Associate Professor Shanyong Wang

© 2017 Springer-Verlag GmbH Austria High geostress is a prominent condition in deep excavations and affects the cuttability of deep hard rock. This study aims to determine the influence of confining stress on hard rock fragmentation as applied by a conical pick. Using a true triaxial test apparatus, static and coupled static and dynamic loadings from pick forces were applied to end faces of cubic rock specimens to break them under biaxial, uniaxial and stress-free confining stress conditions. The cuttability indices (peak pick force, insertion depth and disturbance duration), failure patterns and fragment sizes were measured and compared to estimate the effects of confining stress. The results show that the rock cuttabilities decreased in order from rock breakages under stress-free conditions to uniaxial confining stress and then to biaxial confining stress. Under biaxial confining stress, only flake-shaped fragments were stripped from the rock surfaces under the requirements of large pick forces or disturbance durations. As the level of uniaxial confining stress increased, the peak pick force and the insertion depth initially increased and then decreased, and the failure patterns varied from splitting to partial splitting and then to rock bursts with decreasing average fragment sizes. Rock bursts will occur under elastic compression via ultra-high uniaxial confining stresses. There are two critical uniaxial confining stress levels, namely stress values at which peak pick forces begin to decrease and improve rock cuttability, and those at which rock bursts initially occur and cutting safety decreases. In particular, hard rock is easiest to split safely and efficiently under stress-free conditions. Moreover, coupled static preloading and dynamic disturbance can increase the efficiency of rock fragmentation with increasing preloading levels and disturbance amplitudes. The concluding remarks confirm hard rock cuttability using conical pick, which can improve the applicability of mechanical excavation in deep hard rock masses.

© 2017 Springer-Verlag GmbH Germany This paper presents a non-destructive, low-cost, photo-based, 3D reconstruction technique for characterizing geo-materials with irregular shapes of a relatively large size. After being validated against two traditional volume measurement methods, namely the vernier caliper method and the fluid displacement method for regular and irregular shapes, respectively, 3D photogrammetry was used to analyse the grout bulbs formed in laboratory pressure grouting tests. The reconstructed 3D mesh model of the sample provides accurate and detailed 3D vertex data, which allowed the volume, densification efficiency and bleeding behaviour of the grout bulbs to be analysed. Comparing the bulb section views at different grouting pressures also offers an intuitive observation of the grout development and propagation process. Moreover, the 3D vertex data and surface area included in the model are of great importance in validating numerical predictions of the pressure grouting process and analysing the interface shear resistance of grouted soil nails or anchors. Compared to existing approaches, the new 3D photogrammetry method possesses several key advantages: (a) it does not require expensive, specialized equipment; (b) samples are not destroyed or modified during testing; (c) it allows to reconstruct objects of various scales and (d) the software is public domain. Therefore, the adoption of this 3D photogrammetry method will facilitate research in the pressure grouting process and can be extended to other problems in geotechnical engineering.

© 2017 by the authors. One of the most efficient and environmentally friendly methods for preventing a landslide on a slope is to vegetate it. Vegetation-pervious concretes have a promising potential for soil protection. In this study, the vegetation-pervious concrete with low alkalinity was developed and studied. Combined with a grid beam structure system, the stability and strength between the vegetation-pervious concrete and base soil are believed to be enhanced effectively. For improving plant adaptability, the alkalinity of concrete can be decreased innovatively by adding a self-designed admixture into the cement paste. The effects of the admixture content on alkalinity and compressive strength of the hardened pervious concrete were investigated using X-ray diffraction (XRD) and compression test, respectively. Meanwhile, the permeability of the vegetation-pervious concrete was studied as well. Through comparing with ordinary pervious concrete, the effect of low alkaline pervious concrete on vegetation growth was investigated in a small-scale field for ten weeks. The test results indicated that the alkalinity of the cement samples decreased with the increase of admixture content, and the vegetation grew successfully on previous concrete. By increasing the admixture content to approximately 3.6%, the compressive strength of pervious concrete was more than 25 MPa.

© 2017 Informa UK Limited, trading as Taylor & Francis Group Filtration effect exists widely in the process of turbid fluid seepage in porous media, which directly influence the whole diffusion and migration process of turbid fluid particle. To better understand the effects of grouting parameters on the transport rules (e.g. velocity, viscosity and effective distance) of cement-based particle considering filtration, laboratory tests were carried out on fractal characteristics¿ sand, with different grouting pressure, confining pressure, water/cement and mass fractal dimension taken into account. In this study, the mechanism governing the transport of particles was investigated by analysing the variety of velocity and viscosity of slurry at the column outlet, as well as the porosity of specimens at different grouting parameters. The results indicated that (1)The viscosity of passed grouts and the effective range is increasing firstly and then decreasing with the grouting pressure; (2) The viscosity increases non-linearly when the water/cement ratio is less than 3.0, beyond which it decreases slowly; (3) The effective range presents non-linear increasing firstly and then decreasing with increase of water/cement ratio; (4) The viscosity increases non-linearly firstly, and then decreases rapidly with increase of mass fractal dimension; (5) The effective range decreases when the fractal dimension increases.

© 2017 Elsevier B.V. Mining-induced fractures influence the stability of overburden and may provide pathways for transferring heat and mass in underground environment. A novel approach was proposed to quantify the separation and fracture evolution in the undermined overburden, consisting of (1) theoretical distribution models of the void ratios of fractures (VRFs), based on analytical evaluation of key strata subsidence, and (2) numerical modeling using the universal distinct element code and a sequence of image post-processing procedures. For a longwall mining panel, both theoretical calculations and numerical simulations indicated that VRF first increased rapidly, then gradually decreased, and finally stabilized to a minimum from the surrounding edges of disturbed strata to their centers, and gradually decreased from deep to shallow strata. The fractures exhibited a ¿fracture-rich arch¿ distribution type along a vertical section. Numerous fractures occurred around the arch feet near the perimeters of mined-out area and/or arch crown near the center of disturbed strata. The distributions of VRFs show the heights, shapes and damage intensities of fractured zones, and can also be used as porosity parameters to determine the permeabilities of mining-disturbed overburdens. Therefore, the VRF models can be used as a quantitative parameter to assess the extent of possible risk zones, e.g. for water inflow into the mine or escape of hazardous fluids to the surface.

© 2017 Elsevier Ltd A numerical model is proposed to study crack initiation, propagation and coalescence in heterogeneous materials subjected to expansion pressure in boreholes using the finite element method and damage mechanics. The strength heterogeneity of materials is modeled at the mesoscopic level using the Weibull distribution. Using this numerical model, the initiation and propagation of cracks generated by expansion cement in boreholes were simulated. The numerical simulations qualitatively reproduced the crack patterns in samples tested in laboratory experiments. Moreover, the results clarified the failure mechanisms and fracture processes, thereby contributing to a better understanding of fracture mechanisms in heterogeneous materials subjected to expansion pressure in boreholes. The numerical model allows direct observation of the entire process of crack initiation and growth to a degree that would be difficult to obtain in experimental studies.

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.

©, 2015, Chinese Society of Civil Engineering. All right reserved. 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-RFPA 2D . 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 k 0 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 RFPA 2D (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.

MB series intelligent programmable logical controllers (iPLC) adopt the embedded software and hardware technology, LAN/Fieldbus system framework, and real-time multitasking operating system. Its programming and debugging software MBPro follows international standard IEC 61131-3. Compared with other PLC, MB series iPLC have some obvious characteristics, such as remote programming and debugging, the visual flowchart programming language, special function blocks, rapid processing ability, strong anti-jamming performance, flexible expanding capability, perfect redundancy, high reliability etc. MB series iPLC have successfully been put into operation in a hydropower plant.

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 (MFPA 2D ) 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.

Trend analysis and computerized expression of state parameters are two important factors in the on-line fault diagnosis. Singular spectrum theory is used in this paper to analyze the trend of state parameters. While the artificial neural network (ANN) is applied in the on-line identification of typical trends of state parameters. This method can identify the state parameters effectively, such as vibration, temperature, pressure and so on. So it could be an effective assistant analytical method for state analysis, state assessment and prediction of hydraulic generators as well as could be a powerful reference of state maintenance for hydroelectric plant.

The current study situation of the condition maintenance system for main equipment of hydroelectric plants at home and abroad is discussed. The problems existing in those applied systems are analyzed in this paper. Aimed at these problems. a new method is presented with the integration of SCADA. MIS and condition maintenance system. The framework of the condition monitoring, diagnosis and maintenance decision-making system for main equipment of hydroelectric plants and the functions of corresponding modules are introduced in detail.

Trend analysis and computerized expression of state parameters are two important factors in the on-line fault diagnosis. Singular spectrum theory is used in this paper to analyze the trend of state parameters. While the artificial neural network (ANN) is applied in the on-line identification of typical trends of state parameters. This method can identify the state parameters effectively, such as vibration, temperature, pressure and so on. So it could be an effective assistant analytical method for state analysis, state assessment and prediction of hydraulic generators as well as could be a powerful reference of state maintenance for hydroelectric plant.