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Abstract Proper evaluation of geological conditions and stress environment are critical to ground control in underground openings. For a slope entry, the problem becomes more complicated due to the fact that the entry normally digresses through different types of strata before reaching the coal seam. Furthermore, as the depth increases, the stress level changes. Therefore, it is important to determine the stress distribution and evaluate stability of the opening along different slope sections when designing roof bolting plan and long term ground support. Over the past two years, Keystone Mining Services, LLC of Jennmar Corporation Inc. has developed a new methodology, designated as the Stress, Geologic, Support design system (SGSsm), for underground mine openings. This methodology has been successfully applied in various coal mines across USA. Through an application at an underground slope mine, this paper briefs main concepts of the methodology and details the following: (1) Geological evaluation and stress analysis along the slope utilizing numerical modeling and the identification of strong, fair, and weak sections along a slope; (2) Design of primary and supplemental bolting plans for each section along the slope. (3) Design of long term standing support in the form of steel sets based on the current industry standards by the American Institute of Steel Construction (AISC); and (4) Validation and performance evaluation of the designed steel set structure under extreme loading conditions using numerical modeling techniques. INTRODUCTION A recent increase in energy demand has resulted in a booming of U.S. coal mining industry. Some coal companies plan to develop new mines or expand existing ones. Many of these operations, especially in the Appalachia or Midwest region, access the coal seam through slope entries. Since these openings will be in service for the entire life of the operation, mining industry generally installs roof bolts after rock excavation and either steel sets or reinforced shotcrete as long-term roof support. However, ground control for mine slopes has been traditionally practiced based on trial-and-error and prior experiences. There is currently no well-accepted slope design methodology and steel set design guidelines that can help mining industry to develop an economic and technically sound ground control plan for a given mine slope entry. As a major ground control product supplier in the US, Jennmar Corporation, Inc. (Jennmar) is dedicated to providing the mining industry with advanced ground control technologies and professional engineering services. Based on prior experiences and successful cases, Keystone Mining Services, LLC (KMS) of Jennmar developed a practical ground support design methodology [1]. This method, taking into account the actual geo-technical conditions, identifies strong, fair, and weak sections along the slope, recommends primary and supplemental roof bolting plans, designs optimal steel sets for actual field conditions and engineering needs, and verifies the adequacy of the developed steel sets. The method received positive comments from mining industry and governmental agencies. Jennmar and KMS have been involved in various slope projects, and the ground control plan developed using this methodology has helped coal companies to pass the review.
Abstract A complex mosaic of Sevier (Ordovician) and Rome (Cambrian) Shale are widely distributed throughout the sedimentary sequences in the southern Appalachians. These shales exhibit variable geotechnical characteristics including the strength and durability. We have investigated the factors controlling the Unconfined Compressive Strength (UCS) and Slake Durability Index (SDI) of Sevier and Rome Shale in order to better understand site-specific engineering problems associated with these shales and to predict their geotechnical behavior. The results have shown the variation in mineral content including expanding clay, calcite, gypsum, and presence of microfractures filled with calcite have significantly affected the durability and strength of shale rock mass. In order to obtain realistic estimate of time-dependent weathering patterns in the Sevier and Rome Shale, we have performed multi-cycle SDI; results have indicates that a 5-cycle SDI better estimates the disintegration pattern of shale and can be used to classify shale in terms of the degree of weathering. INTRODUCTION AND OBJECTIVE Shales are very fine-grained argillaceous sedimentary rocks in which more than 50% of the clastic grains are smaller than 0.06mm in diameter [3]. These rocks are often intensely fractured and weathered and have highly variable geotechnical characteristics, which cause significant construction problems and damage to civil structures each year. In order to evaluate geotechnical properties, geologists estimate shale strength in terms of Unconfined Compressive Strength (UCS) and durability in terms of the Slake Durability Index (SDI). UCS measures the strength of a rock and its ability to bear the load of civil structures, and SDI determines a rock’s resistance to weathering. UCS and SDI are widely used in construction design and in rock engineering. Because of their variable clay content, degree of induration, shrink-swell behavior, and intensity and infilling of fractures and micro fractures, shales exhibit geotechnical properties that range from low strength, low durability, fissile rocks to hard and compact types [6, 16, 15, 17]. As a result, quantification of shale strength, weathering characteristics, and capacity of foundation support become challenging. Consequently, common practice among geologists and engineers is to treat shales as if they were soils and not coherent lithified materials. Thus, lithified shales are not often analyzed quantitatively. This practice yields over-conservative design parameters, which, in turn, cause unnecessarily high construction expenditures. A complex mosaic of weathered Sevier (Ordovician) and Rome (Cambrian) Shale are widely distributed throughout the landscape and form a majority of the sedimentary sequences in the southern Appalachians. As ongoing population pressure leads to an increased need for new construction sites (e.g., office buildings, highways, landfills etc.) in eastern Tennessee, many of these sites are being built on Sevier and Rome Shale and/or use shale as construction materials. These shales exhibit varying degrees of disintegration due to weathering (SDI values) and show inconsistent compressive strength (UCS). Therefore, our first objective is to investigate the factors controlling UCS and SDI of Sevier and Rome Shale in order to better understand the site-specific engineering problems associated with shale and to predict its strength and durability behavior in construction sites.
Abstract Problems with wellbore stability while drilling in shale have plagued the drilling industry for a long time. For good reason, the bulk of trouble-related problems while drilling have been in shales, and great expenditures in time and money are made each year dealing with the problem. However, shale interaction with drilling fluids in the drilling process remains a complex and often misunderstood area of study. Compared to cases when water-based drilling fluids are used, fewer wellbore stability problems occur while drilling when invert emulsions (IEF) are used. In this paper, the theory of shale interaction with invert emulsions focusing on osmotic pressure and membrane efficiency is briefly reviewed. Actual measurements of changes in shale strength of two very different shales have recently been directly made using a new test device from the University of Oklahoma: one from a deepwater environment and the other a more competent shale cored in a land-drilling operation. These shales were exposed to invert emulsions having different water phase activities, and the stresses required to cause failure in the samples were directly measured at different confining pressures. The results showed use of invert emulsions under some conditions weakened the shales, while under other conditions, the shales were strengthened. Elastic and porochemoelastic modeling efforts are then used to qualitatively corroborate observed shale strength changes seen in the laboratory 1. INTRODUCTION Mechanical Chemical Hydraulic Most of the formations drilled for oil and gas are clay-bearing shales, and problems in these formations account for the bulk of wellbore instability problems. When exposed to drilling fluids, formation shales can become unstable, a process that if left unchecked can lead to wellbore failure. Failure mechanisms generally fall into the following categories:Formation failure can lead to significant expense with the loss of a well or an interval, in time, and in materials used to correct ongoing wellbore stability issues. Several researchers have described these processes in general. In particular, some researchers have studied the transport of water in shales as a key factor in producing mechanical failure. Similarly, many wellbore stability models have been constructed in which the key failure mechanisms of shale have been coupled to give predictions for compressive shear as well as tensile failure. Most recently, more complete models taking into account the three-dimensional wellbore geometry and the effects of time have also been coupled with earlier models to give a poromechanical analysis of the generation/diffusion of pore pressure in shales in contact with drilling fluids. The constant development of increasingly sophisticated wellbore stability models promises to further expand and deepen our understanding of shale instability problems. 2. PREVIOUS WORK Many studies have attempted to quantify the effects of interaction of drilling fluids and drilling fluid filtrates with shales and the resulting consequences on rock stability. Compared to drilling with water-based muds (WBM), drilling through problematic shales is generally less troublesome when IEF are used. Over the years, many shale stability studies, both theoretical and experimental, have been done for both drilling fluid types.
- North America > United States > Oklahoma (0.51)
- Asia > Middle East > Saudi Arabia (0.46)
- North America > United States > Oklahoma > Anadarko Basin > Cana Woodford Shale Formation (0.99)
- Africa > West Africa (0.89)