Paper Details

TRB 91st Annual Meeting (January 22-26, 2012)

Event Number:	576
Event Title:	Investigation and Management of Geologic Hazards
Event Date:	Jan 24 2012 2:00PM- 3:45PM
Event Location:	Marriott, Salon 2
Event Description:
Event Agenda:

Application of Digital Photogrammetry to Rock Cut Slope Design (12-4414)

To reduce future maintenance along a curved stretch of U.S. Highway 15 on Bald Eagle Mountain near South Williamsport, the Pennsylvania Department of Transportation proposed to remove an existing rockfall fence and modify the existing cut to provide a rock catchment ditch in order to mitigate the rockfall hazard. Digital photographs of the existing rock cut were used to develop a three-dimensional, digital model encompassing a 420-foot-long section of the cut. The orientations of 238 rock discontinuities visible in the model were measured. A Brunton Geotransit was used to collect additional measurements from behind the rockfall fence and to validate the model measurements. Discontinuity measurements were used to analyze the potential for plane, toppling, and wedge failures, to assess the variability of dip angle and dip direction along the alignment, and to optimize the azimuth of horizontal drain holes. The digital model was used to locate the outcrop of clay seams encountered in rock core borings. Using digital photogrammetry greatly enhanced safety since discontinuities in higher parts of the outcrop were measured without rappelling or free-climbing. A great volume of data was collected in a short period of time, reducing exposure to rockfalls and traffic. Discontinuities were measured over a greater area of their extent, and discontinuities having limited surface exposure were measured by digitizing their trace across the outcrop. Using digital photogrammetry reduced the potential for human error in the collection, recording, and processing of data, and facilitated performance of the analyses required for the rock cut slope design.

Authors
Roman, William , Gannett Fleming Inc.