional stress in geomaterials is viewed as a probability event, and without adopting any model and assumption the probabilistic solution to additional stress is derived under point loads in the two-dimensional space. Then the solution is extended to the uniform loading condition in the two-dimensional space. Furthermore, both of the proposed solutions are extended into the three-dimensional space. Finally, all these solutions are compared to the Boussinesq solution. The results match with each other very well, showing that the proposed probabilistic solution to additional stress in geotechnical media is reliable and reasonable.

The freeze-thaw cycle tests were conducted on the remoulded soil samples taken from a highway subgrade in a seasonally frozen area. The triaxial compression tests under the consolidated-drained condition were carried out on the remoulded samples subjected to freeze-thaw cycle, and stress-strain data were obtained. Based on the experimental results and the theory of elasto- plasticity, an elliptic equation is proposed to fit the yield surface in the p-q coordinate system, while a parabolic equation is proposed to fit shear yield surface, from which an elastic-plastic constitutive equation was developed following an associated flow rule with considering freeze-thaw cycles. By comparing the theoretical calculation with the experimental data, it is shown that the proposed double-yield surface constitutive model can accurately predict the frozen soil stress-strain relationship. The model provides a theoretical basis for long-term stability analysis and engineering prediction of subgrade soil in seasonally frozen areas.

Advection-diffusion apparatus was installed on a geotechnical centrifuge under 50g to run for 12 hours in order to investigate migration of Cl- in clay-bentonite barriers. Analytic solution was used to calculate the diffusion parameters. The scaling requirement was studied. The prototype of the centrifuge test was simulated by commercial software and the scale law of solute migration in geotechnical centrifuge was discussed. Efficiency of the tested clay-bentonite barriers used as an amendment measure in an old landfill to prevent pollution was analyzed by numerical simulation. In the centrifuge test, the actual advection velocity and the Péclet number calculated from outflow are smaller than the critical values. Mechanical dispersion can be neglected and the consistent scaling law can be satisfied. Breakthrough has not happened after 3.42 years for the simulated layer with a prototype thickness of 2.5 m and the hydraulic heads of 5 m and 10 m. Saturated hydraulic conductivity and effective dispersion coefficient of the tested soil are 8.5×10-8 cm/s and 7.82×10-7 cm2/s, respectively. Numerical simulation of the centrifuge test prototype shows that under a centrifugal acceleration of ng, solute migration under advection and dispersion in the prototype can be modeled in the centrifuge in size and time. If the tested clay-bentonite is used in old landfills for amendment of early barriers, the migration can be significantly slowed down and the requirement of pollution control can be satisfied.

In the experimental study on the creep characteristics of soil, the drained creep experiments are seldom performed due to the restriction of the experimental condition. Even less effort is made to first retrieving the initial consolidation conditions and then conducting the triaxial drainage creep characteristic tests. In this stuy, consolidation creep test is performed in two stress paths including axial loading and lateral unloading to investigate the creep characteristic of saturated silt soil. Based on the experimental results, some conclusions are drawn as follows. First, the axial creep characteristics for the two stress paths are consistent under the drainage conditions, though the volumetric strain is much smaller than the axial strain, and the volumetric strain shows alternating shear shrinkage and shear dilatancy when time elapses. Based on the three-unit mechanical model, the creep starting time of the oozy soil is estimated as 100-200 min after applying the deviatoric stress during the creep test. The creep coefficient of the oozy soil is defined and its variation is characterized. It is found that the creep coefficient is closely related to the deviatoric stress level, i.e., regardless of confining pressure and loading path, creep coefficient increases linearly with deviatoric stress level, and is not influenced by such factors as the initial consolidation confining pressure, load applying way, etc. Finally, it is proposed that the NHRI model describing the transient elastoplastic strain be combined with the creep empirical formulation describing creep strain, so that a creep constitutive model can be developed.

This paper studies the settlement behaviors of a deep soft clay subgrade in an artificial island. The centrifugal tests are performed to simulate the settlement of foundation soils with a thickness of 60 m. Based on the tests, a 2D finite element model is developed to analyze the settlement behaviors of the foundation soils with implementing an elasto-viscoplasticity constitutive model. Comparisons between centrifugal tests and numerical analysis show that the post-construction settlement curves are in good agreement. The settlement rates are larger in the early stage, but keep stable in the later stage. The dissipation of excess pore water pressure of numerical results is faster than model test for shallow layers; but the tendency from two test has a good agreement in deep layers. The reliability of the numerical method is demonstrated by the consistency between the experimental and numerical results.

According to the “four zones” division of mined-out area overburden and the movement characteristics of continuous deformation zone, this paper presents a view that movement of continuous deformation zone is controlled by the key rock stratum which locates at the bottom of continuous deformation zone and is close to the quasicontinuous zone; the sinking movement is referred to as approximately an elliptical table basic trajectory, the ultimate movement magnitude of continuous deformation zone is the superposition of elliptical table formed by internal strata movement, thus which forms an elliptic paraboloid movement trajectory. Based on this view, the deflection function of the continuous deformation zone is determined firstly. And then an elliptical table model of single stratum movement is put forward for the case of level and nearly horizontal seam mining in continuous deformation zone combining in combination with elastic thin plate theory; furthmore, a mathematical model of continuous deformation zone movement also is developed based on the superposition of single stratum movement. At last, the method of model parameters determination is given. The results enriches the research theory of continuous deformation zone movement, proving a new idea and method to study the movement and deformation of surface and strata.

A series of drained shear tests are carried out on saturated sand samples using hollow cylinder apparatus. Four groups of stress paths are considered to study the deformation characteristics of the sand under drained shearing condition, with emphasis on analyzing the variations of the directions of the principal stress increment and strain increment of the sand along various stress paths. The considered stress paths include fixed principal stress directions with increasing of deviatoric stress ratio (shear loading with fixed principal stress directions), principal stress rotation with constant deviatoric stress ratio (pure principal stress rotation), simultaneous increase in deviatoric stress ratio and principal stress rotation; multilinear simultaneous increase in deviatoric stress ratio and principal stress rotation. The experimental results indicate that the major principal stress increment direction varies between 45° and 135° under the pure rotation of principal stress axes. The major principal strain increment direction moves gradually towards the direction of principal stress. Deformations accumulate under simultaneous increase in stress ratio and principal stress rotation. The direction of principal strain increment coincides with stress increment when 45°, whereas the direction of principal strain increment deviates from stress increment when 45°. Deformation is practically stress-path independent and the strain response under subsequent principal stress rotation is shown to be independent of the previous loading history, if the final stress state is within the approximate bounds of 0.75 and 45°.

Proper determination of drilling parameters plays a key role in applying big diameter drilling to prevent rockburst. The pressure relief evaluation index of burst risk area in coal face is studied based on rock mechanics testing, theoretical analysis and site measurement. The concept of energy dissipation index is presented, and the conversion formulation of energy dissipation index and bursting energy index is derived. Some conclusions are drawn as follows: good correlation is found between energy dissipation index and bursting energy index, which can be used as the index to evaluate the seam residual rockburst hazard of pressure relief. The “regionalization and grading” prevention and treatment ideas of rockburst risk area in coal face is proposed, with effective pressure relief strain rates of 1.5‰, 1.0‰ and 0.8‰ for the pressure relief indices of high, middle and general risk areas, respectively, in Xinjulong Mine. The quantitative calculation method of rockburst prevention relief drilling parameters is derived based on energy dissipation index. The ideas are applied to working face 2302S of Xinjulong Mine with a good result, providing a reference for rockburst control.

The effect of waste landfill on seismic response of transmission tower pile foundation at mountainous slope still remains unclear. Typical models about pile foundation of transmission foundation in southwestern China mountain areas are built and analyzed using FLAC3D. Then seismic response on pile caused by waste landfill is preliminary studied under the condition where there is waste landfill around the pile or not. The results show that: compared with pile without spoil, horizontal peak acceleration, pile displacement, internal force of pile, displacement of soil around piles all increase obviously after waste landfill is built. When gradient of steep slope is larger than 35°, waste soil landfills will increase the seismic response of pile foundation, thereby seismic behavior of steep slope is reduced.

Strong earthquakes, extreme weather conditions and human activities are among the major factors triggering landslides. These strong disturbances can change the physical properties of the landslides and the mechanical properties of the weak surfaces, which are responsible for the failure of the early warning. A new method is examined for quickly evaluating the safety of the landslides after a disturbance, such as an earthquake. The natural frequency of harmful geological structures are measured using the laser measurement technology. The measured natural frequency can quantitatively reflect the parameters of the internal structure. Using the simplified model of the landslide body, the stress loss of the slope surface due to an earthquake or heavy rain can be determined. The experimental results show that the natural frequency can be used to infer the monitoring indices such as the stress loss coefficient when the landslide subjected to a large disturbance. Rapid and remote monitoring can be effectively used to quickly evaluate a landslide. The laser vibration technology will play an important role in disaster prevention and disaster mitigation in the engineering practice.

To evaluate the effect of the intermediate principal stress on the ultimate strength of rock, a new three-dimensional (3D) Hoek-Brown failure criterion is established by adding a quantitative representation of the intermediate principal stress to the power-law item of the generalized Hoek-Brown failure criterion. The new failure criterion in principal stress space is a curved hexahedron circumscribing the envelope of the Hoek-Brown failure criterion through three angular points. It is a nonlinear power-law curve in the plane. Comparative study with three different rock failure criteria i.e. Hoek-Brown criterion, Drucker-Prager criterion, and Mogi (1971) criterion is conducted by fitting the triaxial test data of four different rocks. Then the applicability of four failure criteria is discussed on describing the effect of intermediate principal stress. The results show that the new 3D Hoek-Brown failure criterion fits the triaxial strength data best, followed by the Mogi (1971) criterion, whereas the Hoek-Brown criterion and the Drucker-Prager criterion have a relatively poor performance. Therefore, the new 3D Hoek-Brown failure criterion is the most suitable to predict the true triaxial strength and to describe the effect of the intermediate principal stress on trachy, marble, granite and other hard brittle rocks.

The consolidated drained triaxial compression tests on oil sand, which is from a heavy oil reservoir of Fengcheng oil field in Kelamayi, Xinjiang, are conducted at both room and high temperatures to study its mechanical and thermal properties. Experimental results show that the deviatoric stress-strain behaviour of oil sand at room temperature is divided into three stages: elastic, plastic and softening stages. At high temperature the compaction stage occurs before the elastic stage, however the variations of volumetric strain are significantly different at different confining pressures. Elastic modulus and Poisson's ratio of oil sand show a good linear relationship with the consolidation pressure. There is less effect of high temperature on the peak strength, residual strength, elastic modulus and Poisson's ratio. The values of internal friction angle and cohesion of oil sand are 34°and 0.47 MPa respectively, which are close to those of coarse grained soils. The coefficient of thermal expansion increases with increasing confining pressure, and the circumferential expansion coefficient is sufficiently larger than the axial one. A critical temperature occurs at the confining pressure of 5 MPa. The deformation of oil sand presents varied characteristics as the temperature below or above the critical temperature. The axial, circumferential and volumetric deformations expand linearly with the increase of temperature when temperature is below the critical value, but the deformations reduce linearly when temperature is above it. Finally, comparing the properties of Fengcheng oil sand with Athabasca oil sand and Cold Lake oil sand, it is found that the strength and deformation characteristics of oil sand are similar to great extent. Thus this study is particularly significant in the exploitation of heavy oil from the Fengcheng area.

The ultimate bearing capacity of a strip footing on the reinforced sand is studied based on both the limit equilibrium slice method and the critical slip field method. It is assumed that friction of the interface between the soil and reinforcements is uniform when the reinforced foundation soil is in the limit equilibrium state. Based on the limit equilibrium equations of soil slice, a recursion expression of slice force is derived. Firstly, the borders of the soil mass with potential sliding are determined, then soil mass is divided into a series of slices, and the state points is distributed on interfaces between the slices. Secondly, the recursion expression is used to calculate the parameters of all state points and search the critical slip surface. Finally, the bearing capacity can be determined according to the critical slip surface which meets the balance of forces and moments. The reliability of calculation results is shown by comparing with the results in literature. Effects of distance from footing bottom to top reinforcement, layer numbers and length of reinforcement on bearing capacity and slip surface are also presented. The results show that the bearing capacity increases firstly and then decreases as the depth increases, or it increases firstly and becomes stable lastly as layer number and length increase. It is also shown that the slip surface changes mainly in the vertical and horizontal ranges. Because the proposed method is easy to understand and numerically implement, it provides a new idea to calculate the bearing capacity of strip footing on reinforced sand, and it extends the critical slip field method to the calculation of bearing capacity.

Brittle material such as rock deteriorates subjected to freezing and thawing. It is generally observed that the primary reason of rock deterioration is the water phase transition caused by the change of temperature. Hydraulic pressure is generated by 9% volumetric increase of freezing water in a closed crack, which expands crack, meanwhile water flows into new cracks as the temperature is raised. Therefore, the repeated cycles generate the new damage of rock. The freezing and thawing process of rock is also affected by a number of factors such as the length of cracks, permeability, and heaving stress. Considering the extension length of one single crack subjected to frost heave forces, a formula of the relationship between the macroscopic damage and freezing-thawing cycles is established on the basis of elastoplastic mechanics and fracture mechanics. An analytical model is developed to predict the deterioration degree. The validity of the model is examined by comparing its predictions with the experimental results. The effect of elastic modulus on freezing-thaw cycles, heaving stress and permeability coefficient is also discussed. In addition, the theoretical solutions are compared with the existing experimental results. The conclusions are drawn as follows. Firstly, the crack extension length is dominated by heaving stress and the permeability of rock which increases nonlinearly with the decrease of temperature and the coefficient of permeability. On the other hand, the connectivity increases with increasing crack length, and the permeability of fractured rock mass increases. Secondly, elastic modulus decreases nonlinearly due to freezing-thawing cycles. Thirdly, the initial crack length has great effect on the variability of elastic modulus, according to stress intensity factor theory, the heaving stress decreases as the initial crack length increases, which reduces the elastic modulus to some extent. Finally, by comparing the theoretical results with the experiment data of sandstone under uniaxial compression, it is interesting to note that the results are in good agreement. Although the number of cracks is not affected by the freeze-thaw cycles due to the limitation of the initial assumption, the assumption needs to be improved with the measured data.

Crack initiation stress is one of the key stress thresholds in the process of rock failure under compression conditions. Accurate determination of crack initiation stress is very important for characterizing mechanical properties of rocks and for evaluating the stability of underground excavations. At present, the ISRM has established a commission on rock spalling, and one of the important objectives of the commission is to develop suggested guidelines for determining the crack initiation stress of rocks. By analyzing and summarizing the previous approaches to identifying crack initiation stress of rocks, a new method based on accumulative acoustic emission (AE) hit number is proposed to determine crack initiation stress. Compared with other strain methods, a significant advantage of this developed method is to remove the user's subjective judgment. Using rock mechanics testing machine and AE monitoring system, uniaxial compression tests on granodiorite samples collected from the Tianhu rock block in Xinjiang Autonomous Region, have been conducted to obtain stress-strain relationships and corresponding AE data. According to the comparison of crack initiation stress values obtained from different methods, the effectiveness and reasonability of the proposed accumulative AE hit method are verified. Due to the fact that ISRM has not provided clear guidelines for establishing crack initiation stress of rocks, it is suggested that the strain in combination with AE measurements be used to identify this critical stress threshold of rocks subjected to compressive conditions.

Aftershock often takes place in the wake of a main shock, and the cumulative damage effect of dam structure can become significant after several aftershocks. To explore the deformation and stability of a gravity dam with a complex foundation under the combined effect of main shock and aftershock, a dam section #A of a large-scale hydraulic project close to Wenchuan-epicenter is adopted for a case study. Firstly, only the main shock only is considered, which is simulated using the pseudo-static method in the geomechanical model test, and through experiments the deformation characteristics and the final failure pattern of dam section #A and foundation are studied. Then based on this, the time history analysis is performed, and the combined effect of main shock and aftershocks is analyzed using the 3D FEA software ANSYS. The results show that the model testing results are consistent with calculations. Under the effect of main shock, both the dam and foundation generate large deformation; and the final failure pattern of dam section #A is obtained. Under the combined effect of main shock and aftershock, the cumulative deformation effect of dam and foundation becomes more significant, and the displacement is significantly larger than that induced by the main shock only. The maximum displacement amplification of dam is about 37% which has a significant impact on the stability of dam and foundation. Therefore, the gravity dam on complex foundation in highly seismic region should take into account of the combined effect of main shock and aftershock so as to ensure the project security.

The ultimate shaft resistance of uplift pile is divided into two parts, one is the setting strength of pile and soil , which is irrelevant to the earth pressure of pile, and the other is the force of friction , which is proportional to the earth pressure of pile and can be calculated using the friction law. With assumption of elastic soil, this paper studies the pile-soil interaction through the integral calculation using Mindlin formulation. Pile-soil interface displacement coordinate equation is derived based on the solution of cavity expansion in infinite soil. Then a limit state equation of uplift piles and its solution are presented. The methods for determining the parameters of soil and pile are also given. The equation can be used to calculate ultimate bearing capacity of uplift piles with considering the influence of such factors as pile and soil materials, pile length, pile diameter, depth of pile top, group piles effects, unloading effect due to excavation, and so on. As an example, a full-scale test was performed on a large steel pipe pile with a length of 81.3m, a diameter of 1.7 m and a wall thickness of 25mm. The calculated and measured ultimate uplift bearing capacities are compared, showing that the proposed method for calculating the bearing capacity of uplift piles is satisfactory and applicable and has an accuracy much better than the methods recommended in the current codes of China.

According to the principle of the air element method, which is used to model drainage holes in seepage analysis, a layer of air elements with higher permeability is attached to any possible overflow boundary in the seepage field, and these air elements are included along with the entity elements in a common finite element analysis of seepage, so that the overflow boundary can be automatically solved. The proposed method can not only avoid the numerical iteration in calculating the overflow boundary as in current methods, but also resolve the issues related to the inefficiency and divergence associated with the inaccurate positioning of overflow boundary. The numerical examples indicate that the calculation accuracy of the air element method is correlated with the permeability of air element but independent of its thickness. Once if the relevant parameters are well selected, the proposed method can precisely approach the current ones. Furthermore, the interface film element is introduced into the air element method in order to improve the poor imitation occurring at the contact surface between strong and weak permeable media. Finally, the application of seepage calculation in Xiaowan dam section #22 demonstrates the validity and applicability of the proposed method.

Seepage-stress coupling behavior is a hot issue in the field of rock mass seepage in China, which is particularly common in the stratified slope engineering where the groundwater seepage is involved. Considering the anisotropic properties and seepage-stress coupling behaviors of the stratified rock slope, a seepage-stress coupling model of anisotropic rock mass is established on the basis of the equivalent continuum model and Louis empirical equation. Then the model is implemented into COMSOL software. Numerical results show that the model is competent in reflecting the anisotropic deformation properties of stratified rock mass and the heterogeneous and anisotropic behaviours of groundwater seepage. Moreover, this model is applied for the seepage analysis of the cross-section E800 of the south of Fushun west open-pit mine. To compare and analyze the influence of seepage-stress coupling in stratified rock mass, two different models are employed. The results indicate that the water table calculated by the proposed model is in good agreement with the in-situ measurement, and the model has a good prospect in such stratified rock slope engineering.

The existing of joints has great effect on the mechanical properties and strength characteristics of rock mass. In this study, four different failure modes of rock mass with one group of joints and the corresponding ranges of joint dip angles are obtained according to the strength criterion of statistical mechanics of rock mass and the Mohr-Coulomb failure criterion. An expression of the critical confining pressure is deduced for representing the transformation of rock mass strength from structure control to stress control. Moreover, rock masses with a group of joints are divided into four classes by the relationship between rock and joint parameters. Then the potential failure modes and the corresponding failure conditions are discussed. Finally, the strength characteristics of diorite with a group of joints are analyzed. The results show that the diorite belongs to class I rock mass. The diorite fails firstly along with the direction of joints and then fractures in the rock blocks at a critical confining pressure of 9.12 MPa under the axial pressure condition. It is found that the diorite has significant anisotropy from the spatial analysis, and the increase of confining pressure would result in the transfer of rock mass strength from structure control to stress control under the particular loading directions.

Pillar width and backfill self-sustaining height are two significant factors in the stage-delayed backfill. A mechanical model for the stage-delayed backfill pillar is established and analyzed on the basis of the elastic plane strain assumption. Taking an iron mine for example, the control variable method (CVM) is used to predict the trends of horizontal stress and shear stress of pillars with different widths and heights. The research results show that: (1) The maximum width and height of the room are 19.8 m and 103.2 m respectively. Horizontal stress of the cemented tailing-filling pillar increases with the increase of pillar height. (2) Shear stress reaches the maximum value at the pillar center, and increases continually with increasing pillar height. When the pillar widths are 15, 18 and 20 m, the corresponding shear stresses are 243.8, 292.6 and 325.1 kPa. The primary reason of the caused shear stress is that the sliding friction occurs on the contact surface of the backfill pillar and the spacer pillar under horizontal stress conditions.

To enhance the bearing capacity of plastic tube cast-in-place concrete pile (TC pile), the plastic tube cast-in-place concrete pile with shaft pre-grouting (TCSG pile) was developed in combination with the technology of shaft grouting. The in-situ static load tests were carried out on the TCSG pile, TC pile, and plastic tube cast-in-place concrete pile with large diameter (TCLD pile) installed in different times. Meanwhile, three kinds of calculation models of single pile settlement were introduced to predict the piles settlement. The testing and calculating results indicate that the bearing capacity of TCSG pile is raised by 8.3%-20.0% with a settlement decreased by 19.8%-33.5%; while the bearing capacity of TCLD pile is reduced by 10.0%-16.7% with a settlement increased by 13.2%-43.8%; compared with TC pile; the ratio of axial force attenuation of TCSG pile is greater than that of TC pile or TCLD pile; the difference is trivial between the average ratios of axial force attenuation for TCSG pile respectively obtained in earlier and later static load tests; the average ratio of axial force attenuation of TC pile gained in the later static load test is increased by 1.1%-14.2% compared with that in earlier static load test; while a reduction of 5.9%-21.9% in the average ratio of axial force attenuation is found in TCLD pile; the average skin frictions of TCSG pile under each loading level, compared with TC pile, increase by 14.5%-39.6% and 9.2%-28.6% during the earlier and later static load tests, respectively; while those of TCLD pile decrease by 4.9%-11.8% and 11.5%-30.7% due to enlarging the diameter of TCLD pile; the increasing of bearing capacity of TCSG pile with time is insignificant; the skin friction of TCLD pile diminishes with time elapsing; in contrast, the end resistance of TCLD pile increases; the calculation model of single pile settlement based on the pile-soil load transfer can well predict the settlement of a single plastic tube pile.

Stress-deformation behaviour of a concrete-faced rockfill dam (CFRD) built on sand and gravel foundation is studied based on the in situ monitoring results and finite element analysis (FEA). The mechanical behaviour of the dam body and its impervious structures is investigated and the interaction between the CFRD and the overburden foundation is analyzed. Three-dimensional FEA is performed, with introducing the Duncan-Chang E-B model for gravel and rockfill and the Lagrange method for the interface, to evaluate the stress-deformation behaviour of the CFRD at the construction and filling stages of the reservoir. Comparative analysis shows that the maximum settlement occurred at the bottom height of the dam instead of the middle height and the maximum compressive stress distributed in the overburden. The overburden foundation has a significant effect on the stress-deformation behaviour of the dam body and impervious structures. The stress and deformation values computed using the FEA model are found to be consistent with the measured data for the construction stage. Numerical simulation is used to analyze the different factors influencing the behaviour of the dam body and cut-off wall. The results show that the staged-filling of the dam body will cause uneven deformation and stress concentration in the dam body, but can improve the stress and deformation behaviour of the cut-off wall to some extent; and the rapid dam construction rate results in a larger prestage stress and post-construction settlement which is not conducive to the construction and operation of the dam.

With considering the friction between a micropile and the surrounding soil mass, a new design calculation model of single anti-slide micropile is developed; and a detailed calculation algorithm is presented. Based on the deformation characteristics of micropile in reinforcing a slope, the interaction mechanism between the micropile and the surrounding soil mass is analyzed, and the friction between the micropile and the soil mass is introduced into the force analysis of single anti-slide micropile. According to the different loading distributions along different parts of the micropile, the micropile is divided into three parts along its length, namely, the friction part, the landslide thrust part and the anchoring part. The governing equations for the deformation of different sections of the micropile are derived. The governing equations are solved by using the initial parameter method, and the internal force distribution and deformation characteristics are determined. The calculated results show that, under the action of a landslide thrust, the deformation of micropile mainly occurs near the sliding surface and the upper parts of the pile. The internal force and bending deformations near the sliding surface are larger than those at the other parts of the micropile. Along the friction part of the micropile, the bending deformation is small, and the relatively small bending deformation leads to nearly horizontal movement of the micropile. The friction is an important part of the interaction between micropiles and the surrounding soil mass, and it can significantly reduce the bending deformation of the micropile, so that the landslide displacement can be effectively controlled.

Since viscous debris flow is comprised of coarse particles and viscous mud, its movement process exhibits discontinuous deformation. Thus the fluid theory, which is based on continuous medium assumption, is difficultly applied to describe the process. Considering the influence of viscous media, a numerical model for viscous debris movement is firstly compiled according to the theory of granular materials and the platform of PFC3D software. Then the model parameters are obtained from the experimental results of indoor tensile tests and rotary shear tests on the viscous mud, which is called Chengdu clay and its density is 1.413 g/cm3.Moreover,numerical simulation of viscous debris movement is performed, which reproduces the movement process and the phenomenon of discontinuous deformation during the process. Meanwhile, the numerical simulations are verified by the experiment with the same size of the physical model. The results show that the PFC3D discrete element method, based on theory of granular materials, is applicable to simulate the movement process and present the phenomenon of discontinuous deformation during the movement process of viscous debris soil. This study provides a new way for further analyzing the viscous debris movement on slope under the impact of viscous media.

To describe the permeability evolution process, the strength degradation index is introduced based on Hoek-Brown strength criterion; a strain softening constitutive model with confining pressure for coal rock is established. The relationship between volumetric strain and permeability is given; and combining the strain softening model, a permeability evolution model is proposed. Then the model is implemented in FLAC. Numerical cases are simulated including the post peak strain softening behaviors of a cylinder rock sample under different confining pressures and the permeability evolution of overburden rock during mining, The results show that: (1) The effects of confining pressure on post peak strain softening mechanical behaviors and permeability evolution can be better reflected by the model proposed. (2) With the advancing of working face, more and more coal rock elements fail and the permeability also increases. Gradually the main channels of gas flow appear. (3) The model is capable of reproducing the permeability evolution process of mining coal rock, poviding a reference for the practice of simultaneous extraction of coal and gas, methane recovery and gas disaster prevention.

Based on original FEM/DEM coupling analysis method, a new model for blast simulation is implemented. The model considers increasment of the volume occupied by the gas and stable decrease in gas pressure with the expansion of cracks due to the blast gas embedding, and also takes into account the action of gas on the fissures linked at the explosion chamber. The limitation is overcome in the existing blasting model of FEM/DEM, where the pressure is only applied on the surface rock of blasting chamber without considering action of the embedded gas on the newly generated cracks. Meanwhile, a novel search algorithm of fracture network is proposed by compiling a simple recursive function for the search of complex fracture network; and a very simple method is used to handle the complex problem. Finally, a numerical example indicates that the improved FEM/DEM can simulate crack initiation and propagation of stress waves during explosion, showing a great potential of this method for the blast simulation.