Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
Applying the Observational Approach for Tunnel Design
Mendez, Juan M. Davila (Institute for Rock Mechanics and Tunnelling, Graz University of Technology) | Kluckner, Alexander (Institute for Rock Mechanics and Tunnelling, Graz University of Technology) | Schubert, Wulf (Institute for Rock Mechanics and Tunnelling, Graz University of Technology)
Abstract The inherent uncertainties in the ground model and influencing factors, in most cases, do not allow a reliable direct design of a tunnel. Empirical tunnel design methods do not allow proofing stability or serviceability, thus are not acceptable according to common understanding. To allow for construction of safe and economical tunnels, the uncertainties have to be dealt with by observing the behaviour of the structure, and adjust construction measures to the real ground conditions and behaviours ("observational method"). After characterizing the ground, potential hazards are identified, the possible range of behaviours is assessed and appropriate construction measures to the expected behaviours are assigned. A monitoring plan needs to be established together with a safety management plan including contingency measures for inacceptable predicted behaviour deviations. The paper with the help of a few worked examples illustrates the influence of the rock mass structure and fault zones on the system behaviour. Introduction Optimization of underground structures design has been a topic widely studied by researchers and the industry. New approaches, guidelines and techniques have been developed replacing standard classification systems which tried to simplify/generalize the ground conditions with the inherent shortcomings (Daller et al. 1994, Palmstrรถm & Broch 1996, Riedmรผller & Schubert 1999a, Riedmรผller & Schubert 1999b). New approaches attempted to consider biases and uncertainties that arise from the multiple influencing factors which govern the ground behaviour and focus on achieving an appropriate technical and economical design (Radoncic et al. 2009a, Clayton et al. 1982, Head 1986, Oliveira 1992). Yet each design phase entails uncertainties that have to be considered during construction (Einstein 2001). This paper presents a description on how to achieve a proper design and connect it, through the observational approach, to the construction phase. The first part deals with the design stage and how to attain expected system behaviours and tunnelling classes based on ground types, boundary conditions, and influences. The second part presents some examples showing how to link the work done during the design stage with the observational approach during construction.
Abstract The paper deals with geotechnical study for the final slope of 140m high final open pit mine slope at SE Block of West Bokaro Collieries, Tata Steel. It is mainly characterized by sandstone and coal. The bulk density and direct shear tests were conducted at Rock Mechanics Laboratory of CIMFR on the samples collected from the field. The geotechnical mapping was done on the exposed benches of the quarry as per the norms of International Society of Rock Mechanics (ISRM 1978). The kinematic analysis was done to determine the critical orientation of structural discontinuities. After identifying kinematically possible failure modes, detailed slope stability analysis was carried out by GALENA software based on limit equilibrium method. The present study reveals that the 140m high final slope could be designed with 47 degree overall slope angle. The sensitivity analysis shows that the influence of water is also alarming. It was recommended that the slope should be kept in drained geomining condition by providing suitable drainage and keeping drainage effectively maintained. 1 Introduction The geotechnical study was conducted for optimum slope design of final highwall at SE Quarry, West Bokaro. The Quarry-SE is situated in Jharkhand state and is owned by M/s. Tata Steel Ltd. The rock discontinuities were mapped at the exposed benches of the pit as per the norms of International Society of Rock Mechanics (ISRM 1978). Geotechnical mapping was undertaken to determine the critical orientation of structural discontinuities. After identifying kinematically possible failure modes, detailed slope stability analysis is carried out by limit equilibrium method. Sensitivity analysis was done to determine the most effective remedial measure for any critical slope. 2 Geology and Geohydrology The slopes of the quarry are mainly characterized by Overburden sandstone and coal. The sandstone is well jointed. The average annual rainfall is around 1400 mm. The eastern part of the pit has been fully developed. The groundwater condition in drained geomining condition of the final highwall slope was considered to be with 30m water table from the pit bottom. It was considered based on field observations, engineering judgment and previous experiences in this type of geomining condition in adjacent mines. The most likely geo-mining condition for the quarry would be drained condition. The undrained geomining condition was simulated by the presence 75m water table from the pit bottom. This condition was considered to arise when the mine management does not implement the remedial measures related with the drainage in totality.
- Geology > Geological Subdiscipline > Geomechanics (0.92)
- Geology > Geological Subdiscipline > Environmental Geology > Hydrogeology (0.76)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.67)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.61)
Abstract The present papers deals with in situ characterization of rock formations as per Schmidt Rebound Hammer classification values (R) and portrays a model for spatial susceptibility of landslides in mountainous terrain. A geotechnical classification of rock masses depending on the range of R-value has been proposed and a regional correlation with the structural features traversing in the area has been attempted. Rebound values have been utilized to estimate the geo-mechanical properties of in situ rock to categorize the different lithological assemblages into geotechnical units of varying competencies. Geotechnical units assigned weightings of slope parameters, structure and bedding relations, land use and land cover etc and the terrain has been categorized into susceptibility classes such as very low, low, moderate, high and very high depending on the spatial probability of landslide occurrence highlighting relative severity of landslide hazard. Introduction Rock mass characterization offer many geotechnical challenges as the rock behaves in many different ways in its natural geological environment owing to inherent lithological and structural variations. At times these inherent characters are alone not sufficient to understand the behavior of rock mass under loading and excavations for major civil engineering structures. In an attempt to provide guidance on the properties of rock masses a number of rock mass classification systems have been developed. The most widely known classifications are the RMR system of Bieniawski (1973, 1989) and the Q system of Barton, Lien and Lunde (1974) etc. The classifications include information on the strength of the rock material, the spacing, number and surface properties of the structural discontinuities as well as allowances for the influence of subsurface water, in situ stresses and the orientation and inclination of dominant discontinuities. The strength parameters used are invariably the laboratory tests done on the rock samples which may not represent in situ strength of the rock mass. The present paper deals with characterization of rock formations according to the Schmidt rebound hammer classification values (R) which have been used in rock mass characterization. Rebound values have been utilized to estimate the geo-mechanical properties of in-situ rock to categorize the different lithological assemblages into Geotechnical Units of varying competencies. A case of such geotechnical classification has been attempted in parts of Kali River valleys of Eastern Kumaun Himalaya in order to portray a model of spatial susceptibility of landslides. The likelihood of landslides in such hilly terrains exposing the bedrock along their slopes is, largely dependent on the strength of the rock mass besides other factors that are known to govern the occurrences of landslides.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Abstract Structural geology (a branch of geology aiming at describing the structures โ joints, faults, folds, etc. โ at various scales) can be used in the field of rock mechanics and rock engineering, and particularly in underground engineering works (tunnelling and rock caverns) to gather more reliable data for empirical stability analyses and deterministic calculation models. Methods of structural geology are presented and their applications in rock mechanics/rock engineering are highlighted in particular through the observation of faults and joints arrest. Structural geology allows a better understanding of the origin, the chronology and the mechanical behaviour of discontinuities, and therefore a more accurate rock mass characterization and rock mass classification, as well as a validation of the actual stress regime. Examples selected from different countries of using structural models are also given with emphasize on the necessity and the way to build a 3D model at each stage of an underground project, from site selection to investigation and construction, to ensure the quality and validity of rock mechanical data and assumptions. Introduction In the last five years, several publications and oral presentations insisted on the importance of structural geology in the field of rock mechanics (e.g. during Sinorock 2009 in Hong Kong or the ISRM congress in Beijing in 2011). They highlighted the necessity of using structural geology and structural data as input parameters for rock mass characterization and rock mass modelling. This wish is praiseworthy and corresponds to a real need. The situation is due to the lack of structural geologists on the market: structural geology being less taught in university and often replaced by engineering geology, geologists or engineering geologists are easily involved in big projects (e.g. dams, hydropower plants, tunnelling, etc.) whereas it is nowadays quite uncommon to meet structural geologists in teams in charge of design, modelling or even supervision of site works. In addition, most structural geologists are academics and very few are full-time practitioners, especially in the field of rock mechanics. This short paper cannot be exhaustive but set out the various possibilities offered by structural geology. The objective is less ambitious and is limited to the presentation of practical examples in different geological situations in which a structural knowledge can provide a real help for modelling or for characterizing the rock mass through the two most geology-based rock mass classifications, the Q system (Barton et al. 1974) and the RMR (Bieniawski 1989). Since the vocabulary also acts as a brake, this paper deliberately uses simplified technical vocabulary and concepts, hoping that this will bring rock mechanical engineers to working closer with structural geologists.
- Geology > Structural Geology (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Stability Analysis for to ppling Failure of Unstable Rock in Three Gorges Reservoir Area, China
Wang, G. L. (Xiโan Center of Geological Survey, China Geological Survey) | Wu, F. Q. (Institute of Geology and Geophysics, Chinese Academy of Sciences) | Ye, W. J. (Xiโan University of Science and Technology)
Abstract As distinguished from the former types of toppling failure (i.e. flexural, blocky, blocky-flexural and secondary), another type of toppling failure developed in interbedded hard rock and soft rock slope is very common in Three Gorges Reservoir region. Based on discrete element method, the failure process of toppling failure can be summarized as erosion notches โ tension cracks โ toppling failure โ gravitational transport and accumulation. According to the toppling failure mode, the computing formula of factor of safety is deduced by means of the method of geo-mechanics. The results of a typical case study show that the factor of safety of toppling failure decreases with increasing of notch depth. Supposing the erosion rate of notches is 1 mm/yr and toppling failure of the unstable rock occurs at a notch depth of 1.45 m, we can calculate the time required for the unstable rock to topple as 50 years. Introduction Toppling failure is one of the most serious and hazardous instability of rock slopes (de Freitras and Watters 1973; Goodman and Bray 1976; Wang 1981; Ishida et al. 1987; Goodman 1989; Aydan and Kawamoto 1987, 1992; Adhikary et al. 1996, 1997, 2007). Many toppling failures are observed in practice and hence toppling is an important failure mode that requires further attention (Wyllie 1980; Liu et al. 2010). In general, this failure can be classified into four principal types: flexural, blocky, blocky-flexural and secondary (Goodman and Bray 1976). Flexural toppling failure occurs due to bending stresses (Amini et al. 2009). However, another mode of toppling failure, which mainly developed in interbedded hard rock (i.e. sandstone) and soft rock (i.e. mudstone, shale and limestone) slope is very common in Three Gorges Reservoir region (Chen et al. 2004; Dong et al. 2010). Field investigation indicates that notches of undercut slopes are formed by differential weathering. Furthermore, tension crack on the top surface will occur due to concentration of tensile stress. As result, the unstable rock begins to topple because of momentum unbalance.
- Asia > China (0.69)
- North America > United States (0.46)
The Fracturing of Heterogeneous Caprock During CO2 Injection into a Brine Aquifer
Pan, P. Z. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Feng, X. T. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Yan, F. (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Rutqvist, J. (Lawrence Berkeley National Laboratory)
Abstract This paper presents a study of heterogeneous caprock fracturing processes during underground CO2 injection into a brine aquifer. We simulate CO2 injection and fracturing using a combination of theTOUGH2 multiphase flow simulator and the RDCA rock discontinuous cellular automaton code. Our analysis shows that fluid pressure evolution,CO2 saturation, fracture opening, propagation and fracturing path are strongly dependent on the heterogeneity of caprock. The obvious risk that the fracture propagates upwards to provide a new flow path toward shallow ground water aquifers or released to the atmosphere and thereby reducing the efficiency of the CO2 sequestration and potentially contaminating groundwater resources is demonstrated. Introduction The caprock mechanical integrity associated with deep underground injection of CO2 is very important since the caprock is a natural barrier to prevent CO2 from migrating upwards towards shallow potable ground water or ground surface. When CO2 is injected into a brine aquifer, the reservoir pore pressure increases and creates loading and straining of the overlying caprock. If there is an initial fracture in the caprock, the fluid pressure gradient induced byCO2 injection could more easily lead to fracturing of the caprock. Hydraulic fracturing is widely used in reservoir engineering applications such as the exploration and development of hydrocarbons or geothermal reservoirs (Murphy et al. 1981; Mandl and Harkness 1987; Legarth et al. 2005), estimation of in situ stress in rock masses (Haimson and Fairhurst 1969; Bredehoeft et al. 1976), and for deep underground injection disposal of hazardous liquid and solid wastes (Dusseault et al. 1996). In the case of underground CO2 injection, different geological formations in the caprock may have great influence on the potential for fracturing. Furthermore, this influence is dynamic, i.e. the fracture may propagate upwards due to the increase of fluid pressure and CO2-in-brine buoyancy effects. Although many studies have been conducted to consider the influence of geological formations on the caprock integrity (Rutqvist et al. 2010; Morris et al. 2011; Rutqvist 2012), this study is focused on such influence on potential caprock fracturing.
- North America > United States > Colorado (0.29)
- North America > United States > California (0.29)
- Geology > Petroleum Play Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- North America > United States > Colorado > Piceance Basin > Williams Fork Formation (0.99)
- North America > Canada > Saskatchewan > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- North America > Canada > Northwest Territories > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- (4 more...)
A Preliminary, Calibrated Scheme for Estimating Rock Mass Properties for Non-Linear, Discontinuum Models
Beck, D. A. (Beck Engineering Pty Ltd.) | Lilley, C. R. (Beck Engineering Pty Ltd.) | Reusch, F. (Beck Engineering) | Levkovitch, V. (Beck Engineering) | Putzar, G. (Beck Engineering) | Flatten, A. (Beck Engineering)
Abstract Calibration of 3D, discontinuum, strain softening, dilatant (SSD) models of mines often yields different rock mass scale (representative elementary volume, or REV) properties to empirical methods. In this paper, some steps towards a calibrated empirical scheme for estimating material properties for some types of 3d, discontinuum non-linear models targeting larger than (REV) scale phenomena are described. The scheme uses typical pre-mining rock mass classification date and strength tests to estimate the peak and residual yield, softening and dilatancy parameters. The scheme is a purely empirical device, derived from UCS and GSI field data and calibrated model results, and is a work in progress. The underlying nature of the Hoek Brown-GSI scheme (Hoek, E., and E. T. Brown., 1997; Hoek et al., 2002), is validated by the work. Introduction An essential task of modelling of rock masses is to establish the length scale below which each particular rock mass can be treated as a continuum. On this scale the medium is said to be homogeneous (Witherspoon et al., 1981). Witherspoon et al. (1981) illustrated this with a diagram for permeability similar to the one shown in Figure 1. The REV of rocks is ordinarily large enough to preclude laboratory measurements of REV scale properties, so calibration or an empirical estimate are necessary. Calibration is usually preferred. Quantitative calibration is the process of adjusting model inputs to achieve a like-for-like match between measured data and model results. The quality of calibration qualifies the model for use and is measured by the resolution, precision and coverage of the models match to real measurements across space, time and length scales. When calibration is not possible, REV scale properties must be empirically estimated. The most commonly used empirical scheme for estimating โrock mass scaleโ, or REV strengths for non-linear geotechnical models is the Hoek-Brown Geological Strength Index (HB-GSI) after Hoek, E., and E. T. Brown (1997). That scheme uses the laboratory scale unconfined compressive strength (UCS), a qualitative classification of the nature of the discontinuity network (GSI) and a parameter obtained from triaxial testing of laboratory specimens (mi) to establish the parameters of the yield potential function.
Abstract Progresses in understanding, analysis and control of rock slope movements have been the result of interdisciplinary efforts involving engineering geologists and rock engineers. In addition to rock engineering methodologies, the input from engineering geology is absolutely a fundamental to any rock slope design. This paper aims to emphasize the importance of harmonizing engineering geology with rock engineering on stability of rock slopes. Main engineering geological factors featured in the design and construction of rock slopes, role of engineering geological model and their combination with the stability analysis methods used in rock slope engineering are briefly discussed with their advantages and limitations, and finally current and near future needs related to stability of rock slopes are also described. Introduction The construction, design, remediation and maintenance of rock slopes have always been an important area of geo-engineering. Particularly, in the last two decades, increasing demand for ultra deep open pits and large civil engineering constructions in rocks such as expressways, highways, railways and dams, and the effects of earthquake-triggered slope failures on settlements located in mountainous regions resulted in more attention to be paid to rock slope stability. Progresses in understanding, analysis and control of rock slope movements have been the result of interdisciplinary efforts mainly involving engineering geologists and rock engineers. IAEG states that engineering geology is the discipline of applying geologic data, techniques and principles to the study of rock and soil materials, surface and subsurface fluids, and interactions of introduced materials and processes with the environment so that geologic factors are adequately recognized, interpreted and presented for use in engineering and related practice (Keaton 2010). The engineering geologist, as a predictor, translates the scientific facts, observed or measured, into engineering data to identify areas of significant physical constraint that will adversely affect the design, construction and maintenance of any intended engineering project (Mathewson 1981) (Figure 1).
- North America > United States (1.00)
- Europe (1.00)
- Asia > Middle East > Turkey (0.46)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Rock Type > Sedimentary Rock (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Metals & Mining (0.68)
- North America > Canada (0.93)
- Europe > United Kingdom > England > London Basin (0.91)
Abstract Most of the discontinuities and joints do not have smooth surfaces and they are covered with random distributed roughness. Finding the effective role of surface roughness on the behavior of discontinuities and on the shear strength of joints makes roughness measurement an important factor that has to be taken into account in geotechnical investigations. These information make the basis for realistic design of underground and surface projects such as tunnel, mines etc. Roughness has various features depending on the type of specimens, size and observation scale. In some cases, different methods of measurement return different results for the same specimen. Therefore, it is necessary to measure the roughness by an appropriate method and to represent it quantitatively in a mathematically adequate way. Quantifying the topography of rippled surface is the main challenge in roughness measurement. This quantifying method should return values which should be used in shear strength formulations for discontinuities. The first step is to measure the roughness topography by an appropriate tool and then their roughness must be quantified by a suitable method. There are different tools measuring the surface roughness. One of these tools is three-dimensional geometric system. Furthermore, several converters can be used amongst which the laser convert is one of them. In this paper, geometric methods used to measure roughness are reviewed. This is followed by a discussion on the various quantitative methods measuring roughness. The 3D laser instrument to record the roughness topography is further explained. Finally, a 2-D profile of a rock joint is scanned and interpreted before and after a shear test. Introduction 1.1 Rock mass Properties of a rock mass are very well related to its joints hydraulic and mechanical properties which these discontinuities themselves are related to the morphology of the rock mass. Roughness as the most important factor of the morphology has a substantial role in the hydraulic and mechanical properties of discontinuities. Due to different results for different measuring methods and techniques for the same rock sample, measuring with precise equipments and quantifying with an appropriate method for the determination of shearing strength and hydraulic properties are essential.