1986-09-17_REPORT - M1977211 - Laserfiche WebLink

Home Browse Search

• r SUMMARY At the request of the MSHA Denver Field Office, a rock stability evaluation of the Pikeview quarry was conducted on September 17. 1986. The mine operator was excavating at the toe of a steeply dipping bedded limestone deposit. An immediate recommendation is to terminate the practice of undercuttin (thereby ay i e eep y dipping Ya ing planes o �ithis lj*r+estone deAosi A long-term reco m nae anon is to begin quarrying operations near the ridge line west of the present quarry. then advance the quarry face in a north-south direction along the limestone-granite contact. GENERAL INFORMATION AND OBSERVATIONS The Pikeview quarry (ID No. 05-01443) is owned and operated by the Castle Concrete Company. This limestone quarry is located along the eastern slope of the Rampart Range a few miles north of Colorado Springs at the western end of the Garden of the Gods Road. The sedimentary beds of this quarry were geologically uplifted and subjected to contact metamorphism by the intrusion of the Pikes Peak Granite. As a result, these bedded deposits strike generally north-south and dip steeply toward the east. Some of' these slightly undulating limestone beds, as measured by Brunton Compass during this survey, dip from about 47 degrees to about 53 degrees toward the eat. The north-sou trending Rampart Range Fault occurs within this quarry operation. The fractured joint system near the Rampart Range Fault dips about 74 degrees toward the west. The Pikes Peak Granite, a massive coarsely crystalline red to pink granite is reported to occur at the surface on the ridge immediately west of the present quarry operations. Therefore. the contact between the bedded limestone formation and the massive granite intrusive is located somewhere between the quarry and the crest of this ridge. Benches presently excavated in the limestone beds have undercut the eastward dipping bedding planes; thereby, daylighting the limestone beds. These limestone beds dip at an angle greater than the angle of repose for rubblized limestone and also are subjected to freeze-thaw weathering cycles. CONCLUSIONS If the final west quarry wall is excavated in the steeply dipping limestone beds as currently practiced, an eventual total failure of the entire west wall can be expected. The combination of undercut. steeply dipping beds; edding eparations; and freeze-thaw cycles can be expected to produce this eventual quarry wall failure.