Rock burst which releasing large quantity energy, may damage the roadway severely and reduce the safety of the production of coal mine. Using similarity simulation experiment under explosive loading and the digital speckle correlation method(DSCM), the dynamic failure process of roadway under high velocity impact loading is simulated. The results show that the impact wave is mainly in roadway direction and the deformation of the roof is obvious. At the same time, the roof has a cutting rupture and a displacement between coal body and upper roadway. The roof has a tension-shear rupture, and also the crack extends to roadway gradually. Roof broken or partial collapsing area appeared under the repeat impact loads. Digital speckle pattern observations show that the sinking displacement of roof about 4mm under impact load. And then the impact wave spreads to two sides of the roadway. The rock drops along the surface after broken. It assumes that the blank white space appears on the speckle patterns.

In this paper, MTS 815 test system has been used to study the failure behavior of coal-rock combination bodies under different stress level cyclic loading-unloading. Experimental indicates that brittle failure is also the failure mechanism of coal-rock combination body under cyclic loading-unloading, but the failure under cyclic loading-unloading is more fragmentized than that under uniaxial loading. The failure strength under cyclic loading-unloading is higher than that under uniaxial loading; but the axial and circumferential strain in the contrast. The loading curves of coal-rock combination body are usually not coincidence with the unloading curves. In addition, they usually do not form a closed loop. In the first cycle, the residual deformation is large, and the loading-unloading curve forms a horn-shaped curve. The relationships of the residual deformations and the loading-unloading elastic modulus with the advancing of cyclic loading-unloading have been obtained in our tests, respectively. At the reverse position of unloading and loading, when unloading to about 1 MPa, the unloading line is fluctuant; however loading again, loading line is almost straight line in the early. In the all of cycles, some cycle loading lines are nearly coincidence with the unloading curves, some form sharp edges, or some forms cross lines. With the increasing of the loading, the loading curves separate gradually with the unloading curves. With the advancing of loading and unloading, strain phase gradually lags stress phase. The internal factors are the viscosity of rock minerals and the friction between the interface between coal and rock, and the external factors are the irreversible residual deformation under cyclic loading and unloading.

The interactions between two materials contacted are important for stability of engineering projects. Based on the actual stress state of two contacted materials, uni-body and bi-body models are employed to study the phenomenon. Through analyzing the test results, we conclude that uni-body model can be considered as bi-body model under certain conditions. In addition, the parameters which affect the two models are also analyzed. There are two important parameters that affect the mechanical performance of uni-body model, one is the strength ratio k between two materials; and other is the cohesion c of contact surface. Apart from the main parameter k, fracture toughness ratio ?, volume ratio ? and the surface roughness are influence factors for the mechanical behaviors of bi-body model

Based on the Biot theory, exact solution for one-dimensional transient response of single-layer fluid-saturated porous media loaded arbitrarily at its top surface is developed, where the inertial, viscous and mechanical couplings are taken into account and the solid particles and fluid are assumed to be incompressible. Firstly, the dimensionless governing equations in terms of displacement of solid skeleton are derived; and the boundary conditions are homogenized. Then, the eigen-value problem for the corresponding nonviscous system is solved to get an orthogonal function base in spatial domain. Applying variation coefficient method and making use of the orthogonality of the base functions, a series of decoupled second-order ordinary differential equations together with its corresponding initial conditions are obtained in time domain. To get the solutions for displacement components, the second-order ordinary differential equations are solved by the state-space method. By integrating the dynamic equilibrium equation of porous media and using the boundary condition, total stress and fluid pressure are determined in turn. Finally, two examples are given to demonstrate the correctness of the presented solution

The normal deformation behavior of rock mass with voids and concrete filled solution cave in karst area influences directly the internal stress and safety of cable pylon and anchorage. There were thirty static load tests on rock foundation of Lishui River large suspension bridge. The results of study show that the pressurized p-s curves of natural rock mass look like main concave type, linear type, convex type and sickle type, but the one of grouted rock mass looks like main sickle type, concave type. In the rebound stage, the deformation of rock mass with voids doesn?t decrease significantly until all pressure or countdown level 1-2 is discharged. Located below the compression curve with memory effect, all re-compression curves of rock mass with voids look like concave type. Located below the rebound curve, re-rebound curves run approximately parallel to the rebound curve. For the concrete filled in solution cave, the compression curve looks like sickle type, the re-compression curve looks like concave type, the re-rebound curve runs approximately parallel-horizontal to the rebound curve; residual rate of deformation of re-compression and re- rebound curve is smaller than one. Cement slurry can fill effectively big voids and caves; but can not flow into closed microcracks of rock mass. The proportional limit determining method in the current codes may not meet rock mass with voids. With pressure changing, deformation modulus of rock mass with voids changes. The conclusions may provide the basis for grouting evaluation, design optimization and construction monitoring.

Based on the unified strength theory and a non-associated linear flow rule, an elastoplastic unified solution for displacements around a deep circular tunnel is presented, which takes the true elastic strains in the plastic zone into account. The effects of intermediate principal stress and dilatancy are considered in the unified displacement solution; so the unified solution obtained has very broadly theoretical value. Compared with the simplified analytical solutions for displacement in the literature show that the influence of the elastic strains in the plastic zone on tunnel displacements is significant. The results of the simplified analytical solutions are less than those of the unified solution. The differences between the simplified analytical solutions and the unified solution are strongly related to the effects of intermediate principal stress and dilatancy. The strength potentials of rock mass are achieved due to considering the intermediate principal stress effect. The effect of dilatancy is important for the tunnel support design.

Based on the chemical thermodynamics and chemical kinetics, transition state theory, rock mechanics, a dissolution kinetic model of rock under stress is established; the effect of stress on solid activity and dissolution rate is analysed; the mechanism of water-rock interaction under stress is discussed. It reveals that: chemical potential difference induced by the stress difference between rock and surrounding fluid is the driving force of rock dissolution. Stress greatly enhances the rock solid activity, hence speeds up the mineral dissolution rate. There are two meso models of rock dissolution which are water film diffusion model and island-channel model, respectively. The differences between the two models are stress distribution in solid-fluid interface and preferential dissolution site. Water-rock interaction under stress raises a mechanical-chemical-hydraulic coupled problem. Stress motivates chemical reaction. Chemical reaction alters the rock surface configuration. Local stress distribution and magnitude change with the surface variation, which return to cause the change of chemical reaction region and process. Meanwhile, it also influences seepage path evolution

Although geotextile reinforcement has been widely used in geotechnical engineering, the reinforcement mechanism is still unclear. Centrifuge model tests are conducted on the geotextile-reinforced and unreinforced cohesive soil slopes under surface loading respectively. The displacement histories of the slopes are measured using an image-analysis system. The reinforcement effect is studied; and the reinforcement mechanism is investigated. The results show that the ultimate bearing capacity of slope could be significant increased by geotextile-reinforcement. Under the action of reinforcement, the deformation field is changed; the influence zone of surface loading is extended; and the slide surface is backwards moved. The local effect and its effective zone increase and extend with the increasing of the deformation of slope.

Experimental and numerical simulation researches on the strength property and failure mechanism of different inclined angles coal-rock combination bodies have been carried out. The macro-failure mechanism of coal-rock combination bodies has been obtained. And the effect of the interface between coal and rock has also been analyzed in detail. The uniaxial experimental results indicate that the failure strength of coal-rock combination bodies decreases slowly at first and then rapidly with the increasing of combination inclined angle. For the same inclined angle for coal-rock combination bodies, the whole failure strength increases with the increasing of the confining pressure. In addition, the smaller the combination inclined angle, the smaller the increasing rate of the failure strength; the bigger the combination inclined angle, the bigger the increasing rate of the failure strength. Therefore, the effect of the confining pressure on the large inclined angle of the coal-rock combination body is obvious. The cohesion and internal friction angle of coal-rock combination bodies have also been obtained through the triaxial experiments. The cohesion of combination bodies decreases with the increasing of the inclined angle. However, there are no clearly relationship between the internal friction angle and the inclined angle. The extended finite element method (XFEM) has been applied to simulate the failure of different inclined angles combination bodies. The simulation results from inclined angle 0° to 60°, of which the interval 5° indicate that external force work, yield stress and elastic strain energy decease with the increasing of the inclined angles. However, when the inclined angles are more than 45-50°, the external force work and the yield stress will change inversely with the elastic strain energy. This is an important symbol of failure mechanism changing from shear failure to slip failure mechanism for the coal-rock combined bodies

In order to investigate the progressive failure process of brittle rock, the mechanical properties of red sandstone from south area of Shandong province are studied by the RMT-150C rock mechanical experimental system. The stress-strain curves of samples under different strain rates are recorded. The deformation and progressive failure process of rock samples is divided into several stages, including crack closure stage, linear elastic deformation stage, crack initiation and stable crack growth stage and unstable crack growth stage. Then the crack initial stresses and crack damage stresses are determined by the moving point technique according to the data of stress-strain curves and other deduced data. The influence of strain rate on the ultimate critical strength, the crack initial stress and the crack damage stress are also investigated. The results show that the ultimate critical strength first decreases and then increases as the strain rate increases; and the rate of crack initial stress and crack damage with the ultimate critical strength decreases. The mechanism of the experimental results are analyzed and explained by the stress concentration model of rock with nonuniformities. And the influence of strain rate on the progressive failure process is studied.

Unloading is the same with that of redistribution of surrounding rock’s stress when excavating; and the unloading velocity affects stress field, so the problem of unloading is a dynamic one essentially. Assumed the unloading ruled by a simple function characteristic of the time parameter and based on the elastic mechanics and the Hamilton principle, the regulation of the stress field nearby the tunnel is obtained. The stress fields around the carvity in different depths are generalized. Especially when the in-site stress is larger than the rock strength，the characteristics of the failure nearby the tunnel are analyzed considering the shear failure and tensile failure. The results show that the main mode of the shear failure, intact and tensile failure occurs from the tunnel. In other words, the characteristics of the shear failure, intact and tensile failure is one of the likely failure modes. The situation is concerned with the unloading time

Testing study is made on the strength, deformation and fatigue damage process of salt rock under uniaxial compression condition by the rock mechanics test equipment RMT-150C. The results indicate that when the maximum of cyclic load is above “threshold value”, the fatigue axial deformation can be divided into three stages: initial deformation, constant velocity deformation and accelerating deformation. Changing the maximum and average cyclic load, can affect the process of fatigue failure obviously; the initial axial deformation and cyclic axial deformation ratio will be increased; the total cyclic numbers reduced, while increasing the maximum of cyclic load and average cyclic load. Testing results show that the fatigue failure curve of salt rock is also controlled by complete stress-strain curve under static loading; the error is controlled under 10 percent. The deformation module of salt rock also can be divided into three stages: first, deformation modulus increasing; second, deformation modulus is in slightly decreasing trend; third, deformation modulus decreasing sharply. The damage development and deformation law of salt rock under cyclic loading are analyzed

The sandy slate samples are taken from the Xuefeng mountain tunnel rock. To study the effect of micro-bedding on strength properties and deformation characteristics of samples, a series of uniaxial and triaxial compressed tests are carried out with MTS815 Flex GT rock mechanics test system. The experiment results show that mechanical properties of the rock is obvious anisotropy. The stress-strain curves display unstable broken feature when the bedding parallels to axial stress (angle 0°) and failure faces development along the bedding. Softening rapidly happened after peak when the bedding is perpendicular to axial stress(angle 90°) and failure faces belongs to shear failure. The numerical results of uniaxial test show that compression strength, elastic modulus and deformation modulus of angle 0° is 20%, 50% and 80% higher separately than them of angle 90°. The results of triaxial test show the principal stress difference of them is close in the peak intensity; elastic modulus and deformation modulus of angle 0° is 6% and 20% higher than them of angle 90°. Confining pressure of triaxial tests has weakening effects on anisotropic features of the sandy slate. These conclusions reveal the sandy slate possesses anisotropic mechanical properties and offers important reference to solve practical engineering problems

Giving a discussion on the mechanism of high rock velocity in rockburst, the rock velocity is estimated from the perspective of flexible loading and rigid loading; then the mechanism of it is explained from the point of the buckling of transverse constrained plate, the constraining condition of plate is also discussed, the energy of destroyed rock is analyzed. The result shows that the velocity of rock may reach 10 m/s and the tensile strength of rock also influences the velocity.

Under the freezing-thawing cycles, three types of rocks (clastic-rock, mudstone, and sandstone) chosen from the protecting-slope and berm of the Qinghai-Tibet Railway were studied. Their failure processes and weight were observed. The results show that the severe longitudinal and circumferential cracks appeared on the outside of the clastic-rock specimen; and that the debris shedding caused the weight changes less than 1% during the period of 30 freezing-thawing cycles. In the crack growth process of mudstone specimen, a horizontal, circumferential crack initialized almost parallel to the bottom of the cylinder; the growth of the crack tip then tilted gradually toward the bottom to a degree such that the direction of the crack was almost perpendicular to the axel of the cylinder. Such tilt did not appear in the sandstone specimen, in which only a short-slim circumferential crack grew outside. However, both rocks had no reduction in weight because no debris was shed. Their ultrasonic velocity testing was made by the digital acoustic-waves-monitor (RSM-SY5). According to the changes of the ultrasonic velocity at different freezing-thawing cycles, elastic modulus, rigidity modulus, bulk modulus, and Poisson's ratio of the three types of rocks were calculated and analyzed. The results show that the ultrasonic velocity, three moluli and Poisson's ratios all decrease with the increase of the freezing-thawing cycles, especially the Poisson's ratios begin to be negative values after the tenth freezing-thawing cycle, disclosing the severe failures inside of the rocks. At last, by the uniaxial compression tests of the three types of rocks subjected to different cycles of freezing and thawing, of which the compressive strengths gradually decrease with the increase of the freezing and thawing cycles.

Based on the physical model experiment and the design data of Xiaoda?e tailings impoundment, the course of tailings dam gravitational collapse in flood was modeled with the field tailings. The water system is controlled to model the tailings impoundment to suffer the flood situation, through the technique of side displacement points, water level measurement pipes, stress transducers and digital photography measurement, a series of important test data are obtained; such as displacements, saturation line, stresses and the broken processes, The mechanism and mode of tailings dam failure in flood are explored. The results indicate that: (1) the character of saturation line change has a time lag of the water level of tailings impoundment; (2) in the processes of the flood into tailings impoundment to the maximum water level of tailings impoundment design data in flood, the horizontal stress increment is larger than that of vertical beside dam slope center, and it is one of the important cause of dam failure; (3) the seepage force, buoyant force, gravity and pore pressure are increased by flood; then the cohesion of tailings dam is weakened and the load of dam is augment; then the stability of tailings dam is reduced; (4) the broken mode of tailings dam performs progressive failure; the failure of tailings dam happened in the toe of the dam and evolved from toe to upstream; it is shown pull-typed behavior, the failure slippage faces are composed of multi-arc faces. The model experiment results can provide significant data for deep study the mechanism of collapse and broken mode of such tailings dam in flood, so as to provide useful information for the prevention and control measures in flood disaster.

The P-wave velocities of rock with axial pre-compression cannot be measured during cyclic impacts on coupled static and dynamic test equipment, and the characteristics of rock damage evolution in the process of cyclic impacts are not able to be studied with variation of wave velocities. A method for defining damage variable of rock based on its wave impedance is proposed. Firstly, the good positive correlation between density and P-wave velocity of jointed rock was verified; and it was obtained that the variation range of wave impedance is similar with that of wave velocity on the same damage process; the damage variable of rock can be defined both density and wave velocity by theoretical calculation and analysis; so it was concluded that wave impedance can be used for defining damage variable of rock, and the expression for defining damage variable is given. Then, a formula to express wave impedance from incident wave and reflected wave or transmitted wave is derived. The elastic wave may reflect and transmit time after time on the input bar/specimen and specimen/output bar interfaces when a test is conducted with split Hopkinson pressure bar (SHPB). According to one-dimensional theory, a method for calculating wave impedance of rock is determined from test data on the cyclic test. Finally, a cyclic impact experiment on rock without precompression stress is performed; and the P-wave velocity is measured after impacting every time; the damage variables defined by wave velocity and wave impedance was found to have the same trend approximately. Compared with the variable of acoustic wave velocity, density variation is very smaller, so there is a difference between two damage variable defined by wave velocity and wave impedance. The results show that the damage variable of rock can be defined by wave impedance when rock is subjected to cyclic impact loading with same incident energy.

The surface crack growth and dispersion in layered salt rock under uniaxial compression are studied by fluorescence and mesomechanical techniques; the differences of physico-mechanical properties of salt rock at home and abroad are briefly analyzed. The experimental results show: for pure salt rock, the surface cracks are mainly sliding cracks between salt grains. Destructive macro cracks are shapes with expand and joint coalescence of cracks between salt grains which impacted by size and uniformity of distribution of salt grains, strength and deformation of salt rock grains abroad are greater than domestic salt rock. For pure intercalation salt rock, the surface crack grown at the mixture of several mineral deposits, and which distribution effected by interlayer mineral composition and structure. For laminated salt rock, the surface crack distribution is effected by form of interfacial transition between interlayer interface and salt rocks. Generally, the serrated cracks mainly form by the main crack expansion to interlayer; the cracks with transition clearly and containing a thin layer of mud form by main crack and mud layers loose cracks assemble and expanding

The unsaturated soils upon wetting may swell or collapse depending the soil types or soil’s void ratio. The particle structure of the unsaturated soil is considered to be in sub-stable and super stable states depending on its void ratio. Both the meta-stable and super stable states are maintained by the suction. The sub-stable and super stable structure becomes unstable upon wetting because of the suction reduction. There may exist a stable state that neither swelling nor collapsing will happen upon wetting. Employing the concept of stable state void ratio, a general formula is obtained which can describe both the swelling and collapsing behavior of the unsaturated soil.

Research interest in the temperature effect on the permeability of unsaturated soils is growing as a result of an increasing number of geomechanical problems involving thermal effects, such as high-level nuclear waste disposal, buried heat-supply pipelines and high-voltage cables. Based on the research of temperature effects on soil-water characteristic curve (SWCC) of unsaturated soils, an indirect method for predicting permeability coefficients of unsaturated soils at different temperatures is presented. by using the method of relative permeability coefficients from the SWCCs. The new expressions are made for the entire suction range of SWCC; and hence it has a broader applicability. Based on the experiments of MX-80 bentonite and loess, model predictions of relative permeability coefficient at different temperatures with suctions are made, which show satisfactory results.

In order to investigate the interaction problems between the underground structure and the rich water porous rock, a kind of material similar to the porous medium solid-liquid coupling material was developed according to similarity theory of modeling simulation. The material was mixed and pressed from coarse sand, cement, pervious concrete intensifier and water by certain ratio. Proportioning experiments were carried out based on the orthogonal experiment design principle. Then small model samples were produced to obtain parameters such as the uniaxial compressive strength, the permeability coefficient, the bulk density and the elastic modulus and Poisson's ratio. The effects of different ingredients were studied; so the proportions of ingredient were varied for the different needs in physical simulations. The mechanical behaviours of these materials are stable, and not only meet the requirements of large models, but also suitable for large physical experiment on structure and wall rock destruction. Therefore, the simulation experiment material is feasible for risk assessment of underground structure in rich water conditions

In the elastic mechanics, the general form of mapping function, which represents the area external to a given underground cavern by the area outside the unit circle in another plane, is Laurent series, hence to resolve the coefficients of Laurent series is one of the key points to make analytical solution to underground cavern. A new method for calculating mapping function is put forward by means of searching mapped points on the boundary of underground cavern. While employing this method, one set of mapping relation should be initialized, by which the initial mapping function is obtained; thus corresponding mapped points and mapped shape of the given cavern are achieved. According to the distances of adjacent mapped points in the mapped boundary, the relevant realistic point coordinates in the real boundary are obtained in terms of the principle of equal rate of distance. Then, based on this improved mapping relation, the first iterative mapping function is calculated. In light of this algorithm, the final mapping function, whose accuracy is in the controlling range, can be achieved. Applying this method, the number of series and iteration can be easily controlled; and the accuracy of the mapping function can also be flexibly dominated. The mapping function of single underground cavern with arbitrary shape can be rapidly calculated. Especially with regard to these common engineering caverns with complicated shape, quite accurate mapping function can be obtained by this method

An approach for evaluating the seismic permanent displacement of 3D slope is presented, which extends the famous Newmark’s method to three dimensions. For a certain potential sliding mass, its yield acceleration and average seismic acceleration-time history are obtained from the 3D limit equilibrium theory and numerical analysis, relatively. Then, the seismic permanent displacement is estimated by integrating twice with respect to time over the parts of an average acceleration-time history that exceed the yield acceleration. A case study indicates that the presented method is reasonable. However, by using the traditional 2D method, the yield acceleration and peak of average acceleration are lower and seismic permanent displacement is higher; and the error decreases gradually with the increase of the length of sliding mass.

It was found that in shallow depth in magma and metamorphic rocks, the value of lateral coefficient is higher relative to sedimentary rocks. Taking the granitic rocks for examples, which is widely exposed in ground surface and regarded as originally intruded to form a dome at larger depth, this paper presents the computation result of denudation thickness. The method is started from two kinds of suppositions for representation of dominant stress in 3D in large depth before obvious denudation. One is hydrostatic head, another is Hooke’s law and then the horizontal strain is zero during denudation process. The lateral coefficient formula is used to infer the denudation thickness, which is commonly larger for both of the two suppositions. Statistic results of in-situ stress data of 254 groups in granitic rocks are of a new fitting formula to the average counterparts. From the 2nd supposition, it is inferred the denudation thickness, which is seemed to closed to the updated high limitary values of denudation thickness whether from geological judgment or fission-track data of apatite. To check the feasibility of this method, two case histories are presented. The denudation thickness as Daya Bay is between 1 500 m and 3 000 m, closed to 1300m from geological judgment. The denudation thickness at the shiplock of the Three Gorges Project is 1 700-3 200 m, similar to that test result of fission track analysis. The results further prove that the denudation thickness is relatively larger than most of the buried depth of underground rock engineering.

Based on the collection and review of the domestic and foreign literatures related to rock slopes, the situations and future development of slope stability analysis and monitoring are summarized in the aspect of methods for rock slope analysis, monitoring and forecast approaches. And especially, the characteristics of open-pit slope are analyzed in detail. The questions existing in the studies of open-pit slope stability are also pointed out. Further, a thought that the progressive damage evolution namely acoustic emission is the nature of rock slope instability is proposed; and the future development of studies of rock stability as well as forecasting methods are given. Firstly, the model which can calculate damage of rock slope from back analysis of the basis of microseismic monitoring data should be built; and the characterization methods of strength parameters of rock mass and evaluation methods of dynamic stability in open-pit slope engineering should be developed. These can give objective evidence to the strength reduction method for rock slope and provide mechanical basis for microseismic monitoring. Secondly, the relationship between microseismic activity, degradation of rock mass strength and slope dynamic instability will be investigated. Finally, precursory information of microseism and safety factor of slope are selected to form combined unstable criterion; and the prediction of rock slope instability and dynamic analysis of open-pit slope stability can be realized

According to the viewpoint that the kind of brittle spalling of wall rock is the embodiment of in-situ rock stress, a new evaluation method of general geostress is put forward based on spalling features of wall rock. Firstly, the spatial relationship of three principal stresses is gained through the analysis of spalling features of wall rock from the aspect of spatial distribution and intensity relation. Then, the direction of maximum principal stress is counted according to the trend of spalling’s split veins. The values of three principal stresses are calculated also based on the stress threshold values of spalling and threshold values of crack initiation. The in-situ stress evaluation of right powerhouse region in Baihetan hydropower station is validated by the local measured in-situ rock stress results and contrastively numerical analysis of different directions of maximum principal stress, which prove that the method is reasonable and useful for understanding the break of wall rock and checking the measured in-situ rock stress results.

The paper does some researches on stress field distribution characteristics of the valley in high geostress areas by using numerical simulation and in-situ stress measured data. The result shows that: for the maximum principal stress , the homogeneous elastic slope without unloading zone could be classified into two zones as the stress-releasing zone ( ) and the stress-stable zone ( ) from the slope surface to the inside, where h stands for the original buried depth of the studied point, while there are three zones classified for the homogeneous elastic slope with unloading zone as the stress-releasing zone ( ), the stress-concentrating zone ( ) and the stress-stable zone ( ). The existence of unloading zones is the essential reason for the maximum principal stress existing three zones from the surface to the inside. Due to the existence of the tectonic stress field, the slopes in high geostress areas enhance the stress concentration significantly, extend the concentrating scope obviously and present wide unloading zones generally. Therefore, the stress field of the high and steep slope in high geostress area could be approximately classified into three zones: the stress-releasing zone, the stress-concentrating zone and the stress-stable zone. While the stress concentrating zone of the slopes which possess deep unloading transfers into the inside. The stress of the stress-releasing zone fluctuates and the stress decreases in the zone possessing the deep cracks

Based on the features of Chinese salt rock bed, the comprehensive evaluation system of the stability of rock salt gas storage with multilevel and multi-index has been set up; and the assessment class level of the stability of rock salt gas storage during the operation period also has been defined. According to the test data and the result of numerical simulating, the scoring models of evaluation indices are built and the value of the corresponding evaluation indices for every assessment class is got. The weight of the describing layer and the index layer has been obtained by analytic hierarchy process. Both the extension evaluation and the fuzzy comprehensive evaluation have been used to evaluate the stability of Jintan Xi-1 salt rock gas storage of the West-to-East Natural Gas Transmission Project. And the results of the two above methods are consistent, just like the real situation, which show that it is of great worth to set up the comprehensive evaluation system of the stability of rock salt gas storage with multilevel and multi-index

The tightness analysis of salt cavern as energy storages is very important to underground energy storage construction project. In the salt mine of China, the salt layers are usually intersected by many indissoluble or slightly soluble interlayers. Considering these sedimentary characteristics, a series of experiments concerning the tightness of the salt storages are carried out in Qianjiang mine of Jianghan Oilfield. In-situ tightness tests taking nitrogen as media were carried out at different key points of the testing wells; the capillary pressure tests of the overlay and interlayers were done to analyse the tightness of the carvens. Also the distribution of pore structure characteristics of the interface and interlayer were observed by the scanning electron microscopy (SEM); it is found that the salt rock has characteristics of big size of crystal particles, compact surface and good sealability; and small particles of mudstone can fill the gap very well at the interface; and the two types of rock are cemented completely. The results illustrate that entire tightness of salt rock in Qianjiang mine is very suitable for the construction of underground energy storage. The indoor and in-situ experiments have great reference value and practical significance for the research of underground energy storage construction project.

As salt rock is a typical rheological material, creep property has a significant influence on stability of the underground storage, and the reliability has strong time-variant property. Although much work had been done on the mechanical property and deformation characteristic of salt rock, utilizing stochastic mechanical theory in time-variant reliability risk analysis of salt rock storage was scarcely published all over the world. The reliability function is established to calculate the time-variant reliability and analyze the risk of an underground salt rock gas storage in China. Taking volumetric shrinkage as a risk controlling criterion, and adopting response surface and Monte Carlo methods, creep stochastic mechanical calculations under different intrinsic pressures have been done on the storage during service period; laws of reliability index with time and risk level are obtained; and the equation between volumetric shrinkage limitation within reliability requirements and intrinsic pressure of the storage is fitted. Major random parameters sensitivity to reliability index are further discussed. Some useful conclusions are finally obtained, which could provide scientific basis for the storage safety operation and maintenance

Preferred structural plane combinations are determined by using stereographic projection principle in the engineering geology to statistically analyze the strike-dip of structural surfaces. And to the uncertain position surfaces, they are searched by a certain distance. Then, the kinematic analysis of every combination block is done by kinematic analysis method; and the blocks that can slide out from slope body are finally gained. Combined with three-dimensional rigid limit equilibrium method, the stability factor of each block in different cases is calculated; and the most dangerous slip body is found. Furthermore, the stability evaluation is done. This method is verified by case study. The results show that this method of analyzing complex rock slope combined engineering geology with kinematic analysis and rigid limit equilibrium method can improve the accuracy of slope stability assessment. The results provide a good guidance for slope design and stability analysis

A new calculation method has been established in order to obtain the clip rock of small-distance tunnels blasting cumulative damage rule. The new method is applied to predict Dapingshan tunnel clip rock blasting cumulative damage during construction; at the same time a field test validation is carried out. The results show that: the new method can not only reflect the blasting of mechanical action process, and the calculated parameters are also easy to obtain; the prediction and measured average error is about 12%, which can be used to predict rock cumulative damage; Dapingshan tunnel clip rock cumulative damage rule is as follows: after the second blasting, 6 test holes velocity average drop rate is 4.3%; the largest test holes cumulated damage in increments is 6.1%. The results provide a basis for further small-distance tunnels clip rock stability studies.

Slope stability research under the situation of water level rapid drawdown is much popular for reservoir dike slope; but it is less considered as a working condition in the stability analysis of the Yellow River lower reaches? dikes. We select a typical section of the lower reaches? standardized dike as research object, and build a finite element model of saturated-unsaturated seepage. The criteria of rapid drawdown rate for the lower reaches? dike is put forward; and the changes of saturation lines and slope stability with water level rapid drawdown rate 2 m/d, 4 m/d and 5 m/d are analyzed. Meanwhile, the stability situation of the dike slope under the worst working condition, water level rapid drawdown, is analyzed as well. The slope stability diagram under different situations, such as water level rapid drawdown and rapid drawdown combining flood immersing, is presented, and from which the slope stability situation could be checked when at a certain water falling rate and to a certain water level. This method is much convenient in actual application for engineer

Culvert belong to buried construction, of which the stressing state is different from the buildings. With poor understanding on the mechanisms of the soil-culvert system and improper ground treatment of culvert, many geotechnical and pavement problems occurred for culverts during the construction process or under service conditions. In this study, field test and numerical simulation are conducted to investigate the mechanisms of soil-culvert system, the stressing state and deformation characteristics of which are obtained. Moreover, the ground treatment of culvert is also studied based on the fore-researches. Especially, the influence of ground treatment area and the ground stiffness of treatment area on the stressing state and deformation characteristics of soil-culvert system are analyzed by numerical simulation. This research reveals that vertical earth pressure is obviously concentrated on the crown of culvert; the influencing area is about 3b (b is the width of culvert) on the both sides of the culvert axes. The coefficient of earth pressure on the culvert crown increases with the height of fill, but it’s likely to approach a limit value at a higher fill. The vertical earth pressure on the culvert crown, the foundation pressure of culvert, as well as the internal forces of culvert decrease with increasing the ground treatment width and gradually tend to limit values; but they are nonlinearly increase with increasing the ground treatment depth and the ground stiffness of treatment area. It is suggestion that, in practical engineering, the ground treatment width should be about b+2h (h is height of culvert); the ground treatment depth and the ground stiffness of treatment area should be controlled by allowable settlement and/or differential settlement, but the ground treatment depth and the ground stiffness should not be increased extraneously.

Deformation modulus of rock mass is an important parameter applying to the design of rock engineering; although it can be obtained from various in-situ tests, it is expensive and time-consuming so that many middle-small scale projects and preliminary design phase of large scale projects can’t get this parameter through this method. For this case, many researchers have developed a lot of dependency relations between deformation modulus of rock mass and physico-mechanical parameters or rock mass classification such as RQD, RMR, Q system and longitudinal wave velocity of rock mass, etc. This paper firstly summarizes the existed methods of pre-estimating the deformation modulus and discusses its working conditions and estimated value. Paying attention to the method using longitudinal wave velocity to estimate deformation modulus and taking Maerdang dam project for example, the paper develops a prediction formula. By comparing to the estimated values by various methods, it is shown that the formula developed has a good concordance with Barton’s equation and can be used to pre-estimate deformation modulus of rock mass

In order to probe into the effects of the changes of fracture aperture casued by combined action of normal stress and shear stress on coupled temperature field, seepage field and stress field, introducing the “cubic law” describing the relationship between hydraulic conductivity and fracture aperture, the evolution expressions for hydraulic conductivity of fracture are established, using the 2D FEM code for analysis of thermo-hydro-mechanical coupling in dual-porosity medium for ubiquitous-joint rock mass developed by the author and taking a hypothetical nuclear waste repository located in an unsaturated stratum as a calculation example, the numerical simulations are carried out for six cases in which three kinds of updated pattern of fracture aperture are applied under the conditions in which two sets of joint cross obliquely and perpendicularily respectively, and the distributions and changes of temperatures, pore and fracture pressures, fracture apertures, hydraulic conductivities, flow velocities of groundwater, and stresses in the surrounding rock mass are investigated. The results show that if the fracture aperture depends on only normal stress the closure of fracture aperture is the largest acted by a compressive stress; while the fracture pressure is the highest; if the fracture aperture is a function of normal stress and shearing displacement, the closure of fracture aperture is smaller than the former due to shear dilation effect, so the fracture pressure is a moderate value; but if the fracture aperture is a constant, the fracture pressure is the lowest.

Initial geostress field is very important for engineering design and stability analysis of underground engineering. The back analysis method is often adopted to get the whole geostress field of engineering zone based on the limited measured data. Based on the measured geostress data, geographic and geomorphic conditions and characteristics of geologic framework, the distributing characters of geostress field in underground powerhouse zone of Dagangshan hydropower station are studied. Furthermore, the multiple regression method is applied to back analyze the three dimensional geostress field of underground caverns of Dagangshan hydropower station; and the distributing rule and influence factor of geostress are also discussed. The results show that: the geostress field in underground powerhouse zone of Dagangshan hydropower station is affected by tectonic stress, geologic structure, terrain and physiognomy; among them, lithology has little influence; dyke and fault have great influence; the value of geostress is medium and there is , where is maximum horizontal principal stress; is minimum horizontal principal stress; is vertical stress; the lateral pressure coefficient vertical to powerhouse axis is 0.5～0.6, along powerhouse axis is 1.1～1.3

Blasting excavation disturbance is an important influence factor to the inoculation and evolution of deep tunnel damaged zone. According to the drilling and blasting excavation process of the tunnel, the disturbance effects induced by blast load and transient unloading of excavation load are analyzed; and based on the LS-DYNA dynamic finite element program, the numerical simulation method of blasting excavation disturbance is proposed that using nodes reaction to simulate the constraint of the awaiting excavation tunnel rock, controlling the change process of nodes reaction to simulate transient unloading of excavation load, and using blasting loading change curve to simulate the effect of explosion. After that, the blasting excavation induced damage of tunnel rock mass is analyzed by the method. The results show that the surrounding rock damage zone is mainly caused by the in-situ stress redistribution and increased by blasting load; the surrounding rock damage zone is maximum when the transient unloading of excavation load is taken into account; and in-situ stress is higher, the damage caused by transient unloading of excavation load is more remarkable

In order to study the elastic properties of rock mass using the finite element method (FEM) approach, a reasonable rock mass meshing method is proposed, especially the way in dealing with fracture intersections and end regions; and a Fortran program is developed to generate mesh of rock mass automatically. Based on field investigation results of fracture distribution in Jinping hydropower station, a random fracture network is generated by Monte Carlo method; and the mesh of the generated fractured rock mass is created automatically by the Fortran program. Using the parameters obtained by laboratory tests on rock blocks and artificial fractures, a series of numerical simulations of mechanical deformation of the fractured rock mass at different scales and directions are conducted based on the established FEM model. The results show that the REV of deformation modulus of the rock mass is 8 m. Furthermore, the elastic compliance tensor of the fractured rock mass at REV is studied, and error of the tensor characteristic evaluation is less than 8%

The bottom-hole differential pressure and the three-dimensional in-situ differential stress are the main factors during drilling that affect the distribution of the bottom-hole rock stress; and then affect the drilling speed. The purpose of the article is to quantitatively study the effect of the three-dimensional in-situ stress on the bottom-hole stress distribution under the overbalanced, balanced, underbalanced and air drilling condition. On the basis of the mechanical analysis of the bottom-hole rock, the fluid-solid coupling model with the factors of the three-dimensional in-situ stress of the normal fault, fluid column pressure and pore pressure is set up, without analytical solution of the model; and then the numerical solution method is used to resolve it. The results show that the maximum principal stresses of the bottom-hole surface under different drilling conditions are the same; the minor principal stress increases with the increase of the bottom-hole differential pressure. The minor principal stress decreases with the increase of the horizontal maximum in-situ stress, and keeps stable when the horizontal minimum in-situ stress changes under differential drilling condition. The maximum principal stress of the bottom-hole surface firstly decreases with the increase of the horizontal minimum in-situ stress and keeps stable with the existence of the differential pressure and it keeps stable during air drilling while the horizontal minimum in-situ stress changes, and keeps stable when the horizontal maximum in-situ stress changes under differential drilling condition. Distribution of the bottom-hole stress field of the reverse fault and strike-slip fault is to be studied. Quantitative study of the bottom-hole stress distribution with differential pressure of bottom-hole and three-dimensional in-situ stress provides a numerical stimulation method for study of bottom-hole stress field under actual drilling condition and is the theoretical basis for faster and more efficient drilling.

The mechanism of abrupt large deformation in the sidewall of underground powerhouse is analyzed. The surrounding rock mass dynamic loosening is concerned as a main cause of abrupt deformation in underground powerhouse. Based on the monitored data at Pubugou hydropower station, numerical analysis is conducted with finite element method; and horizontal displacements induced by excavation load quasi-static and dynamic unloading are calculated respectively. The result itself and comparison to monitored data show that sliding and opening on structural surfaces induced by excavation load dynamic unloading are the major causes of abrupt large deformation in underground powerhouse, but which is not so obvious under quasi-static unloading. In actual projects, the transient effect of in-situ stress unloading should be considered; and the disturbance in the surrounding rock mass during each operation should be minimized to avoid potential abrupt large deformation, or even instability

Through tests the soil-water characteristic curves and strength parameters of unsaturated soil are determined; and then by way of theoretical analysis a model of seepage-stress coupling model is built. After that, coupling calculation is introduced to analyze the unsteady seepage flow of the unsaturated embankment due to the change of water level and then by using the shear strength reduction FEM to analyze the stability of the unsaturated slope because of the repeated rise and fall of the water level. The results indicate that when the water level rises, the seepage velocity at the bottom of embankment slope decreases, and then increases and grows steady. With the rapid rise of the water level, the global stability of embankment decreases; with adjustment of pore water pressure in seepage field, the safety factor of the slope stability increases to some extent. When the water level falls too quickly, the degree of saturation in clayey soil changes relatively slowly; the sudden fall of the water level accelerates the seepage velocity of embankment, and so the stability of the slope decreases fast. What’s more, about 120 hours after the fall of the water level the embankment enters a dangerous period. In addition, the matric suction of unsaturated soil increases the global stability of the slope and the repeated rise and fall of the water level decreases the global stability of the slope. What is more, the lower the river water level, the more severely the stability of the embankment will be affected

The geological conditions of large underground cavern group are complicated, of which the support project affects stability of surrounding rock. So it is important to study the support optimization of large underground cavern group excavation. In order to simulate rock mass veritably and analyze its damage in construction, the elastoplastic damage model and damage evolution equation are presented on the basis of the irreversible thermodynamics theory. The 3D elastoplastic damage finite element code D-FEM is programmed by using Fortran language, which has the capabilities of simulating excavation and support, computing quickly and group function. 3D numerical model of underground cavern group is established, input initial geostress is inversion of field stress measurement. The cavern group excavation by different support projects is simulated by D-FEM. The stress, displacement and damage of surrounding rock under three different cases are analyzed. The effect of No.2 support project is best and so is proposed. Considering damage evolvement, damage zones compared to plastic zones of FLAC3D, damage zones in side wall of cavern group increase remarkably. So the elastoplastic damage finite elements can analyze stability of underground cavern engineering.

For the nonlinear fracture phenomena of rock, many numerical methods are carried out for study, but the numerical simulation methods for cracked rock are still being studied. Therefore, this paper combines the bilinear strain softening constitutive model with energy dissipation principle to establish damage constitutive equations; and through the strain energy density theory, energy failure criterion of mesoscopic element is established. When the strain energy of an element stored exceeds a fixed value, the element comes into damage situation and the damage degree increases with the increasing of energy dissipation. Simultaneously, the material properties of the damaged element change until it becomes the element with residual strength. As load increases, the element’s damage degree increases. When the strain energy of the element stored exceeds the established value of the energy criterion, the element gets into fracture. With the increasing of fractured elements, macro-crack generates. This method implements linear calculation instead of the process of nonlinear computation, avoids the singularity of the numerical calculation in element fracture, and simulates the post-peak fracture behaviour of rock. The algorithm can be used to develop a rock fracture process computer program by the FISH language in the fast Lagrangian analysis of continual (FLAC). This program is successfully applied to the simulation of Brazilian splitting and tensile test with cracks. The simulation results agree well with the experimental results. It indicates that the simulation method of rock failure process is correct and feasible.

Borehole radar can probe deep underground geoenvironment through arranging a dipole antenna in a borehole, and it is a good logging tool to obtain the electrical signals of geologic formation. According to the common point unfavorable geo-bodies in borehole radar exploration, such as cavities, karst caves and buried objects etc., the electrical response of the tool to point unfavorable geo-bodies of different geometry and buried depth is investigated. The application conditions and resolution response capabilities of the simulation models are analyzed. It reaches that the proper antenna frequency should be chosen according to the physical dimension of object-of-interest and resolution requirement of the exploration task; and that the radar cross section of geo-bodies with different geometry appears various characteristic. The resolution capacity of borehole radar antenna varies with the buried depth of geo-bodies; and the borehole radar with higher frequency antenna can obtain reflected signals of higher resolution. However, the reflected signals detected by the borehole radar with a higher frequency will attenuate faster than one with lower frequency antenna. The results provide visualized perceptual knowledge and abundant interpretation support for borehole radar using in geologic survey and potential disaster detection, and help to improve the accuracy of geological interpretation

“Mining above aquifer”, as the main method to explore coal seams above confined aquifer, in which the determination of coal seam floor failure depth is the key factor and precondition. Taking the 1066 workface of Taoyuan Coal Mine for example, the high-precision microseismic monitoring technique is used to monitor the continuous and dynamic failure characteristics of an inclined coal seam floor above a confined aquifer, which can overcome the limitation of traditional method in field measurement of floor failure depth, especially for the failure depth of an inclined coal seam floor (the inclined angle of coal seam is between 25°and 45°). The monitoring results show that: (1) compared to the coal seam floor nearby the workface return airway (upper crossheading), the failure depth of coal seam floor nearby the workface conveyance roadway (lower crossheading) is deeper, with wider failure zone. (2) from the whole aspect, the failure zone of the inclined coal seam workface floor presents an asymmetric form. According to the results of microseismic monitoring, the maximum failure depth of the coal seam floor nearby the workface return airway and the workface conveyance roadway as well as the dangerous area of water-inrush from floor are determined. Finally, the floor failure depth determined by microseismic monitoring is compared with the failure depth calculated by the empirical formula; some existing deficiency of the empirical formula for calculating the floor failure depth are pointed out.

Piles are widely used as a foundation for the offshore wind power generation and undergoing a complex combination of loads including the low-frequency cyclic wind loading. A new device has been developed to simulate the complicated loads on the piles during the centrifuge model tests. Apart from the horizontal and vertical static loads, this device can also realize a long-time and low-frequency cyclic load, with a combination of other types of loads that are applied simultaneously or successively. The validity of this device, that it can meet the requirement for simulating the complicated loads that the pile undergoes, is preliminarily verified via a series of tests. The test results show that the displacement of pile top increases with increasing number of cycles of horizontal cyclic loads; but the growth rate gradually decreased with the displacement tending to stabilize after a certain cycles; and the deformation of soils concentrates in a certain region near the pile