A series of dynamic uniaxial compression, dynamic triaxial compression and dynamic tensile tests with different strain rates are conducted on homogeneous sandstone samples by using the RMT－150C testing machine and the multifunction split Hopkinson pressure bar (SHPB) device. The results show that, when the confining pressure remains constant, the compressive strength of sandstone increases with the magnitude of strain rate when the strain rate is less than 102 s-1, the increment trend of the compressive strength is proportional to 1/3 power of the strain rate when the strain rate is larger than 102 s-1. The similar rule above also applies to the tensile strength. Currently, no rock dynamic strength criterion is available for the strain rate in the range of 101- 102 s-1. Based on the analysis of data from dynamic uniaxial tests, dynamic triaxial tests and dynamic tensile tests under low-high strain rates and the principle of Mohr-Coulomb criterion, Hoek-Brown criterion and Griffith criterion, the dynamic Mohr-Coulomb criterion and the dynamic Hoek-Brown criterion under different strain rate ranges are formulated. The experimental results show that the dynamic Mohr-Coulomb criterion and the dynamic Hoek-Brown criterion can be applied to estimate the dynamic strength in the low strain rate range. In the high strain rate range, the dynamic strength can be estimated by using the dynamic Mohr-Coulomb criterion; but the dynamic Hoek-Brown criterion is not applicable. The Griffith criterion can be used to estimate the dynamic uniaxial compressive strength and dynamic tensile strength in high strain rate range only.

There is large area of soft dredger fill in Tianjin Binhai New Area, which hard to meet the requirements of engineering construction, needed to be solidified. Through selecting cement as main agent; gypsum, NaOH, Na2CO3, and FeCl3 as assistant additives, a series of indoor consolidation experiments are performed for soft dredger fill with different water contents in Tianjin Binhai New Area. Using unconfined compression strength as a main factor, analysis of microstructure for solidified soil are made by choosing two kinds of solidification agent which are used for different programs through effective comparison and screening. The results show that solidified soft dredger fill in Tianjin Binhai New Area with cement and appropriate as well as a moderate amount of additional agent has an obvious advantage than solidified with pure cement. Microstructural analysis shows that compared with the same age of cement soil, more hydration and less pore content and more stable microstructure features generated by the solidified soil, which can explain the phenomenon from the mechanism.

Pre-cracked chevron notched Brazilian disc (P-CCNBD) is made by slightly cutting the notch tip of cracked chevron notched Brazilian disc (CCNBD) into a straight crack front. The P-CCNBD specimens of sandstone are diametrically impacted by the split Hopkinson pressure bar, the experimental recordings are then used in the succeeding numerical analysis to get the mode-I rock dynamic fracture toughness. In order to verify the reliability of the numerical simulation, the dynamic finite element analysis for a finite crack in an infinite plate subjected to impact tension at crack faces is simulated first; the results of the numerical simulation are highly consistent with those in the literature. The results of our experimental-numerical method are compared with those of quasi-static method proposed by others, certain difference is observed. On the other hand, results of P-CCNBD are in good agreement with those of the more mature specimen (cracked straight-through Brazilian disc—CSTBD), both are determined with the experimental-numerical method. The derived dynamic initiation fracture toughness increases with increasing loading rate, demonstrating the loading rate effect. The drawbacks of the quasi-static method to test the dynamic fracture toughness are analyzed. The result obtained by experimental-numerical method is more reasonable.

The experimental subgrade is used to model a high embankment in the Yunnan-Guizhou Railway, which has a bottom width of L=60 cm, top width of l=10 cm, and height of h=15 cm. The experiment models are used to study the effect of four ground stabilizing measures (called four groups) on responses of the high embankment under the action of a thrust fault ruptures. Group 1 is the case that no ground stabilizing measure is taken and is a basic test. The results from the other three groups are all compared with that from group 1. Group 2 is the case that a layer of geogrid is laid at the bottom of the embankment, Group 3 is that two layers of geogrids are laid at the middle and bottom of the embankment respectively, and Group 4 is that CFG pile is used to stabilize the ground and two layers of geogrids are laid at the bottom and middle of the embankment respectively. Several displacement gauges and dials are used to record embankment deformation. Deformation and failure modes by caused by different stabilization measures are analyzed. Results show that: (1) In the 4 models, embankment damage is mainly caused by the crack of 45° in embankment. (2) When fault displacement is equal to or less than 13.6% of the embankment height, the engineering measure with two layers of geogrids has the best efficiency for reducing damage; when the fault displacement is greater than 13.6% of the embankment height and less than or equal to 20.5% of the embankment height, the measure with both CFG piles and two layers of geogrids can achieve the best efficiency. (3) Due to part of energy absorbed by soil foundation, failure angle in the ground gradually reduces as engineering measure gradually strengthens, as a result embankment damage extent is reduced because the length affected increases. The conclusions in the paper have significance for engineering practice.

Under the condition of long-term cyclic saturation-air drying, long-term stability of reservoir bank slopes are affected by their dynamic characteristics change rules, and the hydro-fluctuation belt is the sensitive area. Thereafter, taking typical sandstone in the hydro-fluctuation belt of reservoir bank in Three Gorges reservoir area, a test scheme is designed with the consideration of coupling interaction of water pressure changes and saturation-air dry cyclic function, and uniaxial cyclic loading and unloading dynamic response tests of sandstone with different saturation-air dry cycle periods are carried out. The experimental results show that the hysteresis loop area of dynamic stress-strain curve and axial strain of the sandstone samples increase gradually when they experience the same times cyclic loading and unloading, and the dynamic elastic modulus of sandstone samples decrease gradually and damping coefficient, damping ratio increases gradually during the saturation-air dry cyclic process, which indicates that the saturation-air dry cyclic function has a cumulative damage of dynamic characteristics on the samples. Finally, degradation mechanisms of dynamic characteristics under the saturation-air dry cyclic function are discussed in detail based on the microscopic structure change of sandstones. Research results have an important reference for the long-term stability analysis of reservoir bank slopes considering the earthquake action.

Using cement-mortar as similar material, joint specimen with three joint wall strengths and five asperity angles are prepared. Then a series of cyclic shear tests are performed at four normal stresses on the cyclic shear test apparatus. Based on the test results and loading characteristics, the dilation angle and shear stiffness are defined. The normal deformation of joints under cyclic shear is characterized by dilation angle, and the tangential deformation is characterized by shear stiffness. Based on a variety of cyclic shear test results, the relationships between dilation angle and shear stiffness with shear cycles are analyzed. By comparing the results of different experimental conditions, the effects of initial asperity angles, joint wall strength and normal stress on the joint deformation properties are also analyzed. Research discovers that, the dilation angle and shear stiffness all appear a first quick back slow downward trend with the increase of cycle number. For the joint specimens with low and medium asperity angles, downward trend for dilation angle and shear stiffness shows an accelerating tendency with the increase of initial asperity angles and normal stress; but show a decelerating tendency with the increase of joint wall strengths. For the joint specimens with higher asperity angles, the downward trend for dilation angle and shear stiffness keep mainly unchanged.

Lithology and rock structure of a rock slope are two of the most important controlling factors on its deformation and failure process during earthquake. Four shaking table models of slopes are designed to explore the effects of the above two factors on slope seismic responses. Referring to lithology, hard rock with high strength and soft rock with low strength are modeled, at the same time, an isotropic slope and a horizontally layered slope are selected for each kind of lithology. Based on a large number of sensor recordings, results are analyzed under excitations of both the real waves and sine waves which have the similar predominant frequency. The main conclusions are drawn as follows: (1) The horizontal accelerations on the slope surface and inside the slope demonstrate topographic amplification effect for all the 4 model slopes; and the maximum amplification factor occuring at the crest of the soft rock slope model; (2) The topographic effects in soft rock slopes are stronger than those in hard rock slopes, which is more obvious in the two isotropic rock slopes, and the topographic effect in the isotropic and soft rock slope depict nonlinear change laws. (3) When the shaking direction accords with the horizontal structure surface just as in the present study, the layered slopes demonstrate stronger topographic amplification effect for horizontal accelerations, especially in soft rock slopes; (4) Lithology plays a more important role in topographic effect than discontinuity in a rock slope during earthquake. The results provide a reference for the seismic design of rock slopes.

A team of specimens containing two parallel three-dimensional(3D) cracks are made of a newly developed resin，which is completely transparent and has more brittle fracture properties of rock-like material(tension-compression ratio is 1/6.6) than before at room temperature. The propagation and coalescence process of the cracks under uniaxial loading is described and analyzed in detail; and then its produce condition and mechanism are studied. The testing results show that the failure process of specimens can be divided into four stages. The fracture of 3D cracks, which produces many different forms of cracks, is much more complex than that of 2D cracks. Subsequently, the specimen is chosen to carry out the numerical simulation. By employing FLAC3D, the propagation process of the 3D cracks are simulated and studied by establishing a new elasto-brittle constitutive relation and using superfine and reasonable form of unit division. The numerical simulation results match well with the testing results in this paper and that obtained by former scholars, so as to show the effectiveness of the new numerical simulation method. Moreover, the simulation results also have a good consistency with the testing results obtained by former scholars under biaxial loading.

In order to solve the problems of blasting to increase permeability in the coal seam, the methods of directional explosion with shaped charge are investigated. Jet of shaped charge penetrates the coal forming initial cracks and subsequently cracks are expanded by the wedge of explosive gas. The mechanisms of cracks of different directions are researched using numerical simulation and model tests. Through experiments on the work face of coal, it is proved that directional explosion with shaped achieve the aims of protecting roof and increasing cracks in demanding direction. The experiment results show that the change of gas drainage volume is most obvious in 3 hours after blasting; and maximum gas drainage volume is 470 times the original volume. The effective radius of gas drainage is within 7 meters; meanwhile the roof vibration amplitude is about 0.23 centimeters.

In order to explore the effect of physical properties, structural conditions and stress level on the permeability characteristics, consolidation-permeability tests are adopted to investigate the change of permeability coefficient during compression of Taihu swamp undisturbed silty clays and remolded samples experienced different preconsolidation pressures. The experimental results show that the permeability coefficient decreases nonlinearly with increasing consolidation pressure, and the relationship between void ratio and permeability coefficient of undisturbed specimen is almost identical to that of the remolded specimen, which is not influenced by the inter-particle cementation and stress history. For the same soil, the magnitude of permeability coefficient is mainly governed by the size of soil pore. Furthermore, according to the analysis results of the variation mode of permeability coefficient during compression tests in this work and related literatures, the linear lg(1+e)-lgkv permeability model is presented, and the empirical relationship of the permeability index is modified by considering the liquid limit. Using the modified expression, the calculation results of the permeability index agree well with the tested values. This study has important significance in accurately analyzing the nonlinear consolidation behavior of saturated clay foundation subjected to time-dependent loading.

In order to determine the failure criterion of suction anchors with taut mooring systems in soft clay, load-controlled and displacement-controlled model tests are conducted to study the bearing capacities of suction anchors with taut mooring systems under static load at the optimal loading point using an electric servo loading apparatus developed by the authors. The results show that the displacement along the mooring direction is about 0.6 times the diameter of anchor when the failure mode of anchor is vertical pullout; and the displacement along the mooring direction is about 0.3 times the diameter of anchor when the failure mode of anchor is lateral failure. At the same time, the bearing capacities of suction anchors are determined in terms of the failure criterion by model tests. The predicting results of limit analysis are basically in agreement with the results of model tests. Furthermore, it verifies the rationality of displacement failure criterion by the comparison of calculated results between finite element analysis and limit analysis on the full-scale anchors.

The technology of geosynthetic reinforced soils is applied more and more widely in recent geotechnical engineering practice. For further study of reinforced soil foundation, the authors carried out several plate load tests of geosynthetics reinforced sand soil foundation, the influences of different reinforcing materials (biaxial geogrid and quaxial geogrid) and the number of reinforcing layers on the bearing characteristics of geogrid reinforced sand soil foundation are monitored and analysed. The results show that: comparing with sand soil foundation without reinforcement, the bearing behavior of geogrid reinforced sand soil foundation are improved, and the effect of two-layer reinforcement is significantly better than one-layer reinforcement. Lateral deformation of the shallow foundation is confined by the geogrid reinforcement; and the settlements of geogrid-reinforced sand soil foundation decreased under the same load; and the recoverable rebound deformation increased. The monitored strain and tension of the reinforcing material during the loading progress are very small; and the tensile modulus of the reinforcements contributes greater to the bearing capacity of the geogrid-reinforced sand soil foundation than the strength of the reinforcements.

A series of model tests are conducted to study the optimal load attachment point for the suction caissons embedded in sands under inclined loading. The factors of load attachment point, loading angle and length to diameter ratio are considered. Based on the load-displacement curves obtained from model tests, the uplift bearing capacity of suction caisson foundations are determined by a suitable failure criterion. Then the optimal load attachment point is obtained by the analysis of the variation of uplift bearing capacity of suction caisson foundations. It is found that the loading angle has a significant role in the uplift beraring capacity of suction caisson foundations; and the maximum uplift bearing capacity will occur when the loading is in the horizontal direction. The effect of load attachment point on the uplift bearing capacity of suction caisson foundations depends on the magnitude of loading angle. The load attachment point has great effect on the uplift bearing capacity of suction caisson foundations when the loading angle is relatively small. The attachment point associated with the maximum uplift bearing capacity is located at approximately 2/3-3/4 of the suction caisson length from the top; otherwise, it can be neglected. Based on the relationship between load and rotation degree of suction caisson, the failure model of suction caisson foundation under horizontal loading acted on the optimal load attachment point is analyzed.

P-wave propagation tests of red sandstone, marble and granite samples were carried out under dry and water-saturated condition using nonmetal sonic wave testing system to study the velocity characteristics of P-wave propagation in different rocks. Rules of wave form, wave attenuation and wave spectrum were researched using Fourier and wavelet transforms. The experimental results indicate that: (1) The longitudinal wave velocities of red sandstone, marble and granite samples under water-saturated condition are slightly higher than those under dry condition. (2) P-wave velocity of rock samples are influenced by density, porosity and hardness. (3) With the same trigger signal, the energy concentrates on the low frequency band under water-saturated condition, and focuses on the high frequency band of the same samples under dry condition. (4) The energy of acoustic wave signals of the three kinds of samples under water-saturated condition attenuates rapidly, with plump coda wave. The energy of dry samples attenuates slowly, with shriveled coda wave. (5) The distribution of interior pores and microcracks and conditions of water contents in rock are reflected by the wave velocity and wave form of acoustic signal, which are presented in time, frequency and time-frequency domain.

The CT scanning technology based on the X-Ray, which can scan a rock specimen through multilayer continuously and nondestructively, has been introduced into the study of the rock mechanics and engineering widely. It is one of the important content of rock mechanics research, to monitor the failure processing of rock sample under uniaxial compression loading by CT technology. During the 3D microscope CT real-time monitoring of rock condition under uniaxial compression loading, there will be some error caused by the imprecise positioning of the CT scanner device. Aiming at this imperfection, a new CT slice image processing method based on image retrieval (IR) technology, is proposed. Coal and rock sample under uniaxial compression loading, is monitored during its failure process, and with the similarity computing method based on the Manhattan distance measure introduced, the rock sample’s CT image and its similar-slices of different stress stages are retrieved. The results show that: The IR technology may effectively reduce the error due to the displacement during the coal and rock failure process; with the help of CT slice image, microcrack distribution and evolution rule of the coal and rock samples in different stress stages, can be preferably described; moreover, at mesoscopic level, the basic law of coal and rock failure process under the uniaxial compression loading, get further revealed.

In order to reveal anti-frost heaving mechanism of soilbags under different freeze-thaw cycles in seasonally frozen regions, comparative model experiments on soilbags and soil are carried out under different freeze-thaw cycles, to investigate the frost heave relationship and the thawing settlement relationship between soilbags and soil, both in open and close systems. The results show that: Frost heave of soilbags is less than that of soil; thawing settlement of soilbags is also less than that of soil after experiencing 4 freeze-thaw cycles in closed system. Frost heave of soil is 1.9 times that of soilbags; thawing settlement of soil is 2.2 times that of soilbags in open system. Groundwater recharge for soilbags is far less than that for soil in open system. It is concluded that soilbags can efficiently prevent building foundation from frost heave collapse, and it can provide references to frost heave prevention of canal linings.

During testing low impedance materials such as clay by conventional split Hopkinson pressure bar (SHPB), the transmission strain pulse is always too weak to be collected correctly. In addition, the clay specimen will not deform homogeneously during the test, which makes it impossible to get valid data. To overcome these problems, the quartz transducer technique and the controlled loading pulse were introduced to test the unsaturated clay specimen with different moisture contents under different loading rates. Besides, the stress equilibrium in the specimen was monitored by quartz transducer mounted at the two end faces of the specimen. The results indicate that the compressive response of the unsaturated clay is sensitive to moisture content and strain rate, which the axial compressive strength decrease with the increase of moisture content, but increase with the increase of strain rate. Furthermore, the relationship of the axial compressive strength with the moisture content, and the normalized axial compressive strength with the strain rate are given respectively. The fitting curves are better consistent with the experimental data.

According to the geological and mining technical conditions of the seams No.8 and No.6 of closed coal seams group in Paner deep coal mine, the 2D similar material simulation model of seams No.8 and No.6 is designed by using relieving mining method from up to down to study high stress evolution. Based on mining-induced stress monitoring by using pressure sensor, disturbance stress and strata migration after seams No.8 and No.6 mined; and the impact of irregular pillar on stress evolution are systematically analyzed; then the high stress evolution characteristics in roof and floor of seam No.8 and strata movement, mining-induced stress, mining-induced fissure, weighing characteristic of seam No.6 are were obtained; and the development patterns of mining-induced stress and mining-induced fissure influenced by irregular pillar are obtained. Research results not only provide a theoretical basis for mining power disaster prevention with mining-induced abutment stress evolution as its leading factor, but also provide technical support for the design and optimization of parameters of longwall mining by using relieving mining method.

Cyclic wetting and drying usually occurs in rock mass during groundwater water level variation caused by rainfalls and season changing. In order to investigate the influence of cyclic wetting and drying on dynamic mechanical properties of rock, a series of uniaxial dynamic compression tests on sandstone under cyclic wetting and drying are carried out by ?50 mm variable cross-section split Hopkinson pressure bar (SHPB) apparatus. Sandstone specimens from Beifeng shaft -259 m of Hengyuan coalmine are processed into a cylindrical shape with a length to diameter ratio of 0.5. The corresponding dynamic stress-strain curves are obtained. It is found that as the Stefan effect of free water, wetting and drying 1 time gets a potentiation effect on sandstone; thus its dynamic uniaxial compressive strength is the highest. Then, with wetting and drying cycles increasing, dynamic uniaxial compressive strength reduces in a power relationship for physical weakening effect of water erosion; and the size of impact fragments becomes much smaller. The results show that when wetting and drying 12 times, dynamic uniaxial compressive strength of sandstone reduces about 24% compared with the result in wetting and drying 1 time, which shows a strong deterioration effect.

In order to study the influences of seepage pressure on joint stress-seepage coupling characteristics, changing trends of rock stress, displacement, joint hydraulic aperture and conductivity along with shear displacement are analyzed according to compression-shear seepage tests of six groups man-made joint specimens under constant normal load(CNL) and constant normal stiffness(CNS); and the influencing law of seepage pressure on stress-seepage coupling characteristics of joint rock is obtained. The results indicate that shear stress, displacement, hydraulic aperture and conductivity of joint specimen are related to seepage pressure obviously. The shear stress decreases along with the increase of seepage pressure. Normal deformation, hydraulic aperture and conductivity increase as the seepage pressure increases. During the compression shear seepage test, shear dilatancy effect appears in joint specimens under different seepage pressures. The research could provide scientific theory basis for surrounding rock stability when encountering water and control technology of seepage hazard of deep rock engineering.

The acoustic emission (AE) and microseismic (MS) rules in the process of deformation and failure of samples combined with roof, coal and floor are very important to reveal the dynamic mechanism of rockburst. The compound samples were tested by SANS material testing system under uniaxial compression condition. During the whole test process, the AE and MS events were monitored by DISP-24 AE system and TDS-6 MS collection system. The results showed that the larger the uniaxial compressive strength, rockburst tendency and the ratio of roof height to coal height of compound samples are, the stronger the intensity of AE and MS signal is. The amplitude of MS signal can reflect the rockburst tendency of compound samples. The spectrum distribution of MS signal in the high frequency band will increase along with the increasing compressive strength and impact energy index of samples. The above conclusions are of great significance to evaluate, monitor and warn rockburst in coal mines.

The translational failure along liner system at bottom and back slope often happened in municipal waste landfill. The composite failure through the body of waste filling and bottom slope is other failure mode. The relative calculation method of slope stability in landfill for composite failure mode must be modified based on the current stability analysis method. For composite failure, it is assumed that failure surface in waste filling is in Coulomb’s active situation and safety factor is identical at all points on the composite failure surface. On the limit equilibrium of rigid body, a new stability analysis method for composite failure is presented. The stability of a slope and Kettleman Hills’s landfill slope are calculated by the new method and two wedges method. The calculation results show that safety factor obtained by two wedges method for dangerous translational failure is higher than that by the above new method. The most dangerous slide failure surface is composite failure surface. For the Kettleman Hills’s landfill, the composite failure surface is possible sliding failure surface. It can be found that the composite failure is one of the possible failure modes. The composite failure mode must be considered for slope stability safety analysis of landfill.

Searching critical slip surface is very important in slope stability analysis. For the deficiencies of the existing methods, a new search method is put forward. On the basis of global analysis method of slope stability, a nonlinear optimum model for determining critical sliding surface is proposed for calculating safety factor. In this method, both the safety factor and vertical coordinates of discrete points on the slip surface are taken as independent variables, and the safety factor is taken as the objective function. In the model, the equilibrium equations and convexity of the slip surface act as constraint conditions. Because the objective function is linear, and the constraint functions are polynomials of at most quadratic, the model has weaker nonlinearity and so it can be solved easily by those conventional nonlinear optimization tools, such as Matlab. The following two example results show that the proposed method has advantages for numerical stability and convergence.

The risk factors causing karst collapse in Baiyun district are recognized. The hierarchical structure model for evaluating karst collapse risk is formulated. Weight values of basic risk factors resulting in karst collapse regarded as a risk event is calculated by analytical hierarchy process. Karst collapse gradation division is defined as the most likely subsidence area Ⅰ, the more likely subsidence area Ⅱ, the likely subsidence area Ⅲ, the lower likely subsidence area Ⅳ and the stable area Ⅴ. 5 grades of each element whose influential degree on karst collapse is considered, are defined in accordance with karst collapse gradation division. To quantify risk evaluation of karst collapse, the single factor collapse probability pi is introduced and the probability calculation model of karst collapse is established on the basis of Bernoulli trials. Eight basic risk factors including overburden thickness, karst development degree, groundwater depth, bedrock lithology, overburden structure and bottom plate soil properties, groundwater exploitation intensity, underground activity intensity, ground surface construction load and vibration are chosen as the parameters involving in calculation of subsidence probability. Then a narrowly-defined grade criterion of karst collapse is determined, providing a reference for subsidence gradation division. It is indicated that Jiangcun, Gulougang, Quanxi, Xihu and Shegang are attributed to the most likely subsidence area, the more likely and likely subsidence areas distribute mostly in Jianggao town and Yuanshijing town. The risk gradation division results are adaptable to regional subsidence history statistical data and hazard degree assessment of subsidence, so as to prove the effectiveness of the comprehensive evaluation method in this context.

Based on the Mohr-Coulomb strain softening model, applying the convergence confinement method to analyze the interaction of surrounding rock and support in high stressed soft rock, the characteristic curves of the typical support structure are constructed. Using the FLAC3D numerical simulation software to analyze the influencing factors of interaction of surrounding rock and support, such as strain softening model, dilatancy angle, different roadway types; and then the stability of support system is analyzed. The results show that: considering the strain softening behavior of the surrounding rock required support pressure are quite different with the calculation results of the conventional elastoplastic model; the dilatancy angle is less impact on the rock stress release process and the interaction of surrounding rock and support; the surrounding rock of roadway which required the support pressures are different in different sections and section points. The stability of the initial support system is the ultimate key to the stability of surrounding rock and support systems; using convergence confinement method to evaluate the stability of early support system of high stressed soft rock. The results have guiding significance for the supporting structural design and construction of high stressed soft rock roadway.

The weak interface of landfill liner system is easy to be instable. Based on the mechanism analysis of reinforced geomembrane and sand interface, and combined with the traditional two wedges analysis model, the bearing resistance effect on the stability of the landfill liner system is considered; and an analytic solution of the slope stability is also built. Associated with the preliminary design of practical projects, the stability of reinforced geomembrane liner system is studied. The effects of reinforcement shape, reinforcement height and reinforcement space on the slope stability are analyzed. Analysis results show that this analytic solution can better calculate the safety factor of reinforced geomembrane liner system. When the reinforcement space comes to 20 mm, the effect of reinforcement height on safety factor is bigger. When the reinforcement height reaches a certain value, the safety factor decreases with the increasing reinforcement space. But if the reinforcement space is larger than 200 mm, the shear properties of reinforced geomembrane are close to that of smooth geomembrane.

Study of the rock burst mechanism and its control technology in sublevel caving mining face under isolated top coal is done by applying overlying strata spatial structure academic viewpoint. According to the key stratum lithology、layer place、range and other factors, the key stratum spacial structures are divided into big structure of overlying strata and main roof structure leading to limited pressure. rockburst mechanism in island top coal stope is: ① formation process of ?-shaped spatial structure in sublevel caving mining face is the process of gradually increasing pressure, and that is the rockburst power source in this period; ②After the formation of the lowest ?-shaped spatial structure of the main roof, with the face advancing, the main roof block slides and which cause the rock burst phenomena. Through the study of the controlling effect on the key stratum spatial structure movement by segmented pressure theory, the instability of basic roof structure theory and hard roof prefracture theory, the ways and means of overlying strata spatial structure theory analyzing and reducing the rate of caving in different phases, hard overlying strata prefracture technology, microseismic monitoring technology overburden rock hard rock rupture of to prevent rock burst occurred are proposed.

Based on a large amount of microseismic informations and hundreds of rockbursts with different intensities occurring in the deep diversion tunnels of Jinping II hydropower station excavated with drill-and-blast method and tunnel boring machine (TBM), the energy release processes of immediate rockbursts with different excavation methods are compared; and energy distribution of microseismic events are analyzed by fractal theory. The achieved results are as follows: (1) Damage of rock mass are gathering and expanding in the processes of immediate rockbursts. (2) Elastic potential energy which stored within the rock mass has different ways of release with different excavation methods. (3) The energy fractal dimension values would increase continuously before the rockburst happens and they totally increase to a critical value when the rockburst approaches during drill-and-blast method excavation. (4) The energy fractal dimension values in TBM excavation which is bigger than that in drill-and-blast method can describe the mild and moderate rockbursts of the working face.

Based on triaxial rheological experiment, a nonlinear visco-elastoplastic rheological model is proposed which has creep threshold value, long-term strength, nonlinear viscoplastic body and other components. There are many problems in programming of this complex rheological model, for example, one-dimensional creep threshold value and long-term strength are difficult to express when extended to three-dimensional, and it was difficult to deal with nonlinear viscoplastic part. The yield approach index parameter is used as identification criterions of the creep equation piecewise function, the problems which the creep threshold value and long-term strength in three-dimension are difficult to express, are solved. The expression of viscoplastic part is derived detailedly; and three-dimensional central difference form is given, therefore, the secondary development of this rheological model for FLAC3D is achieved. A case study is given to verify correctness of program compiling. The rheological parameters are identified, the fitting curves are in good agreement with the experimental curves, so as to indicate that the model is correct and reasonable.

Rockburst is a kind of surrounding rock failure mode in deep underground engineering, and the occurrence conditions of rockburst are restricted. According to the statistical result of rockburst in Jinping II deep-buried tunnel, even if stress conditon and rockmass strength achieve a certain requirements, the intensity of rock burst is still closely related with rockmass mechanical characteristics. Marble is given priority to Jinping deep buried tunnel, so research works about the marble mechanical characteristic in relation to rockburst are carried out. According to the marble triaxial compression test result, the brittle-ductile-plastic transition characteristic of marbe is verified, and the transition confining pressure and the related Hoek-Brown strength parameters of Baishan group are determined. Adopting the experience method, the rock is evaluated burst risk preliminarily. In order to further study the influence of rockmass mechanics characteristics on rockburst risk, based on the actual rockburst failure pattern, the stress paths of different depths measuring point are investigated, and the mechanical parameters of rock mass are checked. The mechanical state of surrounding rock in rockburst risk is analyzed, and study the influences of rock strength, integrity and brittle characteristics on the occurrence conditions of rockburst are studied. The results show that the rock strength and brittle characteristics can affect the degree of rockburst, but its influence is relatively small, while the integrity of rock mass has the obvious effect on rockburst formation.

The slip surfaces paralleled to each other, which are assumed to be inclined at an angle ? to the horizontal is taken to be the analytical element. Based on the theory of main stress axes rotation, the theoretical formulae of the vertical stress considering the inclination of the slip surface and soil arching, the earth pressure coefficient considering the inclination of the slip surface and the angle between soil and slip surface are obtained by considering equilibrium of the horizontal and vertical forces acting on the analytical element. The results show that the theoretical formulae are rational by comparing the computed results using the proposed method with the results obtained by the existing methods. A parametric study is undertaken to investigate the effect of various parameters involved in the proposed analytical expression; the results obtained reveal that for cohesionless soil, the vertical stress increases with the depth linearly for shallow depth, then increases with the depth slowly until reach some depth; the vertical stress remains constant. The vertical stress increases with the increases of inclined angle and the stope width due to the weakened of soil arching effect, decreases with the increase of the friction angle between slip surface and soil. The earth pressure coefficient increases with the increase of the friction angle between slip surface and soil, but decreases with the increase of internal friction angle of soil.

Bed separation will cause anchor to generate additional stress, when the deformation of surrounding rock of roadway is uncoordinated. Based on the existing elastic analysis, an elastoplastic mechanical model of the bolt additional stress caused by the further expansion of the bed separation is established. According to the bolt pulling load to the bolt function mechanism during the relative movement of the strata, through the selection of two-stage linear function shear slide model, the sliding range in both left and right sides of the bed separation is determined; and the stress distribution mode of the anchored mass under the bed separation effect is obtained. Loading process of the anchored mass under the bed separation function is general divided into four stages, i.e. elastic stage, one side into elastoplastic stage, both left and right sides into elastoplastic stage and another side sliding larger with one side sliding all. By means of the parameters analysis of different separation values and different separation locations, the analysis finds that under the condition of the same bed separation location, the larger bed separation value, the larger the additional stress occurred from the bolt by the bed separation would be. Under the condition of the same bed separation value, elastoplastic stage basic trend and elastic stage trend are same, which presents as the stress at the center of the bolt would be minimum; the additional stress occurred close to the boundary bed separation would be larger.

A modified undrained elastic-plastic model considering the cyclic degradation of clay soil is proposed. Based on this model, a simplified analysis procedure based on shear displacement method is presented. Numerical simulations for axial bearing capacity of single pile are conducted by commercially available finite element software at different cyclic load levels. The results calculated by this simplified analysis have a good consistency and effectiveness with the results from finite element analysis. The axial bearing capacity of single pile will be degraded after resisting cyclic loading, and the degradation will be greater as the increase of cyclic loading levels. As an example, the axial bearing capacities of pile foundation of an offshore wind farm are studied with the application of the proposed simplified analysis method. The proposed simplified calculation method will serve as a useful tool for engineering design.

Countermeasure to solve unknown parameters for Gauss correlation function in Kriging interpolation accurately is presented by means of global optimization ability of genetic algorithm. A universal equivalent explicit formulation for state equation is established by Kriging interpolation to solve a problem that mechanical state equation for lining structure can’t be expressed through basic parameters explicitly because of a highly nonlinear relation between state quantity and basic parameters. A state equation for stretch resistance is taken as an example, construction procedure of mechanical state equation for one tunnel’s lining structure through the universal equivalent explicit formulation in connection with Latin sample way is presented. An analysis approach for stability reliability degree of tunnel’s lining structure based on optimization method for Kriging interpolation in collaboration with genetic algorithm (GA) is founded through calculation mode of reliability degree index established based on constraint condition for the state equation. Some practical examples are given to illustrate the application, which manifests that the relative error between the present approach and the accurate one is found to be 4.8%; and the computational burden of this approach is only 2.5% of that when employing the precise one. The present approach is excellent over existing analogous approaches on computational burden and accuracy.

In order to study the stability of embankment of the Qinghai-Tibet Railway after its operation, long-term monitoring system for the railway in permafrost regions was built in 2005. Monitoring content mainly includes ground temperature and deformation of the embankment. Ground temperature was monitored automatically with data collecting instrument; and deformation was obtained manually. Based on in-situ monitoring data of deformation and ground temperature from 34 embankment sections of Qinghai-Tibet Railway in permafrost regions during the year of 2005-2011, the characteristics and causes of deformation are analyzed. The results indicate that the accumulative deformation for a part of common embankments is more than 100 mm, respectively, which mainly comes from thaw settlement of permafrost with high-ice content and consolidation settlement of thawed soil because of the decline of permafrost table, as well as the compression deformation of warm permafrost due to rise of ground temperature under the embankment. For another part of common embankments and the crushed rocks embankments, owing to the compression deformation of permafrost under the embankment their total deformations are less than 100 mm, respectively. In general, the settlement deformation amount of crushed rocks embankments is remarkably less than that of common embankments, which confirms long-term effectiveness of the active cooling measure.

First, the micro-bond contact model considering hydrate cementation thickness of the deep-sea methane hydrate soil proposed by Jiang et al. was applied to describe micro-bond contact mechanical properties of hydrate between methane hydrate soil particles. Second, the model is introduced into the discrete element method (DEM) by using C++ language to program it. Third, based on the selected hydrate saturation, the corresponding hydrate cementation size is obtained through actual adjustable calculation of two dimensional DEM simulation to revise the values of hydrate critical bond thickness, minimum bond thickness and bond width, then micro-bond parameters are determined. Finally, based on the parameters of methane hydrate, many biaxial tests with different hydrate saturations are carried out to simulate the mechanical properties of deep-sea methane hydrate soils. In addition, comparisons are made between triaxial experimental observations done by Masui et al. and numerical simulation from aspects of stress-strain, volumetric, dilatancy angle of methane hydrate soils. The results show that the macromechanical properties of deep-sea methane hydrate soils are reflected qualitatively by using hydrate micro bond model considering bond thickness; peak shear strength, cohesive force and dilatancy angle of deep-sea energy soil increase with increasing content of hydrate; but the influence of hydrate saturation on internal friction angle is uncertain; peak shear strength, residual shear strength and volume shrinkage increase with increasing effective confining pressure while dilatancy angle decreases.

Based on the meso-scopic damage mechanics and the finite element method, a numerical code of rock fragmentation process analysis (RFPA) is used to simulate fragmentation process under three different loading conditions, i.e. single dynamic, combined dynamic and static loading, and the combined dynamic loading under the confining pressure. In the analysis model, the visco-elastic boundary is considered to eliminate the influence of the reflected stress waves from the boundary. Numerical simulation results show that the presence of static pressure has little effect on the value of the minimum principal stress within the rock mass, but significantly improve the level of the maximum principal stress; so the value of the shear stress is increased, as well as the possibility of the shear failure. While in the confining pressure condition, the tensile zone in the rock reduces and rock mass strength increases on the other hand. In according to the property of the rock which preformed strong in resist pressure but weak in the resist tensile, the capability of the rock increased within the certain range of the confining pressure. The cracks extend towards both side of the free surface and the failure in the rock becomes more complex under the influence of the confining pressure. The proportion of the pressure failure increases obviously while almost all the damage is tensile failure occurred in the single dynamic loading and combined dynamic and static loading model. The research results will be helpful for understanding the mechanism of rock failure under the dynamic-static loading and underground engineering construction.

Through the theoretical analysis and numerical calculation, cracking of surrounding rocks in deep tunnel induced by excavation unloading is studied. The cracking mechanisms and their characteristics of quasi-static and transient unloading under high in-situ stress are discussed respectively. For a case of deep circular tunnel the effect of this transient process on cracking of surrounding rocks is investigated by adopting an initiation model of crack under biaxial compression, and revised stress intensity factor is taken as cracking criterion. The analysis results show that the stress of unloading is a significant cause of surrounding rock cracking; the tensile stress zone exists under transient unloading; and the tensile stress plays an important role in the surrounding rock cracking under high in-situ stress; the less the duration of excavation unloading is, the larger the tensile zone and cracking range will be. The cracking depth and range increase with increasing lateral pressure coefficient; and the cracking region is approximately in V-shape. This study may be of great significance for further understanding the failure mechanism of surrounding rocks.

Based on the Biot's consolidation equation, transient response of single pile embedded in isotropic saturated soil under horizontal loading is investigated by applying Novak's thin layer method. The potential function is introduced to decouple the governing differential equation, then by means of differential operator splitting and variable separation method coupled with lateral vibration differential equation of pile foundation, the expression of the horizontal displacement and the internal force of the pile in Laplace space is obtained. The closed solution of displacement of the pile is calculated by using an optimal model of numerical inverse Laplace transforms. When the soil is reduced to the single medium, the good agreement is found in the comparison between the calculated data and that of previous made by boundary element method, so as to verify the correctness of the method. Parametric studies have been carried out; and it is found that the influences of pile-soil modulus ratio, pile slenderness ratio and permeability are significant, but the effect is limited when the slenderness exceed a certain value. Besides, pile-soil stiffness ratio pays a critical role in bending moment and its distribution.

To study the rock fragmentation properties by the shield disc cutters and how the disc cutter structure parameters (the blade width and the blade angle of the disc cutter) influence the rock fragmentation properties by the disc cutters, numerical simulation of the rock fragmentation by the disc cutter is developed. Based on discrete element method (DEM), a series of two-dimensional numerical modeling between the rock and the disc cutter are established. This study researches the relationship among penetration、the cutting force and the crack number in the process of the disc cutter intrusive the rock. And then the law between the disc cutters structure parameters and fracture characteristics of rock has been discovered by a simulation example. The results show that the extension of the crack in the rock is related to the forces of the disc cutter. The cutting forces in the rock-fragmentation increases at first and then decreases. The phenomenon above proves the rock's jump break property. It demonstrates that the additional stress in the rock is stress bubble which is downward. Meanwhile, the stress bubble disperses unlimitedly under the action of the disc cutter. Besides the stress bubble is symmetric. What’s more, in the blade working region, the additional stress reaches a maximum when it is close to the edge of the disc cutter. While the maximum additional stress decreases when the penetration of the disc cutter increases. When it is far away from the disc cutter edge, the additional stress in additional stress bubbles form decreases gradually in layers until the additional stress reaches 0 MPa.When the blade width of the disc cutter is chosen properly, which arranges from 10 mm to 15 mm it can not only avoid the thrust force being too large but also improve the efficiency of the disc cutter working in the rock fragmentation. The crack in the rock occurs under the blade of the disc cutter and the crack propagation is downward and it is axial mainly. When the angle of the blade is between 10° and 20°, it can not only reduce the wear of the disc cutter but also improve the efficiency of the disc cutter.

The plane-wave propagation can be generalized as a definite-solution problem of one-dimensional wave equation. In spite of the simple formality, solutions of one-dimensional wave equation in inhomogeneous media have to be solved with the aid of numerical methods. The classic three-level five-point finite difference scheme is a usual numerical method to calculate partial differential equations, which must meet the stable condition as an explicit iteration method. The stable condition is , where is wave velocity, is time sample interval, and is space sample interval. When or , the finite difference scheme is just up to the critical stable state. In such a case a space sample interval just equals wave propagation distance in a time sample interval , so the classic difference scheme exactly expresses plane-wave propagation theory and can be used to obtain exact solutions of one-dimensional wave equations. However, because of existence of wave impedance interfaces, the algorithm is unable to calculate wave fields in heterogeneous layer media. In order that the classic difference scheme in the critical stable state can be generalized to apply to heterogeneous layer media, an improved scheme is put forward, which can deal with impedance interfaces. Its stable condition is also given by Fourier transform analysis and the correctness is proved by some numerical model tests.

To investigate the influence of testing rock dynamic fracture toughness by dynamic load calculated using different methods, some holed-crack flattened Brazilian disc specimens（HCFBD）with diameter of 80 mm are impacted in SHPB system. The stress waveforms in the elastic compression bar are got, and the dynamic loads applied on the disc are calculated indirectly using three kinds of methods. When the different loads are inputted in ANSYS dynamic finite element mode, the dynamic stress intensity factors could be made, and the corresponding test values of dynamic rock fracture toughness are got on the base of experimental—numerical method. Results show that the average dynamic fracture toughness of marble is 3.92 MPa•m1/2, as the loading rate is about 4.0× 104 MPa•m1/2/s. Compared with the test value by “three wave method”, it is 11.22% less by “one waves method”; and 20.15% more by “two waves method”. So, the results are very different using three methods. The dynamic loads on both ends of disc specimen are not equal, because part of energy is released continually when the stress waves scatter through the surfaces and the prefabricated crack of the disc specimen in the whole transmission process. “Three waves method” is a relatively ideal one to determine the dynamic load on the disc specimen in three methods, but the dynamic stress balance should be surveyed.

Based on the theory of stress containment cage, the effects of stress containment cage of underground strong blast in granite are studied by numerical simulation. A numerically simulated example of strong explosion with yield of 100 t TNT demonstrated the phenomena of cavity rebound and the dynamic formation process of stress containment cage. The relationships between radial stress and hoop stress with distance from explosive point after the formation of stable stress containment cage are given. The relationships between the size of stress containment cage and the formation time with serial explosive yields are analyzed. Numerical results indicate that: cavity begins to rebound and the stress containment cage begins to form when the cavity radius expending to maximum; stable cavity and stable stress containment cage are formed when the progress of cavity rebound ended; the bigger of explosive yield is, the larger of the formed stress containment cage region is; stress containment cage could not form when the explosive yield is lower than 10 t TNT.