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ABSTRACT: New physics experiments, proposed to study neutrinos and protons, call for the use of large underground particle detectors. In the United States, such detectors would be housed in the US Deep Underground Science and Engineering Laboratory (DUSEL), sited within the footprint of the defunct Homestake Mine, South Dakota. Although the experimental proposals differ in detail, all rely heavily upon the ability of the mined and reinforced rock mass to serve as a stable host for the detector facilities. Experimental proposals, based on the use of Water Cherenkov detector technology, specify rock caverns with excavated volumes in excess of half a million cubic meters, spans of at least 50 m, sited at depths of approximately one to 1.5 kilometers. Although perhaps sited at shallower depth, proposals based on the use of Liquid Argon (LAr) detector technology are no less challenging. LAr proposals not only call for the excavation of large span caverns, but have an additional need for the safe management of large quantities (kilo-tonnes) of cryogenic liquid, including critical provisions for the fail-safe egress of underground personnel and the reliable exhaust of Argon gas in the event of a catastrophic release. These multi-year, high value physics experiments will provide the key experimental data needed to support the research of a new generation of physicists as they probe the behavior of basic particles and the fundamental laws of nature. The rock engineer must eliver caverns that will reliably meet operational requirements and remain stable for periods conservatively estimated to be in excess of twenty years. This paper provides an overview of the DUSEL site conditions and discusses key end-user requirements and design criteria likely to dominate in determining the viability of experimental options. The paper stresses the paramount importance of collecting adequate site-specific data to inform early siting, dimensioning and layout decisions. Given the large-scale of the excavation and likely timeline to construction, the paper also strongly suggests that there are exciting opportunities for the rock mechanics and engineering community to identify and efficiently integrate research components into the design and construction process. 1. INTRODUCTION The Deep Underground Science and Engineering Laboratory (DUSEL) is a new facility dedicated to underground research. DUSEL brings together a diverse group of science and engineering partners to plan and perform a new generation of scientific and engineering experiments. Since its conception in the early 2000?s the DUSEL initiative has generated a great deal of interest amongst key underground research communities (physics, biology, geosciences, engineering). Approximately one hundred research proposals have already been submitted, including several that represent the early fruits of synergistic collaboration between the partner disciplines. To accomplish the diverse goals of DUSEL, multilevel occupancy is planned with laboratory clusters sited at depths from a hundred meters to roughly two and an half kilometers below surface. These underground campus facilities will be largely selfsufficient, with space provided for laboratories, workshops, offices and access to site-wide infrastructure. In addition, outpost facilities may be strategically developed to provide for drilling and sampling in areas of particular geologic and biologic interest.
- North America > United States > California (0.29)
- North America > United States > South Dakota (0.25)
- Government > Regional Government > North America Government > United States Government (0.94)
- Materials > Metals & Mining (0.88)
- Materials > Chemicals > Industrial Gases (0.69)
- Energy > Oil & Gas (0.68)
ABSTRACT: Based on detailed geological-geotechnical investigations on the Blagovica-Konpolje motorway section (E-W corridor in Slovenia), the influence of time on the changes of the stress-strain in the physical behavior of Carboniferous-Permian mixed soft rock mass was defined. Significant volumetric and distortion deformations appeared after a long period of rainfall after unloading of the excavation. Finally, gradual structural degradation caused sliding of the altered or disintergrated soft rock mass as this soft rock mass took on the characteristics of the saturated residual soft soil. Most important in this process were pre-existing weak soft rock zones. As a result of the suction process of pore water pressure dissipation out of the micro-cracks (dilatation suction and dissipation), viscous creeping developed. The presentation focuses on numerical back analyses which were made at three scales: mineralogical petrography specimens at micro-scale, at the scale of borehole samples and at the scale of land-sliding slopes. 1. INTRODUCTION Based on a detailed geological-geotechnical investigation of the Blagovica-Kompolje motorway section, Carboniferous-Permian soft rocks were divided into three typical layers with different strength and deformability parameters. The purpose of the investigation and analysis was to determine the input parameters for numerical analysis which were needed to specify support and retaining measures for the excavation of cutting slopes. Excavation for the foundation caused unloading and, along with heavy rainfall during autumn in 2002, activated a deep landslide in the building area of this motorway section. The landslide was successfully stabilized with an anchored pile wall, material exchange below the pile wall and a special drainage system. With detailed laboratory analysis, "in situ" examination and monitoring results, we have gathered enough data for the creeping analysis of the landslide. The analysis was conducted using a special method of calculation enabled by the software used. During each calculation step, the grid is updated and active pore pressures are recalculated. Geometric nonlinearities, occurring in deformations of this extent, are thus avoided. With the slowing of creeping, conditions were established to begin a planned restoration using an anchored pile wall. Technical observation is ongoing while the structures are operational. 2. GEOTECHNICAL INVESTIGATIONS Prior to the motorway construction, geological-geomechanical investigations were first conducted in the preliminary project phase and later in the main project phase. For those sections where the route was planned to cut into slopes, additional investigations were conducted. During the motorway construction, the back slopes of the planned supporting and retaining structures became accessible. For the main project, technical observation and monitoring were called for. For determining rock mass characteristics, we engineering geologically mapped the slopes in detail during the excavations and catalogued bore holes, outcrops and piles. For that we used the new rock mass classification for mixed and soft rock mass by determination of the geological strength index GSI [1]. In selected bore holes, preasuremeter measurements ("in situ" measurements) were conducted and intact samples taken. During laboratory examination, we conducted triaxial consolidated undrained shear tests ("CU"-tests) of fifteen intact samples and nine compressibility and permeability oedometric tests.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.30)
ABSTRACT: The Qomroud Long Tunnel lot number 1 (QLT1), a 10.4 km tunnel, is under construction as part of the Dez to Qomroud water conveyance tunnel projects (total length 55 km) in west central Iran, Lorestan province. The project involves four tunnels, three small dams and a large dam. The longest tunnel in the Dez to Qomroud projects is known as Qomroud Long Tunnel (QLT) with length of nearly 36 km. QLT1, the subject of this study, was defined as the first 10.40 kilometers of the QLT. Construction of QLT1 stopped in June 2000 after severe stability problems because of the nature of geological strata along the tunnel. Additional engineering geological investigations were commissioned. In this article, we highlight engineering geological problems along the QLT1 tunnel route such as water inrush, water jet potential in meta-dolomite, tunneling in fault and crushed zones, potential for high water pressures, raveling, swelling and saturated material flow in alluvial sections, and ground squeezing in weak rocks. Also, some geotechnical design considerations are proposed as special measures to consider in design and implementation of a new construction method in this difficult ground condition. 1. INTRODUCTION Tunnels are perhaps the most geologically dominated civil projects undertaken. There are numerous examples in the literature from around the world where poor engineering geological investigations or unexpected ground conditions led to severe construction problems. Clearly, a well-designed, comprehensive geotechnical study can examine directly only a negligible portion of the rock mass along a tunnel. The volume of samples taken from boreholes drilled along the tunnel axis is minuscule compared to the volume excvated. The rock volume from an aggressive drilling program compared to the excavated tunnel volume for even a small 3 m tunnel is perhaps one part in 50,000. Thus, there is always substantial uncertainty associated with the engineering geology data collected for a tunnel project, even with a comprehensive engineering geology investigation. Engineering geological problems associated with the nature of geomaterials in a tunnel project include high water inrush, water jet potential in karstic formations, tunneling through faults or heavily crushed zones, potential of high hydrostatic water pressure in saturated ground, raveling, flowing behavior (massive watertriggered erosion) in alluvial sections, swelling and ground squeezing in weak rocks. These problems often lead to human life loss or a project shut-down, causing huge unexpected costs for the client. Problem identification well in advance can minimize the risk of unexpectedly encountering severe engineering geological problems during construction. Central Iran is an arid area with limited water supply. Providing enough water to this area is a great challenge for the Iranian water supply industry. To help address the water needs, a project known as the Dez-Qomroudwill convey water from the adjacent Dez Highlands to the central Iran watershed; it involves four tunnels (total length of 54 km), three small dams and a large dam. The longest tunnel of this project is known as the Qomroud Long Tunnel (QLT) with length of 36 km. Describing engineering geological problems along the first lot of the QLT " QLT1 " is the subject of this article.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Geological Subdiscipline > Geomorphology (0.93)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.50)
- Well Drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (0.93)
ABSTRACT: The mechanical stability of a tunnel is subjected to the development of loosening zone. Convergence measurement is the most convenient and practical method to estimate support requirements. In 12 m span tunnels, in order to predict the final deformation and the development of loosening zone based on the measurement at the earlier stage of excavation, the Rock Behavior Classification in Tunneling (RBCT) had been proposed. It has five classes: Class I to V. Japan Atomic Energy Agency has excavated a 4.5 m diameter ventilation shaft and a 6.5 m diameter access shaft in Horonobe URL project since 2005. And, it is expected to build a practical guide to feed the results from the convergence measurement to the excavation work at deeper stages. Therefore, the authors confirmed the applicability of RBCT to the convergence curves in tunneling projects with smaller crosssectional dimensions. Based on the evaluation, they applied RBCT to the measurement in the shafts. Consequently, it was clarified that the final deformation ratio converged in the range of Class II and approximately 15 % wide loosening zone in excavated diameter developed in the case that the initial deformation ratio was observed in the range of Class III in the shaft excavation. 1. INTRODUCTION The mechanical stability of a tunnel is significantly subjected to the development of loosening zone around the tunnel wall. Terzaghi [1] had proposed a relationship between the rock condition and the support load caused by the loosening. Kastner [2] had studied the stress distribution around a tunnel and the support pressure by a theoretical model focusing on the development of the plastic zone around an opening. According to the earlier experiences of underground projects, the loosening of rock related to the stability of a tunnel could be defined as the rock behavior which consists of dilatancy caused by shear deformation along the joints of rock and the inelastic deformation of the rock itself. The magnitude and the width in the field can be estimated by investigating the change of the permeability and elastic wave velocity of rock between before and after excavations. The loosening should be controlled by the appropriate choice of an excavation method, the magnitude of support members installed, and the timing of the installation. In addition, the allowable limit of the loosening zone should be determined by the required performance as an underground structure and should be one of main reasons for the determination of the practical guide of convergence measurements in tunneling, which is used as the allowable limit of deformation by site engineers. Therefore, in the stage of both design and construction in tunneling, it is necessary to estimate the mechanical stability of a tunnel from the viewpoint of not only the stresses of support members but also the development of loosening zone. Tanimoto et al. [3] suggested that the loosening of rock could be divided into strain-softening behavior and plastic flow, and the allowable limit of loosening zone was the strain-softening behavior. And, by means of analyzing a number of convergence curves observed in 12 m span tunnels, Tanimoto et al. [4, 5] indicated that the excessive deformation was allowed in a number of tunnels in Japan, and built the relationships among the initial deformation rate, the final deformation, the width of loosening zone, and the allowable limit of convergence.
- North America (1.00)
- Asia > Japan (1.00)
- Geology > Rock Type (0.95)
- Geology > Geological Subdiscipline > Geomechanics (0.94)
- Energy > Power Industry (0.68)
- Energy > Oil & Gas > Upstream (0.34)
ABSTRACT : Thermal loading can impact the mechanical properties of rock. In deep excavations, for example, ventilation can result in a significant rapid cooling of the rock. In this study sandstone samples were subjected to slow heating followed by rapid cooling, referred to as thermal shock. An initial suite of tests were conducted at temperatures of 100ยฐC, 200ยฐC, and 300ยฐC. In these tests, samples were subjected to a single cycle of heating and cooling and then tested. Measurements included P and S wave velocity, fracture toughness and tensile strength. Even though only small changes were seen at 100ยฐC, further studies were conducted at this temperature because of the practical importance of this temperature range in mining and civil design. Cyclic heating and cooling was conducted at 100ยฐC, with measurements of fracture toughness and tensile strength at 10, 15 and 20 cycles. Even though the overall results from the tree types of measurements (seismic velocity, fracture toughness, and tensile strength) are quite complicated, they can be at least partially explained by considering three types of crack density changes: a small decrease in crack density (crack healing), a small increase in crack density (blunting of macrocracks), and a large increase in crack density (rock damage). 1. INTRODUCTION Thermal stresses are generated in rock from changes in temperature due to two primary causes, steady state heat flow and transient heat flow. Under steady state heat flow, thermal stresses are generated in the rock microstructure due to elastic mismatch between grains and pre-existing cracks and pores. Under transient flow, rapid heating can result in large compressive stresses, and rapid cooling can result in large tensile stresses [1, 2, 3]. Deep underground excavations are subjected to cyclic thermal stresses due to rapid ventilation cooling and intermittent stoppages. For example, for an underground excavation at a depth of 2000 meters, rock temperatures as high as 80ยฐC could occur and rapid cooling by as much as 60ยฐC could occur due to ventilation. This could result in increased drift degradation due to micro- and macro-cracking [4]. Laboratory tests have been conducted to evaluate the effects of thermal loading on the mode I fracture toughness, tensile strength, and seismic wave velocity. To determine the mode I fracture toughness, the Edge Notched Disc (END) method was used [5]. To determine tensile strength, Brazillian disc tests have been conducted. A seismic test has been conducted to investigate the compressional wave velocity and crack density after the thermal loading. Coconino sandstone has been used to investigate the change of rock properties after the thermal loading. 50.8 ยท 25.4 mm, 50.8 ยท 25.4 mm and 50.8 ยท 50.8 mm (diameter ยท thickness) samples are used for the END test, the Brazillian test, and the seismic test respectively. In this study, thermal loading is modified compared to most previous investigators [3,6,7,8]. To simulate the ventilation in the deep underground mines, samples are slowly heated up to a specific temperature, and then cooled rapidly using a fan. This kind of thermal loading will be referred to as "thermal shock."
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.45)
ABSTRACT: The proposed Caldecott 4th Bore, located along State Route 24 in Oakland, California is a 15 m wide, 9.7 m high, highway tunnel that will be constructed using the New Austrian Tunneling Method (NATM). Rock mass strength and deformability properties including local effects due to strain softening, intact rock softening and strength degradation due to erosion and softening of joint infillings are key design considerations for the project. Ground/structure interaction issues modeled in numerical analyses include stress relaxation ahead of the tunnel heading, arching of loads across weak zones, face stability, effects of early age creep in shotcrete and stress redistributions due to the formation of plastic hinges in the shotcrete lining. The design also evaluated forces, moments and rotations in the shotcrete lining to determine ground support requirements. 1. INTRODUCTION 1.1. Project Background The existing Caldecott Tunnel complex includes three bores along State Route 24 (SR 24) through the Berkeley Hills in Oakland, California. The California Department of Transportation (Caltrans) and the Contra Costa Transportation Authority (CCTA) propose to address congestion on SR 24 near the existing Caldecott Tunnels by constructing a fourth tunnel that will provide two additional traffic lanes. The proposed horseshoe-shaped fourth bore is 1,036 m (3,399 ft) long, with a span of 15 m (50 ft), and a height of 9.7 m (32 ft). The fourth bore will be constructed using the New Austrian Tunneling Method (NATM). The project will include short sections of cut-and cover tunnel at each portal, seven cross-passageway tunnels between the fourth bore and the existing third bore, electrical substation buildings, and a new operations and control building. State Route 24, considered a lifeline route by Caltrans, is required to be open to emergency vehicles 72 hours after an earthquake with a return period of 1,500 years and a peak ground acceleration of 1.2 g. Construction of the fourth bore is anticipated to begin in the summer of 2009 and be completed in 2014. 1.2. Geology The geology of the alignment is characterized by northwest-striking, steeply-dipping, and locally overturned marine and non-marine sedimentary rocks of the Middle to Late Miocene age. The western end of the alignment traverses marine shale and sandstone of the Sobrante Formation. The Sobrante Formation includes the First Shale, Portal Sandstone, and Shaly Sandstone geologic units as identified by Page [1]. The middle section of the alignment traverses chert, shale, and sandstone of the Claremont Formation. The Claremont Formation includes the Preliminary Chert, Second Sandstone, and Claremont Chert and Shale geologic units [1]. The eastern end of the alignment traverses non-marine claystone, siltstone, sandstone, and conglomerate of the Orinda Formation. Major formations and geologic units within these formations are shown Figure 1. The geological structure of the project area has been characterized as part of the western, locally overturned limb of a broad northwest-trending syncline, the axis of which lies east of the project area. The fourth bore alignment will encounter four major inactive faults, which occur at the contacts between geologic units. These faults strike northwesterly and perpendicular to the tunnel alignment.
- Government (1.00)
- Energy > Oil & Gas > Upstream (0.94)
ABSTRACT: Working under high walls in open pit mines presents potential slope stability issues and rock fall hazards that require remediation in order to carry out the work safely. Diavik Diamond Mines Inc. manages an open pit and underground mine in the sub-arctic Northwest Territories, Canada. One of the ore bodies is located in the pit wall, and will require mining beneath a 50 metre high bench wall. This paper presents the ground support measures taken, the monitoring system implemented, and the planned procedures to allow safe open pit mining of the A154-North kimberlite ore body in the summer of 2008. A segmental approach is planned for mining under the high wall, and slope reinforcement will follow each segment of kimberlite excavation to minimize and control the rock fall hazard. Slope movement monitoring will be carried out simultaneously to manage any risks associated with potential larger scale slope movements. By implementing a combination of slope stabilization and rock support measures, together with a practical site specific slope monitoring program, the challenges of mining safely beneath this high face will be met. 1. INTRODUCTION The Diavik Diamond Mine (Diavik) is located at Lac de Gras, 300 kilometres northeast of Yellowknife, in Canada's Northwest Territories. Diavik is an unincorporated joint venture between Diavik Diamond Mines Inc. (DDMI) (60%) and Harry Winston Diamond Mines Ltd. (40%) Both companies are headquartered in Yellowknife, Canada. DDMI is a wholly owned subsidiary of Rio Tinto plc of London, England, and Harry Winston Diamond Mines Ltd. is a wholly owned subsidiary of Harry Winston Diamond Corporation of Toronto, Canada. DDMI is the operator of the project. DDMI has undertaken to mine the diamondiferous kimberlite pipes on the property using a combination of open pit and underground methods. The A154 open pit is the focus of this report. It has two kimberlite pipes as shown in figure 1, with A154 South (A154S) central to the pit and A154 North (A154N) adjacent, but in the NE pit wall. There are currently four 10 metre high benches in the A154N kimberlite pipe where the kimberlite is exposed in the wall and floor of the open pit between El. 320 and 280 metres. Preliminary plans propose the top 3 benches to El. 290 will be mined from the surface with the balance mined from underground, under a cemented rock fill to facilitate underhand drift and fill mining below the cemented rock fill cap. Figure 1 A154 Open Pit with two kimberlite pipes. (available in full paper) DDMI proposes to excavate some, or all, of the four remaining kimberlite benches if 1) it can be done safely with stability analyses indicating that mining of these benches will not reduce the overall slope factor of safety to an unacceptable level, and, 2) the slope support and monitoring measures necessary are not cost or schedule prohibitive. Stability analysis of the upper portion of the NE wall indicates an acceptable factor of safety of 1.441 if the granite rock fabric behind the kimberlite pipe is similar to pit wall exposures above the pipe.
- North America > Canada > Northwest Territories > Yellowknife (0.45)
- Europe > United Kingdom > England > Greater London > London (0.24)
- Geology > Rock Type > Igneous Rock (1.00)
- Geology > Ore Deposit Type > Magmatic Ore Deposit (1.00)
- Geology > Mineral > Silicate > Nesosilicate > Olivine (1.00)
- (2 more...)
- Management (0.34)
- Health, Safety, Environment & Sustainability (0.34)
ABSTRACT: Researchers from The Natural Earthquake Laboratory in South African Mines (NELSAM) project are investigating the physics and mechanics of mining-induced earthquakes using the access to seismogenic depths provided by deep South African gold mines and the large number of seismic events that occur near these mines. To study these events, it is necessary to quantify the far-field stress field around the mine, determine how the presence of the mining excavation perturbs this stress field, and investigate how these mining-induced stress changes affect the pre-existing faults. In this paper, we develop and test a new technique for determining the far-field virgin state of stress near the TauTona gold mine. The technique we used to constrain the far-field stress state follows an iterative forward modeling approach that combines observations of drilling induced borehole failures in borehole images, boundary element modeling of the mining-induced stress perturbations, and forward modeling of borehole failures based on the results of the boundary element modeling. Following this approach, we determined that the state of stress is a normal faulting regime with principal stress orientations that are slightly deviated from vertical and. Modeling of breakout rotations and gaps in breakout occurrence associated with recent fault slip on critically stressed faults further confirmed this stress state. 1. INTRODUCTION As mining around the world moves deeper underground, understanding the stress field at depth and how mining activity perturbs it becomes increasingly important for mine safety. As a result of the mining-induced stress perturbations, deep underground mines tend to have appreciable mining-induced seismicity associated with them. In cases when these seismic events cause damage to the excavation, they may result in injuries and fatalities. A more complete characterization of the farfield stress will lead to better modeling of the mining induced stress perturbations around the excavation. In turn, this can guide mining activities in the future and improve overall safety in the mines. Constraining the far-field stress state is an important part of the Natural Earthquake Laboratory in South African Mines (NELSAM) project, which is working to develop a very near-field laboratory to study earthquakes at seismogenic depths [1-3]. The deep gold mines of South Africa are unique locations for near-field studies of earthquake mechanics because of the high rate of mining-induced seismicity and the direct access to faults at seismogenic depths. However, the perturbation of the in situ stresses by mining activities creates a complex stress field that complicates the understanding of the physical mechanisms controlling the induced seismicity. As part of the NELSAM project, we developed a new method to constrain the far-field in situ stress state surrounding the TauTona gold mine in the Western Deep Levels of the Witwatersrand Basin of South Africa. Much of the previously published work on characterizing the far-field in situ stress state near the deep mines in the Witwatersrand Basin relies on borehole strain relief measurements [4-6]. In their review of global stress measurements, McGarr and Gay [7] showed that in South Africa the stress state at depths below 2 km is typically a normal faulting stress regime, in which the vertical stress exceeds the horizontal stresses.
- Africa > South Africa (0.74)
- North America > United States > California (0.28)
- North America > United States > Oklahoma (0.28)
- North America > United States > Utah > Washington County (0.24)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Oceania > Papua New Guinea > Papuan Peninsula > Central Province > National Capital District > Petroleum Retention License 15 > Pโnyang Field (0.98)
- Oceania > Papua New Guinea > Papuan Peninsula > Central Province > National Capital District > Petroleum Retention License 15 > Elk-Antelope Field (0.98)
- Oceania > Papua New Guinea > Papuan Peninsula > Central Province > National Capital District > Petroleum Retention License 15 > Angore Field (0.98)
- (10 more...)
ABSTRACT: One of the key factors for designing power tunnels is the prevention of hydraulic jacking in the surrounding rock. This problem is occurred when the water pressure within tunnel exceeds the in-situ compressive stress in rock. As a result of this phenomenon the existing joints can be opened. This may lead to the jacking of a large mass of rock away from the tunnel towards ground surface or adjacent underground space resulting in excessive leakage or large scale landslides. The ratio of minimum principal stress to internal water pressure is used as a factor to determine the kind of lining needed against hydraulic jacking. According to design recommendations if this factor is not satisfied, the application of steel lining as a waterproof liner will be necessary. For in-situ stress measurements in power tunnels, the method of hydraulic fracturing tests has been suggested as the most relevant tool. Seymareh dam and hydropower plant project is located in the western province of Ilam in Iran. Because of disastrous probable consequences of hydraulic jacking in the power tunnel of project and the high cost of steel lining on the other hand, it was intended to perform hydraulic fracturing tests in this project in order to measure in-situ stresses and determine the required length of steel liners. Recently two horizontal boreholes with the length of 60 m were drilled at the center of penstocks and within each nearly 10 hydraulic tests were carried out. In this paper the situation of power tunnel, the geological characteristics and some of the test results are explained. 1. INTRODUCTION Seymareh dam and hydropower plant project is nearly located 25 km far from the northwest of Darreh Shahr city in the west province of Ilam in Iran (Fig. 1). The objectives of the project are to control the upstream water flow, supply and distribute water to the neighboring agricultural lands and generate a hydroelectric energy of 835 GWH annually. This concrete arch dam with 180 m height and 200 m crest length is to be placed on Seymareh River with creating a reservoir of 3.2 billion m. The levels of probable maximum flood (PMF), normal water in the reservoir and rock foundation are 730, 720 and 550 m above the sea level, respectively. The dam is to be founded on the north wing of Ravandi anticline, which geologically includes the Asmari formations containing limestone layers and Gachsaran formations containing marlgypsum masses. The construction work of project started from 2003. Figure 1 illustrates a view of the gorge in which the location of dam axis and the entrance of power tunnel in the left bank are shown. The power system in Seymareh dam project consists of a pressure tunnel which is converted at trifurcation point to three penstock tunnels and finally reaches a surface powerhouse containing three units. The water head in penstock tunnel will be 1.3 MPa in normal condition of service load. An investigation program is proposed to estimate the possibility of hydraulic jacking in penstock tunnels and determine the in-situ stresses by hydraulic fracturing tests.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.39)
ABSTRACT: Inter-panel barrier pillars are relatively wide pillars between longwall panels and may be used in deep coal mines, say, below 700 meters. Narrow pillars are favored for resource recovery and operational efficiency, while wide pillars are favored for safety and stability. Finite element analysis in two and three dimensions provides useful guidance in determining a satisfactory pillar width. At a deep coal mine (828 m depth) in central Utah where a two-entry system is used, a width of 150 m is adequate in consideration of stratigraphy, rock properties, premining stress, panel and pillar geometry and the excavation sequence. Three sets of four borehole pressure cell measurements at the study site were of some value in assessing model results. 1. INTRODUCTION This paper presents an analysis of inter-panel barrier pillar width in deep, underground coal mines. Analysis is based on the popular and powerful finite element (FE) method. Inter-panel barrier pillars may be used in conjunction with longwall mining at depths where conventional side-by-side panel excavation is difficult. Wider pillars provide better isolation and therefore reduction in mined panel interactions that increase stress, while narrower pillars increase resource recovery and reduce development entry lengths and therefore costs. Inter-panel barrier pillars are usually many times wider than they are high, although pillar width depends on panel width. Longwall panel widths are usually greater than about 250 m (750 ft). A barrier pillar in a 3 m (10 ft) thick seam mined full height may be over 120 m (400 ft) wide. Two- and three-entry systems are commonly used for longwall panel development in the coal mines of central Utah. Figure 1 illustrates a two-entry longwall panel with the possibility of side-by-side panel mining or the use of inter-panel barrier pillars. In side-by-side mining, the previous head gate becomes the next tail gate. Design of chain pillars in these access roads is an important feature of the overall system as Gilbride and Hardy explain [1]. In either system the chain pillars do not survive panel excavation. Indeed, significant supplemental support in the development entries is usually required, frequently in the form of "cans", thin-walled steel cylinders filled with particulate material [2]. Wire mesh or chain-link may be strung along the supplemental support to control slough from ribs. Fig. 1. Two-entry longwall panel development with an adjacent next panel or inter-panel barrier pillar. (available in full paper) Barrier pillar safety and economy involve more than width, of course. Of particular interest are possible modes of barrier pillar failure that range from sudden, violent expulsion of coal from pillar ribs into development entries to slow yielding of ribs with maintenance of a strong, confined pillar core. Gas pressure and strata interfaces at seam top and bottom may be of importance in abetting or inhibiting release of horizontal confinement that appears essential to pillar stability. Gas trapped between impermeable strata in roof and floor may also contribute to excavation instability. Mine seismicity is associated with pillar, roof and floor instabilities. Mining may induce movement on existing faults, while fault slip may induce additional stress about mine excavations.
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- North America > United States > New Mexico > San Juan Basin > San Juan Basin Field > Mancos Formation (0.99)
- North America > United States > Colorado > San Juan Basin > San Juan Basin Field > Mancos Formation (0.99)