High temperature and high pressure can lead to a lateral global buckling of unburied or shallowly buried submarine pipelines. Because soil resistance determines the deformation and stress distribution of post-buckling pipelines, it is important to characterize the soil resistance in the pipeline global buckling analysis. A series of model tests based on the sand sampled from Bohai Gulf is conducted. The soil resistance to pipelines with different buried depths are measured. A dynamical soil resistance model varying with the buried depth of pipeline is developed, and the influence of buried depth on peak soil resistance and final soil resistance is analyzed. As the built-in penalty interaction model in ABAQUS software cannot simulate the dynamical friction in pipe-soil interaction, a user-defined subroutine VFRIC is developed to implement the established soil resistance model and used to simulate the variation of soil resistance with pipeline displacement for accurate pipeline global buckling analysis. The study shows that the soil resistance model can significantly affect the results of post-buckling pipeline. Because the dynamical soil resistance model has a peak value and an attenuation process, the critical buckling force of post-buckling pipelines with dynamical soil resistance model is larger than pipeline with constant soil resistance, the deformation of post-buckling pipelines with dynamical soil resistance model is more concentrated, and the maximum bending moment and strain are larger.

The critical state, as an important failure characteristic of clays, is the basis of most existing constitutive models. Since the temporal effect cannot be neglected in laboratory tests, the critical state observed in tests is actually a failure phenomenon occurring in clays under the influence of time or a loading rate. Rate-dependent constitutive models, which consider the influence of time on the stress-strain relation of clays, should be able to describe the critical state. In order to characterize the critical state for rate-dependent constitutive models, the overstress elasto-viscoplastic (EVP) constitutive models are used to simulate the triaxial undrained and drained compression tests. The simulated results show that: 1) The triaxial undrained stress paths predicted by the first kind of overstress EVP models (which consider the yield surface to be a locus of constant viscoplastic volumetric strain rate) show strain softening below the critical state line, and they approach the origin of the coordinate system, but cannot attain the critical state. 2) In predicting the triaxial drained compression test at a high strain rate, the final stress ratio calculated by the second kind of overstress EVP models (which consider the yield surface to be a locus of constant viscoplastic scalar factor) exceeds the critical-sate stress ratio. 3) The third kind of overstress EVP model, i.e. the time-dependent UH model (which takes the stress-induced plastic deformations into account, and considers the yield surface to be a locus of the constant rate of unified hardening variable) can describe the critical state well in simulating both the triaxial undrained and drained compression tests.

To investigate the effects of bond sizes (including width and thickness) on the idealized inter-granular mechanical properties of cement, an unified strength expression of cement is proposed with considering the bond sizes, based on the previous research results and the results of experiments performed on inter-granular bonds with different sizes. The results reveal that, both the peak compression force and tension force are associated with the factor λ which is representable for the end constraint and the factor ξ which refers to the ratio of height to width of samples. Shear and torsional capacity of cemented sample with different bond sizes can be expressed uniformly by the fitted shear coefficient and anti-rotation coefficient. In the three-dimensional peak force space, the strength envelopes of the cemented samples of different bond sizes show opening hollow oval balls. In addition, the values of the peak forces increase significantly as the bond width increases; the values of the peak forces decrease with the increase of bond thickness,and when the bond thickness approaches a certain extent, the trend of force decrease becomes insignificant.

A conceptual model of soft rock in the red layer regions of China is developed with considering the softening characteristics and the mesoscopic images of the rock. Based on this, the characteristics of friction and contacts (including static and kinetic frictions) in the soft rock is analyzed. The maximum coefficient of static friction increases with the increase of actual contact area, normal stress and residence time, whereas the kinetic friction increases with the sudden increase of velocity. For the indirect contact particles, the tangential stress is mainly dependent on the shear strength of clay minerals which is dominated by the friction coefficient and adhesive strength. Furthermore, the water softening of skeleton particles is analyzed, it is found that hydration weakening effects mainly show as changing the contact stress between skeleton particles as well as degrading clay mineral particles, namely, the water reduces the effective stress between skeleton particle and clay mineral particle, and hence both the cohesion and internal friction angle of clay minerals. Owing to this, the friction between the particles and the strength of soft rocks decreases, and the soft rock becomes weaker. The above results can be reflected, to a certain extent, by the compression process of the soft rock under the triaxial compression test.

In this study, shear tests are conducted on gas-containing coal with different binder contents using a self-developed meso-shear test equipment. Firstly, mechanical behaviors of coal are investigated, including strength characteristic, crack evolution mode, variation law of crack length, morphology and formation mechanism of mesoscopic crack. Then the effects of binder content on shear mechanical properties, crack macro-meso evolution and damage characteristics are discussed. The results show that shear strength of coal increases linearly with the increase of binder content, and the number and bifurcation of macroscopic cracks also increase, however the proportion of post-peak stable stage decreases. The development of total effective crack length can be divided into three stages: surge, slow increase and steady stage. With the increase of binder content, the type of damage zone between neighboring cracks changes and the mode of formed fracture surface converts from direct coalesces of cracks to bifurcation of main cracks and damage zone connection of the main wing cracks. The mechanism of formed shear mesoscopic crack of gas-containing coal with a binder content of 5.3% is analyzed. It is found that there are several mesoscopic cracks ahead a macroscopic crack, which changes from narrow to wide and approximately distribute along a straight line. Wing cracks connect, which are caused by the continuous appearance of new cracks in the front and the growth of original cracks in the rear . Once the overlap of wing cracks damages, a macroscopic crack occurs and then expands forward step by step. Secondary crack of the main crack wall is composed of several wing cracks arranged as an echelon. Coalescence modes of macro main cracks are connected by wing and anti-wing cracks, which depend on the relative position of adjacent cracks.

To better understand the concept and calculated method for acting force due to seepage, based on the research in composition characteristic of saturated soil, concepts related to acting force due to pore water are clarified generally. The essence of acting force of pore water on soil skeleton is also reveled. The mechanical models for soil mass, soil skeleton and pore water under seepage condition are developed, and the corresponding formulations for the calculating acting force due to seepage are deduced in different ways. The calculation methods of acting force in finite element method(FEM) and in the limit equilibrium method(LEM) are debated completely. It indicates that effective stress principle used in FEM can reflect the loading effect of acting force. The boundary force model in LEM can also represent the effect of acting force. However, for reason of hypothesis of side forces on slice in slice method, the effect of acting force can not be completely reflected. The total earth pressure method for the stability analysis of slope is not perfected on theory. The separate calculation method for water and earth pressure based on effective stress concept considers all the water pressure on slice boundaries as the loads acting on the slice, so it can completely represent all the effect of acting force

A new empirical physical model is presented to estimate the soil-water characteristic curve approximately. The capillary theory is used to infer capillary water height in granular materials of a specific grain diameter. For most soils, the correction factor introduced in this model shows remarkable linear relationship with the suction water head in logarithmic coordinates and their relationship can be expressed as . Data of 406 soil samples from the unsaturated soil database UNSODA are used to analyze the fitting coefficients and . It is shown that they are affected by neither grain-size distribution nor void ratio, and they might be related to the mineral composition of soils. Predictions of the soil-water characteristic curve (SWCC) of a specific soil can be achieved using the grain-size distribution of the soil, and the parameters and can be calculated from some experimental results of soils with similar mineral compositions. The mean values of a and b calculated in this paper may also be an alternative in the absence of related data.

Since traditional hydraulic fracturing initiation models are primarily based on linear elastic theory, they are not applicable for the elastoplastic reservoirs. Therefore, it is necessary to explore a new initiation model on the basis of the nonlinear constitutive equation. Considering the total deformation theory of plasticity, a model is established for the stress field around a well. Furthermore, an elastoplastic hydraulic fracturing initiation model is proposed according to the stress distribution model and failure criteria of elastoplastic rock. The results show that once the rock is yielded, the effect of stress concentration around the wellbore is greatly weakened and the circumferential tensile stress decreases and even disappears. The initiation pressure is higher than that predicted by the linear-elastic theory. There are two types of fracturing initiation modes including tensile and shear failures, and the shear failure is characterized by a failure angle. When the hardening index of rock is not greater than 0.5, only shear failure takes place. However, when the hardening index is greater than 0.5, the shear failure tends to happen more frequently when the values of yield stress, hardening index, internal friction angle and cohesion are small; on the contrary the tensile failure occurs.

The strength criterion of soil in plane strain state is set up according to the strength criteria of Mohr-Coulomb, Lade-Duncan, general Mises, Matsuoka-Nakai, AC-SMP, plane strain condition and associated flow rule. The analyses of strength criteria in different plane states are made to determine the variation laws of the ratio of major principal stresses to minor principal stresses with internal friction angle. The applicabilit of every strength criterion is also analyzed. When the friction angle is less than 30°, the differences among different criteria are insignificant; otherwise, the differences become significant gradually. When internal friction angle is large enough, general Mises strength criterion in plane strain is not applicable to describe the failure of soil. Considering the cohesion effect, the strength criterion of cohesionless soil in plane strain state can be applied to cohesive soil and every strength criterion is verified by the plane strain test of loess. The results show that the Matsuoka-Nakai strength criteria is suitable for describing the strength of sand soil , and Lade-Duncan, AC-SMP strength criteria can characterize the strength of loess.

Based on the frost heaving deformation theory of foundation soil, an integral equation for three-dimensional viscoelastic problem of pile frost heaving force computation is theoretically derived, with considering the relationship between frost heaving force of pile and displacement of pile lateral soil, and introducing the classical theory of viscoelastic mechanics and the Mindlin solution of concentrated force in an elastic half-space. Three-parameter model coefficients are inverted from the creep testing data measured by the simplex method. In addition, the freezing depth of soil body, the amount of free frost heave and the variation of frost heaving displacement of pile foundation vs. time are obtained by fitting the field monitoring data available in the literature, and they are utilized in theoretical calculation of the frost heaving forces of pile foundation. Numerical examples indicate that the distribution of the frost heaving force along the depth calculated with the proposed equation agrees very well with the measured values and previous results of calculations. The spatiotemporal three-dimensional presentation of the frost heaving force is obtained, which can intuitively show the frost heaving force distribution.

Considering that the tunnel diseases caused by earthquake are different in various depths, shaking table tests for seismic response of tunnels are conducted. Firstly, the programme and similarity ratios of the tests are designed according to similarity principles. And then, the shaking table test under different seismic waves, seismic intensities and depths are done. Test results show that the lining stress caused by earthquake is the largest in shallow buried tunnel; When the buried depth of the tunnel reaches about 40 m, the lining stress significantly declines, subsequently the lining stress remains relatively stable with the buried depth. The relationships between lining stress caused by earthquake and tunnel depth are analogous for various kinds of earthquake waves and various acceleration peaks. The acceleration magnification factor increases with the depth of tunnel decreases. Meanwhile, the cracks in the surround soil around shallow tunnel are found to be more than those in the soil sound around deep tunnel. The research verifies the findings of earthquake disaster and will supply the reliable assurance for seismic design of tunnel.

Based on the theory of stress wave propagation and interaction, the propagation process and damage mechanism of coal are studied when stress wave propagates through the coal comprising plastic coal, elastic coal, tectonic coal and initial coal in front of the tunneling. Furthermore, the dynamic response of tectonic coal is revealed. The results show that the main tensile stresses distribute centrally in coal regions, where the wave impedance changes under dynamic loading. It is also found that the maximum tensile stress is around the interface of plastic and elastic coal. In addition, the occurrence of tensile stress is closely related to the unloading wave, which result in the tensile-shear failure of coal in combination with the effect of in-situ stress. It is clearly shown that the carrying capability of tectonic coal to dynamic loading is weak. Due to the existence of tectonic coal, the strong tensile stress is generated in elastic coal under unloading stress waves, which easily leads to heavy damage in some parts of elastic coal. Stress waves are frequently reflected and transmitted in loading and unloading processes and consequently multi-beam unloading waves are produced. Under the effect of such unloading waves, the formation of tensile stress area in the vicinity of coal bed results in the spalling phenomenon at the moment of coal and gas outbursts. This study has theoretical significance as it contribute to controlling and preventing the dynamic disasters of coal and rock in mine.

Based on the multi-threshold Otsu method, the characteristic image of granite microstructures is obtained by using the digital image processing method, and a mesoscopic model, which can reflect the actual heterogeneous structural properties, is reconstructed using Particle Flow Code. With conducting the uniaxial compressing tests based on the propoed model, the failure process and the effect of mesostructured (interface, mica, feldspar and quartz) on failure strength are analyzed. The results show that there are four types of cracks in the failure process of the granite. In the initial loading stage, cracks generate in the interface, and then in mica; when stress is close to the peak value, the cracks begin to generate in feldspar and quartz. As the strength of interface or mineral increases, the compressive strength of the granite increases, while the gradient of growth decreases. The increase of the strength of interface or the minerals can lead to a reduction in the number of cracks corresponding to the interface or the minerals, which can increase cracks in other areas. Compared to the feldspar with moderate strength and the quartz with high strength, the interface and mica are the key mesostructures that can significantly influence the granite compressive strength and failure modes. Combining Otsu digital image processing with PFC, a mesoscopic model of rocks is rebuilt, which provides an effective method for studying the mechanical properties of heterogeneous rocks.

The anisotropic behavior of layered shale is particularly important during exploring shale gas. To investigate the anisotropic behavior of layered shale of Longmaxi Formation in Shizhu County, the scanning electron microscope tests and uniaxial compression tests are conducted on shale specimens cored at different angles to the shale bedding. The results of microscopic features and uniaxial compressive parameters indicate that the shale is distinctly anisotropic. The stress-strain curve belongs to type II and its five phases are not clearly identified. Under the uniaxial compression condition, there are three types of failure mode: vertical splitting tensile damage with the coring angle of 0°－15°, shear sliding damage along the beddings with the coring angle of 30°－60°, and shear failure across the beddings with the coring angle of 75°－90°. Therefore, the curves are significantly different when the coring angles are variable. It is found that the uniaxial compressive strength (UCS) is minimum when the coring angle is 30°to the shale bedding; the value of UCS is substantially high when the coring angle is around 0°or 90°. The elastic modulus is in good agreement with longitudinal wave velocity, and moreover, both of them decrease with the increase of the coring angle. Since it is difficult to identify the transverse anisotropy of cored samples parallel to the bedding plane, the layered shale of Longmaxi Formation is considered as a transverse isotropic body. The micro fracture and the unique destruction type mainly contributes to the anisotropic properties of the layered shale.

To investigate the influence of structural properties on strength parameters, yielding stress and yielding suction of unsaturated Q3 loess, a series of unsaturated soil tests, including direct shear test, hydrostatic triaxial compression test and triaxial shrinkage test, is carried out on Lanzhou undisturbed and remolded Q3 loess, using four-alliance direct shear apparatus and improved triaxial shear apparatus. The results show that the cohesions and internal friction angles of undisturbed and remolded loess increase linearly with matric suction. The greater the matric suction, the greater the shear strength. Because the undisturbed Q3 loess has well-developed structures, it possesses a higher strength. Compared to the undisturbed loess, the bonds between the remolded loess particles are weaker, so that the remolded loess shows lower shear strength than undisturbed loess, especially at low matric suction and high water content. The cohesion structural parameter and internal friction angle structural parameter are defined, and the variations of the coupling values of both cohesion and internal friction angle with suction are determined, providing a new approach to selecting shear strength parameters of practical engineering projects. It is shown that both yielding stress and yielding suction of undisturbed loess are higher than that of remolded loess, and elastic area of undisturbed loess is larger than that of remolded loess in p-s plane. The difference between the yielding stresses of undisturbed and remolded loess increases linearly with the increase of the suction, and yielding suction approaches a constant, which is almost unaffected by net mean stress. Before yielding, due to intensive structural characteristics, the deformation of undisturbed loess is less significant than that of remolded loess; but after yielding, the deformations of both are similar. The test results provide the experimental foundation for the development of structural model and some guidelines for the engineering construction in loess area.

To determine the deformation characteristics of silt clay under long-term static loadings, small-sized plate loading creeping tests are performed using the element model with filling soil at compaction efforts of 0.90, 0.95 and 1.00m, respectively, through which the vertical settlement-time curves and rebound deformations under designed load levels are obtained. According to the concept of creep limit, long-term strength and relative instantaneous strength in the soil rheology, four categories including fast stability, long-term stability, long-term damage and rapidly damage are identified. Based on the attenuation characteristics that the soil creep rate shows a negative power function with the time, the fractal characteristic during convergence-type decay creep is revealed. To discriminate the category of deformation characteristics, a “power criterion” is proposed for quantitatively distinguishing soil deformation evolution state, based upon which three loading thresholds are determined by the small-sized plate loading creep tests. Combined with the feature that rebound deformation amount grows approximately linearly as load increases, three rebound strain thresholds for the four deformation evolution states are obtained. These results provide theoretical and experimental bases for determining the deformation evolution state of geotechnical structures.

Environmental temperature is one of the external factors that influence the cracking of expansive soil; and initial water content and dry density are the important internal factors. In order to study the cracking characteristics and influencing factors for expansive soil, the tests of cracking process are conducted on remolded Nanyang expansive soil with different initial water contents and different initial dry densities. The results indicate that cracking process can be divided into three phases, i.e. soil shrinkage-crack generation, rapid crack expansion and stabilization. The ratio between shrinkage area plus crack area and initial area is defined as fissure ratio, which can describe not only the drying shrinkage characteristics but also the cracking characteristics, and is suitable for depicting the crack propagation process of small size sample. Temperature has a certain extent influence on the dehydration process of expansive soil; a higher temperature can result in a small fissures ratio. Initial water content is positively related to cracking degree. Initial dry density has a negative correlation with cracking degree.

The teeth of the bit break rock continuously when drilling in oil or gas well. However, the primitive crushing work ratio is used to evaluate single rock crushing effect, thus it is unsuitable to estimate and predict the second rock crushing and continuous breaking effects. Based on a second development of damage constitutive model in ANSYS software, the new models of crushing work ratio are developed. The applicability of the developed damage constitutive model and numerical simulation is verified by experiments and theoretical calculation under the condition of single rock crushing. Then the model is employed to analyze the single, the second and the total crushing work ratios. It is found that the evaluation model is efficient to predict the rock breaking effects of the second and total breaking by using the new crushing work ratio which decreases slowly with the increase of load. Moreover, the work ratios of the second crushing and the total crushing is reduced to approximately 80% and 60%, respectively, in comparison with the first crushing work ratio.

The aim of this paper is to investigate the effects of surrounding rock and the behavior of support on energy transmission and dissipation when stress wave generated by impact loading propagates in rock mass. Based on a dynamic model of surrounding rock block and support system, the kinetic energy of the rock block around the support is analyzed to study the damping of absorbed energy. It is found that the impact energy of rock block around the support is controllable. When the damping of local rock blocks increase, the kinetic energy of the rock block around the support substantially decreases and the impact energy is absorbed effectively. Meanwhile, the effect of dissipated damping between the local block rocks is better in absorption of energy than that of the concentrated damping. When the damping of support increases, the ability of absorbing impact energy is lower than that of the surrounding rock with the same level of damping. When the combined dampings of surrounding rock and support are applied to absorb energy and to counteract impact energy, surrounding rock is regarded as the primary medium to actively absorb energy, and the support is the supplemented medium to passively absorb energy. Based on these characteristics, a new theory of energy absorption and anti-impact is developed, which provides a new approach to preventing dynamic disaster of rockburst.

The dynamic shear modulus of loess under bidirectional dynamic loading is determined by using a SDT-20 dynamic triaxixal apparatus. The experimental results show that although the initial cyclic deviatoric stress and radial vibration amplitude trivially influence the Gd-γd (dynamic shear modulus-dynamic shear strain) curves of loess, they can significantly affect Gd-N (dynamic shear modulus-cycle number) curves of loess. The dynamic shear modulus at the identical cycles decreases with the increase of initial cyclic deviator stress and radial vibration amplitudes. At the same dynamic shear strain, the dynamic shear modulus of loess increases significantly with the growth of consolidation ratio. There exists a threshold of cyclic deviator stress under bidirectional dynamic loading condition, which is about 0 kPa. When cyclic deviator stress is lower than the threshold, the dynamic shear modulus of loess increases with the growth of dynamic shear strain, but when cyclic deviator stress is higher than the threshold, the dynamic shear modulus decreases with the growth of dynamic shear strain. By reducing the shear modulus at the inflection point and with the modified Hardin-Drnevich model, the Gd-γd relationship of loess under the bidirectional dynamic loading condition is quantitatively described, and the applicability of the proposed model is demonstrated.

Unsaturated hydraulic conductivity is a key parameter in unsaturated loess analysis, it is a function of matric suction or volumetric water content, but difficult to deternine which specific function relationship is. Moreover, the unsaturated hydraulic conductivity is difficult to measure, indirect deduction from soil water characteristic curve (SWCC) is more random, steady-state and indoor transient profile method require taking the soil disturbance into account. Under these circumstances, the in-situ transient profile method is adopted to process the natural rainfall infiltration monitoring data, the relationship between the unsaturated hydraulic conductivity and the volumetric water content of loess is obtained. In addition, based on the actual distribution of volumetric water content at different times, the relationship between the volumetric water content and depth is proposed by using a logarithmic curve, and applied to the data processing step of the transient profile method. The results of the in-situ transient profile method show that the relationship between the unsaturated hydraulic conductivity and the volumetric water content is an exponential function. Meanwhile, due to rapidly evaluating the unsaturated hydraulic conductivity in field, the method is introduced. The calculated results show that method has a high degree of agreement with in-situ transient profile method. On the other hand, the logarithmic curve is used to fit the relationship between the volumetric water content and depth when using the method; thus, one of the basic assumptions of the method is amended by the logarithmic curve relationship; and the results of the modified method are closer to the actual conditions.

A series of disintegration tests was performed on an argillaceous shale in various acid and alkali solutions, from which the relationship between the percentage content of different size particles and the cycle number is determined. Results show that the lower the pH value is, the larger the percentage composition of granules, and the percentage increases with the increase of disintegration cycles and finally tends to be constant. Based on the principle of energy dissipation, theoretical computational formulations are developed for the incremental surface energy and cumulative incremental surface energy, and the influence of pH on the cumulative incremental surface energy is characterized. The incremental surface energy decreases with the increase of cycle number in an individual disintegration cycle, and is significantly influenced by acidity. Lower pH value may lead to more cumulative incremental surface energy; but disintegration characteristics are not influenced by alkaline solution. The energy dissipation of argillaceous shale in the process of disintegration is characterized as a logarithmic function. It is found that all the relationship curves have the same attenuation trend. The model parameters, which are inverse-analyzed from test data, decrease analogously with the increase of pH value.

The effect of intermediate principal stress on the analysis of slope stability is seldom considered by commonly used strength criteria. However, it is found that the intermediate principal stress exists in the practical rock engineering, and moreover it plays a significant role in potential strength of rock. The intermediate principal stress is considered in Hoek-Brown (H-B) criterion, which is established under the unified strength theory, the simplified expressions for H-B criterion are derived by using Taylor series and the assumption of stresses on slip surface. Therefore, these stresses on slip surface are calculated according to the static equilibrium conditions of the sliding body and the safety factor of slope can also be obtained. When the impact factor of intermediate principal stress b is equal to zero, the expressions in this study convert into the basic H-B strength criterion. The Swedish method 1 is a linear M-C strength criterion, including simplified Bishop method, Spencer method and Morgenstern-Price (M-P) method, which is equivalent to the basic H-B strength criterion. The Swedish method 2 is also established under the unified strength theory, and thus the feasibility of this study is verified by comparing the example results with the Swedish methods 1 and 2. Meanwhile, the effects of slope height H, slope angles and b are selected to analyze slope stability. The results show that the calculated safety factor increases with increasing slope angle b, which means the impact of intermediate principal stress on slope safety is more obvious. The above results indicate that the obtained slope stability is safer by using basic H-B strength criterion. The proposed expressions satisfy the static equilibrium conditions of the sliding body and amend the initial normal stress on the sliding surface without considering the effect of inter-slice force, and therefore the calculated results are larger and more rigorous than those by Swedish method 2.

The hydro-physical orthogonal tests are conducted on the similar materials (with cement and plaster as binding agents and sand as aggregate) at different similarity ratios. The relationships among the water-absorption, softening coefficient, permeability coefficient and sand-binder ratio, cement-plaster ratio and grain-size variation are developed. Contrastive analysis demonstrates that the similar material fails to disintegrate at certain proportion ratios when it meets water, but shows behavior similar to rock softening. This material can be used in the solid-liquid coupling tests without water absorption as a surrogate material of limestone or sandstone whose pore is well developed. By the multivariate regression analysis of the sample data, empirical relationships are developed among the water-absorption, softening coefficient, permeability coefficient and the sand-binder ratio, cement-plaster ratio and grain-size. Using the similar material, the solid-liquid coupling tests are performed on the sandstone aquifer with a large thickness of Zhidan Group of Cretaceous at Taigemiao mining in Shenhua New Street, showing that the surrogate material made of cement, plaster and sand can be used in solid-liquid coupling tests, and the proposed empirical equations can be used to check calculation results of the hydro-physical parameters of similar materials.

This paper aims to explore the mechanism of rockburst occurrence without dynamic loading. Taking a mine of Pingzhuang Region as an example, the start-up mechanism of rockburst in short wall work face under magmatic rocks roof is studied by employing numerical analysis, theoretical analysis and field measurement method. The results show that, when the work face under magmatic rocks roof moves forwards or backwards, the lower roadway start-up occurs without dynamic loading, since the hard diabase roof provides sufficiently concentrated static load. Due to short wall mining, the lower roadway is brought into a high position and high stress area, which exacerbates the risk of rockburst occurrence. When bursting of the lower roadway happens in inclined coal seam, the principal stress of the surrounding rock is perpendicular to the dip direction of coal seam. Therefore, the burst and bulge of surrounding rock are asymmetric and localized and even its direction is corresponding to the normal direction of seam inclined plane. This study provides a new argument that asymmetrical method should be adopted to prevent rockburst in roadway support and pressure relief in the inclined coal seam.

Slope-top loading is a non-negligible factor in the stability analyses of highway slope, railway slope, mine slope and so on. Toppling failure is one of typical deformation failure modes of steep stratified rock slopes. Analysis of toppling failure of rock slopes subjected to the load applied on the top has an important bearing on engineering practice. Based on the gradual analysis method of limit equilibrium proposed by Goodman and Bray, a geomechanical model of the toppling failure of rock slopes under slope-top loads are developed and the related analysis method is proposed. Using the transfer coefficient method, a formulation is derived for calculating the residual sliding force at the toe and the supporting force required to meet the requirements of the slope stability under slope-op load, which provides a theoretical basis for the design and support of this type of slope. Two examples are introduced, in which the influence of slope-top load on the residual sliding force as well as the sliding ratio coefficient is analyzed for the cases of diverse block widths and slope cut angles. The results show that there exists a critical block width for a given slope such that when the block thickness is less than the critical value, the influence of slope-top load on the residual sliding force is more significant. The influence of slope-top load on the slope stability increases with the slope cut angle. There is a positive correlation between the sliding ratio coefficient and slope-top load. Finally, the theoretical and numerical solutions calculated by UDEC are compared and consistent results are obtained, showing the applicability of both methods.

Analysis of seepage field and prediction of the quantity of inflow towards hydrocarbon storage caverns are the core issues associated with evaluations of water-sealed effects of a water curtain. Nowadays, equivalent continuum models are predominately used in analyzing this kind of large-scale seepage field; and the reliability of analysis results depends on whether or not the equivalent permeability of rock masses can be reasonably and reliably obtained. A great number of in-situ hydraulic tests concerning water curtain boreholes are conducted during the construction stage. Based on these tests, the equivalent permeability of rock masses can be analyzed and determined. However, the issues of theoretical background of test, the rationality of experiment procedure and the analysis of experiment data need to be studied in depth. Firstly, the procedures and features of four kinds of in-situ hydraulic tests about water curtain boreholes are presented, which are conducted in the Huangdao water-sealed oil storage cavern project in China. Secondly, the impacts of drainage of water curtain galleries on the seepage fields during construction are investigated by using a three-dimensional seepage numerical analysis method. Based on the water injection tests of water curtain borehole during construction, an empirical relation between the equivalent permeability of rock mass surrounding the water curtain boreholes and water injection rate is established under the Darcy flow postulation. According to the relation, the permeability of rock mass can be inverse calculated, the influences of various fracture formations on both the injection rate and the rock permeability are also analyzed by using a fractured porous flow model. At last, the practical test data is analyzed and the partition map of the permeability of rock masses is accomplished. The research results are of reference values for both the theoretical analysis of hydraulic tests regarding water curtain boreholes and parameterization of permeability of rock masses.

It is crucial to determine the evolution and distribution of the base pressure of wind turbine spread in designing the large-scale and large eccentric shallow foundations and ensuring the safe and stable operation of wind turbines in the mountain areas. Based on the measured data of the base pressure of wind turbine spread subgrade on an inland residual soil, the long-term and short-term changes and distributions of the base pressure are analyzed. A concept of the flatness of measured base pressure is defined according to the testing results, and the formulation from the building code is modified according to the calculated flatness of measured base pressure. It is shown that the values and distribution of the base pressure have a close relationship with wind speed and operating conditions, and the distribution of the base pressure can be represented by a trapezoid or a parabola. It is also shown that the variations of the base pressure with rotor rotation, cabin vibration or wind randomness should not be completely ignored. There is a disparity between the distribution of the measured base pressure and the ideal plane distribution. When the current code is used to calculate the maximum and minimum of wind turbine base pressure, correction factors of 1.2 and 0.8, respectively, are suggested.

Considering the characteristics of the surrounding rock structure and the stress field for gob-side entry retaining, the unbalanced bearing characteristics of gob-side entry retaining is presented, and the main roof structure is simplified as a mechanical model composed of roadside support body and the roadside coal body. The unbalanced bearing coefficient is proposed, which is defined as the ratio of solid coal body bearing and roadside support body bearing, and then an expression is derived for calculating the unbalanced bearing coefficient. The main factors influencing the change law of the unbalanced bearing coefficient are analyzed. The results show that the unbalanced bearing coefficient is positively correlated with solid coal elastic modulus and the immediate roof damage variable, and negatively correlated with the roadside support body elastic modulus, the immediate roof elastic modulus, the roadway width and the roadside support body width. Based on the change law of the unbalanced bearing coefficient for gob-side entry retaining, the control countermeasures are determined against surrounding rocks around gob-side entry retaining of 4211 air-return gate in Liujiazhuang Colliery. The unbalanced bearing characteristics of gob-side entry retaining with high-water materials as roadside backfill is demonstrated by the methods of FLAC3D numerical simulation and the field monitoring. The research results have been applied to the gob-side entry retaining of large mining height successfully.

To address the chaotic characteristics of landslide displacement sequence and to overcome the deficiency of the traditional time series forecasting models, a WA-ELM prediction model of landslide displacement is proposed based on chaotic time series. The chaotic characteristics of the landslide displacement sequence is analyzed, in which the wavelet analysis(WA) is employed to decompose the displacement sequence into characteristic components with different frequencies. The characteristic components are reconstructed in the phase space and predicted using the extreme learning machine (ELM). Finally, the characteristic components are superposed to obtain the prediction values. A comparative study of Bazimen landslide in Three Gorges Reservoir area is made using WA-SVM and ELM models, respectively. The results show that the predictions of the WA-ELM model based on chaotic time series has higher accuracy and better versatility and stability.

Unloading and rebound of soil induced by excavation can result in an adverse effect on existing piles with the action of the tensile force, meanwhile the tensile stress of pile reaches the maximum at the neutral point. The variation of neutral point of the additional skin friction is analyzed theoretically with a simplified distribution model. The variations of the neutral point location with pile length, excavation depth and the properties of surrounding soil are obtained by summarizing and analyzing the reported data of pile foundation during excavation. The results show that there is approximately linear positive correlation between the ratio of neutral point depth to pile length and the ratio of excavation depth to pile length. The location of neutral point descends with increasing the unit weight and the internal friction angle of the surrounding soil. Similar downward movement of the neutral point can also occur in the case of the absence of retaining structure for excavation or the presence of expanded pile tip. Based on this, a calculation model is put forward to predict the neutral point location. The predicted result is close to the numerical result.

This paper aims to study the effect of the interior bonding section length on axial force of prestressed anchor rod and its supporting effect on surrounding rock. In this study, the ratio of interior bonding section length to total length of anchor rod is defined as interior bonding section length coefficient. Based on the equation of the shear stress of anchorage interface, an expression is deduced, which describes the relationship between the axial force and total extensional length of anchor rod. Then the effect of the interior bonding length coefficient on axial force of prestressed anchor rod is analyzed, and it is found that axial force of anchor rod increases with decreasing the interior bonding section length. According to the combined arch theory of prestressed anchorage, the influence of the interior bonding length of prestressed anchor rod and its supporting effect are studied by using the FLAC3D numerical software. The results show that the decrease of the interior bonding section length is beneficial to enlarging the influence scope of prestress field, increasing the thickness of the ‘effective load-bearing ring’ and minimizing the depth of plastic zone and deformation of the surrounding rock. Finally, changing interior bonding section length is significant to coordinate the support the stiffness of supporting structure in engineering.

A constitutive relationship of Kelvin model’s type is developed by sequentially combing a Maxwell component and any number of Kelvin components. Through compiling the head and source files of generalized Kelvin model by using C++ on Microsoft Visual Studio platform, the dynamic link library (DLL) file of the generalized Kelvin constitutive model is developed, and a user-defined generalized Kelvin model is implemented by calling the DLL file in two-dimensional Particle Flow Code (PFC2D). Through stress relaxation tests, in which different numbers of Kelvin models are included in the generalized Kelvin model, the relationship between contact force and time is obtained, which turns out to coincide with the analytical solution. Based on these research results, the programmed generalized Kelvin model is used to simulate the failure process of a silty clay slope of an open pit coal mine. The numerical results illustrate that the failure surface is brim-shaped, whereas the elastic model does not predict such a failure mode, and instead it yields a circular sliding surface, implying that the developed generalized Kelvin model can be used to study the failure mechanism of silty clay slope.

On the basis of the precise time-integration method, a time-domain method for the wave propagation of the fluid-saturated porous media is proposed to calculate the dynamic response of the fluid-saturated porous media with the formulation of solid phase displacement u and pore pressure p. The solid phase displacement u is computed by precise time-integration method and fluid pressure p is computed by backward difference method. The proposed method is verified by a standard example. Moreover, the proposed method is compared with Newmark algorithm proposed by Zienkiewicz. The verifications indicate that the proposed method has high computational precision. In the meanwhile, the calculating course of the proposed method can be executed in an iterative manner, coupling equations do not need to be solved in each time step, so the proposed method has considerable efficiency. The proposed method has the basic characteristic of time-domain explicit calculating methods. Therefore, the method is capable of analyzing the dynamic response of the fluid-saturated porous media, reasonably.

In this paper, rheological equations at different plastic conditions are derived on the basis of visco-elastoplastic Nishihara model, and then these equations are further implemented into discrete element method. By studying the numerical integral scheme of force-displacement relationship between particles, the methods for developing contact constitutive model in Particle Flow Code (PFC) are summarized. Thus a user defined visco-elastoplastic Nishihara contact constitutive model is proposed under PFC in 2 dimensions (PFC2D). Through stress relaxation experiments between two fixed balls, the accuracy of the developed model is verified for three cases. Numerical parameters are obtained by the uniaxial and triaxial compression experiments on rock specimens from underground roadway in Zhangjiawa Iron Mine, and then it is applied to simulate the uniaxial compressive creep experiment. The feasibility of Nishihara model in PFC2D for rock rheological properties is proved by comparing the results with experimental data, and then failure modes of a D-shaped roadway are investigated using Nishihara model and a linear-elastic model. Numerical results of Nishihara model are in good agreement with the theoretical result of Hoek-Brown strength criterion. The deformations of two sides are substantially greater than those of the top and bottom and the corresponding failures of two sides are more serious due to the creeping of wall rock. Numerical results, to large extent, agree with the field monitoring data. It is suggested that the support on both sides should be greatly strengthened for satisfying requirements of long-term stability.

CO2 breakthrough pressure is a key parameter of caprock sealing efficiency evaluation for CO2 geological storage technology, which is one critical technology for greenhouse gas mitigation. It is mainly acquired by laboratory tests, including indirect and direct methods. The indirect methods mainly consist of mercury intrusion porosimetry. The direct methods consist of continuous injection method, step-by-step method, displacement method and pulse decay method (residual capillary pressure approach). Based on a literature review of existing laboratory breakthrough pressure measurement methods, measurement principles, testing procedures, error sources analysis and application ranges are introduced. Mercury injection method can obtain breakthrough pressure quickly, however, its measuring accuracy is comparatively low due to the impacts of such factors as conversion from mercury-air condition into CO2-brine condition including surface tension and contact angle, damage of porous structures, and so on. Step-by-step approach is based on the definition of breakthrough pressure. This approach has a high accuracy, but it is time-consuming. It always costs several months to conduct one test on caprock samples with a low permeability. Continuous injection approach also has a good accuracy, but it could over-estimate the CO2 breakthrough pressure due to the neglect of pressure gradient in the water phase and the delay between flow rate change and pressure change. Displacement method is widely used in natural gas industry in China. The experiment process is easy and timesaving; however, conversion and correction of the experiment results are complicated and high experience-dependent. Pulse decay method, which stems from step-by-step approach, has certain accuracy and efficiency. However, the difference between snap-off pressure and breakthrough pressure is still not clearly explained. At last, the application range and research demands of CO2 breakthrough pressure measurements are recommended based on the measurement principles, experiment procedures and error sources.

The three-dimensional pressure cell (3DPC) provides a novel method to measure the geostress of the deep soft surrounding rock. However, due to the installation of 3DPC, the distribution of initial stress field of the surrounding medium is inevitably changed, and then the redistributed and concentrated stress result in the significant indetermination of the relationship between the measured stress by 3DPC and the initial stress field of surrounding rock. The above problem also exists in the applications of earth pressure cell. In order to study the embedding effect of 3DPC on the initial stress field of medium and stress properties measured by 3DPC, numerical software is employed to simulate the installation process and the stress redistribution of the medium. Under different conditions of stress state and the elastic modulus ratio of 3DPC to surrounding medium, the characteristics of the principal stress redistribution field and the stress distribution of each part of 3DPC are analyzed. Moreover, the analytical models are established on the basis of the variations of measured stress by 3DPC with different initial stress state and modulus ratio. The well-fitted results show that the proposed theoretical expressions are validated to reflect the relationship between the 3DPC measured stress and the initial stress of the surrounding medium.