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1.
Summary Although hard rock is not usually associated with large creep deformation, data collected from the tunnels and stopes of the deep South African gold mines illustrates significant time-dependent behaviour. Apart from application in mining, a better understanding of the time-dependent behaviour of crystalline rock is required to analyse the long term stability of nuclear waste repositories and to design better support for deep civil engineering tunnels in these rock types. To illustrate the subtle problems associated with using viscoelastic theory to simulate the time-dependent behaviour of hard rock, a viscoelastic convergence solution for the incremental enlargement of a tabular excavation is discussed. Data on the time-dependent deformation of a tunnel developed in hard rock further illustrates the limitations of the theory, as it is unable to simulate the fracture zone around these excavations. To simulate the rheology of the fracture zone, a continuum viscoplastic approach was developed and implemented in a finite difference code. This proved more successful in modelling the time-dependent closure of stopes and squeezing conditions in hard rock tunnels. A continuum approach, however, has limitations in areas where the squeezing behaviour is dominated by the time-dependent behaviour of prominent discontinuities such as bedding planes. To overcome this problem, a viscoplastic displacement discontinuity technique was developed. This, combined with a tessellation approach, leads to more realistic modelling of the time-dependent behaviour of the fracture zone around excavations. Received January 15, 2002; accepted June 3, 2002 Published online September 2, 2002  相似文献   

2.
Summary  This paper is a contribution to the study of tunnelling in difficult conditions, with attention paid to large time-dependent deformations, which may develop either during construction, causing instabilities of the tunnel heading and of the face, or during the service life of the tunnel. Under these circumstances the construction costs may rise due to the delays in excavation time, the stabilisation and heavy support measures that need be adopted. Following a review of characterisation and modelling of time-dependent behaviour in rock, the mechanical behaviour of Clay Shales (CS), a structurally complex formation of the Apennines (Italy), is described. Then, the key factors involved in the selection of the constitutive model for CS are identified. Two constitutive models are selected and discussed and their specific material parameters determined. A case study of a large size tunnel is presented where numerical modelling by the finite difference method is carried out. The results of modelling are compared with the monitoring data in terms of radial convergence of the tunnel and extrusion of the tunnel face.  相似文献   

3.
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4.
Summary In the exploration phase for the design of an underground cavern in a limestone formation a large number of triaxial compression tests were carried out on laboratory specimens which were characterized by a variable degree of fracturing. The data were analyzed to investigate the influence of fracture intensity and of confining stress on the mechanical parameters. In particular, investigations focused on the relationships between the parameters of the strength criteria, respectively in residual and peak conditions, on the decay of the Young modulus with stress level in the prepeak phase of the test, and on the brittleness of the rock in the postpeak phase. The tested rock can be considered as a small-scale model of a jointed rock mass, and the laboratory data therefore provide useful insight into the mechanical behaviour of rock masses, especially the relationships between residual and peak strength parameters, which are required in many analytical models and in numerical codes for the analysis of underground excavations.  相似文献   

5.
A reaction zone between a metamorphosed basic dyke and marble at Hirao-dai, north Kyushu, Japan, consists of well-organized sequential zones of diopside, garnet and wollastonite; textures are characteristic of diffusion-controlled structures. The reaction zone formed during contact metamorphism associated with intrusion of a Cretaceous granodiorite at ∼300 MPa and 700 °C. The metamorphosed basic dyke consists of diopside, biotite and plagioclase ( X Ab = 0.4–0.8), whereas the marble is almost pure calcite. The initial boundary between the dyke and the marble is probably located within the current diopside zone, as calcite occurs as remnants among diopside grains in areas close to the boundary with the garnet zone. This observation provides a criterion to judge the stability of the zonal sequence in our modelling. The formation of the reaction zone is attributed to a single-stage steady-state process with five overstepping reactions. CaO, MgO, FeO, SiO2 and AlO3/2 are the reaction-controlling components that are necessary to describe the growth of the reaction zone. An isochemical steady-diffusion model cannot reproduce the measured phase ratios of product minerals; this indicates open-system behaviour of the reaction zone. The choice of closure components is an essential task in the treatment of open-system modelling, together with determination of phase ratios (Ashworth & Birdi model) or estimation of boundary fluxes (Johnson & Carlson model). Of all the possible combinations of closure components, closure conditions for CaO and MgO provide the best results for both models. The stability of the zonal sequence is limited at relatively large values of L SiSi/ L CaCa. Similar results from the two models confirm their consistency under the same closure conditions.  相似文献   

6.
Deformation adjacent to faults and shear zones is traditionally thought to correlate with slip. Inherited structures may control damage geometry, localizing fluid flow and deformation in a damage aureole around structures, even after displacement has ceased. In this paper we document a post-shearing anastomosing foliation and fracture network that developed to one side of the Mesoarchean Marmion Shear Zone. This fracture network hosts the low-grade, disseminated Hammond Reef gold deposit. The shear zone juxtaposed a greenstone belt against tonalite gneiss and was locked by an intrusion that was emplaced during the final stages of suturing. After cessation of activity, fluids channeled along fault- and intrusion-related fractures led to the pervasive sericitization of feldspars. Foliated zones resulted from flattening in the weaker sericite-rich tonalite during progressive alteration without any change in the regional NW-SE shortening direction. The anastomosing pattern may have been inherited from an earlier ductile fabric, but sericite alteration and flattening fabrics all formed post-shearing. Thus, the apparent foliated fracture network adjacent to the Marmion Shear Zone is a second-order effect of shear-related damage, distinct in time from shear activity, adjacent to an effectively dormant shear zone. This phenomenon has implications for understanding the relative timing of fault zone activity, alteration and (in this case) gold mineralization related to long-term fault zone permeability.  相似文献   

7.
Summary Discontinuous behaviour is being observed and measured in the vicinity of excavations constructed in a bedded salt formation 650 m below ground surface for the Waste Isolation Pilot Plant (WIPP) Facility. The 2 m thick salt layer in the immediate roof acts as a beam, shearing along a thin overlying anhydrite/clay seam. Vertical separations between the immediate roof layer and the overlying strata are often observed at the anhydrite/clay seam above the centre of excavations of larger span (11 m). The floor of the excavations is comprised of a 1 m thick salt layer underlain by a 1 m thick predominately anhydrite layer (referred to as MB139). Fractures in MB139 develop beneath most excavations, with increased fracture frequency with drift span and age. In the excavations of larger span (11 m), MB139 eventually debonds along the underlying clay layer. The salt layer overlying MB139 develops both shear and tension failure. In a few locations below excavations of large span, continuous fracture systems are developing from rib to rib through MB139 and the overlying salt. In the ribs, there is limited fracturing within the first metre of most larger excavations. Vertical fractures develop in pillars at most intersections. The discontinuous behaviour is qualitatively consistent with analyses of the formation behaving as a layered medium (elastic beam analysis) and limited tensile and compressive failure of the rock salt. The significance of the discontinuous behaviour is that it can dominate the effective fluid transport properties of the formation near the excavation, and therefore requires consideration in the design of repository seals. Discontinuous behaviour must be monitored and is an important factor in the maintenance programme designed to assure a safe underground environment.  相似文献   

8.
In this paper, a fully coupled model is developed for numerical modeling of hydraulic fracturing in partially saturated weak porous formations using the extended finite element method, which provides an effective means to simulate the coupled hydro‐mechanical processes occurring during hydraulic fracturing. The developed model is for short fractures where plane strain assumptions are valid. The propagation of the hydraulic fracture is governed by the cohesive crack model, which accounts for crack closure and reopening. The developed model allows for fluid flow within the open part of the crack and crack face contact resulting from fracture closure. To prevent the unphysical crack face interpenetration during the closing mode, the crack face contact or self‐contact condition is enforced using the penalty method. Along the open part of the crack, the leakage flux through the crack faces is obtained directly as a part of the solution without introducing any simplifying assumption. If the crack undergoes the closing mode, zero leakage flux condition is imposed along the contact zone. An application of the developed model is shown in numerical modeling of pump‐in/shut‐in test. It is illustrated that the developed model is able to capture the salient features bottomhole pressure/time records exhibit and can extract the confining stress perpendicular to the direction of the hydraulic fracture propagation from the fracture closure pressure. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

9.
Squeezing intensity in tunnelling often varies over short distances, even where there is no change in the excavation method or lithology. Reliable predictions of the ground conditions ahead of the face are thus essential to avoid project setbacks. Such predictions would enable adjustments to be made during construction to the temporary support, to the excavation diameter and also to the final lining. The assessment of the behaviour of the core ahead of the face, as observed by means of extrusion measurements, provides some indications as to the mechanical characteristics of the ground. If the ground exhibits a moderate time-dependent behaviour and the effects of the support measures are taken into account, the prediction of convergence is feasible. If the ground behaviour is pronouncedly time-dependent, however, convergence predictions become very difficult, because core extrusion is governed by the short-term characteristics of the ground, which may be different from the long-term properties that govern final convergence. The case histories of the Gotthard Base Tunnel and of the Vasto tunnel show that there is a weak correlation between the axial extrusions and the convergences of the tunnel. By means of the case histories of the Tartaiguille tunnel and Raticosa tunnel, it is shown that to identify potentially weak zones on the basis of the extrusion measurements, careful processing of the monitoring data is essential: the analysis of the data has to take account of the effects of tunnel support and time, and has to eliminate errors caused by the monitoring process.  相似文献   

10.
Monitoring of strata control parameters and behaviour of a powered support was carried out during an experimental trial of a mechanized longwall sublevel caving face for exploitation of a 7.5m thick coal seam. Field observations indicated that the requirement of support density for underwinning of top coal by sublevel caving under intact strata is different from that for underwinning under broken and fractured rock mass. Analysis of the leg closure observations and support resistance variations during different mining cycles showed rapid increase of the setting load density of the support in relation to the yield load density. This resulted in a large amount of leg closure during mining cycles of the sub level caving face under broken rock strata. Due to operational constraints, the field observations could not provide enough information to visualize the behaviour of the overlying rock strata. Simulation of the field conditions was therefore performed on a physical model to bridge this gap of information. Results of laboratory investigations on the physical model are combined with those of the field to explain the critical behaviour of the support system during sublevel caving under broken rock strata.  相似文献   

11.
Evaluating rock mass geometry from photographic images   总被引：4，自引：0，他引：4  
Summary The importance of discontinuities in controlling rock mass behaviour in any engineering project involving excavations calls for a sound and spatial characterization of the discontinuity structure present. Such a characterization necessitates field work that requires sufficient rock exposures in order to obtain an adequate number of data, time and considerable cost. Photoanalysis techniques can help in overcoming the above difficulties equally well or better than other techniques. This paper refers to simple photographic techniques and their implementation for computer aided analyses for the characterization of the rock mass fracturing features. In particular attention is focused on scale problems and on reconstruction of fracture density stereoplots on the basis of data collected from one or two images according to different lithologies and outcropping conditions. The methodology for evaluating the volumetric fracture intensity follows in a slightly modified way a technique previously suggested in the literature. Certain reported examples allow to validate the photoanalytical technique used and the proposed method of analysis. Furthermore, analyses on planar density, spacing, frequency, terminations in solid rock or against other discontinuities and spatial correlation have been implemented in a software to yield a more complete rock mass characterization. At the same time input data and analysis results are produced in data files available as input for numerical analyses.  相似文献   

12.
Summary  During the crossing of brittle rock formations at the L?tschberg base tunnel, failure phenomena have been observed both at the tunnel face and at the walls. A detailed analysis has been undertaken to explain these behaviours, based on the recent developments of Canadian research on brittle failure mechanisms. At the tunnel walls, a very good agreement is found between the calculated and observed damage and between two prediction methods, i.e. a semi-empirical failure criterion and elastic calculations with the “brittle Hoek-Brown parameters.” Near the face, due to the 3D nature of the stress conditions, some limitations of these approaches have been highlighted, and the growth of wall failure has been analysed. This research allowed a better understanding of the brittle rock mass behaviour at the L?tschberg base tunnel and showed that brittle failure processes dominate the behaviour of deep, highly stressed excavations in massive to moderately jointed rock. It also illustrates where improvements to the adopted approaches are required.  相似文献   

13.
Groundwater flow is a major issue in underground opening in fractured rocks. Because of finding the fracture connectivity, contribution of each fracture in flow, and fracture connectivity to excavation boundary, the prediction of water flow to underground excavations is difficult. Simulation of fracture characteristics and spatial distribution is necessary to obtain realistic estimation of inflow quantity to tunnel and underground excavations. In this research, a computer code for three-dimensional discrete fracture network modeling of water inflow into underground excavations was developed. In this code, the fractures are simulated as ellipsoid while geometrical properties of the fractures are reproduced using a stochastic method. Properties such as the size, orientation, and density of the fractures are modeled by their respective probability distributions, which are obtained from field measurements. According to the fracture condition, the flow paths in rock mass are determined. The flow paths are considered as channels with rectangular sections in which channel width and fracture aperture determine geometry of channel section. Inflow into excavation is predicted ignoring matrix permeability and considering the hydrogeological conditions. To verify presented model, simulation results were compared to a part of the Cheshmeh-Roozieh water transfer tunnel in Iran. The results obtained from this research are in good agreement with the field data. Thus, the average of the predicted inflow has just an approximation error equal to 17.8%, and its standard deviation is 8.6 l/s, which is equal to 21% of the observed value that demonstrates low dispersion of the predicted values.  相似文献   

14.
工作面回采过程中,覆岩破坏特征对于煤矿水灾害和瓦斯防治具有重要意义,为了进一步研究综放开采覆岩破坏特征。以山西某矿5.82m大采高工作面为试验面,采用分段注水、钻孔电视、地质雷达、微震监测探测覆岩破坏高度,对破坏过程进行了数值模拟研究,并对裂隙演化进行了相似模拟试验,同时对传统经验公式进行了修正,研究结果表明:综放开采垮落带发育高度为43.1m,断裂带发育高度为86.7m;垮落带、断裂带、导水断裂带各测试方法之间相差分别小于4.5%、7.1%、9.0%;工作面采动前,裂隙发育度低,而采动后,裂隙数量明显增多,发育度增加;近煤壁区域为裂隙聚集区,密度曲线呈“蛇”型分布;得到新的适合该矿地质条件下的覆岩导水断裂带发育高度经验公式。  相似文献   

15.
断层破裂带附近采场采动效应的流固耦合分析   总被引：4，自引：0，他引：4  
卢兴利  刘泉声  吴昌勇  赵军 《岩土力学》2009,30(Z1):165-168
矿井底板突水是一个复杂的多物理场耦合问题,结合含断层破裂带条件下采场开采的工程背景,通过离散元流固耦合分析,研究了采场工作面推进过程中断层带的变形与受力情况以及底板支承压力、渗流矢量和渗流速度的动态发展规律和分布特征。相关模拟结果表明,采场中煤层的开采与断层破裂带之间是相互影响的,以支承压力为代表的采动应力是底板破坏形成导水裂隙带及断层“活化”突水的一个主要诱因,而断层的存在也使得工作面与断层带范围内的围岩应力更加集中,增大了底板破坏突水的危险性。采动过程中,底板破坏所形成的导水裂隙带主要集中在工作面前方及下方围岩中,这些区域渗流速度较大,是形成突水的主要通道。  相似文献   

16.
In situ measurements of deformations, stresses, and closure of fractures, affecting water inflow following coal mining, are challenging due to the inaccessibility of fractured rock. In this paper, the authors studied the closure process of the fractured rock mass with the cover stress re-establishment based on a theoretical analysis and a scale model testing. A quantitative analysis is used to study the fracture distribution in the fractured zone. A function to describe a fracture aperture distribution in the fractured zone is proposed, which takes into account the curvature and thickness of the fractured rock. The theoretical analysis and a scale model testing both indicate that the cover stress re-establishment with mining distance increasing and the relationship between the fracture closure and cover stress re-establishment both satisfy a logarithmic function. The scale model test also shows the following features: (1) the fracture ratio (which is the fracture area divided by the total area of fracture and intact rock with a unit width in the vertical or horizontal direction) in the lower part of the fractured rock mass is greater than that in the upper part; (2) the initially fast decreased of fracture ratios is then followed by a slower decrease during the cover stress re-establishment process; (3) in the upper part of the rock mass, the vertical directional fractures with small apertures are being closed with cover stress re-establishment, which indicates an increase in the water resistance reducing the seepage from these parts of the fractured zone. This study improves the general understanding of the fracture closure process and cover stress re-establishment in the fractured rock mass after coal mining ceased, and provides a theoretical basis for water resource protection in case of underground coal mining.  相似文献   

17.
This paper presents a case study of water inrush on a mine working face from roof strata. The flow-rock failure process analysis (F-RFPA2D) code with an improved flow-stress-damage (FSD) model was adopted to perform the failure and coupling analysis. The improved FSD model was used to represent the permeability variation at the four stages (elastic, damaged, cracked, and crack closure) of the rock failure process. The fracture initiation, propagation, and coalescence in the stressed strata and the seepage field evolution in the stress field are represented visually during the whole process of water inrush. The failure zone with high permeability induced by mining disturbance becomes the water-conducting zone after full excavation of the coal seam. The height of the water-conducting zone obtained in this study is in reasonable accordance with that predicted by an empirical formula. It is definitely clarified that the water inrush from the roof strata is induced by the failure zone full of vertical coalesced mine fractures. It is unlikely that roof accidents resulting in water inrush would occur if the water-conducting zone does not grow upwards into the aquifer. The main task for mine extraction under a confined aquifer is to locate the aquifer and find the maximum height of the water-conducting zone, which is very important for mine construction and support design.  相似文献   

18.
四川省青川断裂的特征及形成的物理条件   总被引：3，自引：0，他引：3  
本文详细地讨论了四川省青川断裂的断裂特征及形成的物理条件。对断裂构造岩的微构造和宏观构造进行了细致的描述分析,将断裂岩分为四个带。结合区域资料,讨论了断裂的形成时代及与邻区的关系。  相似文献   

19.
针对煤层顶板导水裂缝带部分波及含水层时涌水量预测不准确问题,通过对煤层回采后顶板水文地质条件变化、顶板含水层地下水渗流场变化进行分析,建立工作面水文地质概念模型,得出了基于达西定律和承压水Dupuit理论的顶部进水型涌水量预测模型。通过对数学模型的分析论证,并将此涌水量数学模型应用于实际生产,得出涌水量预测模型概化合理,符合煤层开采实际情况下水文地质条件,对于顶板导水裂缝带部分波及含水层情况下工作面涌水量预测有借鉴意义。   相似文献   

20.
A numerical procedure has been developed for predicting dilation (porosity) and gas permeability changes in rock salt. The hierarchical single-surface constitutive model of Desai and co-workers is used a finite element program to calculate the state of stress and strain surrounding excavations in rock salt. The elastoplastic constitutive model accounts for strain hardening, a non-associative volumetric response and stress-path-dependent behaviour. The calculated stress and strain fields are used in a flow model based on the equivalent channel concept to predict permeability. Parameters for both the mechanical and permeability models are developed from laboratory test results. Two field experiments adjacent to underground excavations are modelled. The extent of the dilated rock zone around the excavation is predicted well, but the magnitude of the porosity and gas permeability is underpredicted very near the excavations. This discrepancy is attributed to model parameters derived from loading-only laboratory tests, whereas significant unloading occurs in the field. The shape of the yield surface was found to be an important factor in dilation and permeability predictions. Similar stress, strain and permeability fields were obtained with different model types (plane strain or axisymmetric) and initial stress states, and with instantaneous and progressive excavation.  相似文献   

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