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Tunnels & Tunneling Abstracts—Titles List (click to view abstracts)
Application of Numerical Methods in Design of Mining Shafts and Tunnels:
Selected Case Histories In recent years, numerical methods have gained a measure of acceptance in design of underground openings, not as a means of supplanting traditional methods, but as an aid to engineering judgement to be used in conjunction with traditional methods. The use of efficient pre- and post-processors make these tools user friendly, encouraging investigations of the influence of varying material properties and loading conditions. The design studies presented here were performed using the two-dimensional finite-element method (FEM) implemented in the JAC code. This code provides a number of nonlinear rock models suitable for modeling jointed and yielding rock. This paper presents two case histories from mining involving decline (inclined tunnel) and shaft design. One of these projects was designed and constructed in the early 1980s when numerical methods were more cumbersome and not as commonly used in design as now. The original analysis of deformation for jointed rock was reanalyzed for this paper using more complete models, with feedback from construction and subsequent operations providing insight into the adequacy of the design. The second project is in the final design stage.
Pillar Stability in Large Underground Openings: Applications from a Case
Study in Competent, Jointed Rock During the last three decades, the mining and construction industries have required that underground openings be increased in size. In mining, the larger equipment needed for higher productivity has made necessary the excavation of larger openings. In the construction industry, an increased number of larger openings has been required for power stations, tunnels, storage chambers, and military installations. In many cases, these excavations have been made in competent, jointed rocks. The purpose of this monograph is to provide applications from a case study in an area of rock mechanics where there is little available information—pillar stability in large underground openings excavated in competent, jointed rocks.
Rock Reinforcement Longevity
Rock reinforcement has been accepted in mining and construction since the 1950s. The longevity of rock reinforcement is often questioned in engineering design because it's historical performance is measured in just decades, relies on natural systems to function, and is not easily inspected. The elements of a typical rock reinforcement fixture include an anchoring device, a bar or tube, a plate, a head bolt, and possibly grout.
19th Conference on Ground Control in Mining, Morgantown, West Virginia,
August 8–10, 2000 Rock reinforcement has been in widespread use and generally has been accepted in underground mining and tunneling since the 1950s. The first rock reinforcement technologies employed were mechanical anchors such as split wedges or expansion shells with ⅝-inch-diameter steel bolts. Failures occurred in weak strata which provided poor anchorage or in ground with corrosive waters. Friction rock fixtures consisting of relatively thin-walled tubes have been in use for about 15 to 20 years. While generally performing adequately, longevity problems have developed from corrosion in water bearing ground. Longevity of rock reinforcement is much enhanced with grouted bolts. Portland-cement-grouted rock reinforcement has been in use since the mid-1950s, primarily in tunneling and other civil engineering underground construction. Tests of decades-old installations have revealed few problems except in ground with aggressive waters. Polyester-resin-grouted rock reinforcement was introduced in the United States to mining in the late 1960s and to tunneling in the early 1970s. Experience from 30 years of resin-grouted bolt installations and field tests have identified longevity problems associated with degradation of steel reinforcing bars, but in generally unusual situations. Improvements continue in resin chemistries, packaging, corrosion protection, grout quantities, and mixing and distribution in the drilled hole to achieve long-term performance. Specific case histories cited with resin- or Portland-cement-grouted rock reinforcement longevity or performance problems, upon close examination, reveal that the causes of the problems were quality control procedures being inadequate and not in accordance with good practice. Manufacturers' recommendations and engineering specifications, if followed in the field, and with competent inspection and supervision, would have prevented most, if not all, reported longevity or performance difficulties. |
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