Chain instability of residual coal pillars can lead to the dynamic disaster, such as the overburden caving, surface collapse, dynamic shock, gas leaking and water releasing.Revealing the chain failure mechanism of residual coal pillars is the basic prerequisite for its accurate control.Starting from the chain instability source, the weakest failure model of residual coal pillars was firstly proposed.The basic concept of key pillar was defined and its characteristics was analyzed.The determining method of key pillar was developed and the chain failure of residual coal pillars was revealed.Then, the key pillar theory in the instability of residual coal pillars was formed.At last, the potential application scope and field of key pillar theory was discussed.Results show that ¿ the differences in the internal physical-mechanical properties and external environmental factors have led to the weakest instability model of residual coal pillars.When any form of instability models appears in the residual coal pillar system, the weakest instability model must have occurred.That is, the coal pillar with the weakest stability factor fails inevitably when the chain instability of pillar system occurs.¿ The key pillar refers to the pillar that the local instability occurs earliest in the pillar system.Only the local failure of key pillar appears, the collapse of adjacent coal pillars with stronger stability can be activated.And the chain failure of residual pillar system can occur.¿ The pillar with the smallest safety factor can be determined as the key pillar in the pillar system.Four principles of regionality, relativity, dynamics, and compound should be followed in determining the position of key pillar.¿ Linear increase of load for the nearest adjacent coal pillar is triggered by the gradual reduction of load for key pillar.That is, the local instability of key pillar will cause the shift of overburden stress, which will transfer to the nearest coal pillars and lead to further instability and damage.Eventually, the chain failure and destruction of residual pillar system may also be caused.¿ The key pillar theory can be used in the fields, such as the adjacent seams mining in the pillar areas, the strong pressure behavior controlling, the coal pillar designing, the backfilling mining, the gas extraction and the water disaster prevention.It can also be applied to the controlling of rock pillars in the non-coal resources mining.The key pillar theory in the instability of residual coal pillars is expected to promote the development of the theories and technologies of Chinese green mining.

The diffusion of cement slurry in a fracture with flowing water is an important factor ensuring the grouting effect and a key factor influencing the environment, including natural and social traffic. To better understand the influence of the characteristic fracture parameters and the water flow rate on the cement slurry diffusion law, first, diffusion testing of a cement slurry in a simulated tortuous fracture with flowing water is carried out. Then, the results obtained from these tests are applied to an engineering site. The results of the experimental and engineering tests support the following conclusions. 1) At a low water flow rate, the sealing efficiency of test points near the grouting source increases rapidly with time, while the sealing efficiency of test points far from the grouting source exhibits little change with time. 2) Near the grouting source, the sealing efficiency corresponding to a high fractal dimension of fracture tortuosity is higher than that corresponding to a low fractal dimension of fracture tortuosity; far from the grouting source, this pattern is reversed. 3) When the inflection point of the grouting pressure is reached at a test point, the sealing efficiency of the fracture at this test point is the greatest.

Prestressed anchor support is one of the most important support methods for coal mine roadways. As the coal mining depth increases, the adaptability of existing prestressed anchor has become weaker and weaker, which is mainly reflected in the current anchor prestress is much smaller than the support resistance required for the stability of the roadways and makes it difficult to effectively control the roadways. In order to solve the problem, a group anchor structure was proposed to realize higher prestressed anchor support technology and improve the support status of deep roadways. For coal mine roadways, group anchor structure is a new technology and new topic, and the design method and theoretical basis of the group anchor support are lacking. Therefore, the paper studied the bearing capacity of the group anchors through physical tests and numerical simulations. Among them, a special set of group anchor drawing tooling was designed and processed to match the physical test. The test results show that the group anchor structure can double the bearing capacity and bearing rigidity compared with traditional anchors, and the group anchor support can further optimize the support parameters to improve the bearing capacity of the surrounding rock. Therefore, the group anchor support is helpful to the stability control of the surrounding rock of the deep roadway.

Numerous tunnel excavation projects have been undertaken in China to address the ever-increasing demand for tunnels, which is driven by the rapid development of urban cities. Tunnel excavations generally induce the settlement of existing tunnels and sometimes result in the derailment of metro vehicles. In this study, the Nanyan Fourth Circuit Transmission Reconstruction, located in Dalian City in China, was selected to investigate the local settlement of a metro station caused by an underlying tunnel excavation project. The theoretical solution of the stochastic medium theory was calculated for a horseshoe-shaped tunnel based on the Gauss¿Legendre integral in a non-uniform convergence situation. Results were compared with data measured at the metro station. A three-dimensional model was developed to further explore the variations in stress and deformation, which were difficult to measure during the excavation. The results showed the existence of a settlement gradient of the metro station in the direction of the excavation after the underlying tunnel was excavated. The numerical results were in good agreement with the data measured onsite. The non-uniformity of the settlement in the direction of the excavation was investigated. The findings of this study can provide a reference for predicting and controlling the impact of undercrossing tunnel excavation on the deformation of metro stations.

Fracture mechanism of hydraulic fracturing for anisotropic shale is of very importance in shale gas mining technology. The classical fracture criteria can better predict tensile (Mode I) fracture under arbitrary loading condition (pure tensile, pure shear and mixed-mode), but have difficultly in predicting shear (Mode II) fracture. In this paper, a new mixed-mode fracture criterion (modified K-ratio criterion) of anisotropic rock is established based on the ratio of stress intense factors (SIFs) and fracture toughness of arbitrary plane to predict both the crack initiation angle and fracture mode. New physical influencing factors are proposed to describe effects of both the geometry and the material parameters of anisotropic rock on the SIFs of the original crack plane, KI(0) and KII(0), in order to calculate the SIFs on arbitrary crack plane, KI(¿) and KII(¿). Prediction results show that under the pure tension, pure shear and tension-shear loads applied onto the original plane, Mode I fracture can occur on the sedimentary plane or on the plane of KI(¿)max. Mode I or Mode II fracture can occur under compression-shear load. The semi-circular bend (SCB) test results of anisotropic shale specimens with different ¿ (crack inclined angle) and ß (sedimentary plane angle) are in good agreement with the predicted results and can verify the validity of the modified K-ratio criterion.

Ore recovery and dilution in caving mines are strongly determined by the flow characteristics of broken rock, especially under inclined boundary conditions. A physical draw model was designed and used to investigate the gravity flow characterization of granular materials during longitudinal sublevel caving. The three-dimensional (3D) shapes of flow axis, isolated extraction zone (IEZ) and ore remnants under inclined walls were obtained using the discharged quantity method and 3Dmine software, which indicated that stope boundary conditions and orebody dip have an impact on the characteristics of gravity flow. The experimental results also showed that the gravity flow characteristics of 3D draw experiments under the inclined walls were significantly different from those of the two-dimensional (2D) draw experiments. The flow axis is a line segment and lies in the same plane and only the width of the IEZ can be displayed in 2D experiment. However, the flow axis is a space curve segment in 3D draw experiment. Since being cut off by the front and inclined upper walls simultaneously, the 3D IEZ is more complicated than the 2D IEZ and both the width and thickness of the draw body are displayed simultaneously in 3D state. The shape and location of ore remnants in 3D state are also different from that in 2D state. Therefore, the 3D IEZ is more consistent with the actual situation than 2D IEZ for sublevel caving stope. The 3D gravity flow presented may be used to determine the design of the extraction layout and improve ore recovery during longitudinal sublevel caving.

Stress conditions and preflaws are prominent conditions influencing the cuttability of deep hard rock. This study aims to investigate the cuttability of intact, prefractured, and drilled rocks under biaxial confining stress, uniaxial confining stress, and stress-free conditions using a conical cutter in rock fragmentation tests on true triaxial loading apparatus. Peak cutter force and penetration depth at rock initial fracture and final failure of the rock specimen were used to reflect rock cuttability. The results show that the rock cuttability increases with stress in one direction decreasing under biaxial confining stresses, and presents a decreasing trend followed by an initial increase as uniaxial confining stress increases. The prefractures and boreholes in rock can further improve the rock cuttability, compared with intact rock. A series of cuttability improvement measures were proposed to provide a suitable condition for the application of nonexplosive mechanized mining in hard rock. Finally, comparative field tests were performed on a single-face entryway and a peninsula-shaped pillar, in which the mean value of cutting efficiency increased from 32.6 to 107.7 t/h, and the dust production and cutter wearout failure reduced significantly.

A series of dynamic fracture experiments on semicircular bend (SCB) marble specimens were conducted to characterize the loading rate effect using the INSTRON testing machine and the modified SHPB testing system. The fracture toughness of the marble specimens was measured from a low loading rate to a high loading rate (10-3106 MPa·m1/2s-1). The results show that the fracture toughness will increase with the loading rate. Since the fracture toughness at a magnitude of 10-3 MPa·m1/2s-1 is regarded as the static fracture toughness, the specific value of DIFf (the dynamic increase factor of fracture toughness) can be obtained at the other loading magnitudes from dynamic fracture tests. To describe the variation in DIFf from low to high loading rates, a new continuous model of DIFf was put forward to express the quantitative relation between the loading rate and rock dynamic fracture toughness. It is shown that the new DIFf model can accurately describe the loading rate effect on the dynamic fracture testing data for rock materials.

Aiming at the shortcomings of the existing micro-source localization algorithm based on the uniform speed assumption and the iterative method leading to large amount of calculation and poor robustness, a new method of micro-source location considering the velocity anisotropy was proposed through the transformation of time-distance equation. The new method used six effective detector data to implement positioning. Stochastic simulation method was applied to produce a large number of source alternative solutions considering the complexity of wave velocity characteristics. Final source solution was discussed from the angle of information fusion, the gross error criterion and the clustering analysis method was used to obtain the source solution. The examples show that the analytical method is correct and reasonable, and the information fusion method is scientific and reasonable, and suggest the final micro source is determined through gross error criterion.

Prediction of rock burst tendency is one of the basic tasks of disaster prevention and reduction in underground engineering. In view of the existing mathematical models, there are some shortages in the necessary inspection process determining the comprehensive weight of the rock burst index, and there is low accuracy for predicting the rock burst. An improved cloud model for predicting rock bursts is proposed. The improved model is fused with the index weight through cloud atomization conditions in the cloud theory. And the comprehensive weight of the index after the test is obtained. By modifying the standard cloud model and generating the hierarchical integrated cloud by comprehensive cloud algorithm, the deficiencies that the standard cloud model is too sensitive to the average grade range are made up. A number of rock burst examples are used to verify the proposed model. The results show that a more reasonable comprehensive weight can be obtained using the weight fusion method based on the cloud theory. The improved model can be well applied to the prediction of rock burst tendency.

The quality classification of rock mass is a basic geotechnical engineering issue. The classification of rock mass quality shows the uncertainty due to the fuzziness and randomness of the rock mass parameters. The effect of parameter uncertainty on the classification results is ignored in the existing classification model. The reliability method was thus introduced into the classification of rock mass quality, and a coupled model of Monte Carlo simulation(MCS) and technique for order preference by similarity to ideal solution(TOPSIS) was proposed, which can consider the effect of the parameter uncertainty on the classification. The model consists of two parts. One part is to obtain the weight of classification system index with the game theory and to determine the limit-state equation of the reliability with the TOPSIS model, and the other part is to perform uncertainty analysis and to provide the final classification result based on the probability function. The TOPSIS model was tested with 25 sets of samples. The analysis results of the MCS-TOPSIS model indicate that the misjudgment ratio of the model is 0. The quality classification of the surrounding rock at Shuibuya underground powerhouse is examined based on the certainty and uncertainty methods using Matlab programs. The results demonstrate that it is feasible to use the MCS-TOPSIS model to classify the rock mass quality and the model has high accuracy and is easy to use.

Micro-seismic source location is crucial for the micro-seismic monitoring technology. The existing algorithms usually minimize the function of time arrival values(time difference) from all detectors to obtain the location of micro-seismic source. The positioning results deviate usually from the actual locations of the sources because all the known micro-seismic parameters have errors. To overcome the shortcomings of the present algorithm, a two-step inversion method for the micro-seismic source location is thus proposed. The first inversion is to identify the abnormal detector, and the second inversion is to search the exact location from the space coordinates of sources. The 3-parameter, 4-parameter and 5-parameter inversion models on the assumption of uniform velocity are established and compared. A multi-objective genetic algorithm(Non-dominated Sorting Genetic Algorithm-II, NSGA-II) is used for the first inversion. A single objective optimization algorithm is suggested in the second inversion in order to achieve the accurate source searching and to reduce the computing time. The results from a case study indicate that the proposed method can effectively identify the abnormal detectors and the positioning is greatly improved compared with the results with the abnormal geophone. The 4-parameter inversion model is better than the 5-parameter inversion model.

The creation of microfractures within rock is commonly observed as rock is strained. The presence of these microfractures constitutes damage to the rock, and this damage can reduce the rock¿s strength. This paper explores the evolution of rock strength as microfractures within a rock accumulate. Two approaches involving different laboratory tests are used to study how cohesion and internal friction evolve during progressive damage to rock. The mobilized cohesion and friction angle are measured for intact and damaged rock specimens. Intact rock specimens tested under compression were used to determine the peak values of cohesion and friction angle for two types of rock. Specimens of rock with varying amounts of accumulated microfracture damage were tested under direct shear or multi-stage triaxial compression to measure the Coulomb strength parameters for damaged rock. The laboratory testing shows that cohesion decreases with strain as the rock accumulates internal damage caused by microfracturing before the peak strength. The frictional component of the rock strength starts to be mobilized as strain causes internal microfractures. The mobilized internal friction angle increases up to and slightly beyond the peak strength. A small amount of post-peak strain is required to initiate macroscopic slip surfaces, and until these are created, high frictional resistance is mobilized between the many interacting and interlocked pieces of rock in the test specimen. With further post-peak strain, the friction angle decreases as the macroscopic slip surfaces in the rock become well established.

In geotechnical engineering, when the strength of soft soils is relatively low, a rapid loading rate can lead to ground failure. In this situation, a multi-stage loading scheme can be utilized to achieve higher soil strength by consolidating the soil layer to a certain degree before applying the next, larger load(s). Additionally, the total stress in the soil layer usually varies, and, in many cases, this variation is not uniform with depth, for example, when the loading is applied within a small area over a thick soil layer. In this study, a thorough, explicit analytical solution is presented for the consolidation of a single soil layer using a multi-stage loading with depth-dependent total stress. The particular case of a two-stage loading scheme is selected to investigate the consolidation behavior of a soil layer. Finally, the convergence of the analytical solution is assessed by comparing the calculated results using the various terms of the series to facilitate the use of the solution by engineers and to provide sufficient accuracy.

© 2014 Elsevier Ltd. The consolidation behavior of ground with vertical drains is known to be greatly affected by the finite permeability of the sand drains, also called the effect of well resistance. However, up to now, no analytical methods have been reported for evaluating this effect on the nonlinear consolidation behavior of vertical drains. In this paper, by considering the nonlinear compressibility and permeability of soil during consolidation, the effect of well resistance was incorporated into the derivation of the equations that govern the nonlinear consolidation of a vertical drain with coupled radial-vertical flow. In addition, the smear effect was considered by assuming three decay patterns for the radial permeability coefficients of the soil toward the sand drain in the smeared zone. After obtaining the governing equations, a simplified analytical solution is derived for a general time-variable surcharge loading. Based on the general solution obtained, detailed solutions are provided for three special types of loading schemes: constant loading, single-stage loading, and multi-stage loading. The validity of the solution is verified by reducing it to several special cases and comparing these to existing solutions. Finally, the effect of the well resistance, the ratios of the compression index to the radial and vertical permeability indices, various loading schemes, and various variation patterns of the radial permeability coefficient of the soil in the smeared soil zone are investigated using parametric analysis.

In this paper, a coupled thermal-mechanical-damage model, Material Failure Process Analysis for Thermo code (abbreviated as MFPA-thermo), was applied to investigate the formation, extension and coalescence of cracks in FRCs, caused by the thermal mismatch of the matrix and the particles under uniform temperature variations. The effects of the thermal mismatch between the matrix and fibers on the stress distribution and crack development were also numerically studied. The influences of the material heterogeneity, the failure patterns of FRCs at varied temperatures are simulated and compared with the experimental results in the present paper. The results show that the mechanisms of thermal damage and fracture of the composite remarkedably depend on the difference between the coefficients of thermal expansion of the fibers and the matrix on a meso-scale. Meanwhile, the simulations indicate that the thermal cracking of the FRCs at uniform varied temperatures is an evolution process from diffused damage, nucleation, and finally linkage of cracks.

One small-scale physical model test on the PVD (Prefabricated Vertical Drain) treated Hong Kong marine clay was simulated using finite element method (FEM) in this study. A User MATerial (UMAT) subroutine describing an Elastic Visco-Plastic (EVP) constitutive model was developed and incorporated into one commercial finite element code ABAQUS. A degressive permeability of the PVD strip was included to consider variations of its permeability during the consolidation process. The UMAT and the adopted reducing technique were demonstrated to be effective by good agreement between the observed consolidation settlement and excess pore water pressures and the simulated ones.

A series of numerical model tests were performed to investigate the behaviour of the anisotropic rock surrounding circular excavations under high confining pressures. The aim was to provide information on the formation of fractures and failure around deep level rock tunnels under controlled conditions. Solid cubes containing a circular hole were confined to a vertical pressure with same as the confinement in the horizontal directions. In this modeling, the inhomogeneous rock is generated by using Weibull parameters which are related to the microstructural properties determined by crack size distribution and grain size. The fracture angle is assumed to be 45°. The observed failure zone around the excavation was simulated using both the maximum tensile strain criterion and Mohr-Coulomb criterion respectively (as the damage threshold). And RFPA (Realistic Failure Process Analysis) code was used as the calculating tool in this modelling, three opening modes are simulated and compared. Computational model predictions that include crack propagation and failure modes of rock show a good agreement with those of the observation in site. It is pointed out that the damage evolution of EDZ strongly depends on the inhomogeneous, the excavation mode, anisotropic property, and the various loading conditions. Concerning the existence of a weak plane, the amount of displacement at the side wall of the tunnel was quite large, since the shear deformation occurred in EDZ. The model is implemented in RFPA code and is able to represent the change in fracture patterns between the solid and jointed parts. This provides confidence for the application of the numerical model to the design of rock tunnels at great depth.

Soil nailing is a widely used technique for stabilizing slopes and excavations. In all current design methods, the nail-soil interface shear strength, that is, the pull-out resistance of a soil nail is an important parameter which controls the design and safety assessment of the soil nailing system. The pressure grouting is a cost effective method for increasing the soil nail pull-out resistance and in turn improving the performance of the nailed structure. In this paper, a three dimensional (3-D) finite element (FE) model for pull-out tests is established and verified by comparing simulated results with measured data. This model is then used to simulate the effect of grouting pressure on the soil nail pull-out resistance.

In this paper, a Material Failure Process Analysis code (MFPA) was employed to investigate the interaction of end effect zone of specimen with the wing crack propagation inside the brittle specimen containing pre-existing flaws under uniaxial compression comparing with the experimental results. The numerical results show that the shorter the distance between the pre-existing flaw and the specimen's end, the slower the crack propagation process and the shorter wing propagation length is, and vice versa. In addition, the end effect zone was also influenced by the wing crack propagation.

An Elastic Plastic-Damage (EPD) model is developed to model the softening behaviour of the cement-soil admixture based on continuous damage mechanics. The softening behaviour is considered to be characteristic outcome of the material degradation due to damage in material. Material degradation is modelled by reducing progressively the stiffness and yield stress of the material when the damage variable has attained a critical index. The basic equations of the model are derived and presented. A Fortran program for this model has been developed and implemented into a finite element code ABAQUS. In order to evaluate the applicability of this model, several unconfined compression tests are simulated using ABAQUS with this model. The computed results are compared with measured data and good agreement is achieved.

In numerical simulation of engineering problems, it is important to properly simulate the interface between two adjacent parts of the model. In finite element method, there are generally three methods for simulating interface problems: interface element method, surface based contact method and the method by using a thin layer of continuum elements. In this paper, simulation of interface problems is conducted using continuum elements and surface based contact methods. The results from each method are presented and compared with each other.

Since non-stationary signal of hydro-power unit can be analyzed by using continuous wavelet transform (CWT), implicated information about the operational status can be extracted in the scale domain using the CWT. Power rate of each frequency is proposed to be refined to deal with the CWT coefficient figure pixel brightness. Gray moment is then introduced to quantitatively indicate the characteristics of the CWT coefficient figure. It is demonstrated that the gray moment is effective to be a hydro-power unit vibration symptom for the hydro-power unit analysis and diagnosis.

Laboratory compact grouting was performed using a modified triaxial test on Hong Kong CDG (completely decomposed granite) soils to investigate the effect of effective confining pressure and grout injection rate on the compact grouting effect. In this study, compaction grouting was simulated by expanding a latex balloon inside a triaxial sample using de-aired water. When the balloon is expanded, it first needs to overcome the effect of the confining pressure of the soil; further expansion will compact and density the surrounding soil. The compact grouting effect can be control by measuring the total void ratio change during injection and the following consolidation. The injection rate was controlled by a GDS using a volume control technique. The results of the experiments showed that the effective confining pressure on soil specimen plays an important role in the effect of compaction grouting, and the injection rate has an effect on the rate of excess pore pressure dissipation but minor effect on soil density. © 2007 Taylor & Francis Group.

Based on cusp-type catastrophe theory, a sample rock-rock model for studying the pillar rockburst mechanism is presented in this paper. It is shown that the stiffness ratio, K, of the roof and floor to the pillar plays an important role in the outbreak of instability. Additionally, simple formulae for the deformation jump and the energy release are derived. Based on the assumption that there exists a proportional relationship between the number of microseismic events and microfractured elements, the theoretical microseismic event rate produced by the double rock sample, loaded in series under uniaxial compression, is obtained. Using a newly developed numerical code, RFPA 2D, the progressive failure process and associated microseismic behavior of the twin rock samples are simulated, which shows that the spatial distribution of microseismic events develops progressively from disorder at the initial loading stage to order prior to the main shock. The numerically simulated results also confirm that a soft roof and floor promote an unstable failure or collapse of pillars, while a stiff roof and floor can lead to a stable failure of pillars. Additionally, the simulated results reproduce the deformation jump and the energy release that occur during a pillar rockburst. It is demonstrated that the proposed model properly simulates the pillar failure process. © Springer-Verlag 2006.

Rock is a very heterogeneous material, containing various types of weaknesses such as gain boundaries, pores, and cracks and other defects. When rock is subjected to surrounding loading or the increase of hydraulic pressure due to rainstorm, the pre-existing fractures will initiate or propagate at the point of least resistance, which may cause failure of the entire structure of slope, dam and so on. By using Flow-Rock Failure Process Analysis code, F-RFPA2D. Firstly, a numerical simulation and similar materials experiment on rock samples with two pre-existing cracks without hydraulic pressure were conducted to investigate the initiation, propagation, coalescence of cracks and failure mechanism of rock considering the heterogeneity of rock; secondly, another sample with two pre-existing cracks subjected to hydraulic pressure under the loading conditions of different k0 is used to investigate the behavior of hydraulic fractures evolution, and their coupling action. Numerical results reproduce the process of pre-existing cracking evolution process which agreed with the experimental results.

Many stiff clays forming part of natural slopes and earth dams exist in the fissured state. When these cracks are subjected to gravity induced normal and shear stresses they may propagate. The present discussion presents a numerical method to study the propagation direction of cracks under stress fields similar to those found in the field. Not only did the results on one crack propagation direction obtained from the numerical method and the analytical results agree well, but numerical results have been used to investigate the mechanisms of the whole process of two horizontal cracks initiation and propagation and coalescence in stiff soils.

Rock and concrete are typical heterogeneous material that the meso-scale heterogeneity may have a significant effect on their macro-scale mechanical responses. In this work, a digital image-based (DIB) technique is employed to characterize and quantify the heterogeneity of concrete, and the obtained data is directly imported into a numerical code named RFPA (Rock Failure Process Analysis) to study the effect of heterogeneity on the failure process of concrete. The upgraded RFPA is capable to simulate the progressive failure of brittle materials such as rock and concrete, representing both the growth of existing fractures and the formation of new fractures, obviating the need to identify crack tips and their interaction expl icitly. The simulated results are in reasonable agreement with experimental measurements and phenomenological observations reported in previous studies.

The purpose of this paper is to investigate shear behaviors (failure progress, failure pattern, failure mechanism and shear resistance) of rock specimens containing four joints with different joint azimuth angles using RFPA2D (rock failure process analysis) code. Specimens are placed in a direct shear box. The upper surface of shear box is loaded with a constant normal stress 0.5 MPa, and the left surface is controlled by a constant increasing horizontal displacement at 0.002 mm/step. The whole shear failure process is visually represented and the failure pattern in reasonable accordance with other experimental results is obtained. In general, the failure pattern is mostly influenced by joint azimuth angle while shear strength is closely related to failure pattern and its mechanism. Two phases of shearing can be identified. Wing cracks firstly initiate from the tips of pre-existing joints with an initiation angle, and then propagate towards another joint through rock bridge. The second phase of shearing is characterized by friction process and volume increase in shear zone. The shear resistance obtained is a function of joint azimuth angle.

A geo-material failure process analysis, considering the coupling of stress distribution, fluid flow, and element damage evolution, has been used to investigate the mechanisms of crack initiation and propagation around a 2-D cylindrical cavity in heterogeneous stiff soils during grouting. Numerical simulations were performed using the specifically developed computer software F-RFPA2D. The results indicate the analysis is a powerful tool for the studying of soil behavior during fracture grouting. Moreover, they give us a better understanding of the crack initiation and propagation mechanisms during hydrofracturing.

A numerical model is developed to study hydraulic fracturing in permeable and heterogeneous rocks, coupling with the flow and failure process. The effects of flow and in-situ stress ratio on fracture, material homogeneity and breakdown pressure are specifically studied.

By investigating the influence of hydraulic pressure on the deformation of north side slope of Fushun open cast, the slide and inclination deformation mechanism of high steep slope in the area W200-W600 are presented, as well as the evaluation of effect of reinforcement for anti-slide pile and dewatering. The results show that most of the maximum deformation appears in layers No.1 and No.2, and the deformation decreases greatly after being reinforced. Otherwise, the slide depth will get into layer No.5 and this will lead to the slide of the whole layer No.5. Finally, some practice effects are introduced and it can provide references to the prediction and control of failure and instability of the similar slopes.

The changing rule for infrared thermal image boding of the rock with crack is essential for the geotechnical engineering, especially for the underground engineering. In order to study the rule, infrared thermal images for the failure process of rock with fracture are carried out. The size of the rock sample is 20 cm × 10 cm × 2 cm with a crack of 45° to the horizontal direction at the center and with the length of 2 cm. Considering the fact that sample will effect the results of the observation for infrared thermal image during the experiment, the laminated granite sample is used to replace the cylinder or cuboid sample. The achieved results under uniaxial compression indicate that intensity of the microruptures has close relation with the thermal effects. When the main fractures happen, there is a strip of high temperature that will appear at the destructive local area. During loading process, the abnormality of infrared temperature has three kinds of behaviors as follows: (1) temperature falls first and rises just before fracture; (2) temperature rises and falls alternately, and rises before the fracture; and (3) temperature rises slowly at first, and then rises quickly before the fracture appears. Even for the same rock sample, the behaviors of the infrared phenomenon may be different during failure process.

The coupling action of seepage and fracture on crack coalescence process under loading and hydraulic pressures are investigated. Numerical results demonstrate that the trend and magnitude of the permeability variations are controlled by the stress and the damage evolution developed in rocks. This includes the induced stress evolution of flow properties, and the regions of both diminished and enhanced flow depending on which the rock is in the linear-elastic, nonlinear, or post-failure portions of the stress-strain curves are presented. In elastic deformation region, rock permeability reduces when the rock compacts, and the decrease rate of the permeability starts to slow down or gradually to increase again when micro fractures begin to nucleate. Dramatic permeability increase occurs as soon as the macro-fracture forms in the rock.

The numerical simulations on the influence of mesoscopic structures on the macroscopic strength and fracture characteristics are carried out based on that the concrete is assumed to be a three-phase composite composed of matrix (mortar), aggregate and bond between them by using a numerical code named MFPA. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. It can be found from the numerical results that the bond between matrix and aggregate has a significant effect on the macroscopic mechanical performance of concrete.

Based on cusp-type catastrophe theory, a sample rock-rock (hypocenter surrounding the rock) model for studying the pillar rockburst mechanism is presented in this paper. It is expounded theoretically that the stiffness ratio, K, of the roof and floor to the pillar plays an important role in the outbreak of instability. Using a newly developed numerical code, RFPA2D, the progressive failure process and associated microseismic behavior of the twin rock samples are simulated. The numerically simulated results also confirm that a soft roof and floor promotes an unstable failure or collapse of pillars. Additionally, the simulated results reproduced the deformation jump and the energy release that occur during a pillar rockburst. It is demonstrated that the proposed model properly simulates the pillar failure process.

Disastrous rock slope failures have been posing a hazard to people's lives and causing enormous economic losses worldwide. Numerical simulation of rock slope failure can lead to improve the degree of understand of such phenomenon so as to predict and avoid the occurrence of these disastrous events. In order to simulate the global behaviors of rock slope failure under the high seepage pressure and the local behaviors of the occurrence of hydraulic fracture in the pre-existing rock joints effectively, a powerful finite element tools F-RFPA2D, is adopted. The simulation takes into account of the growth of existing fractures and the initiation of new fractures under various of hydraulic pressure in different heterogeneities medium. The behavior of fluid flow and damage evolution, and their coupling action are studied in small specimens that are subjected to both hydraulic and biaxial compressive loadings. The influence of the ratio (the initial horizontal stress to the initial vertical stress) and the distance between the two existing cracks on the fracture propagation behaviors are investigated. Moreover, based on the fundamental study of hydraulic fracture, the progressive failure of rock slope under the influence of the increase in hydraulic pressure was also studied in the paper.

Borehole breakout is the process by which portions of borehole or tunnel wall fracture or spall when subjected to compressive stresses. The stress-strain characteristics of rock during loading and unloading confining pressure are studied firstly. To overcome the difficulties in analytical model studies, a numerical code, RFPA2D (Rock Failure Process Analysis), developed by CRISR, Northeastern University, China, is used to investigate the progressive failure of breakout around tunnel. The heterogeneity of rock was also taken into account in the software. The numerical simulation reproduces the formation notch in rocks by the growth, interaction and coalescence of randomly distributed macrocracks. It is illustrated from the numerical simulated results that breakout direction of tunnel is parallel with the minor stress tensor in the plane perpendicular to the borehole axis. Specifically due to the inclusion of heterogeneity, some peculiarities are studied both in the evolution of fracture and the influence of borehole on the peak intensity of specimen as well as the AE event patterns.

By using numerical code RFPA2D (Rock Failure Process Analysis), the evolution of fracture around cavities subjected to uniaxial and polyaxial compression is examined through a series of model simulation. It is shown from the numerical results that the chain of events leading to the collapse of the cavity may involve all or some of the fractures designated as primary tensile, shear and remote fracture. Numerical simulated results reproduce the evolution of three types of fractures. Under the condition of no confining pressure, the tensile mode dominates with collapse coinciding with the sudden and explosive appearance of the secondary tensile fracture; at moderate higher confining pressure, the tensile mode is depressed, comparatively, the shear effect is strengthened. Nevertheless, tensile fractures especially in remote fractures stage still play a role; at higher pressure, the shear fracture dominates the remote fractures, In addition, the evolution and interact of fractures between multiple cavities is investigated, considering the stress redistribution and transference in compressive and tensile stress field.

Using a Material Failure Process Analysis (MFPA2D) code, the influence of crack continuity in heterogeneous materials containing two existing parallel flaws under uniaxial loading is numerically studied. The numerical simulation reproduces the stress field in the vicinity of cracks and the processes of propagation and coalescence of cracks during compression. The numerical simulation results showed that, with the decrease of the crack continuity, the stress field between the tips of internal cracks gradually changes from tensile stress to compression stress and the propagation mode of cracks also changes from tensile mode(T), tensile-shear mode(T-S) to compressive mode(C), and the initiation angle between the flaw and the direction of the maximum compression increases gradually as well. In addition, the initiation stress on the tips of cracks is about l/2-1/3 of the failure strength of the specimens.

This study is to evaluate the effect of the heterogeneity on the failure processes and strength characterization of brittle rock containing the single pre-existing crack (or flaw) under uniaxial compression loadings. The numerical simulation reproduces the evolution of the stress and strain fields in flaw propagation process, the mode of acoustic emission related to the heterogeneity of rock and the phenomenon related to discontinuous. It is shown that the lower the value of the homogeneous index, the more influence of local variation on the propagation process of the pre-existing flaw, and there occurs more randomly distributed microfractures throughout the specimen. Studying the details of macrofracture formation in relatively homogeneous specimens, it is interesting to find that there exists a "constant jump" propagation pattern of the wing crack, which is responsible for the formation of the pre-existing flaw. The numerical results also demonstrate that the stress-strain relation and strength characterization depends strongly on the heterogeneity of the specimen. The heterogeneous rock has a gentler post-peak behavior and lower strength, while the more homogeneous specimen has a higher strength, accordingly, the curve becomes more linear and the strength loss is also rapidly.

By using the code RFPA2D (Rock Failure Process Analysis), the influence of the excavation of No.2 subway of Guangzhou on the new south supermarket was simulated. The simulation reflects macroscopic damage-evolution process induced by microscopic fracture and the spatial-temporal distribution characteristics of acoustic emissions event hypocenter. Both the sedimentation of the cavity gore and the sedimentation of the building were analyzed, and the future evolution of the fragmentation belt was forecasted. The data of the in-cave observation is in agreement with the results of the analytic method.

The aim of this paper was: (1) to establish soil-specific laboratory calibration equations for two types of volumetric water content sensors (5TE and GS3); and (2) to evaluate their measurement accuracy and precision for estimating the soil moisture contents in sand, based on the established laboratory calibration equations and the corresponding default factory calibration equations provided by the manufacturers. The study revealed that the developed laboratory calibration equations (linear and polynomial) improved the sensors' measurement accuracy compared to that obtained using their corresponding factory calibration equations. Based on the root mean square error (RMSE), the 5TE sensor exhibited higher accuracy (RMSE=1.15%) with the third-order polynomial equation, followed by the second-order equation (RMSE=1.32%) and a linear regression equation (RMSE=1.63%). Thus, the third-polynomial type equation was considered to be the most suitable calibration model for the 5TE sensors in sand. In contrast, the second-order polynomial calibration equation provided highest accuracy for the GS3 sensors with the lowest RMSE of 0.86%.

The unpredictable and instantaneous collapse behavior of coastal rocky cliffs may cause damage whose influence is beyond the collapse area significantly. The gravitational movements during the coastal cliff recession involving two major stages, i.e., the small deformation stage and the large displacement stage. In this paper, in order to simulate the whole progressive failure of the coastal rocky cliffs, a calculation model is developed based on the rock failure process analysis method (RFPA) and the discontinuous deformation analysis method (DDA). The small deformation stage including crack initiation, propagation, and coalescence processes and the large displacement stage including translation and rotation processes during the rocky cliff collapse are simulated by the developed model. The stress field variation, displacement law, crack propagation, failure mode, etc. are further analyzed. The calculation and analysis results are consistent with the previous numerical studies, which indicates the developed model has offered an effective and reliable approach for the rocky cliff stability evaluation and the coastal cliff recession analysis.

Considering the heterogeneity of rock, the hydraulic fracturing process of rock specimen due to internal hydraulic pressure was numerically simulated in a meso-scale by RFPA2D2.0 (Realistic Failure Process Analysis). The differences of perforation angle, bedding angle and bedding material of rock specimens are considered. The numerical results showed that the initiation and propagation of hydraulic fractures were controlled by both global pore pressure¿s distribution gradient and local pore pressure around the crack tip. Both the lateral compressive pressure ratio and the bedding angle could affect the evolution of the hydraulic fractures. The numerically simulated results were in agreement with the experimental results.

A numerical code RFPA2D (Rock Failure Process Analysis), was used to simulate the initiation and propagation of fractures around pre-existing cavities in brittle rock. The dynamic loadings were applied to the rock specimens to investigate the mechanism of fractures evolution around single cavity. In addition, the evolution and interact of fractures between multiple cavities was investigated. The numerical simulated results reproduced tensile and remote fractures due to dynamic loading. Moreover, numerical results suggested that both the compressive wave and tensile wave could influence the propagation of tensile cracks. Especially the reflected tensile wave accelerated the propagation of tensile cracks.

Joints and fractures contained make rock mass complex mechanical and hydraulic properties. The randomicity of fractures shape factors (fracture orientation, dip, trace length, width, and spacing) is considered and Monte-Carlo simulation technique is adopted to develop the digital fractured rock mass model, which can be combined with numerical methods to solve practical engineering problems. FEM is adopted to simulate the mechanical and hydraulic properties of rock mass with different scales. Identifying representative elementary volume (REV) is a fundamental problem in studying rock mechanics and rock hydraulics, and it is a quantitative criterion for identifying if equivalent continuum approach is available for rock engineering problems and what the REV size is if it exists. On the basis of numerical modeling results, REV of fractured rock mass is discussed. The results show that REV size can be determined by the method in this paper and it can reflect the size effect of mechanical and hydraulic properties of rock mass. In addition, for the different research objects, such as mechanical property and hydraulic property, there exists different REV size.