Stability analysis of rock slopes with the direct sliding blocks method

Abstract

The Boulevard of the Allies is a major four lane roadway in Pittsburgh, Pennsylvania that is constructed atop a near vertical, 35 meter high rock slope known locally as the Duquesne Bluff. Stratigraphic relief observed on the bluff consists of alternating sequences of flat lying sedimentary deposits of sandstone, siltstone, shale, carbonaceous shale, claystone and limestone. Expsoure of alternating sequences of durable and less durable rock has resulted in differential weathering and the formation of precarious overhanging conditions. In the interest of motorist safety and roadway improvement, a major remedial program was undertaken by the Pennsylvania Department of Transportation (PennDOT) in the mid 1980s. Primary remedial activities included rock trimming, rock bolting, the construction of dental concrete buttressing for overhanging rock support and shotcrete slope facing to arrest continued weathering of less durable claystone and carbonaceous shale exposures. As part of a current roadway improvement project, PennDOT and their consultant, Gannett Fleming, Inc., are evaluating the performance of previous remedial construction and are developing preliminary alternatives for future remediation. This paper will discuss the slope geology, overall favorable performance of the previous remedial construction and unfavorable slope conditions that may have resulted from large scale trimming operations.