In order to accurately and conveniently determine the mechanical behavior of hard rock in deep engineering structures, the following works have been conducted in this paper: according to the similar mechanism of damage and plastic, determination scheme of initial yield is assumed to be used for the damage threshold. Unified energy yield criterion of rock is adopted as the decision criterion of damage threshold. Based on the definition of damage variable by Rabotnov and hypothesis of Lemaitre strain equivalence, a simplified damage constitutive law is formulated by assuming the stress- strain relation of undamaged portion to conform Hooke’s law. Aimed at expressing brittle-ductile transition of hard rock under the condition from low confining pressure to high confining pressure, a modified Mazars damage evolution equation is proposed. Damage model parameters are determined based on conventional triaxial compressive test of T2b marble. The proposed model is contrasted with the model based on Mazars damage evolution and damage threshold criterion used by Mohr-Coulomb criterion respectively. It is suggested that the damage model can express brittle-ductile transition and simulate damage evolution after damage threshold in an accurate way, which has some reference for engineering calculation of brittle hard rock.

In order to describe the stress-strain characteristics of unsaturated soils, based on the triaxial shear tests of unsaturated soils, a concept of change rate of Poisson’s ratio (that is the change rate of tangent Poisson’s ratio with the axial strain) is proposed. It is found that the tangent modulus and Poisson’s ratio rate of unsaturated soils under triaxial shearing attenuate exponentially with axial strain. Based on this law, a new nonlinear model for describing the stress-strain relationship of unsaturated soils is proposed. It can depict both the strain-hardening and strain-softening behaviors of unsaturated soils, and also it is suited to describe the stress-strain characteristics of unsaturated soils under unconsolidated undrained, consolidated drained and consolidated undrained triaxial shearing conditions. This model contains six parameters. All of these parameters have clear physical meanings, and their values can be determined easily. The triaxial shear tests in the open literature are simulated by using the new model, it is found that this model gives a satisfactory prediction of stress and strain of unsaturated soils compared with test data, thus the rationality and applicability of the proposed model are validated.

Soil moisture evaporation is one of the main processes of mass and energy exchange of soil-atmosphere, which has an important influence on soil engineering properties. It is also the direct cause of many engineering and environmental problems, however, this issue has never been taken into account in geoengineering disciplines. Based on the recent research achievements on soil moisture evaporation in other disciplines, the advances of some important aspects on this topic, i.e. soil moisture evaporation capacity determination, test method, evaporation process, influencing factors and theoretical model, are summarized and shown as follows: (1) To accurately determine the actual evaporation capacity of soil is one of the most important tasks in soil moisture evaporation study. Generally, there are two categories of methods: theory calculation and direct measurement; (2) To carry out evaporation test is an important approach to understand soil moisture evaporation process and the related mechanism. There are two categories of tests: laboratorial test and in-situ test. As compared, evaporation test by environmental chamber has better application prospect; (3) Soil moisture evaporation process can be divided into three stages: constant rate, falling rate and residual rate phases; (4) The factors influencing soil evaporation can be categorized as internal soil factors and external environmental factors. The former one mainly affects soil moisture transportation characteristics, and the latter one mainly influences evaporation energy supply intensity; (5) Many soil moisture evaporation calculation and prediction models have been proposed, however, they show some disadvantages such as large errors, narrow range of adaptation or difficulties on parameters acquisition. Based on the above understanding, and to combine with the research background of geotechnical and geological engineering, some important research topics that should be well investigated in future are proposed, including the evaporation mechanism of falling rate stage, the quantitative relationship between the soil properties and evaporation rate, soil moisture evaporation and transportation mechanisms in clayey soil especially in expansive soil, development of high precision in-situ soil moisture evaporation test apparatus and construction of universal soil moisture evaporation theoretical model.

SINGH M proposed a nonlinear Mohr-Coulomb (M-C) criterion by adding a correction term to the original M-C criterion which could only linearly express rock strength variation with confining pressure. The nonlinear M-C criterion assumes that there is a critical state when the confining pressure reaches the uniaxial compressive strength of rock material, however it has a large discrepancy with some triaxial experimental results. In order to expand the application of the nonlinear M-C criterion, a general expression of M-C criterion is developed by further improving the correction term. A comparison among the general expression of M-C criterion, the nonlinear M-C criterion and the hyperbolic model is made by using triaxial data of 11 different kinds of rock. Analytical results show that the M-C criterion with the modified expression has a higher accuracy than the other two criteria. The strength values predicted by the generalized M-C criterion is consistent well with experimental values. Thus, the generalized M-C criterion has wider application than the nonlinear M-C criterion.

Based on the results of compression test of marbles from Jinping Ⅱ hydropower station, an expression of plastic internal variable considering the volumetric stress effect is derived, and the evolutions of strength parameters and dilatancy with the internal variable are studied. The results show that: the cohesion of marbles decreases slightly in pre-peak stage while the cohesion decreases rapidly in post-peak stage; the internal friction angle increases with increasing internal variable and it reaches the maximum value when the internal variable reaches 0.8-0.9; the dilatancy angle increases firstly and then decreases with increasing the internal variable under different confining pressures, and the variations of dilatancy angle are different under low and high confining pressures. A mechanical model of marbles is established considering the effect of volumetric stress based on the above results, and the laboratory triaxial compression test is simulated with the established model using FLAC3D. The simulation results show a good agreement with the test results, indicating that the established model can reflect the main mechanical properties of marbles. The research methods and results will provide an important reference to the analysis of deformation and failure of other deep brittle rock masses.

To investigate mesoscopic cracking propagation and coalescence mechanisms of rocks under shearing conditions, tests on sandstone samples are conducted using a self-developed mesoscopic test equipment. The effects of saturation degree on mesoscopic cracking and crack morphology are discussed. It is shown that in general cracks initially appear at the middle of the shear plane with stress dropping during the shearing process. Several cracks distribute discontinuously, and cracks within a short distance coalesce into large cracks. At the moment of stress dropping, all cracks connect with each other into a coalesced surface. The rock strength is affected by water weakening, which leads to large secondary cracks appearing at the bottom of specimens. When the saturation degree is higher, there are more bifurcation cracks appear around the main crack, and the specimen has more complicated surface patterns. When the number of fractured surface is increased, the secondary crack is growing slower and overall damage area is increasing faster. From the mesoscope aspects, the local independent crack coalescence process is accompanied by the beam rotation and bending fracture of the cemented rock bridge; the weakening effect of water results in the internal and external microcracks in the rock bridge increase. With the increase of saturation degree, the numbers of both independent cracks and secondary cracks show an increasing trend during shear process.

The spalling of deep-buried medium hard coal wall often presents obvious time-lag characteristics. In order to analyze deformation and failure features of coal, uniaxial compressive and step loading tests are carried out on coal samples using a testing system RMT-150B. Experimental results indicate that the pre-peak stress-strain curves of two loading modes are similar, but the post-peak stress drops gradually under uniaxial compression. There is no obvious peak when final level stress is higher than yield strength of coal samples, then a yielded platform appears and the post-peak stress-strain curve has a rapid drop. Mechanical parameters obtained by uniaxial compression tests are significantly higher than that obtained by step loading tests. It is shown there are time-lag characteristics, but the axial and circumferential deformations of coal samples have no obvious characteristics when the loading stress ratio is lower than 70%. Although the axial stress force is a constant value, the axial and circumferential deformations increase gradually when the loading stress ratio is higher than 70%. The circumferential strain is far greater than the axial strain, and the volume also increases. Coal samples absorb energy, and then new microcracks are evolved, developed and assembled, which thus results in gradually damaged internal structure. The higher the step loading stress level is, the shorter the time of delayed damage is and vice versa. Therefore, the stress-strain relationships of coal samples present obvious time-lag characteristics. The failure of coal is relatively simple under uniaxial compression, which has obvious tensile-shear fracture plane. However, the coal is broken completely under step loading, the failure is complex and circumferential expansion feature is obvious. It is similar to the time-lag characteristic of coal wall spalling in the working face. The research results provide some references for the control of coal wall time delay in the mining face.

Pile-soil stress ratio is an important index in the research of composite foundation. Currently, the studies regarding the pile-soil stress ratio mainly focus on the general composite foundations, such as mixing pile and gravel pile. However, the theoretical calculation of stress concentration ratio of stiffened deep mixed (SDM) pile has been rarely reported. From the deformation modes of soil, cement and the composite pile element, the negative friction resistance of pile, pile cap and pile tip penetration to bearing layer is considered comprehensively, the compression deformations of soil around the pile, cement soil pile and composite pile body are analyzed, and a stress ratio calculation formulation is derived to describe the relationships among stiffened deep mixed composite foundation piles, cement soil pile and soil. Further, the effects of core pile diameter of stiffened deep mixed pile, core pile length and soil cement pile length on the pile-soil stress ratio are analyzed. It is found that the pile soil ratio increases with increasing the core pile diameter, length of stiffened deep mixed pile and pile length of cement soil. By comparing the computed results with the field data from a field test, the computed results and measured data agreed well and the reliability and feasibility of the proposed method was verified, which can be beneficial to guiding the actual practice.

Taking the stress state of soil around jacked pile as the initial condition, a Terzaghi's consolidation equation is modified under the axisymmetric conditions considering that the consolidation coefficient varies with time regarding the correlation between void ratio, permeability coefficient and effective stress. Subsequently, a semi-analytical and semi-numerical solution of excess pore water pressure dissipation is derived by using separation of variables and discrete analysis and compared and verified with the measured data. On this basis, the soil 3D undrained shear strength is defined by using SMP criterion-based Cam-clay model. The strength of soil around jacked piles and the variation of shear modulus with consolidation time are researched. The results show that the theoretic solution is well consistent with the measured data because of considering the change of the consolidation coefficient. And the ratio of the compressibility index and the permeability index has significant effects on the variations of consolidation coefficient and the consolidation rate. When the ratio equals to 1, the consolidation coefficient will be constant, the solution is degenerated into the conventional Terzaghi’s axisymmetric consolidation equation. Also the soil strength and the shear modulus gradually increase along with the consolidation time. In the long-term stage of consolidation, their values exceed in-situ strength and in-situ shear modulus.

Chemical consolidation is one of the most effective methods for solving the engineering problems of saline soil, such as salt expansion, collapse and erosion. Based on the unconfined compressive strength test, X-ray diffraction, chemical analysis and scanning electronmicroscope, the solidification mechanism and strength characteristics of the sulphate saline soil solidified by lime, fly ash and sodium silicate are analyzed. The results show that when the lime content is less than 8%, the compressive strength and shear strength of lime-reinforced soil, fly ash and sodium silicate are higher than those of the sulphate saline soil solidified by lime and fly ash; the strengths of the former grow almost linearly with the concentration of sodium silicate. The alkali-activated action on fly ash caused by sodium silicate and adsorption between sodium silicate and saline soil generate mass gels, leading to an increase in contact area between framework grains, a reduction in intergranular pore, and a transformation from point-contact to surface-contact. The grains of saline soil bond each other into 3D framework via gels, resulting in an increase in the strength of saline soil. Meanwhile, the salt expansion behavior of saline soil is also restrained effectively due to the sharp reduction in the content of induced by complex physicochemical reactions as saline soil is solidified.

The petrophysical properties and structures of rock materials are changed when they contact with cryogenic nitrogen that has an extremely low temperature of ?195.8℃, and thus the principle can be used to improve reservoir fracturing. To study the effect of cryogenic nitrogen freezing on rock strength and mechanical parameters, different types of rock are selected, such as marble, sandstone and granite with different moisture states (dry and saturated), to freeze them with cryogenic nitrogen, and then to determine tensile strength and uniaxial compressive strength of these samples before and after freezing. The results show that the uniaxial compressive strength, tensile strength and elastic modulus of rocks are decreased after freezing with cryogenic nitrogen. When the rock sample is dry, the influence of cryogenic nitrogen freezing on the strength of marble is greater than that of red sandstone. However, when the rock sample is saturated, the influence on red sandstone is greater than that on marble. When the saturated rock is frozen with cryogenic nitrogen, there is a break point on the elastic deformation stage of stress-strain curve. For the same type of rock, the effect of cryogenic nitrogen freezing on the damage of saturated rock is more obvious than that of dry rock. Scanning electron microscope (SEM) tests are further conducted on these three types of rock and particularly the marble samples are analyzed in detail. It is found that intergranular fractures occur after cryogenic nitrogen freezing. This study provides an experimental basis for further studying the mechanism of induced fracturing by cryogenic nitrogen.

The weathered granites in the eastern foothills of Lüliang Mountain are significantly different from those occurring in the southern China, Japan and South Korea. To understand comprehensively the physical and mechanical properties of the compacted weathered granite in Lüliang Mountain, a series of laboratory tests including routine soil test, X-ray diffraction test, large consolidation test, large-scale triaxial test and so on is performed to analyze the compaction, load-bearing, deformation, dilatancy and strength characteristics of strongly weathered granite. The experimental results show that the clay content has a remarkable influence on the compaction characteristics of compacted weathered granite and the load-bearing characteristics, and there exist two threshold values of clay content, when the clay content is about 8%, the dry density of the sample reach the maximum, while about 4%, California bearing ratio(CBR) has a maximun value. The soil samples in this study have no expansion potential and their compressibility are generally low. Two salient phenomena of plastic deformation can be observed on the secondary loading and unloading compression curve due to particle breakage of compacted weathered granite. Because the soil particles might undergo compacted, dislocated, overturned or crushed processes, the soil samples show different dilatancy characteristics under different confining pressures. In addition, due to the existence of particle breakage, the strength of sample exhibits nonlinear characteristics.

Bidirectional loading experiments are conducted on granite specimens with holes to simulate the tunnel rockburst. The infrared thermal images and the minimum infrared radiation temperature are employed to determine the temporospatial evolution characteristics of infrared radiation temperature in the process of rockburst. The results show that the temporospatial evolution characteristics of infrared radiation in rock blasting process are synchronized well with the process of initiation and development of the rockburst. Before the rockburst, it is found that there is the low temperature field in the infrared thermal images nested in the banded temperature field. The low temperature field extension reflects the rockburst breed and development process in the temperature field, and its position of appearance corresponds to the region that rockburst occurs. The evolution of the lowest infrared radiation temperature shows a 4 stage characteristics as rise - brief fall - rise - fall. Three abrupt turning points are observed in the lowest infrared radiation temperature before the rockburst. The above results have some theoretical significance for temporospatial prediction of tunnel rockbursts.

To investigate the rate-dependent deformation characteristics of subgrade compacted clay of high-filled embankment, a series of CD triaxial shear tests on the unsaturated compacted clay with different compaction degrees is carried out under different loading rates and confining pressures, and the shear strength parameters under different working conditions are examined. A method is proposed for indirectly measuring the volume change of unsaturated compacted clay, i.e. using the confining pressure controller of GDS saturated static triaxial system to obtain the volume change. The experimental results show that the strength and deformation of compacted clay shows significant time-dependent characteristics. At the greater loading rate, the shear strength is higher and the over-consolidated properties are stronger, and the value of cohesion c increases more quickly but the value of the internal friction angle increases more slowly. Under low confining pressure, compacted clay shows dilatant and softening behavior. As the compacting degree increases, shear dilatancy and strain softening become more and more pronounced, shear strength index c increases quickly, whereas increases slowly. An elastic-viscoplastic constitutive model based on the subloading yield surface is adopted to describe the rate-dependent deformation characteristics of the over-consolidated compacted clay. The predictions of the proposed model are in good agreement with the experimental data, showing that the proposed model is suitable for analyzing the long-term settlement of high-filled embankment.

The embankment of heavy-haul railway is typically subjected to greater dynamic loads than those of conventional and high-speed railways and thus exhibits greater deformations. The majority of heavy-haul railway embankment layers is comprised of coarse-grained soils (CGS). The primary objective of this paper is to investigate the strength and deformation characteristics of such coarse-grained soils under repeated train loading. For this purpose, a series of large-scale laboratory triaxial tests is conducted for the effects of varying dynamic stress amplitudes, confining pressures and moisture contents on the accumulated permanent deformation behavior. The characteristics of dynamic strength behavior with different combinations of static strength and confining pressure levels are analyzed. According to the permanent deformation accumulation characteristics, that is the increase of confining pressure or reduction of dynamic stress is helpful to enhance the soil stability of CGS obtained at different levels of deviatoric and confining stress values, a criterion for determining stable state of CGS is proposed, and the parameters of the criterion are given. The research results contribute to improving evaluation of the dynamic stability of heavy-haul railway embankment and to the establishment of the design philosophy based on the dynamic deformation control.

The surrounding rock of the deep and long tunnels at Jinping II hydropower station shows pronounced rheological deterioration during excavation. According to the fractional calculus theory, a fractional order derivative constitutive model for rock creep is developed by replacing the traditional Newton dashpot with Abel dashpot in the classical Nishihara model. To address the unsteady nature of a creep process, especially when the suffered stress becomes larger than the long-term rock strength, an unsteady creep constitutive model is developed based on the fractional order derivative by introducing the unsteady feature of creep parameters into the constitutive equation. Based on the results of shear creep tests on marble, which is one of the main rock types at Jinping II hydropower station diversion tunnel, the material parameters can be determined by fitting the experiment results. It is shown that the unsteady creep constitutive model based on the fractional order derivative can describe the experimental results very well at the beginning of the creep and the turning points, overcoming the deficiency that Nishihara model cannot describe the third stage of the creep process. The parametric analysis clearly demonstrates the effect of fractional derivative order and unsteady parameters on a creep strain. The proposed model can reflect the whole creep process very well.

Karst collapse column, as a special geological body with chaotic internal structure, is easy to be a vertical water channel under the coal floor. Thus it is a major potential safety hazard in Carboniferous coalfield of North China Permo. The water channels in collapse column under the coal floor are composed of collapse column and floor water-conductive fissure zone. To investigate the mutation mechanism of seepage in the hidden collapse column, a broken rock permeability test system is independently developed. A series of experiments is conducted to examine the seepage in the collapse column under different floor damage conditions. Experimental results show that: the fundamental reason of the seepage mutation is caused by the changes of broken rock pore structures resulting from the large particle loss. The flow velocity increases with the increase of the pore diameter at the seepage boundary, and the initial porosity of the sample is higher than 0.21 when the seepage mutation occurs. The seepage boundaries have negligible effect on seepage without the occurrence of seepage mutation. The permeability of the sample increases with the increase of its porosity, and there is a power function relation between permeability ratio and porosity ratio. The negative non-Darcy factor is a sufficient and necessary conditions for the occurrence of seepage mutation, and the non-Darcy factor controls the degree of the seepage mutation intensity.

Fracture toughness of rocks characterizes the resistance to crack initiation and propagation. As an important index of mechanical property, it plays an irreplaceable role in the theoretical research of rock mechanics and practical application to rock engineering problems. Due to the complexity of rock structures, most of rock fractures occur under mixed mode loading conditions. Therefore, it is important to investigate the mixed mode fracture toughness of rocks. Rust rocks are widely used in the construction, and thus are selected to study the fracture behavior. A series of radial compression tests is carried out on 18 cracked straight through Brazilian disc (CSTBD) specimens to obtain the pure mode I, pure mode II and mixed mode I/II fracture toughness. Then experimental results are compared with theoretical values calculated by the generalized maximum tangential stress (GMTS) criterion. The results show that the values of fracture toughness for pure mode I and pure mode II are 1.01 MPa?m0.5 and 1.51 MPa?m0.5, respectively. The fracture toughness of pure mode II is 1.49 times higher than that of the pure mode I. The fracture toughness of pure mode II is close to the value of 1.34 obtained by the GMTS criterion, but is larger than the value of 0.87 achieved by the maximum tangential stress (MTS) criterion. The T-stress and the critical distance (rc) related to the size of fracture process zone in front of the crack tip have a great influence on crack propagation path and mixed mode fracture toughness of rock materials. As the generalized maximum tangential stress (GMTS) criterion takes into account the T-stress, it has a good agreement with experimental results.

Due to shield tunnel construction disturbance, additional soil stresses can occur and thus soil plastic zones around tunnel may appear around the tunnel. The range of the plastic zone is closely related to grouting parameters, such as grouting pressure and grouting amount. To analyze the disturbance range caused by shield tunneling, the cavity expansion theory is introduced to determine the plastic zone and the disturbance range of the surrounding soil. The effects of backfill grouting pressure and grouting amount on the plastic zone and the range of disturbance by shield tunneling are investigated, and a functional relation between the plastic zone and grouting parameters is derived based on the cavity expansion theory. By defining a disturbance evaluation criterion, a simple numerical method for calculating the plastic zone and the disturbance range during shield construction is proposed based on the finite element method. The results obtained by theoretical formulation and finite element method are compared with the static cone penetration test (CPT) data, showing that the theoretical and numerical results are in a good agreement with those obtained by field tests, demonstrating the validity of the proposed approach. The results provide a theoretical support for the proper choice of grouting parameters in shield construction.

A simple and effective method is proposed to apply the hydrodynamically induced mass to the marine wind power structure in the finite element analysis. The proposed method can be readily implemented into the ABAQUS software, by which the preprocessing efficiency is improved in the finite element analysis. A finite element model is developed, and the influences of the hydrodynamically induced mass and different boundary conditions on the natural vibration of marine wind power structure are analyzed. Based on the finite element method, the sensitivity analysis is carried out for the hydrodynamically induced mass and various boundary conditions, through simulating the response of offshore wind power tower under the earthquake loading. The numerical simulation and theoretical analysis show that the proposed method yields good results. Applying the hydrodynamically induced mass decreases the natural frequency of the structure, and as the order number increases, the natural frequency and its absolute magnitude increase. The boundary conditions can influence the modal parameters more significantly than the hydrodynamically induced mass, and the natural frequencies of each order decrease significantly if the viscoelastic transmitting boundary condition is adopted. The model with a viscoelastic transmitting boundary yields a greater displacement response compared to the model with a fixed boundary.

The water curtain hole design is the core part of water curtain system, which is crucial to the operation of the underground water-sealed cavern. Based on the first water-sealed underground cavern in China, the impacts of spacing of water curtain hole and fracture width on the water sealing is studied using the underground water seepage theory. The results show that spacing of horizontal water curtain hole and the fracture widths have important influences on water sealing in steep-inclined structural planes. In the calculation condition, the water sealing reaches the best effect when the water curtain hole spacing is 10 m. Water curtain hole spacing of 30 m is unable to meet the requirements of water sealing. Under the same water curtain hole spacing, the wider the gap width is, the better the effect of water sealing is, the best spacing of water curtain hole is 10 m for the project investigated; the poorer the effect of water sealing is in the crown area of main cavern. The research results provide a theoretical basis for water sealing evaluation of water-sealed oil storage cavern

Based on 1 174 sets of testing data of shear strength parameters from 103 hydropower projects in China, a Copula-based function is adopted to investigate the joint distribution model of shear strength parameters for rock foundation. The construction method of the joint distribution model is explored. Firstly, the statistics of shear strength parameters have been achieved using the least square method. Then, based on the Akaike Information Criterion (AIC), the best-fit marginal distributions of shear strength parameters is identified. Finally, four Copula functions are chosen to build the bivariate distribution of shear strength parameters. The advantages of using Copulas to model the bivariate distribution of shear strength parameters are discussed. The results indicate that there exists a strong negative correlation among the shear strength parameters of rocks in hydropower projects. The proposed Copula-based approach can incorporate various marginal distributions and Copulas into a multivariate distribution, which provides a flexible way of modeling the bivariate distribution of shear strength parameters. With the known marginal distributions and correlation coefficient of shear strength parameters, the bivariate distribution of shear strength parameters cannot be determined uniquely. The bivariate distributions using various Copulas differ considerably under the premise that the edge distribution function and the correlation coefficient are exactly the same. Compared with the commonly used bivariate normal distribution of shear strength parameters, the proposed Copula-based approach provides a more general way of modeling the bivariate distribution and thus its modeled results are more accurate. Design values of shear strength parameters in hydropower projects are commonly determined by using the small value average method in China. The conditional cumulative distribution functions of cohesion associated with various Copulas differ considerably when friction coefficient takes a smaller value. Such differences directly lead to a significant effect on the determination of design values of shear strength parameters and the associated design schemes of hydraulic structures.

To investigate the anchoring mechanism and its influential factors of the bolt, a series of uniaxial breaking tests is conducted on the specimen with prefabricated fracture anchored with a single row bolt. A concept of the main-control crack (i.e., one or several large cracks controlling the strength weakening and the ultimate failure) is proposed. Under different conditions of anchorage, the main-control crack of specimen have different occurrences. In the effective anchoring zone, there are two types of main-control cracks observed in the fractured specimens, called the horizontal main-control crack and vertical main-control crack. It is found that specimens without rock bolt or with the cracks beyond the effective anchoring zone only have the vertical main-control crack. Acoustic emission and stress monitoring data show that the bolt can delay the initiation of the main-control cracks and improve the strength of the fractured specimens. Additionally, the stress intensity factors on the tip of cracks under different anchoring conditions are calculated using ANSYS software. Then the relationship among the anchoring spacing, anchoring angle and the stress intensity factor is obtained. The coalescence modes of main-control cracks are also simulated under different anchoring spacings by using FLAC3D software, and numerical results agree well with the experimental results.

The Shangwan giant old landslide in Qinghai province, belonging to Upper Pleistocene series loess of Quaternary System and Guide Group mudstone of Neogene System, is a typical multi-stage rotating landslide and the sliding surfaces are mainly in the mudstone of Guide Group. Based on the full use of the materials obtained by the field landslide survey and drilling test, through analyzing the spatial position relation between key layers (loess soil and conglomerate deposits) in the landslide deposits and mudstone deposits, as well as the sliding surface morphology of the old landslide body and the sludge (dammed lake sediment) on the top of the loess, it is confirmed that the Shangwan giant old landslide body had mainly experienced two large-scale slides. And then, with the theory of groundwater dynamics, the groundwater level can be calculated before the two slides, and a numerical model of landslide deformation and destruction mechanism can be established. Combining the regional neotectonic movement characteristics, the dynamic change of underground water level, the feature of significant decrease in strength of mudstone in the saturated state and the FLAC3D numerical simulation results, it is concluded that the first sliding of the old landslide is mainly caused by river incision, and three stages of slope deformation in the process of the river incision are provided. The first sliding results in the steepening of slope’s free face, the concentration of shear stress at the slope toe, and the formation of a dammed lake in the front of the landslide, which leads to an accumulated traction sliding caused by the rising of ground water level and the softening of the mudstone.

Gravel soil landslide has a unique internal seepage system, since the soil contains a large number of gravels constituting a matrix structure. Depending on the diversity of gravel soil structures, the network of flow channels can be different and correspondently the landslide pattern is also different. Hence, it is difficult to make the targeted mitigation plans for slope failures. In this study, the case of Yanshanjiaoluo landslide, which is located in Anxi County of Fujian Province, is investigated. The relationship between the seepage system of the gravel soil with multivairiate-structure and the material composition of the landslide is obtained based on the comprehensive geotechnical investigation including geophysical prospecting, drilling, water level monitoring as well as SketchUp modeling analysis. Comparative analysis is performed to evaluate the deformation and rainfall sensibilities of two sorts of seepage system. The results indicate that the coarse gravel soil area is characterized by concentrated seepage, while the false porphyritic gravel soil area is characterized by pipe network seepage. The former is more sensitive to the rainfall than the latter. However, influenced by the overall strength of the seepage channel and seepage stability, the latter is more sensitive to the deformation of landslide than the former. Based on the above analysis, a combined measure of anti-slide pile and blind drainage ditch is employed to improve the stability of the landslide. The field observation confirms the effectiveness of the mitigating measures.

Tunnel excavation can reduce the bearing capacity of adjacent pile foundation. How to accurately evaluate the additional pile responses is a problem yet to be solved. A simplified analytical method is developed based on a Pasternak-type two-parameter elastic foundation model and a three polyline-elastic-plastic load transfer model; a two-stage analytical method is used and the effect of lateral soil and heterogeneity characteristics of soil are considered. The validity of the proposed method is verified by the comparative analysis of the results obtained from proposed method, Winkler foundation beam method and boundary element method. Combining with parametric studies of the influencing factors of lateral response of a single pile, correction coefficients are used to correct the maximum lateral response of a single pile in the baseline engineering case, the maximum horizontal displacement and the maximum bending moment of a single pile under the calculation working condition are obtained. The results indicate that in calculating the horizontal displacement, the effect of lateral soil can be ignored, while it should be considered in calculating bending moment. The average ground loss ratio is linearly related to while it presents a nonlinear relationship with tunnel radius R, tunnel axis depth H, distance from the center line of the tunnel x and pile flexibility coefficient .

To overcome the inefficiency that not less than two landslide sections are required in the back analysis of shear strength parameters based on the traditional slope stability analysis method, a new method is developed for back analyzing soil strength parameters based on the probability reliability theory, by combining the Excel spreadsheet method and the upper bound limit analysis method. The proposed method is applied to back analyze Zhuequedong landslide in Hunan province. The results indicate that the shear strength parameters of slip surface obtained by the proposed method are in good agreement with the measured data of the engineering site. The applicability of the new analytical method is verified. Based on this method, the inverse problem of shear strength parameters of a single slip surface can be resolved by using the measured data of only one landslide section, showing the effectiveness of the proposed method.

To discriminate and measure the whole stability of unlined shallow earth tunnel in theory, considering the effect of oblique slip surface beside tunnel body, a theoretical solution of ultimate surcharge is deduced by adopting the limit equilibrium method during the occurrence of the tunnel overall instability, and then the solution is examined using the typical loading tests. It is found that the solution of ultimate surcharge formulation is close to the test results. On the basis, the ratio of sliding resistance to sliding force is defined as the whole stability safety factor, and its influencing aspects are analyzed. It is shown that the stability safety factor increases along with the increment of the cohesive force and the internal friction angle, and the effect of cohesive force on the safety factor is significant, but the effect of internal friction angle is less potent. The stability safety factor decreases with the increment of the span, the depth-span ratio, and the surcharge of earth tunnel, but the surcharge has less effect on the stability safety factor when it is larger. With the increment of the height-span ratio, the stability safety factor decreases as the cohesive force is low, but it increases firstly and then decreases as the cohesive force is high. Finally, the whole stability safety factor is verified by typical loading experiments, demonstrating that the calculation error is within the engineering allowance.

Although the upper bound approach of limit analysis has attracted extensive attention in the slope stability analysis, its derived analytical solutions have not been directly applied to the stability analysis of the slopes with arbitrary complicated multistep and multilayer. Adopting the rigid body assumption and the combined log-spiral rotational failure mechanism, we derive a unified integral expression for the external work rate and the related virtual work equation for slopes with arbitrary surface geometry and multiple soil layers. A generalized upper bound approach of limit analysis is proposed, by which the overall stability of complex multistep and multilayer slopes can be achieved. To overcome the difficulty in calculating integral formulations, the numerical integration technique is introduced. Based on this, the global factors of safety (FSs) and the corresponding CSSs of complex layered slopes are obtained by using the strength reduction technique combined with an optimization method. Several representative examples are employed to validate the analytical solutions and comparisons of the FSs and the corresponding CSSs obtained by various methods are also conducted. The results show that the proposed approach can yield the high-accuracy solutions and is widely applicable to the stability analysis of complex layered slopes. The new approach is applied to a typical multistep and multilayer slope case.

Underground lined tunnels are sometimes exposed to hydraulic fracturing, blasting loading and sudden excavations in operation. The loadings mentioned above are idealized the uniform axially symmetric transient radial loads acted on the internal lined tunnel and the dynamic responses of lined cylindrical tunnels due to the suddenly applied constant load, step load and triangular pulse load are analyzed. The governing equations of the lining and the surrounding saturated medium are derived based on Biot’s theory and elastodynamic theory, respectively. The straight boundary of half space is modeled as a convex arc with the maximum large radius. A set of general solutions in rectangular coordinate system is transformed into solutions in polar coordinate system using addition theorem proposed by Graff. According to the boundary conditions, ground displacement, hoop stress in the lining and pore pressure between the lining and saturated soil are obtained in Laplace transform space and then transformed to solutions in time domain using the numerical calculation method of inverse Laplace transform. The distribution of ground displacement and hoop stress of lined cylindrical tunnel and pore pressure between the lining and saturated soil are obtained.

The rating of rockburst is fuzzy and uncertainty, though the cloud model of rough set theory has a unique advantage to dealing with fuzzy and uncertainty problem. A new cloud model for evaluating rockburst grade is proposed on the basis of the rough set of fuzzy C-means (FCM) algorithm. Some main evaluation factors of rockburst are chosen in this study, such as uniaxial compressive strength , the maximum tangential stress , tensile strength and elastic energy index Wet . According to the criteria of rockburst classification, each evaluation factor is calculated by using the characteristics of cloud number of different rockburst levels. The rough set theory based on FCM algorithm is employed to analyze each factor attributed in the forty samples of rockburst engineering in China and internationally, and then the weight of each evaluation factor is calculated. The comprehensive degrees of certainty of the samples for evaluation are calculated by the positive normal cloud generator, and the level of rockburst is finally specified by the maximum certainty degree. The results show that the evaluated results agree well with the practical records, which implies that the proposed procedure is of feasibility and reliability, and is a new idea for rockburst prediction.

The traditional discontinuous deformation analysis (DDA) has high efficiency by adopting simple linear displacement mode, and the high-order polynomial displacement mode of the large blocks retains the characteristics and improves the calculation accuracy. The recently developed DDAs coupling FEM or natural element method (NEM) is a kind of the DDA models that use the FEM or NEM shape functions to construct block displacement functions, and has the properties of interpolation and high precision, and displacement boundary conditions can be directly imposed. However, these methods are less efficient than the original DDA. To combine the advantages of the traditional DDA and the DDA coupling method, a hybrid method is established for the linear displacement mode and the coupled DDA using the traditional DDA. In this method, the nonlinear model is mainly used for large blocks, and the natural element interpolation is adopted with certain characteristics of non-grid, and the efficiency is higher than that of the finite element method. The integral matrix of the mixed mode is developed and the expressions of the contact and other factors such as the stiffness sub-matrix and the load subvector are derived. The computation efficiency and precision of the new DDA is between the linear DDA and the DDAs coupling FEM or NEM. Some basic examples are provided to verify the new DDA; and the calculation results of the overall analysis of jointed surrounding rock-tunnel lining are given, showing the superiority of the new method.

A new numerical approach is proposed to simulate bolt supporting by considering interactions among anchor plate, anchor arm and rock based on the analysis of traditional load transfer mechanism of the bolt. The effects of concentrated stress from one bolt on the surrounding rock are investigated by employing analytical integral of Kelvin’s solutions. The displacements equations of the anchor free section and the relative section of drilling holes are established according to the same displacements of them along the axis of anchor arm. Coupled with the previous 3D fictitious stress method (FSM) system, a new boundary element simulation system is formed completely on the partially grouted bolt supporting by considering anchor plate, which can be applied to calculate the stress and displacement of an arbitrary point in the rock after bolting. The reliability of the system has been verified by a comparison of numerical results obtained by a commercial software Flac3D. Meanwhile, a multi-core parallel improvement in terms of OpenMP is conducted to improve the operation efficiency. The principal ideas and the comparison chart of speedups are presented in detail. The system has great application value in the course of advantages of boundary element such as simple modelling, large computable domain and high accuracy.

Based on tensile and shear failure mechanisms of rock breakage, a synthetic failure hypothesis has been proposed. With the establishment of the non-collaborative and collaborative cutting volume model, a theoretical model is deduced for the specific energy of tunnel boring machine (TBM) cutters working in the collaborative cutting mode. The relationship between the crack length and penetration is established by a discrete element model (DEM). A theoretical formula of optimal cutter spacing is then derived by the fitting method. Additionally, indentation experiments are conducted the cement simulation material as cutting objects using the TBM rotary cutting test platform. The relationship between the hob penetration and the crack length of the rock is obtained, and then the simulation results are verified by experimental results. The broken-rock volume is counted through 12 cutting experiments with different penetrations and spacings between cutters. Then the specific energy consumption fitting curve is obtained, which verifies the conclusion of optimal cutting spacing equation. The research results show that the characteristics of rock properties and the structure of the hob are comprehensively considered in the optimal cutter-spacing calculation formula of the full-face rock TBM, which potentially has wide applications. When the cutting spacing is greater than the collaborative spacing, the shear failure mechanism plays a dominant role in rock-breaking process. However, when the cutting spacing is less than the twice lateral crack length, the tensile failure mechanism has more significant effects on rock breakage. As the penetration increases, the optimal spacing increases while the optimal S/P decreases.

A slope reliability analysis method based on limited shear-strength parameter data is proposed by adopting the Bootstrap sampling method. The traditional method of slope reliability analysis is first introduced briefly, and then the Bootstrap method is adopted to model the statistical uncertainty in probability distributions of shear strength parameters. An example of the infinite slope is given, the influence of the distribution parameters of shear strength and the uncertainty of distribution type on the reliability of the slope is studied. The results indicate that the sample mean, sample standard deviation and AIC values derived from the limited data of shear strength parameters show a large variability. This variability further aggravates the statistical uncertainty in the probability distributions of shear strength parameters. By considering the statistical uncertainty in the probability distributions of shear strength parameters, the reliability index of a slope is presented as a confidence interval instead of a single, fixed index derived from a classical reliability analysis. The range of this confidence interval increases with increasing slope safety factor. Meanwhile, when both the uncertainties in distribution parameters and distribution types of shear strength parameters are taken into account, the reliability index has a higher variability and thus a wider range of confidence interval. The Bootstrap method provides a practical access to modeling the uncertain probability distributions of shear strength parameters and to determining the associated slope reliability with limited data of shear strength parameters.

A 3D grouting model test system, which consists of bearing test rig, servo voltage supply unit, grouting unit, multivariate information monitoring unit and image acquiring unit, is developed to investigate the grouting diffusion process and reinforcement mechanism. The main functions of this system are the lacunose, multiple sequence and parameter flexible model test of the grouting and the real-time collection of the physics field information during the grouting. The major advantages of the system include: (1) The test cavity is designed as composite barrel structured, strong leak tightness and convenient disassembly, in favor of studying grouting solid details; (2) the loading method of multi-cavity control hydraulic pneumatic joint can provide continuous steady pressure groundwater environment; (3) a multi information parallel real-time monitoring system can collect the information of the total pressure, pore water pressure and displacement of different spatial positions in the injected rock body, and realize the spatial and temporal variation of physical parameters in the grouting process. The testing system is used to perform the simulation tests of single hole grouting and grouting in a single hole, and the variation of grouting pressure P and the mechanical response of soil are obtained. The p - t curve shows multiple peak - trough cycle and characterizes strengthening mode of splitting grouting. The total pressure, pore water pressure, effective stress and grouting pressure change almost synchronously under the grouting loading; reach the peak values at the end point of grouting, and then begin to attenuate and gradually to be stabilized. Compared with single-hole grouting method, the multi-hole grouting method can improve the effective stress of soil dramatically. It is demonstrated that fracturing grouting is the main clay medium. The contact relationship between different orders of slurry veins is complex, and can be divided into 3 basic modes: shear splitting, in situ splitting and intrusion splitting. The test method of porous and small grouting rate can reduce the disturbance of surrounding rock, increase the amount of grouting and the degree of consolidation of soil, and improve the effect of grouting reinforcement.