Discontinuous Rock Mass Research Articles

Optimization of LiDAR scanning and processing for automated structural evaluation of discontinuities in rockmasses

Terrestrial light detection and ranging (LiDAR) can be used for the delineation and evaluation of geomechanically controlled hazards. The United States Geological Survey [1] has adopted the use of LiDAR through numerous projects, as discussed in [2]. Other examples of the use of LiDAR surveys for geological data collection include discussion of the process of acquiring digital outcrop models for stratigraphic modelling [3], mapping basalt flow units [4], structural mapping of a large landslide [5], and evaluation of rockfall source and accumulation zones [6,7]. In non-geologicalbased applications, LiDAR has been used for projects ranging from volumetric analysis in open pit mines [8], to recording and cataloguing archaeological digs in ancient ruins [9]. The equipment mobility, accuracy, and rate of data collection, in comparison to conventional surveying and stereophotogrammetric methods, have allowed existing surface analysis projects to proceed at unprecedented levels of detail and have promoted new applications. The use of terrestrial (ground based) LiDAR as a structural analysis and measurement tool has been investigated in detail by Kemeny and Post [10], Feng and Roshoff [11], Pringle et al. [12], Slob et al. [13] and others. Once the data is acquired and the primary 3D model is generated (as x, y, z data points with intensity scalars or mapped colourization via photo coupling), the analytical process can proceed in a similar fashion to modern photogrammetric techniques such as those applied by Haneberg et al. [14]. Both applications can replace traditional field mapping processes including the use of a compass or inclinometer to measure orientation, photos and notebooks to keep records, and manual data entry. Further, the conventional measurement of

Contributions to Géotechnique 1948–2008: Engineering geology, rock mechanics and rock engineering

Throughout its history Géotechnique has regularly published papers on the fundamentals of engineering geology, the core concepts of rock mechanics, and the practice of rock engineering. In totality these papers provide a concise history of the development of these areas of geotechnics. Here, a review of many of these papers is presented in terms of the specific themes of engineering geology, rock slope instability, behaviour of intact rock and discontinuities in rock, field measurements in rock mechanics, discontinuous rock masses, numerical modelling, and rock engineering. Papers covering a wide range of issues within these themes are outlined, together with an indication of how they have influenced later developments. The review clearly demonstrates how Géotechnique has been at the forefront of rock mechanics, rock engineering and engineering geology for the whole of its 60-year existence.

Stress recovery procedure for discontinuous deformation analysis

The discontinuous deformation analysis (DDA) has been widely applied for rock engineering problems due to its special features in modeling the discontinuous rock mass. A linear polynomial function is often used in the standard DDA to ease the complex contact determination between the blocks. This linear displacement function generates a constant stress field within a block, which cannot be effectively used to model the stress variation within a block and across the block interface, especially in the region with a large stress gradient. In this paper, a stress recovery procedure is proposed for those DDA blocks which are glued together. Such a procedure can improve the stress accuracy along the block interface, and can be used for more accurate contact determination. Two numerical examples are presented to study the stress accuracy of the proposed method, and the results show that the proposed stress recovery method provides a better accuracy than the direct DDA and the averaging method.

Practical Rock Engineering

Practical Rock Engineering is an e-book based upon Dr. Hoek's years of experience in rock engineering and has recently been reissued as the 2007 edition. The book presents rock engineering in a practical manner and in 17 individual chapters. Each chapter stands alone with its explanations, figures, tables, conclusions, and references. Fourteen chapters present topics ranging from development, design, rock mass classification, discontinuities, instability of tunnels, safety factors, analysis of rockfall hazards, rock mass properties, weak rock tunnels, rockbolts and cables, and shotcrete support to blasting damage in rock engineering. Chapters 6, 7, and 13 present solely case histories; these refer to underground tunneling, slope stability, and the design of underground caverns. The book can be downloaded via the Internet at the Rocscience web page (http://www.rocscience.com) either as a single PDF file or as single chapters. A brief explanation of each chapter follows. Chapter 1 discusses the development of rock engineering. This chapter introduces historical developments in rock engineering from 1773 to 1979. Three major disasters making a major contribution to the general development of rock engineering are explained. This chapter also introduces the reader to rock burst and elastic theory, discontinuities in rock masses, geological data collection, rock mass classification, rock mass strength, in situ stress measurements, groundwater problems, rock reinforcement and support design, excavation methods in rock, etc. The purpose of Chapter 2 is to draw attention to acceptable designs in rock engineering. The chapter is extended by four case histories such …

不連続面を有する材料の変形挙動に関する実験的および数値解析的研究

The mechanical behaviors of a discontinuous rock mass are strongly affected by discontinuities included in the rock mass. The surrounding rock mass around an underground cavern is sub-jected to compressive stress even after the cavern excavation. In this case, the shear properties of the discontinuity play an importantroll in the macroscopic behavior of the rock mass. Thus, the studies on the shear properties are well carried out from not only experimental but also numerical points of view so as to clarify the behaviors of the rock mass. However, there is few studies in which the mechanism of the alteration of the shear properties under various conditions is discussed. In this article, the experimental and numerical studies in terms of the material having a single discontinuity is conducted in order to seize the mechanism of the alteration of the shear properties. In the numerical study, the alteration is modeled by the concept thatthe surface ofthe discontinuity can be worn away with increasing the load which is applied to the material. Through the comparison between the experimental and numerical studies, it is turned out that the macroscopic behaviors of the rock mass are influenced by the friction of discontinuity.

Integrated techniques for behavior evaluation of large-scale underground openings by using distinct element method

The stability and support effects of large-scale underground openings located in the jointed rock masses are principally ruled by the mechanical behavior of discontinuities. The major deformations of the host rock masses containing underground openings originate from the normal and shear movements along the walls of discontinuities. A number of experimental and numerical investigations have demonstrated the significant influences of discontinuities on the mechanical, thermal and hydraulic behaviors of discontinuous rock masses, indicating that the deformational mechanism and stability of underground facilities in the discontinuous rock masses depend not only on the existing discontinuities but also the new cracks, which are generated and thereafter keep propagation due mainly to the stress relaxation induced by excavation. In this study, a two dimensional distinct element method was used to analyze the behavior of underground cavern based on in-situ geological data and experimental feature of rock joints. The properties of rock joints used in the analyses were obtained by using the newly developed high-performance direct shear test apparatus. Some local deformational behaviors of deep underground cavern influenced by the characteristics of discontinuity distributions were also discussed. A multiple system for analyzing the feature of geometrical distribution of rock joints was furthermore developed. The results revealed that the orientation, position and density of discontinuities around a cavern influence its deformational behavior and stability significantly.

Practical determination of mechanical design parameters of intact rock considering scale effect

As a rule, the change in mechanical properties of rock by specimen size is regarded as scale effect. A rock mass basically consists of two components: intact rock and discontinuities, each of which has different scale effects. In order to numerically analyze the behavior of discontinuous rock masses, sufficient mechanical properties must be determined not only for discontinuities but also for intact rock taking into consideration the different scale effects. This paper reviews the scale effect on strength and deformation characteristics of intact rock, and also discusses the possibility of using standard specimens to estimate strength and deformation characteristics of actual-scale rock. Finally, we propose an adequate method for the practical determination of mechanical design parameters based on the above discussions.

Research on Fracture Damage Coupled with Crack Arrest by Anchorage Model of Discontinuous Jointed Rock Mass under the State of Complex Stress

Based on the hypothesis of equivalent strain energy and the theories of fracture mechanics and damage mechanics，the constitutive model and fracture damage mechanism of bolted discontinuous jointed rockmass are systematically studied under the state of complex stresses. Initially ， considering the equivalent strain energy ， the constitutive relation of anchored discontinuous jointed rockmass is derived under the state of compression-shear stresses. The constitutive relation under the state of tension-shear stresses is also developed according to the theory of self-consistence. Next，the damage evolution equations of discontinuous multi-crack rockmass under compression-shear and tension-shear are put forward according to the wing crack-initiating criterion. Finally，based on the above constitutive models and the damage evolution equations three-dimensional finite element procedures have been developed to evaluate the stability and deformability of the surrounding rock mass during excavation and supporting. The calculated results indicate that above-mentioned constitutive relation and the damage evolution equations are available.

Fragmentation Energy in Rock Blasting

The theoretical explosive energy used in blasting is a common issue in many recent research works (Spathis 1999; Sanchidrian 2003). It is currently admitted that the theoretical available energy of the explosives is split into several parts during a blast: seismic, kinetic, backbreaks, heave, heat and fragmentation energies. Concerning this last one, the energy devoted to the breakage and to the creation of blocks within the muckpile can be separated from the microcracking energy which is devoted to developing new and/or extending existing micro cracks within the blocks (Hamdi et al. 2001; Lopez et al. 2002). In order to investigate these two types of energy, a first and important task is to precisely study the main parameters characterising the two constitutive elements of the rock mass (rock matrix and discontinuity system). This should provide useful guidelines for the choice of the blasting parameters (type of explosive, blasting pattern, etc.), in order to finally control the comminution process. Within the frame of the EU LESS FINES research project, devoted to the control of fines production, the methodology was developed in order to: (1) characterize the in situ rock mass, by evaluating the density, anisotropy, interconnectivity and fractal dimension of the discontinuity system and (2) evaluate fragmentation (both micro and macro) energy spent during the blasting operation. The methodology was applied to three production blasts performed in the Klinthagen quarry (Sweden) allowing to estimate the part of the fragmentation energy devoted to the formation of muck pile blocks on one side and to the muckpile blocks microcracking on the other side.

Fracture-Damage Model for Anchored Discontinuous Jointed Rockmass and its Application

According to the theories of fracture mechanics and damage mechanics, the constructive model and fracture damage mechanism of brittle discontinuous jointed rockmass are systematically studied under the state of complex stress in this paper. By the aid of the method of equivalent strain energy, the constitutive relation of anchored brittle discontinuous jointed rockmass is derived under the state of compression-shearing. The constitutive relation under the state of tension-shearing is also developed according to the theory of self-consistence. Finally, based on the above constructive models, the three-dimensional finite element procedure has been developed to model the ground movements that occur when underground power-houses of pumped-storage power station are installed in discontinuous jointed rockmass. The anchor supporting is an important component of this underground power-houses excavation work. Besides the displacement field and the secondary state of stress induced by the excavation disturbance, the effect of anchoring and the damage evolution around the power-houses have been particularly described during the process of installation. The numerical results obtained by numerical simulation were compared with that of field monitoring in order to verify the validity of the proposed models.

Utilizing rock mass properties for predicting TBM performance in hard rock condition

The key parameters on the estimation of tunnel-boring machine (TBM) performance are rock strength, toughness, discontinuity in rock mass, type of TBM and its specifications. The aim of this study is to both assess the influence of rock mass properties on TBM performance and construct a new empirical equation for estimation of the TBM performance. To achieve this aim, the database composed of actual measured TBM penetration rate and rock properties (i.e., uniaxial compressive strength, Brazilian tensile strength, rock brittleness/toughness, distance between planes of weakness, and orientation of discontinuities in rock mass) were established using the data collected from one hard rock TBM tunnel (the Queens Water Tunnel # 3, Stage 2) about 7.5 km long, New York City, USA. Intact rock properties were obtained from laboratory studies conducted at the Earth Mechanics Institute (EMI) in the Colorado School of Mines, CO, USA. Based on generated database, the statistical analyses were performed between available rock properties and measured TBM data in the field. The result revealed that rock mass properties have strong affect on TBM performance. It is concluded that TBM performance could be estimated as a function of rock properties utilizing new equation ( r = 0.82).

Composite element method for the bolted discontinuous rock masses and its application

This paper presents a composite element method (CEM) for discontinuous rock masses reinforced by fully grouted bolts. This element allows one to generate mesh without considering exactly the existence of bolts and joints, which further allows for an important simplification in the pre-process work. The sub-elements of rock, grout, bolt, joint, rock/grout interface and bolt/grout interface are defined using corresponding mapped nodal displacements at the composite element. The mapped nodal displacements can be determined using the governing equations established by means of the virtual work principle. Based on the mapped nodal displacements deformation and stress in each sub-element can be further obtained. The comparative study of the CEM and the conventional finite element method (FEM) has been carried out for the preliminary verification example. The numerical study for the rock bolt crane girder of an underground powerhouse by FEM and CEM is presented as the engineering application example, in which the attention has been paid to the portion of the contact face between the girder and surrounding rock masses, the contact faces between the bolts and surrounding rock masses, as well as to the portion where the rock bolt penetrates the contact face. The comparative and application studies show the validation and advantages of the CEM.

Three-dimensional modeling of borehole data cored from engineering rock mass

Vast data from the drilling and geophysical prospecting are reliable original information to describe the space state of engineering rock mass, and one of the main difficulties in three-dimensional (3D) modeling of engineering rock mass is the processing of the primary data. From the view-point of 3D modeling, the engineering rock masses are classified as four basic types according to their geometric characteristics of geologic structure: (1) continuum rock mass; (2) discontinuous rock mass; (3) overturned fold rock mass and (4) intrusive rock mass. Because drilling data are very important to describe the characters of multi-scale of the spatial data for rock mass, the rule of how to process drilling data is developed to help appropriately display them in the viewpoint of 3D space. According to the characteristics of rock mass layers, the processing method of drilling data for 3D modeling of engineering rock masses, along with the layer thicknesses, is also proposed, including the evaluation rules and the extensive direction for original borehole data. By this method, the typical 3D data modeled is completed and the model form of the engineering rock mass is developed. By this example, it is finally verified that the method presented is successful and feasible to process 3D engineering rock mass.

Features of forming an explosive fracture zone in a hard rock mass

The effect of extended discontinuities in a hard rock mass on regularities of forming explosive fracture zones is considered. The comparison of the numerical and in situ experimental results permits to conclude that, in common with the known effect of seismic blast wave screenage, transformation of the wavefront configuration is of drastic importance. In a number of cases, that results in the generation of complex-structured fracture zones: new fractured zones can form beyond unbroken areas. It is demonstrated that the similar effects may cause redistribution of the blast energy and, as a consequence, the higher seismic efficiency produced by flat charge blasting as compared with concentrated charge blasting.

Mountain slope deformations along thrust fronts in jointed limestone: An equivalent continuum modelling approach

Engineering–geology studies of natural slope stability have rarely relied on continuum modelling of discontinuous rock mass or the use of conventional constitutive laws in FEM or FDM codes. The paper proposes the use of numerical modelling based on a practical equivalent continuum approach, for analysing the deep-seated gravitational slope deformations (DSGSD) observed in the thrust front area of the Lepini Mountains (Italian Apennines). The DSGSD phenomena affect a carbonate ridge close to the villages of San Sebastiano and Sgurgola, inducing a significant risk. This study began with the construction of engineering–geology sections, by distinguishing lithotechnical units on the basis of both site and geomechanical parameters. Considering geological and geomorphological field evidence, the numerical simulations validated the assumed kinematic model of the slope. These simulations aimed at estimating the instability of the affected rock masses, by identifying a critical mass beyond which ongoing deformations become morphologically evident on the involved slope. A ratio of the weight of a critical mass, which is the minimum mass required to produce some geomorphological evidence to the weight of the mass involved in the gravitational slope deformations, was calculated in order to quantitatively assess the evolutionary stage of the ongoing deformations. The calculated ratio demonstrates a more advanced evolutionary stage for the slope sector near the village of Sgurgola, due to its particular geological setting, than the one near the village of San Sebastiano.

Estimating the Influence of Surface Characteristics of Rock Joint on Shear Behavior and Coupled Shear-Flow Characteristics

Discontinuities in rock masses have an important influence on the deformational behavior and stability of deep underground spaces, and the surface roughness of discontinuities in rock masses is an important factor to analyze the mechanical and hydraulic characteristics of rock joints. In this study, we carried out direct shear tests on rock joints under both constant normal load (CNL) and constant normal stiffness (CNS) conditions, and measured the surfaces of rock joints before and after shear by using a 3-D laser scanning profilometer system. By using the projective covering method (PCM) and the measured data, we evaluated the relation of surface characteristics of rock joints to their shear behaviors. Moreover, a new hydro-mechanical test apparatus for rock joint was developed, based which a number of coupled shear-flow tests were conducted to estimate the hydraulic behavior of rock joints during a shear process.

Natural and anthropogenic hazards in karst areas: an introduction

The distinctive hydrology and landforms of karst create a very special environment. Although several types of karst have been identified worldwide, a common thread is the dominantly subterranean drainage. The paucity of water flowing at the surface, a consequence of rapid infiltration underground through a network of discontinuities in the soluble rock mass, results in two important but contrasting points: the considerable value of karst water resources (representing about 25% of the drinkable supply in the world) is strongly counteracted by the ease with which human activities can negatively impact this precious resource. The same narrow discontinuities, and the larger dissolution conduits and karst caves, are the main pathways through which potential pollutants may travel swiftly to regional groundwater bodies, or directly to springs. Contaminants can be introduced by means of dispersed infiltration as well as from point sources and are frequently transmitted with minimal filtering. This example, just one of the many natural and/or anthropogenic hazards that may affect karst areas, illustrates the fragility of karst environments. Their high vulnerability is further expressed by a very simple concept that is true for many other environments but probably shows its best evidence in karst: it is very easy to damage or destroy natural resources but restoration to a pristine situation is an extremely difficult and commonly impossible, task. Where some degree of remediation is possible, the economic cost is commonly very high. Since the early 1960s there has been a great deal of progress in understanding the processes and landforms of karst areas (e.g. Ford & Williams 1989; Gillieson 1996; Klimchouk et al. 2000; Gabrovsek 2002). There have also been several initiatives designed to translate theoretical knowledge into practical application, for example work by the International Geographical Unions Karst Commission (Williams 1993; Barany-Kevei & Gunn 2000), the IUCN (1996) and the World Bank (Vermeulen & Whitten 1999). However, projects continue to fail, and resources are lost or damaged owing to a failure in understanding the peculiarities of karst (for examples see Waltham et al. 2005). Hence, there remains a strong need to develop appropriate techniques to manage karst landscapes and protect karst resources. There are many human activities that, intentionally or not, produce severe impacts in karst, often with irreparable damage. For example, in some regions land degradation has been intense with deforestation and overgrazing leading to soil erosion, destruction of the epikarst and rocky desertification. Rehabilitation of these desert lands is extremely difficult, although in some parts of the Mediterranean reduction of grazing has been followed by a return of shrubs and small trees. Legislation, and even more its practical enforcement, still appears to be extremely inadequate at facing these problems, even in well-developed countries. Lack of laws and acts specifically devoted to karst is very common, but even when legislation takes into account the complexity and peculiarity of karst the potential benefits deriving from these acts frequently remain on paper owing to a lack of enforcement and control by the authorities. The best example is probably provided by the management of aquifers in carbonate rocks, as this requires an understanding of the character and type of water circulation within the rock mass. For many years the principles developed for non-carbonate aquifers, and the resulting methodologies created for groundwater vulnerability assessment, have also been applied to karst environments. However, it has long been known that the planning and management of carbonate aquifers poses different problems to those encountered in non-carbonate groundwater. Karst groundwater watersheds often do not coincide with topographic divides, to indicate just one of the main differences between karst hydrology and those in other environments. Only in recent years have some significant efforts been produced to give due weight to the peculiarity of karst hydrology and hydrogeology (for example, the COST 65 (1995) and subsequent COST (Co-Operation in Science and Technology) programmes in Europe and the report by Eckenfelder Inc. (1996) in the United States).

Characterizing block geometry in jointed rockmasses

The intersection of discontinuities in a jointed rockmass creates in situ blocks of variable three-dimensional (3D) geometry. The size and shape of rock blocks in a rockmass assembly have a dominant influence on the engineering properties of a rockmass, and control, for example the failure geometry of a rock face and the optimum associated support and surface restraint strategy. The distribution of block volumes within a rockmass can be effectively analyzed and communicated using a cumulative volume distribution curve. Integrated with this analysis, a methodology has been developed to characterize the shape and volumetric shape distribution of rock blocks in 3D models of jointed rockmasses. The proposed Block Shape Characterization Method takes into account two factors: the first, α, describes the shortening of the minor principal axis of the block while β describes the elongation of the major axis. When merged with the block volume distribution, the Block Shape Characterization Method can effectively describe and classify both the size and shape distributions of any jointed rockmass and is not limited to orthogonal blocks or hexahedra. This methodology can classify any polyhedra and has been developed and calibrated based on synthetic joint data and simulated block assemblies. A demonstration is given of its effectiveness in characterizing block geometries in the field using mapped fracture data.

Estimating the relation between surface roughness and mechanical properties of rock joints

Discontinuities in rock masses have an important influence on deformational behaviour of blocky rock systems. For a single rock joint, the roughness of its surface is of paramount importance to its mechanical and hydraulic properties, such as friction angle, shear strength, and dilatancy/aperture. Many methods have been used to characterize the surface roughness of rock joints, such as joint roughness coefficients (JRC), root mean square (RMS) value, structure function (SF) etc. However, most of these methods can only be used in the 2-D models. In this study, we carried out direct shear experiments on rock joints under both constant normal load (CNL) and constant normal stiffness (CNS) conditions, and measured the surfaces of rock joints before and after shearing, using a 3-D laser scanning profilometer system. By using a 3-D fractal evaluation method of roughness characterization, the projective covering method (PCM) and a direct shear apparatus of high accuracy, the relation between mechanical properties of rock joints under different boundary conditions and the change of their fractal dimensions in both 2-D and 3-D models have been examined, which gives a new approach to accurately evaluate the evolution of roughness of rock joint surfaces and its influence on the hydro-mechanical behaviours of rock joints.

Influence of geometrical distribution of rock joints on deformational behavior of underground opening

Mechanisms of deformation and failure of underground opening in jointed rock masses are governed by the characteristics of the geometrical distribution of discontinuities. In this paper, the extracting method of geometrical distribution of discontinuities in rock masses by image processing is presented and used to make networks of rock joints from the construction field. Next, using those networks, fractal characteristics of the discontinuities are described by using the box-counting method for quantitatively evaluating the state of the discontinuous distribution. Finally, numerical analysis based a case of the excavation of underground power plant is carried out to find the relation between geometrical distribution of rock joints and deformational behavior of underground opening by using distinct element method.