Hydraulic properties and mechanical properties of rock fractures are intimately linked and the accurate understanding of the poromechanical link/behavior is essential for the crustal energy utilizations, such as geothermal and hydrocarbon. In particular, such a relationship under high pressure environment (more than 50 MPa) is important but has remained unclear due to the difficulties of its insitu monitoring and laboratory experiment. The present study explores this relationship via the pressurized water injection experiments on granite fractures with rough surfaces. We first imitate and hold the critical-stressed state of granite fracture, then gradually increase the pore fluid pressure to trigger the shear slip on fracture. During the experiments, we record the fracture permeability, normal/shear stresses on fracture, and shear displacement. In addition, to classify the failure mode (tensile or shear), we acquire the full waveforms of acoustic emissions and evaluate RA values and average frequency, which are proposed by Ohno and Ohtsu (2010), for the respective waveforms. As a result, we find that pressurized water injection first triggers the aseismic motion, which can be simply interpreted as jack-up opening of fracture, and contributes on the reversible permeability enhancement. The onset of the aseismic motion is possibly constrained by the Mohr-Coulomb failure criteria. This aseismic motion then induces the shear slip, which leads to the irreversible self-propped deformation and the associated permeability enhancement. New fractures concurrently propagate from the contacting asperities with stress concentrations and these newly created fractures significantly enhance the reservoir permeability. Our results reveal the importance of the mixed-mode failure behavior during reservoir pressurizations. 1. Introduction Hydraulic stimulation on the geothermal reservoir is the well-known operation for improving or maintaining the transmissivity and fracture connectivity within the reservoir (Norbeck et al., 2018). In this operation, by injecting pressurized water into the reservoirs, pre-existing fractures are reactivated in shearing mode with the opportunity for self-propping on asperities. Although it is important to explore the mechanical and hydraulic coupling of rock fracture/fracture network during hydraulic shearing, the laboratory experiments for exploring such coupling are very limited (Ye and Ghassemi, 2018; Ishibashi et al., 2018).

The Silurian Longmaxi shale formation is a widely distributed gas reservoir in the Sichuan Basin of southwest China. The thick clay rich shale has relatively high organic content, is thermally mature and is a major target for China's shale gas production. In recent years the shale has become the host to an increasing number of induced earthquakes potentially linked to fluid injection related to hydraulic fracturing. These induced or triggered events are linked to the reactivation of faults. This paper explores the frictional and stability properties of Longmaxi shale to provide insights into the causal mechanisms of induced seismicity and their geological and structural controls. Rock samples from a geological section spanning ~150 m were powdered for friction experiments at recreated in-situ stresses and temperatures. Experimental results show that fault frictional and stability properties are strongly controlled by mineral composition. Frictional strength increases with a reduction in phyllosilicate content and exerts a significant control on seismicity. Two of the ten samples exhibited velocity weakening behavior under in-situ conditions, potentially identifying compositions that contribute to unstable slip. These findings have important implications in understanding the frequency and occurrence of induced earthquakes triggered as a result of hydraulic fracturing. 1. Introduction The rapid growing earthquakes induced by shale gas hydraulic fracturing have aroused wide concerns in recent years (Bao and Eaton, 2016; Ellsworth, 2013; Lei et al., 2017). The large-scale fluid injection can generate high pore pressure in the subsurface and may activate the pre-existing faults (Elsworth et al., 2016). Previous researches demonstrated that the fault sliding behavior is governed by the frictional properties of fault gouge (Kohli and Zoback, 2013; Zhang et al., 2019). Thus, a careful examination of the fault gouge friction properties is important for understanding the underlying mechanism of fault activation and mitigating the seismic hazard during shale gas fracturing. The Silurian Longmaxi shale is a major target for shale exploitation in southwest China. In this work, the Longmaxi shales recovered from the outcrop in Sichuan Basin, southwest China were sieved to simulate the fault gouge. The friction experiments were conducted on these simulated fault gouges at hydrothermal conditions to explore the effect of mineralogy on gouge frictional and stability properties.

Abstract Smeared crack approach coupled with cohesive zone model has been an attractive way for the realistic simulations of dynamic fracturing of rocks and frequently utilized in the framework of the Finite Element Method (FEM). In many cases, cohesive elements (CEs) with initially-zero-thickness are inserted at the onset of numerical simulations and these are used to express the dynamic fracturing, which is called "intrinsic cohesive zone model (ICZM)". However, since the ICZM must introduce penalty terms to express the intact behavior of the CEs, this tends to render higher compliance of bulk rock, resulting in smaller wave propagation speed. In this paper, by introducing a so-called "extrinsic cohesive zone model (ECZM)", which adaptively inserts the CEs, we compared the results of 3-D dynamic fracturing simulations by the ICZM and ECZM using the experimental data obtained from the dynamic spalling test for rocks. Using the same Young's modulus, Poisson's ratio, density and strengths estimated from the experiments, our results suggest that the outcome of the ICZM and experiment showed large discrepancy especially for the intact stress wave propagation while the ECZM showed good agreement with the experiment. Therefore, our results could have some implications on the current situation in which more and more simulations using the ICZM such as in hybrid FEM-DEM have been applied to rock fracture mechanics problems. 1. Introduction Hybrid finite element method (FEM)-discrete element method (DEM) has been increasingly applied to the simulation of dynamic fracturing of rocks including blasting problems. In the majority of these simulations in previous research, cohesive zone models have been applied where cohesive elements (CEs) with initially-zero-thickness were inserted at the onset of simulation (e.g. Mahabadi et al., 2010; Rougier et al., 2014; An et al., 2017) and used to express fracturing behavior. This approach is a so-called "intrinsic cohesive zone model (ICZM)". Since the ICZM must introduce penalty terms to express the intact behavior of the CEs, this may render higher compliance of bulk rock, resulting in smaller wave propagation speed. On the other hand, a so-called "extrinsic cohesive zone model (ECZM)" has also been proposed for ceramics and concrete which adaptively inserts the CEs where and when they are needed (e.g. Ortiz and Pandolfi, 1999; Ruiz et al, 2001; Pandolfi and Ortiz, 2002). This approach has been rarely applied to the dynamic fracturing problems of rocks except our in-house 2-D Dynamic Fracture Process Analysis (DFPA) code (e.g. Cho et al., 2003).

Abstract KURT is a generic URL with a total length of 551 m and six research modules. The maximum depth of the tunnel is about 120 m from the surface. The host rock is granite, which is considered as a potential host rock type for HLW disposal repository in Korea. Various in-situ tests and experiments have been carried out since 2007, and tracer test and In-DEBS are two representative experiments that are being carried out in KURT. The research experiences gained using KURT are providing important information to validate the safety and feasibility of the deep disposal system. KURT is currently playing a major role in the development and demonstration of the proposed disposal concept and technologies, and particularly public acceptance. 1. Introduction KAERI (Korea Atomic Energy Research Institute) has developed a deep geological disposal system for high-level radioactive waste (HLW) through a long-term research project since 1997. KAERI is currently developing an advanced Korean reference disposal system (A-KRS) and its related technologies for HLW from the advanced fuel cycle system, which include pyro-processing of PWR spent nuclear fuel (KAERI, 2011). To dispose HLW safely in geological formations, it is necessary to assess the feasibility, safety, appropriateness, and stability of the disposal concept at an underground research laboratory (URL) constructed in deep geological formation as the desired host rock. The Planning Committee for the Korean Nuclear Energy R&D Programme decided to construct a small-scale generic underground research facility at the KAERI site to experimentally investigate the proposed disposal concept and relevant technologies in underground conditions in 2003. The phase I facilities of the KAERI Underground Research Tunnel (KURT) were constructed in November 2006 based on the decision, and various in-situ tests and experiments have been carried out since 2007 (Cho et al., 2008). The extension work for the planned tests and experiments of the phase II programme was completed in 2015. KURT is a generic URL, and not a potential site for waste disposal. The main geology of the KURT site is crystalline rock such as granite, and it is not allowed to conduct any experiments using radioactive nuclides in KURT. In this paper, the current status and representative activities of KURT, and KURT's role in HLW disposal technology development in Korea, are described.

Abstract In Finland and Sweden, the geological nuclear waste disposal is heading for the implementation phase in the next ten years or so. In the disposal concept, the knowledge of the rock mass strength and in situ rock stresses are important for long-term safety analyses. The rock mass strength of_the nuclear waste disposal site in Olkiluoto, Western Finland, was researched as a part of Posiva's Spalling Experiment (POSE). The POSE experiment was conducted as an in situ rock mass strength test that revealed the rock mass failure in Olkiluoto being governed by fracture growth at lithological borders instead of spalling type of failure commonly encountered in sparely fractured crystalline rock conditions. Based on the POSE experiment results, a structurally controlled failure is distinguished as a new rock mass failure mechanism. A back-calculation campaign was established to study the new rock failure mechanism with multiple modeling techniques, of which the results of fracture mechanics code FRACOD simulations are presented in this paper. Fracture Mechanics is able to mimic failure conditions, however after excessive calibration. 1. Introduction In Finland, Posiva Oy is currently in process of building a high active spent nuclear fuel repository in Olkiluoto Island, located at Western Finland. At the moment, detailed site characterization studies of the Olkiluoto Island are being conducted through ONKALO underground research facility at the corresponding site. Also several rock mechanics in situ experiments have been executed lately. The third Phase of Posiva's Olkiluoto Spalling experiment (POSE) was executed in ONKALO in 2013, where an experiment hole (Ø1.524 m) located at depth of −345 m was heated from inside while rock failure and deformation was observed (Valli et al., 2014). Predecessors of the test were the spalling experiments conducted both in the URL at Canada and ÄSPÖ in Sweden. In previous tests, it was observed that the in situ strength of sparsely fractured crystalline rocks is in the order of 40% – 60% lower than the measured uniaxial compressive strength in laboratory testing conditions (Martin et al., 1997; Andersson 2007). The mechanism leading to the macro scale rock mass failure in the in situ tests reported both in Martin et al. (1997) and Andersson (2007) was observed to be of spalling type.

ABSTRACT: To date, the Fiber Bragg Grating sensor (FBG) is one of strain measurement elements which can be embedded inside the rock model, this providing us an effective method to detect model deformation. The attachment methods, form of FBG sensor and the coupling status between the sensor and rock model are the major obstacles in the application of FBG sensor for model test. This study tried to research the detecting behaviors of FBG sensors which were packaged in different forms and materials. Two overlying strata models were built and two different forms of FBG sensors were embedded. Two FBG sensors were embedded vertically in model 1 and 2, respectively. The dimension of two models were 500 mm (L) × 400 mm (H) × 73 mm (W). The embedded two FBG sensors were named as FBG01,02 in modell and FBG03,04 in model2. FBG01,03 used copper substrate packaging, FBG02,04 used acetate ethylene plastic cylindrical packaging. The geometric similarity ratio of modell and 2 were 1:400. The experiment results showed that the model strata settlement deformation and the wavelength shift of sensors caused by deformation have linear-relation, the correlation coefficient reached to 0.9. The average sensing ratio of acetate ethylene plastic sensor and substrate sensor were 52.22 pm/mm and 26.81 pm/mm. The average sensing ratio of acetate ethylene plastic sensor was bigger due to the physical and mechanical properties of acetate ethylene plastic were closer to the rock model. However, the substrate sensor showed a better data variance due to the surface area of substrate packaging was large than cylindrical packaging. This suggests that the FBG sensor could be better applied to the rock model test if it has a large surface area and the sensor material is closer to the rock model.

ABSTRACT: Studies of brittle rock samples failure were carried out in Laboratory of Geodynamics of Far-Eastern University, Vladivostok, Russia. It was assisted by servocontrol loading machine MTS-816, acoustic emission complex and multi-channel complex. Regularities of formation and development of dissipative mesodefects structures in rock samples under uniaxial compression were determined as a result of complex deformation and acoustic experiments at final stage of loading. Study of acoustic emission in rock samples under at final stage of loading were carried out with the release of the source forming stage and its preparation. Anomalous deformations of high stressed rock samples were associated with failure source forming stages defined by the acoustic method. System of reliable precursors of failure involving long-term, medium-term and short-term precursors was established. This system of precursors reflects the stages of formation and development of dissipative mesodefects structures in high stressed rock samples. 1 INTRODUCTION Research of the mechanism for brittle rock samples failure prepares is important part of prediction and prevent geodynamic phenomenon in rock mass. Phenomenon of reversible linear deformations was discovered during previous research (Makarov et al. 2012). And two-stage model of rock spacemen failure source forming was state during acoustic investigation of high stressed rock samples (Kuksenko et al. 1996). Research of this phenomenon has been continued during experiments with rock samples under uniaxial load in Laboratory of Geodynamics, Far Eastern Federal University (Vladivostok City, Russia). It was found during research, that reversible linear deformations at local measuring areas should be divide up two different types. Relation between reversible linear deformations at local measuring areas and source of failure was determine by means 3-D model of source of failure, made at basis of acoustic emission data. This kind of anomalous deformations of high stressed rock sample was explained by the model of "soft-inclusion" (Guzev et al. 2007). Also, rock samples failure source forming stages was state at basis of the amplitude-frequency signal analysis. Identification of the relationship between reversible linear deformations at local areas and forming of failure source allow to state the complex system of rock samples failure precursors.

ABSTRACT: To make a better understanding of the meso-surface structure of fractured rocks in influence of the long term behavior of rock mass, two types of rock fractures were induced in sandstone by means of modified shear test and Brazilian split test. The shear creep experiments were performed in the mode of constant normal force with a step-wise increased shear loading force. The morphology of fractured rock surfaces were scanned before, in the mid and after the creep test, respectively. The variation of roughness and waviness of the fractured rock surfaces during creep deformation were analyzed by using of fractal theory. Under consideration of the surface roughness of fractured rock, a modified generalized Kelvin model was established, which presents stable creep behavior with the characters of instantaneous deformation, retard elasticity and plastic deformation. The study shows that the model can nicely describe the creep deformation law of fractured rocks with the influence of the surface roughness, and the predicted results agree well with the experiment. 1 INTRODUCTION In recent years, with the development of geological engineering projects, the long term mechanical behavior and stability of rock mass have been paid much attention. Griggs (1939) was the first to conduct creep test with limestone, shale and siltstone, which have moderate strength. He pointed out that some amount of creep deformation occurred in rocks when the applied load reached to 12.5%- 80% of the ultimate load only. After nearly 30-years bending creep test on the granite, Ito and Sasajima (1987) found that the granite showed viscous flow without yield. Xu (2005), Yan (2008) and Zao (2009) et al, respectively, conducted shear creep tests for jointed rocks, and obtained the typical shear creep deformation curve of jointed rocks. In addition, they established shear creep models for different types of rock. Chen (2008) carried out creep test on the cylinder silty mudstone with weak interlayer under constant normal stress and step-wise increased shear loading force, and derived a generalized Kelvin shear creep model. Li (2009) made a study on the creep characteristics of the marble's structural surface, and found that creep deformation of rock could be expressed as decay creep and steady creep under the low stress level; they also verified the normal linear shear creep model.

ABSTRACT: A series of consolidation tests and tri-axial tests under high compression are carried out to obtain suitable constitutive model for Gaomiaozi bentonite and the regarding parameters. The elastic-plastic mechanical features of Gaomiaozi bentonite are studied based on the constitutive model and the relative experiments. In addition, a numerical simulation using ABAQUS is carried out to verify the validity of the suitable constitutive model, i.e. Cam-Clay model, and the rationality of the values of the parameters. Thus this research contributes a lot to the further study about the mechanical features of Gaomiaozi bentonite. 1 INTRODUCTION Deep geological repository is admitted internationally as high-level radioactive nuclear waste disposal method, while bentonite, due to its high adsorption, expansibility, low permeability and good thermal conductivity, is chosen as buffer/ backfill material for the repository internationally (Liu Yue-miao et al., 2001 and Ye Wei-min et al., 2008). Scholars at home and abroad have made quite a few experimental researches on bentonite, however their searches mainly concentrated on the basic physical and chemical properties such as microstructure characteristics, cation exchange, expansion deformation and also expansion force, heat conduction characteristics and penetration performance. Research results on physical and mechanical properties and features of bentonite under different soil-water conditions are rare. Shen Zhen-yao et al. (1998) researches on Xinjiang sodium base bentonite. Through uniaxial and triaxial compression tests on bentonite under high pressure with different moisture content, he gets the stress-strain curve. Through triaxial shear experiments, Zhu Guo-ping et al. (2008) gain stress-strain relationship of Gaomiaozi bentonite under different moisture content and dry density. They summarize curve and laws on changes between cohesive force, internal friction angel and moisture content as well as dry density.

ABSTRACT: The sub-salt reservoirs of High Temperature and High Pressure (HTHP) are often drilled with Oil-Based Mud (OBM), for the OBM has better rheology and better keeping stability performance than Water-Based Mud (WBM) under HTHP condition. This paper aims to analysis the influence of OBM on salt formation creeping rate, based on the difference on interface tension of OBM. Through the experimental research, it get the relations between salt formation creeping with different exposing time and different interface tensions. An Electron Microscope Scanning Investigation (EMSI) has also been applied for saturated and unsaturated salt samples. Through EMSI, the micro change of salt samples has been testified. The research shows that the interface tension has a great impact on salt creeping. When interface tension increases, the infiltrate length of drilling fluid per unit time increases when quantity of micro-cracks increases, the infiltrate length of drilling fluid per unit time decreases. The experiments in this study were conducted under simulated high formation temperature. The OBM with different interface tension were obtained by adding surfactants into the OBM used in real drilling operations. 1 INTRODUCTION The sub-salt reservoirs are often drilled with OBM, because the WBM's inherent shortage in rheology and in keeping wellbore stability under HTHP condition. On the other hand, the OBM has a better performance in keeping wellbore stability under high temperature. The creeping of salt under WBM has been investigated in variety of studies (Fabre 2006). Some scholars have proposed several different equations for expressing the relationship between stress creeping rate and temperature (Homand 2006). In studies concerned with the micro mechanics of salt creeping, Fredrich (2007) employed statistics analysis on experimental data obtained from the salt rock experiments of Gulf of Mexico. Fuenkajorn (2010) analyzed the changes of Young's modules, and Poison's ratio on salt rock under repeated load and unload procedures. Popp (2000) investigated the changes of rock's permeability and acoustic logging data under different stress load. In the studies concerned with the interaction between salt and drilling mud, Chen, X. analyzed the salt dissolving under WBM (Chen et al. 2011). De Meer, S. & C.J. Spiers studied the creeping rate of salt formation under WBM (De et a!. 1999). G & Baoping proposed a theoretical model incorporated the couple effects of thermal conduction and fluid infiltration on salt formation (Bao et al. 2008). To sum the above studies up, the previous studies have concluded that when the stress loading increases, the pre-existed internal micro cracks will expend (Chan et al. 2001).

ABSTRACT: The design of High-Level radioactive Waste (HLW) repository in deep geological media shows that the highly compacted bentonite is a kind of ideal buffer material. Buffer materials between waste tank and the surrounding geological body is the last artificial barrier neighboring waste. The coupled Thermo-Hydro-Mechanical (THM) behaviors of the compacted bentonite are of importance for the HLW repository when operation and closed. This mock-up test was carried out to investigate the properties under THM coupled conditions, which will be helpful for the future design of engineered barrier system of China-mock-up. The characterization of compacted GaoMiaoZi (GMZ) bentonite related to swelling pressure, relative humidity and temperature are presented and interpreted. 1 INTRODUCTION The deep geological disposal for High-Level radioactive Waste (HLW) has been considered as an urgent worldwide environment issue. China pays more and more attentions to nuclear waste with the development of great economical growth. The long-term and reliable insulation from the human environment has raised worldwide attention for the countries who build nuclear power stations. Safe disposal of high level radioactive waste is a challenging task facing the scientific and technological world (Wang et al. 2006a). In order to safely dispose of the high-level radioactive waste generated from the nuclear power plants and other nuclear facilities, a number of disposal concepts have been developed in many countries, and results show that the deep geological disposal of High-Level radioactive Waste (HLW) is considered worldwide as the most safe and feasible method to protect human being and environment for tens of thousands years (Zhang et al. 2006). The behavior of HLW repository is determined, to a large extent, by the characteristics of the design and construction of the engineered barriers and especially by the changes that may occur in the mechanical, hydraulic, and geochemical properties as a result of the combined effects of heat generated by the radioactive decay and of the water and solutes supplied the surrounding rock (Villar et al. 2012). The concept design of repository in different geological formations generally relies on a multi-barrier system, which typically comprises the natural geological barriers provided by the repository host rock and an engineered barrier system (Liu & Wen 2003; Wang 2010).

ABSTRACT: A general framework for probabilistic damage in rock using maximum entropy theory is proposed to describe the failure process of marble from hydropower station at Jinping II, China. In this paper, the failure process of marble is divided into three stages. In the first stage, a parameter D 0 is employed to describe the compaction of rock before elastic period which can be calculated by maximum entropy theory. In the second stage, elastic theory is used to express no damage in the rock. In the last stage, a parameter D is performed to define and calculate the damage of rock based on maximum entropy theory. The proposed model is used to simulate the failure process of marble under uniaxial compression. The simulated result is well agreement with experimental data, validating the proposed computational framework. 1 INTRODUCTION The failure process of rock generally experiences compaction, elastic, pre-peak damage and post peak damage or failure stages. A model suitable to describe such a process helps to understand the failure mechanism of rock. The probabilistic damage model is widely used to describe the process of rock failure which can be easily introduced to computer code for numerical simulation. This method is performed to characterize the process of rock failure from a mesoscopic view to a macro view and has achieved some success (Tang et al. 1998, Tang et al. 1998, Tang et al. 2000, Zhu et al. 2004). In those methods, many probabilistic distributions have been employed to characterize the strength distribution of rock elements. Some researchers have made many discussions about those methods (Zhang et al. 2005, Li et al. 2012, Liu et al. 2007, Wong et al. 2006, Basu et al. 2009). In those methods, it's hard to describe the complete process (e.g., compaction stage) of rock under mechanical loading. It's easily to observe the phenomenon of compaction in conventional experiment especially in some hard rock such as marble. In this paper, the maximum entropy theory is combined with probabilistic damage method to compensate the disadvantage above. Based on the experiment of marble failure process, a new model is proposed to describe the whole process of marble failure and the failure mechanism is explained.

ABSTRACT: Because the large collapse pits appeared in the surface of stoped-out area in the lower iron belt of the southeast of Gong-chang-ling iron mine, the sliding danger of side wall of collapse pit threats seriously the production safety of open-pit of upper iron belt. In Order to prevent the side wall of collapse pit from sliding and improve the efficiency of stripping rock, a technical scheme of drawing the open-pit stripping rock along the collapse pit was proposed. For assessing the reliability of the scheme safety, the harm forms of collapse pit, especially the subsided harm of the bottom of granular media is analyzed. The experiment shows that the possibility of the granular media forming the arch in the course of mining and analyzes the continuity of bulk movement, then it can be concluded that the granular media of pit bottom will not suddenly subside in the process of downward shift. Therefore, the rock can be dumped along the collapse pit trend and wall. 1 INTRODUCTION The southeast of Gong-chang-ling iron mine has two parallel ore belts, which are 40~200 m apart, and the lower iron belt is magnetite iron conducted to the underground mining and the upper iron belt is Hematite lagging behind the open pit mining, Which caused a 300 m dispersion between upper and lower iron surface. Besides that, when the goaf is caving through the surface, a collapse pit, with the size of 30–100 m width and 20–55 m height formed near the open pit. Because the wall of collapse pit is close to vertical, the production safety is threatened by the rock movement of the open-pit. For the protection of the collapse pit wall and improving the rock breaking efficiency, we put forward the technological scheme of discharging strip waste to the collapse pit. The plan needs to discharge waste rock alone the collapse pit direction with the coordination of side wall, namely the waste rock should be filled above the dispersion in the collapse pit. Therefore, it is need to analyze the harm form of collapse pits, evaluate the reliability of this method to guarantee production of the waste rock safely.

ABSTRACT: In order to improve accuracy of Physical Simulation Experiment (PSE), an approach with hybrid mechanical experiment on evaluation of mechanical response and Acoustic Emission (AE) signal characteristics of model materials employed in the PSE is one of the most significant techniques for optimization of PSE. This paper emphasized mainly on damage-mechanical properties of a specific model material for simulating coal-rock masses in the PSE, Porous Rock-like Composite Material (PRCM). We formed a real-time mechanical testing system which was composed with unconfined pressure equipment and AE monitoring in PRCM mechanical experiment. Crucial functional relationship between stress and strain would be described precisely. Also real-time damage characteristics of PRCM AE source location in various stress level were realized with analysis of AE data in the mechanical experiment. The results indicated that AE source location has a high consistency with damage fracture surface, and that damage process of PRCM which was similar to the process of coal-rock masses drilled from the site. According to AE data and mechanical response traits of PRCM in different stress levels were remarkable separately, which would be prerequisite to optimal design of PSE. 1 INTRODUCTION Rock sample damage characteristics analysis method based on Acoustic Emission (AE) signal has significant advantages. It can be used to monitor damage characteristics of the research object in a long-term, continuous, real-time way (Cai et al. 2003, Zhao et al. 2002, Jiang et al. 2010). In particular, micro damage and tiny energy during the process can also be described precisely. Accurately damage evolution mechanism of model material can further improve the accuracy, reliability of PSE (Cai et al. 2002).

ABSTRACT: Meticulous study on each component of the bolting support system plays an important role in assuring scientific and secure support for the mine roadways. For further understanding the influence of arch structure on steel pallet's mechanical property, and its bearing applicability when matching with different bolts, bearing capacity and deformation characteristics of square pallets with different thickness and different arch height were investigated by using laboratory loading tests; experiment results well verified the correctness of the theoretical relationship, which also was shown, The size and strength of adjustable ball-pad played an important role for complete bearing capacity of arched pallet. Simulation tests of FEM were employed to predict load-displacement and stress distribution feature of different arched pallet area. At last, based on the previous studies, arch structure calculation and the coal industry standard, a reasonable reference table was proposed for matching different bolts specification and ordinary arched pallets' size, which can be used in mines support engineering. 1 INTRODUCTION With the continuous improvement of anchor bolts support rate and level in China's coal mine roadway, meticulous study of every bolting system components are becoming increasingly important. Anchor bolt pallet, as a basic roadway support member for retaining rock surface, its mechanical effect on the pre-stress proliferation in a quite wide range, and timely on controlling surface deformation and failure for surrounding rock is very important. Engineering practice in the mining field for several decades show that, arched steel pallet has become an indispensably important component of bolting systems for roadways because of its high load-bearing performance, better stability. A number of pallets application study was conducted in a wide range of mines engineering, papers (Kang & Wu 2012, Wu et al. 2009) studied pallets load-deformation state, stress distribution feature and its effect on roadway support by the use of special stress-measuring arched pallet. Papers (Yuan & Qi 2006, Yang & He 1991) carried out a detailed study of the pallet pressure effect for the full grouted anchor bolt in actual bearing state. The arch structure's mechanical theory analysis of the butterfly-shaped tray was carried out in papers (Wang & Cai 1996, Meng & Zhang 1999), aiming at important influencing of the arch geometric parameters on its bearing strength. Papers (Liu & Zhang 1998, Wang & Chen 2013) conducted strength study of arched tray by finite element numerical simulation and mechanical loading experiments.

ABSTRACT: Applying finite different method FLAC and neural network to back-analysis the displacement of tunnel, the testing samples based on orthogonal test design and FLAC numerical simulation are used to constitute mapping of rock parameter and rock displacement, then the modulus of elasticity and lateral pressure coefficient of surrounding rock were obtained by the mapping from the measurement data. The accuracy of inverse parameters is checked by FLAC. The result shows that optimal solution of parameter can be reached from the displacement back analysis. The results can be feedback for the design of tunnel and also applied to the informative tunnel construction. The complicated geotechnical condition makes some difficulties in determination of physical and mechanical parameters of rock mass. By the finite element and boundary element methods, the obtained mechanical parameters and initial geostress usually deviate from actual values. Therefore, back-analysis methods have been proposed in which the easiest, available and precise testing parameter is displacement in extremely complex rock and soil mass. The required parameters could be solved accurately by the back-analysis method based on the displacement monitoring (Zhu & Guo 2006, Lv & Jiang 1998). In this paper, the method of displacement back-analysis combining neural network with FLAC3D is studied, and a practical solution has been established. In practice, it enables the displacement back-analysis used for this kind of surrounding rock, and the mechanical parameters and initial geostress could be obtained. PARAMETERS AND MODEL OF TUNNEL 1.1 Modeling On the issue of modeling, the closer to the objective reality in the employed mechanics model, the more number of parameters needed to be back-analyzed. However, the objects of study are rock and soil mass which are not homogeneous at all, it is a composite geologic body including joint, crack and faults.

ABSTRACT: Because of higher space of mined out area in large mining height stope, and direct roof cannot completely fill the space of mined area, hence, there is a larger space need main roof rotary deformation, violent strata pressure behavior and catastrophic accidents easily occurred. In this paper, the law of breaking about overlying strata and disaster characteristics of before and after main roof breaking by acoustic emission, which could be studied during the large mining height stope mining through imitation test with similar materials. The results showed that strata pressure behavior initial mining stage more violent than normal mining stage, main roof was broken after hydraulic support was moved when the main roof reached the maximum span, so the hydraulic support must be sliding advance of support during periodic weighting. The lead abutment pressure peak was located in front of the 5–10 m range of working face, the influence range of lead abutment pressure was located in front of 95–100 min working face, the stress concentration coefficient was between 1.35 and 2.12; The first breaking span of main roof was 90 m, the periodic breaking span of main roof was between 10 to 40 m, AE event number reached 1035 per second during the first breaking of main roof, energy rate reached 4962 MV us /s, acoustic emission signal fluctuates frequently during the periodic breaking of main roof, but the small event and low energy efficiency were main. 1 INTRODUCTION The high mining height fully mechanized is a new coal mining technology in recent years for large mining (Ju et al. 2011, Wang 2006), and it is applied to mining height of 3.5 m-7 m thick seam mining (Ju & Xu 2013). The high mining height fully mechanized is widely applied because its mining rate is higher than fully mechanized top coal caving mining (Liu et al. 2010). But there are a set of problems of violent strata pressure behavior and coal wall caving and roof fall and poor hydraulic support stability during the mining, because of mining height increases and equipment performance. The fundamental reason is overlying strata movement and breakage essential difference with the ordinary mechanized mining when the mining height is increased. So it is very necessary to study on law of breaking about overlying strata and disaster characteristics of large mining height stope, which effectively control the large mining height of safe and high efficient mining.

ABSTRACT: This paper is a numerical study on the HE-D experiment within the Opalinus clay formation at the Mont-Terri underground rock laboratory (Switzerland) using a self-developed code, i.e. a 3D Elasto-Plastic Cellular Automaton (EPCA 3D ),in which the unsaturated fluid flow, transient heat conduction and anisotropic model have been implemented. The temperature-dependent water viscosity was considered during the simulation. The simulated temperature evolution and the consequences on pore water pressure and rock deformation for Opalinus clay were well consistent with experimental data. It indicated that, the temperature distribution, pore pressure and mechanical behavior are greatly influenced by the anisotropic characteristic of Opalinus clay in HE-D. 1 INTRODUCTION Deep geological repository of high-level radioactive wastes is one of the most promising options to isolate wastes from the human environment. High-Level radioactive Waste (HLW) produces heat due to the continuous decay of radionuclide. Thus the geological disposal of HLW will impose a temperature increase upon the surrounding rock. Argillaceous rocks have a lower heat conductivity compared to granite or salt resulting in higher temperatures around the waste canister for a given heat loading. Moreover, the rock reacts sensitive to high temperatures. The increasing temperature will also influence the pore water pressure and might induce deformation of the rock, which again changes the pore water pressure. Various in-situ heating tests (Gen et al. 2007) have been performed involving the observation of the response of natural sedimentary clay. For instance, in the Hades laboratory the following experiments have been performed: the CACTUS test (Picard et al. 1994), the ATLAS test and the CERBERUS test (Bernier & Neerdael 1996, Bruyn & Labat 2002). A comprehensive understanding of coupled thermal, hydraulic and geo-mechanical processes (THM) will be a key element for the design of deep geologic repositories. Therefore, based on a self-developed numerical code, i.e. a 3D Elasto-Plastic Cellular Automaton (EPCN 3D ) (Pan et al. 2009a, 2009b), this paper presents a numerical study on the coupled THM processes in Opalinus clay in HE-D test.