Geo-Strata, Fall 2003, pp. 9–12
Author: F. S. Kendorski (AAI)
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.
Downloadable PDF: Rock Reinforcement Longevity
19th Conference on Ground Control in Mining, Morgantown, West Virginia, August 8–10, 2000
Authors: F. S. Kendorski (AAI)
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.
Downloadable PDF: Rock Reinforcement Longevity-19