基于结构面网络模拟的桥基岩体空间状态分析

分析结构面在岩体中的分布和组合特征是研究岩体稳定性的前提。根据结构面网络随机模拟方法,通过对岩体表面结构面的测量,可以建立岩体结构面空间分布的概率统计模型,从而确立了岩体结构面的网络结构模型。在此基础上分析了局部临空块体的空间几何形态,指出了块体的可能破坏形式,从宏观角度对块体系统整体稳定性进行了预测。     

Developments in the Assessment of In-situ Block Size Distributions of Rock Masses

Summary  The block sizes in a rock mass play an important role in many rock engineering projects and therefore the assessment of in-situ block size distribution (IBSD) has been an increasing pursuit of researchers in mining, quarrying and highway cutting operations. This paper discusses further developments in the assessment of IBSD which build upon a broadly accessible approach for engineers published previously by the Geomaterials Unit. The original research provided look-up tables appropriate for field data, with theoretical joint set spacing distributions and an assumption that discontinuities extend indefinitely. The developments reported in the paper include: the prediction of IBSD with special reference to discontinuity sets with fractal spacing distributions; the influence of impersistence of discontinuities on the prediction of IBSD; and the use of grey correlation analysis when selecting a closely fitting theoretical distribution for discontinuity spacing data. Various approaches to IBSD assessment are discussed.     

Kinematic and Block Theory Analyses for Shiplock Slopes of the Three Gorges Dam Site in China

The granitic rock mass that exists in the shiplock region of the Three Gorges dam site contains a number of major discontinuities and about four sets of minor discontinuities. One hundred and thirty three major discontinuities have been mapped around the shiplock covering an area of 1740×600 m. These major discontinuities were used to perform rock slope kinematic and block theory analyses. Kinematic analyses were performed under the following two cases: (1) assuming all the mapped discontinuities cross the shiplock; (2) using only discontinuities that actually intersect the shiplock. Under case (1) and case (2) the shiplock faces in the proposed permanent shiplock region in fresh rock were found to be stable up to a cut slope of about 45° and 58°, respectively. Block theory was applied to identify different block types that exist on the shiplock faces and to estimate the maximum safe slope angles on the shiplock faces. The orientations of the major discontinuities that actually intersect the shiplocks were considered in this analysis. The total length of the shiplock (1750 m) was divided into 50 m segments. From the stereo-plots, the key blocks (Type I) and/or potential key blocks (Type II) were found for only five segments of the shiplock slopes. It was found that the dip of the cut slope should be less than about 60° to avoid creation of a key block on the proposed shiplock slopes. However, it is important to keep in mind that these conclusions are based on the kinematic analyses performed using only the major discontinuities. Further kinematic as well as kinetic analyses are recommended incorporating minor discontinuities, water forces, earthquake forces etc. before making the final conclusions about the maximum safe slope angle for the shiplock region.     

汤屯高速公路某变质砂岩边坡块体稳定性评价

汤屯高速公路存在大量变质砂岩组成的高边坡,岩体质量一般较好,但结构面发育,组合形成大量潜在失稳块体,这些块体的稳定性状况直接影响边坡安全.本文选取一个典型边坡,通过对边坡结构面详细地质素描,查明构成可能失稳块体的边界条件,并利用块体理论对可能失稳的块体在各种工况下的稳定性进行计算,并结合块体工程特性,对边坡的稳定性进行系统评价.该研究成果对该边坡的支护优化设计提供了基础资料,同时对同类型的边坡设计具有一定的指导意义.     

Estimation of Block Sizes for Rock Masses with Non-persistent Joints

Summary  Discontinuities or joints in the rock mass have various shapes and sizes. Along with the joint orientation and spacing, the joint persistence, or the relative size of the joint, is one of the most important factors in determining the block sizes of jointed rock masses. Although the importance of joint persistence on the overall rock mass strength has long been identified, the impact of persistence on rock strength is in most current rock mass classification systems underrepresented. If joints are assumed to be persistent, as is the case in most designs, the sizes of the rock blocks tend to be underestimated. This can lead to more removable blocks than actually exist in-situ. In addition, a poor understanding of the rock bridge strength may lead to lower rock mass strengths, and consequently, to excessive expenditure on rock support. In this study, we suggest and verify a method for the determination of the block sizes considering joint persistence. The idea emerges from a quantitative approach to apply the GSI system for rock mass classification, in which the accurate block size is required. There is a need to statistically analyze how the distribution of rock bridges according to the combination of joint orientation, spacing, and persistence will affect the actual size of each individual block. For this purpose, we generate various combinations of joints with different geometric conditions by the orthogonal arrays using the distinct element analysis tools of UDEC and 3DEC. Equivalent block sizes (areas in 2D and volumes in 3D) and their distributions are obtained from the numerical simulation. Correlation analysis is then performed to relate the block sizes predicted by the empirical equation to those obtained from the numerical model simulation. The results support the concept of equivalent block size proposed by Cai et al. (2004, Int. J. Rock Mech. Min. Sci., 41(1), 3–19).     

A rigorous solution for the stability of polyhedral rock blocks

Block theory has been widely applied to stability analysis of rock engineering due to its clear concept and elegant geometrical theory. For a general block with multiple discontinuity planes, it is assumed that contact is only maintained on a single plane (single-plane sliding) or two intersecting planes (double-plane sliding) in block theory analysis. Since the normal forces and shear resistances acting on the other discontinuity planes are omitted, it can cause unreasonable estimations of block failure modes and incorrect calculation of factors of safety. In this study, a new method is presented that permits to consider the contribution of the normal forces and shear resistances acting on each discontinuity plane to the block stability. The proposed method meets all of the force-equilibrium and moment-equilibrium conditions and provides a rigorous solution for stability of general blocks with any number of faces and any shape. Some typical polyhedral blocks in rock slopes are analyzed using block theory and the proposed method. The results indicate that the traditional block theory may give a misleading conclusion for the predictions of stability and sliding direction of rock blocks when contact occurs on more than two discontinuity planes.     

金沙江溪洛渡水电站拱肩槽工程边坡块体稳定性评价

采用层次性分析原理，研究了金沙江溪洛渡水电站拱肩槽工程边坡各类结构面和临空面组合而成的块体特征，将边坡块体分为确定性块体、半确定性块体和随机块体三个层次；采用块体理论计算评价了不同层次的块体在天然、地震、爆破、地下水状况下的稳定性，并对影响块体稳定性各种内外因素做了敏感性分析，建立了一套非规则边坡块体稳定性分析评价的技术思路和方法体系。研究表明，拱肩槽边坡出现确定性块体的可能性较小，边坡中的不稳定块体大部分为半确定性块体，且规模较小，影响深度有限，切割边界不完善。     

Numerical Modelling of Steep Slopes in Open Rock Quarries

The key question regarding steep rock slopes along rock quarries is their stability because a rock slope failure can have critical results. In this study, the aim is to investigate the areas with potential risk for jointed karstic limestones in a rock quarry. First, to determine rock mass properties, scan-line surveys were performed, and the major orientations of discontinuities were analyzed using stereographic projection. Then, the physicomechanical properties of the slope-forming rock were determined in the laboratory, and geomechanical properties of the rock mass were determined using an empirical failure criterion. Finally, the quarry slope stability was assessed in accordance with numerical modelling. According to the results obtained, the numerical modelling of steep rock slopes can be efficiently evaluated by using finite element method. Beside this, the presence of joints intersecting the main discontinuity sets, the filling materials of discontinuities resulting from weathering of limestone and surface deposits, surcharge load due to mine waste dumped on the slopes and excavation blasting during construction of quarry area play a key role when modelling the steep rock slopes by using finite element method.     

Landslides and neotectonic activities in the Main Boundary Thrust (MBT) zone: Southeastern Kumaun,Uttarakhand

Main Boundary Thrust (MBT) zone is constituted of some of the landslide prone areas in southeastern part of Kumaun Sub-Himalaya. Role of landslides as natural hazard and hill slope modifying agent is well documented from various part of Himalayan region and southern hills of Kumaun particularly in the MBT zone, which are susceptible to various type of mass movement. The rocks making up the slopes has been put to a number of brittle deformation phases during the movement along the MBT, and are traversed by number of joint sets. In the open slope these intersecting joint sets forms wedges and are the most favorable site for initiation of rockfalls and other types of landslides. Landslides are taking place primarily due to high angle slopes, formation of structural wedges along the free steep slopes, sheared nature of the rocks due to proximity to the MBT and neotectonic activities along the MBT and other transverse faults. Wedge failure is a common type of landslides in rock slopes characterized by multiple joints and acts as sliding planes for the failed blocks. Field observations and wedge failure analysis indicates most of the landslides taking place in MBT zone of Kumaun Sub-Himalaya are joint controlled. Safety Factor analysis suggests MBT zone of Kumaun Sub-Himalayan region is prone to landslides and related mass movements. This zone is also neotectonically active as indicated by various geomorphic signatures such as structurally controlled drainage pattern, offsetting of fan by MBT and formation of number of small lakes.     

缓倾外层状结构边坡变形破坏模式及支护对策研究

高速公路开挖形成越来越多的工程边坡。缓倾外层状结构边坡作为一种典型的岩质边坡,一般情况下整体稳定性较好,但在特定的结构面组合状况下,开挖后也可能产生整体变形破坏。本文以软弱结构面和长大裂隙发育的公路工程边坡为例,通过岩体结构及边坡一定范围内已有边坡破坏现象的调查研究,采用工程地质类比和三维离散元法综合分析边坡变形破坏模式,并针对变形破坏模式的特点,提出支护对策。研究结果表明,结构面贯通坡体形成切割块体的后缘和侧缘边界时,缓倾外层状结构边坡可沿层面产生滑移-拉裂变形,若滑面与临空面具有一定夹角,边坡的变形可表现为旋转式滑移-拉裂;结构面组合控制的缓倾外层状结构岩质边坡稳定性受坡体中下部的关键块体控制,一旦关键块体失稳,将引起上部块体的连锁失稳,此类边坡变形控制的重点是对关键块体分布区域进行强支护;支护工程实施后的变形监测结果表明,基于变形破坏模式分析的边坡支护方案保证了边坡施工和运营过程中的安全。     

Influence of discontinuities and clay minerals in their filling materials on the instability of rock slopes

To assess the influence of discontinuities and clay minerals in their filling materials on the instability of rock slopes, seven rock slopes along the margin of Ganjnameh–Shahrestaneh Road, Hamedan Province, Western Iran were selected, and the physical and mechanical properties of their rocks and discontinuities were determined. By statistical studies of the discontinuities, rock slope stability analysis has been performed using kinematic and limit equilibrium methods so that safety factors for the rock slopes can be calculated. Also, sampling of filling materials and X-ray diffraction tests have been done to identify the clay minerals in the filling materials. The lithologies of the studied rock slopes are granite, diorite and hornfels. The presence of discontinuities and weakness planes with different orientations and clay minerals in filling materials of discontinuities are effective factors that cause plane, wedge and toppling failures in the rock slopes. Clay minerals as filling materials of discontinuities in the studied rock slope facilitate their instability by two different methods. First, absorption of water by infilling clay minerals causes the friction angle of discontinuity surfaces that leads to plane and wedge failures to be reduced. Second, water absorption causes the swelling of clay infilling minerals that leads to toppling failure.     

Determining the size and shape of blocks from linear sampling for geotechnical rock mass classification and assessment

Classifying and assessing geotechnical aspects of rock masses involves combining parameters in various ways, guided by empirical considerations, to derive quantitative geotechnical parameters. Geological structures and the deformation history of rocks underpin the nature of rock masses. The kinematics of a deforming rock mass may occur as sliding along throughgoing discontinuities or as distributed sliding on block faces. Distributed sliding will tend to disrupt the continuity of planar structures such that data on the size and shape of blocks is needed, rather than relying on discontinuity orientation data alone. Orientation and spacing data can be combined to provide a geometric analysis of block systems from linear samples, such as drill core. Dihedral angles and spacing of sequential pairs of discontinuities provides a sample of the size and shape of blocks that can be interpreted stereologically. Further detail can be derived by combining neighbouring intersections that enclose or partially enclose individual blocks. The shape and size of a block can be represented on a stereograph with the enclosing faces shown as poles and their perpendicular distance from an arbitrary point inside the block shown as a number. Identifying the size and shape of specific blocks rather than relying on statistical methods is beneficial to critical aspects of design such as analysing keyblocks that would be exposed during excavations. The detailed characterization of block size and shape is also a step toward interpreting the kinematics of rock mass deformation and the analysis of rock masses as ultra-close packed dilatant granular systems.     

岩质边坡复合型破坏机制的改进运动单元法研究

目前运动单元法的研究主要集中于土质边坡,未涉及到岩质边坡稳定性分析问题;而岩体中孕育有不同特性的结构面,控制着岩质边坡的力学行为。为求解结构面控制作用下岩质边坡“结构面滑移-岩桥剪断”复合型破坏问题,研究了塑性滑移区节点在岩桥内和结构面上的运动约束条件,推导了含结构面的运动单元计算公式,提出了改进运动单元法。通过经典算例的对比分析,验证了改进运动单元法计算结果的准确性。研究结果表明:岩桥位置、结构面贯通度和结构面倾角是控制岩质边坡力学行为的3个主要影响因素。岩桥越接近坡顶,改进运动单元法所得安全系数越大,而Jennings法无法反映岩桥位置的影响效应。高贯通度的结构面导致岩质边坡发生“结构面滑移-岩桥剪断”复合型破坏模式,安全系数较小;而低贯通度的结构面导致完整岩石发生破坏,安全系数较大。水平或陡倾角结构面导致滑裂面穿切结构面,安全系数较大;而对于其它倾角情况下的结构面,岩质边坡发生“结构面滑移-岩桥剪断”复合型破坏模式,安全系数较小。实例应用结果说明该方法可以有效评价岩质边坡的稳定状态,可在类似工程中应用推广。     

弹粘塑性块体单元法在龙滩水电站右坝肩边坡稳定分析中的应用

介绍了三维弹粘塑性块体单元法的基本原理。该方法假定岩石块体为刚体,只考虑结构面的变形和强度特性。在建立块体系统的平衡方程、结构面的变形与块体位移的几何相容方程以及结构面上的弹粘塑性本构方程的基础上,出块体系统位移与稳定的基本方程。针对龙滩水电站右坝肩边坡地质条件复杂,块体稳定问题较为突出的情况,采用块体单元法计算了边坡中典型结构面切割形成的特定块体在不同工况下的强度储备安全系数,并针对结构面的几何参数和力学参数等重要影响因素进行了敏感性分析,为工程设计提供了依据。应用表明,作为一种新型的水工结构数值方法,块体单元法应用于复杂地质条件下的岩石高边坡的稳定和变形分析具有准确、适用和简便的特点。     

Terrestrial Photogrammetry and Numerical Modelling for the Stability Analysis of Rock Slopes in High Mountain Areas: Aiguilles Marbrées case

Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as “permafrost”, can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features.     

An Experimental and Theoretical Approach on the Modeling of Sliding Response of Rock Wedges under Dynamic Loading

The stability of rock slopes under dynamic loading in mining and civil engineering depends upon the slope geometry, mechanical properties of rock mass and discontinuities, and the characteristics of dynamic loads with time. The wedge failure is one of the common forms of slope failures. The authors presented some stability conditions for rock wedges under dynamic loading and they confirmed their validity through the laboratory experimental studies in a previous paper in 2000, which is often quoted by others to validate their softwares, including some commercial software. In this study, the authors investigate the sliding responses of rock wedges under dynamic loads rather than the initiation of wedge sliding. First, some laboratory model tests are described. On the basis of these model tests on rock wedges, the theoretical model proposed previously is extended to compute the sliding responses of rock wedges in time domain. The proposed theoretical model is applied to simulate the sliding responses of rock wedge model tests and its validity is discussed. In the final part, the method proposed is applied to actual wedge failures observed in 1995 Dinar earthquake and 2005 Pakistan–Kashmir earthquake, and the results are discussed.     

乌东德水电站右岸地下厂房随机块体特征研究

随机块体的几何特征和稳定性是水利水电工程中地下厂房支护设计的重要依据。对乌东德水电站右岸地下厂房随机块体的特征进行了深入研究。对研究区域内实测的裂隙参数进行了分组统计,确定了各组裂隙产状、迹长等参数的分布形式和大小。利用逆建模方法建立了三维裂隙网络模型,获取了各组裂隙的直径和三维密度。采用一般块体方法对地下厂房进行随机块体的识别和稳定性分析,利用GeneralBlock软件进行了10次随机实现,对10次计算结果进行了统计分析和讨论。研究结果表明,结构面与开挖面形成的随机块体集中在地下厂房的顶拱部位,10次随机实现中,地下厂房全长范围内平均每次形成的随机块体为414个;随机块体的平均体积为2.9 m³,最大块体的体积达152.0 m³;可移动块体中,大部分为稳定块体,不稳定块体均以坠落形式破坏;构成可移动块体的结构面多为3~4条,最多可达12条,其中倾W向的中等倾角裂隙是构成块体并可能造成块体失稳的最危险结构面;随机块体的平均深度为1.2 m,最大深度为8.8 m。建议支护锚杆应尽量穿透倾W向中等倾角的长大裂隙,且锚杆支护长度大于8.8 m。     

A rational and realistic rock mass modelling strategy for the stability analysis of blocky rock mass

Due to the importance of a realistic rock mass model for the achievement of accurate and reliable results from numerical analysis of blocky rock mass, a probability based rock mass geometrical model is proposed in the present study. The rock mass geometry is built based on site investigation data and stochastic analysis of the discontinuity mapping results. The discontinuities and/or sets of them, either finite or infinite in size, planar or non-planar, convex or concave in shape, can be implemented in the three-dimensional rock mass model. Key block analysis and support design are then suggested to the stochastic rock mass models. To achieve a realistic stability analysis of the rock mass with the proposed probabilistic rock mass model, a few suggestions have also been made. These include the adoption of realistic constitutive models to intact rock and rock discontinuities, use of numerical model to technically handle numerical difficulties and development of a realistic modelling strategy to achieve realistic and affordable computational cost, etc.     

岩体结构稳定分析原理和方法

工程实践表明,在边坡、地基或地下工程岩体中几组地质结构面和临空面的组合往往构成可能失稳的岩石结构体、存在向临空面运动的可能性、影响到工程岩体的稳定性。这时必须针对这种可能失稳的结构体进行分析,采取必要的加固或处理。关于岩石结构体的稳定分析,文献中已有一些报导,但偏重于图解和计算方法、一般是针对特定单一块体的解析,仅应用于边坡工程。     

Geological controls on rock mass classification of coal from Huntly East Mine, New Zealand

Rock Mass Rating (RMR) measurements from 65 sites within Huntly East underground coal mine are presented. All measurements are in coal, for which the dominant discontinuities are vertical cleat. Basic RMR values using two discontinuity spacings are presented: overall RMR based on the average spacing of all individual discontinuities; and cleat zone RMR based on the average spacing between zones of cleat. Cleat orientations are highly variable, but on average approximately parallel horizontal stress axes (face cleat follows maximum horizontal stress axis, butt cleat follows minimum horizontal stress axis).Contours of RMR variations throughout the mine are used to compare rock mass conditions with geological structure. It is apparent that: (1) RMR is least within downthrown fault blocks, and particularly immediately on the downthrown sides of faults, and greatest in upthrown fault blocks; and (2) RMR contours parallel horizontal stress axes within fault-bounded blocks, and bend to parallel faults at block boundaries. From similar contours for parameters contributing to RMR, the Rock Quality Designation (RQD), groundwater rating, and discontinuity condition rating create most of the observed variations in RMR. RQD is determined from the measured discontinuity frequency and hence is a measure of the degree of fracturing of the rock mass. This is interpreted as influencing the groundwater and condition parameters directly by allowing greater water ingress. Discontinuity frequency is greatest (least spacing) in the immediate vicinity of faults, and in downthrown fault blocks, generating low RMR values. Within fault blocks RQD varies little, so RMR contours align with cleat orientations.As RMR contours, faults, stress field and cleat orientation are clearly interrelated, there is unequivocally a connection between RMR and structural geology; this allows some predictive capacity in terms of ground conditions. If geological features can be accurately defined through either drilling programs or seismic surveys, then ground conditions may be predicted before panels are driven.