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ARMA/USRMS 05-671 American Rock Mechanics Association, 2005. - 9 p.
This paper was prepared for presentation at Alaska Rocks 2005, The 40th U.S. Symposium on Rock Mechanics (USRMS): Rock Mechanics for Energy, Mineral and Infrastructure Development in the Northern Regions, held in Anchorage, Alaska, June 25-29, 2005.<em>ABSTRACT: Molas Pass is located in Southwestern Colorado on US 550. In August 2003, Colorado Department of Transportation (CDOT) began a rockfall mitigation project to all eviate potential dangers caused by rockfall and/or rockslides and to improve the sight distance and reduce the blind corner caused from the rockslope. The work involved rock excavation by production blasting, rock reinforcement with dowels and rock bolts and rockfall mitigation using wire mesh drape. A contractor’s access road was constructed across the upper rock face about 85 feet above the shoulder of the highway to facilitate excavation of the rockslope. The excavation created an unstable highwall specifically a large rock block above the access road. Blasting of the access road exacerbated the rockslope instability of the high wall by day lighting the failure plane and unweighting the toe of the slope of the highwall. The stability of the highwall was aggravated by the excessive backbreak created from blasting. A combination of factors in the blasting such as over-stemming of the shot holes and short timing delays in the firing sequence between the second and back shot hole rows may have led to the severe backbreak. Moreover, the adverse geologic structure appears to have exacerbated the excessive backbreak.
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ARMA/USRMS 05-671
Analysis of Rockfall and Blasting Backbreak Problems, US 550, Molas Pass, CO William C. B. Gates Kleinfelder, Bellevue, Washington, USA
L. Ty Ortiz Colorado Department of Transportation, Denver, Colorado, USA
Robert M. Florez Colorado Department of Transportation, Denver, Colorado, USA Copyright 2005, ARMA, American Rock Mechanics Association This paper was prepared for presentation at Alaska Rocks 2005, The 40th U.S. Symposium on Rock Mechanics (USRMS): Rock Mechanics for Energy, Mineral and Infrastructure Development in the Northern Regions, held in Anchorage, Alaska, June 25-29, 2005. This paper was selected for presentation by a USRMS Program Committee following review of information contained in an abstract submitted earlier by the author(s). Contents of the paper, as presented, have not been reviewed by ARMA/USRMS and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of USRMS, ARMA, their officers, or members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of ARMA is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgement of where and by whom the paper was presented.
ABSTRACT: Molas Pass is located in Southwestern Colorado on US 550. In August 2003, Colorado Department of Transportation (CDOT) began a rockfall mitigation project to alleviate potential dangers caused by rockfall and/or rockslides and to improve the sight distance and reduce the blind corner caused from the rockslope. The work involved rock excavation by production blasting, rock reinforcement with dowels and rock bolts and rockfall mitigation using wire mesh drape. A contractor’s access road was constructed across the upper rock face about 85 feet above the shoulder of the highway to facilitate excavation of the rockslope. The excavation created an unstable highwall specifically a large rock block above the access road. Blasting of the access road exacerbated the rock