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Enhancing Block Rock Failure Understanding Through Geosma-3D Numerical Analysis
Wang, S.H. (Northeastern University) | Guo, M.D. (Northeastern University) | Yang, Y. (Northeastern University) | Wang, Y. (Northeastern University) | Zhang, Y.B. (Northeastern University) | Che, D.F. (Northeastern University)
ABSTRACT Numerical analysis provides a useful tool to enhance the understanding of block rock masses. The stability of rock blocks of tunnel or underground opening are commonly analyzed based on rigid body limit equilibrium theory only by considering gravity, while the secondary stress field after excavation of the block is usually not taken into account. Existence of structural planes affects dynamical properties greatly in rock tunnel structures. Especially in hard rock tunnel engineering, the stability of rock is controlled in a sense by the number of blocks, i.e. the size, orientation and locations of the discontinuities. Key-block failures occur where blocks of rock which are separated form the rest of the rock mass by discontinuities slide of fall into an excavation. According to the geometric stochastic block theory and reliability analysis, a new program GeoSMA-3D (Geotechnical Structure and Model Analysis-3D) for simulating tunnel structural planes in rock mass is put forward to develop based on geometric stochastic block theory and modern computer technique. The new model assumed that rock mass consists of blocks, thus formulating a combination of block model. This program adopts vector analysis, which can simulate all excavation planes especially in the tunnel and other underground structure. It can also create three-dimensional structural model and analyze mobility of key-block in the simulation plane by means of geometry and kinematics theory. The distribution of all key blocks and the quantitative data are analyzed by means of the newly developed program. The results show that parts of the blocks' crown zone are under compressive stress, which gradually increases as the underground opening in Shimian Tunnel, Liaoning, China. It can be concluded that the new program is an effective tool for modeling blocky rock masses. 1 INTRODUCTION In all civil or mining engineering projects, there is an in situ state of blocks in the ground before any excavation or construction is started. It is very important in the development of a numerical model for rock engineering analysis to reproduce this in situ state as closely as possible. The design is so far mostly empirical. It assumes that the block is rigid and is located in an otherwise fixed body of rock and bounded by a combination of flat discontinuities and excavation surfaces. In practice these conditions are most likely to be approximated when extensive discontinuities occur in hard rock. In common with most other solutions for three-dimensional blocks, possible block movements are assumed to be limited to translation only, and rotation is excluded. Existence of structural planes affects dynamical properties greatly in rock tunnel structures. It assumes that the block is rigid and is located in an otherwise fixed body of rock and bounded by a combination of flat discontinuities and excavation surfaces. In practice these conditions are most likely to be approximated when extensive discontinuities occur in hard rock. In common with most other solutions for three-dimensional blocks, possible block movements are assumed to be limited to translation only, and rotation is excluded.
- Overview > Innovation (0.34)
- Research Report > New Finding (0.34)
ABSTRACT Foroptimaldesignofrock-socketedshaftsusedtosupportaxialloading,theendbearing resistance should be considered. The existing empirical methods for determining the end bearing capacityqmaxofrock-socketedshaftsuseempiricalrelationsbetweenqmaxandtheunconfined compressive strength of intact rock, σc. Since rock-socketed shafts are supported by the rock mass (bothintactrockblocksanddiscontinuitiesseparatingthem)notjustbytheintactrock,one should consider not only the intact rock properties but also the influence of discontinuities when determiningqmax. Inthispaper,a databaseconsistingof25testshaftswith RQD (rockquality designation) value available is developed. Using the developed database, a new empirical relation betweenqmaxandtheunconfinedcompressivestrengthofrock mass, σcm,isderived. The new empirical relation explicitly considers the effect of discontinuities by using σcm, which is directly relatedto RQD. Finally, an example is presented to show the application ofthe newly derived empirical relation. Theresultsindicatethatthenewempiricalrelationbetweenqmaxandσcmprovides more accurate prediction of qmax than the old empirical relations between qmax and σc. 1 INTRODUCTION Drilled shafts socketed into rock are nowadays amongst thewidelyusedvarietyofdeepfoundations. Loads appliedtotheshaftsaresupportedbytherocksocket throughthesideshearresistanceandtheendbearing resistance(Horvathetal.1983). although "There are significant advantagesin designingtoinclude a base[or end bearing] resistance component" (Williams and Pells 1981), the end bearing resistance is often ignored in current design practice(Crapps and Schmertmann 2002; Turner 2004). According to Crapps and Schmertmann (2002), the most common reasons cited by designers for neglecting endbearingresistanceindesigninclude settled slurrysuspension,reluctancetoinspectbottom, concern forunderlyingcavities,andunknownor uncertain endbearingresistance. Obviously, neglecting the endbearingresistanceindesignwillresultin excessive rocksocketlengths. Due to the high cost of shaft construction in rock, an over-designof sock length will leadtoagreatwasteofmoney. Crapps and Schmertmann (2002) suggested that accounting for end bearing resistanceindesignandusingappropriate construction andinspectiontechniquestoensurequality base conditionsisa better approachthanneglecting end bearing resistance. To include the end bearing resistance in design, it is necessary todeterminetheendbearingcapacityfirst. Although some methods are available for predict
- North America > United States > Missouri (0.28)
- North America > United States > Florida (0.28)
- North America > United States > Arizona (0.28)
ABSTRACT The objective of this paper is to outline the methodology proposed to determine the in-situ stress field and geomechanical properties of the Bakken Formation in Williston Basin, North Dakota, USA to increase the success rate of horizontal drilling and hydraulic fracturing so as to improve the recovery factor of this unconventional crude oil resource from the current 1% to a higher level. The success of horizontal drilling and hydraulic fracturing depends on knowing local in-situ stress and geomechanical properties of the rocks. We propose a proactive approach to determine the in-situ stress and related geomechanical properties of the Bakken Formation in representative areas through integrated analysis of field and well data, core sample and lab experiments. We plan to use Kaiser Effect technique to estimate in-situ stresses. CDISK method will be used to determined fracture toughness. Geomechanical properties will be measured following ISRM suggested methods. By integrating lab testing, core observation, numerical simulation, well log and seismic image, Intelligent Geomechanical Logging and Imaging methods are proposed to estimate geomechanical properties in locations where no results of lab testing and core observation are available. 1 INTRODUCTION The Williston Basin is a roughly oval-shaped structural down-warp with a surface area between 120,000 and 240,000 square miles. The basin underlies most of North Dakota, western Montana, northwestern South Dakota, southeastern Saskatchewan and a small section of southwestern Manitoba. All sedimentary systems from Cambrian through Quaternary are presented in the basin, with a rock column more than 15,000 ft thick in the deepest section near Williston, North Dakota (Fig. 1). The basin became a major oil province in the 1950s when large oil fields were discovered in North Dakota. (Figure in full paper) The Bakken Formation is a thin (maximum thickness 145 ft), naturally fractured Upper Devonian- Lower Mississippian sedimentary unit. It can be divided into three intervals: the upper shale, the lithologically variable middle member, and the lower shale. The upper and lower shales have rich organic content, and are the source rocks for oil and gas in the Bakken Formation. In North Dakota, the middle member is mainly gray interbedded siltstones and sandstones with a maximum thickness of 85 ft occurring at depths of approximately 9,500 to 10,000 ft (Heck et al., 2002). Although the Bakken Formation is very thin compared to other oil producing horizons, it has recently attracted much attention because its extremely high carbon content places it among the richest hydrocarbon source rocks in the world. Estimates of original oil in place (OOIP) range from 200 to more than 400 billion barrels (Price, 2000). For comparison, excluding these Bakken Formation reserves, so far the total US discovered OOIP is less than 600 billion barrels, of which only less than 200 billion barrels has been produced. With the growth rate of demand outpacing that of new reserves on oil and gas, the importance of these unconventional reserves in the Bakken Formation becomes increasingly important.
- North America > United States > South Dakota (1.00)
- North America > United States > North Dakota (1.00)
- North America > United States > Montana (1.00)
- (2 more...)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.76)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- North America > United States > South Dakota > Williston Basin > Bakken Shale Formation (0.99)
- North America > United States > North Dakota > Williston Basin > Bakken Shale Formation (0.99)
- North America > United States > Montana > Williston Basin > Bakken Shale Formation (0.99)
A Realistic Fracture System Model For Engineering Analysis of Underground Excavations
Liu, Q. (Institute of Applied Geosciences, Graz University of Technology) | Kieffer, D.S. (Institute of Applied Geosciences, Graz University of Technology) | Klima, K. (Institute of Applied Geosciences, Graz University of Technology) | Brosch, F.J. (Institute of Applied Geosciences, Graz University of Technology)
ABSTRACT This paper presents a novel method for realistically characterizing discontinuity systems for underground excavations. The basic idea is to sample and simulate discontinuities at different scales. A combined sampling technique, which consists of axionometric projection and 3D-digital images, makes possible the efficient acquisition of detailed discontinuity data. Minor discontinuities are simulated stochastically based on their representative orientation statistics, with size parameters estimated using analytical methods for circular window sampling. Censored major discontinuities are simulated conditionally using actual intersection locations and true orientations, with discontinuity sizes first assessed using stochastic forward modeling. This method has been applied to the Raabstollen adit, part of an underground mine complex in eastern Styria, Austria. 1 INTRODUCTION Discontinuity pattern assessment is often a key issue for underground excavations (Hudson, 1991), but the complete three-dimensional description of discontinuities is inherently data limited. Nevertheless, for engineering applications, it is necessary to describe the overall discontinuity system, which can be treated as simplified mathematical representations of discontinuity geometries (Dershowitz 1984). Increasing the quality of discontinuity system representation with more advanced and efficient means is currently being addressed in the context of rock mechanics and rock engineering (e.g. Jing, 2003, Pine et al. 2006). With the recent improvements in remote three-dimensional photogrammetric systems (e.g. Gaich 2001, Fasching 2001) and advanced discontinuity modeling technologies such as FracMan (Dershowitz 1995, Rogers et al. 2006, 2007), it is becoming possible to assess discontinuity patterns with more confidence. It is the author's experience that besides discontinuity type, orientation, etc., the actual discontinuity location and size are crucial. In this paper we summarize an approach for realistically characterizing discontinuity systems for underground excavation. As a case study, the method is applied to the Raabstollen adit, part of the Arzberg underground mining complex in eastern Styria, Austria. 2 SAMPLING DISCONTINUITY IN RAABSTOLLEN ADIT Host rocks in the Raabstollen adit are mainly chloritic schists. Within a 31.5m length of the adit is a relatively uniform schist unit and this location was chosen for discontinuity system modeling. The horse-shoe shaped adit has the cross-sectional area of about 2m×2m. Discontinuity sampling was performed along the tunnel ribs and crown area. Observations of discontinuity traces showed that there are five main discontinuity sets. The schistosity set is predominantly gently dipping to flat-lying. The slickensided set has very little attitude dispersion and the largest trace length, which usually takes several meters. The others are joint sets (J1, J2, and J3) with relatively shorter trace length. Larger slickensides and small faults within the selected mapping interval usually intersect more than one excavation surface, and in the small adit it proved difficult to include the entire trace of a larger discontinuity in a single 3D digital image photo. It has been shown (e.g. Schubert 2001) that large discontinuities control the displacement pattern of the tunnel periphery. Therefore, large discontinuities should be characterized deterministically, with an unbiased representation in the eventual discontinuity model. We applied an unrolled tunnel mapping technique based on axionometric projection, as depicted schematically in Figure 1.
ABSTRACT Discontinuities are responsible for mechanical anisotropy causing directional variation of rock strength. Therefore the effect of discontinuity dip and dip direction on anisotropic response of rocks has been the focus of researches. Although numerous studies have been concentrated on the effect of dip variation, but no attention has been paid to the dip-direction variation on the strength response of the rocks. Hence, the effects of dip-direction on the rock mass strength were studied through testing of artificial material. Specimens were fabricated using plaster. A specific mold was used for this purpose. The samples were tested under triaxial tests subjected to different confining pressures. A parameter was defined known as. Anisotropy Effect. in order to highlight the changes in strength of rocks due to the discontinuities dip-direction variation. The details of the investigations, tables of the evaluated test results and the empirical equation deduced are presented in the paper. 1 INTRODUCTION Discontinuities are one of the most important phenomena that cause the mechanical anisotropy in rocks. This mechanical anisotropy would, in turn, impose reduction of strength. Therefore, the discontinuities and degree of their influence on the rocks must be studied carefully in order to define the rocks behavior. There have been efforts to investigate the effects of discontinuities on rock strength in recent years, but dip-direction of joints and their effects on rock strength were ignored. An extensive investigation was planned and undertaken in order to study the strength response of rocks when the dip-directions, of two induced discontinuities, are changing with respect to each other. The investigations were conducted using artificial specimens made out of plaster. The result of these studies is presented in this paper. 2 LITERATURE SURVAY ON THE BEHAVIOUR OF THE ANISOTROPIC ROCKS Many investigators have carried out the measurement of the strength anisotropy for various rock types e.g. Chenevert and Gatline (1965), McLamore and Gray (1967), Hoek (1968) Attewell and Sandford (1974) and Brown et al. (1977) concentrated their studies on Shales and slates, Deklotz et al. (1966), Akai et al. (1970) McCabe and Koerner (1975) Nasseri et al. (1996,1997) and Singh (2000) researched on response of gneisses and schists, Ramamurthy et al. (1988), on Phyllites Horino and Ellicksone (1970), Rao et al. (1986) and Al-Harthi (1998) considered sandstones, Pomeroy et al. (1971) on coal, Allirote and Boehler on diatomite (1970) and Tien and Tsao (2000) undertaken their investigation through artificial materials. An overall analysis and review of their works exhibit that maximum failure strength is either at β= 0° or 90° (β= angle of discontinuity with respect to σ1) and the minimum strength is usually attained around β=30°, more precisely at (45-φ/2), where φ= friction angle along the plane of weakness. 3 ANISOTROPY 3.1 Inherent Anisotropy In this type of anisotropy, the weak surfaces are related to the rock formation processes, such as the foliation and schistose planes which are developed during the formation of rocks, Ramamurthy (1993).
- North America (0.28)
- Asia > Middle East (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.54)
ABSTRACT The paper deals with geotechnical study and slope stability analyses of the final slope at Lanjiberna Limestone open cast mine. The Lanjiberna open cast mine is mainly characterized top soil, dolomite, dolomitic limestone and limestone. 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 96m high final slope could be designed with 58 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 Lanjiberna Limestone open cast mine is located in the Orissa state of India. There are three nos. of quarries in this mine namely Q-1_3,Q-4_5 and Q-2_6 respectively. The study was conducted at quarry no. 2–6. Presently quarry no. 2 and 6 are named as two different quarries. The mine management is going to join and merge these two quarries and proposed to work as a single pit by removing the ramp centrally located and by shifting the road towards north. The purpose of study was to suggest optimum slope design of quarry2–6. Presently the pit is being mined with 45 degree overall slope angle. The present Limestone production is 1.70 million tonne from the captive mines, which had been planned to increase to 4.20 million tones per annum. With the proposed enhanced production of mines from 1.70 million tones to 4.20 million tones per year, the total deposit will last for more than 27 years. 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 The slopes of the quarry are mainly characterized by topsoil, dolomite, dolomitic limestone and limestone, which are well jointed. Geologically, Langiberna limestone area belongs to Birmitrapur stage of the gangpur series of Indian Dharwars. In Lanjiberna, there are two, almost parallel, bands of limestone running East West separated by a band of dolomitic limestone of about 200 to 300m width. 3 GEOHYDROLOGY The climate of the area is sub-tropical. The average annual is around 1200 mm. The area of the quarry area does not have top-aquifer, as the weathered mantle is not developed below soil profile.