LiDAR-Based Rock Slope Assessment State Route 8 Sandisfield, Massachusetts

摘要

In spring 2013, a wedge-shaped failure released approximately 100 cubic yards of rock and debris from a slope, filled the catchment and southbound shoulder, and partially blocked the southbound lane of Route 8 in Sandisfield, Massachusetts. Fortunately, no one was injured. A GZA and MassDOT response team visited the site and found saturated, heavily vegetated, 20- to 55-foot high, near-vertical rock slopes extending along 1/2 mile of roadway. Concrete Jersey barriers were installed to temporarily enhance the catchment and to buy time to clean up the fallen rock, clear the vegetation, and make a comprehensive assessment of the slope and catchment. The comprehensive assessment included a LiDAR survey and hand measurements to characterize joints in the rock mass. The LiDAR allowed the team to survey about 1/2 mile of slope, in places 50-plus feet above the ground in three days of scanning. The software package Split-FX? was used to create a mesh from the LiDAR point cloud, interpret the mesh to identify repeating planar features (joints), group the joints into sets, and display the joint sets on lower hemisphere stereographic projections. GZA evaluated the completeness of the LiDAR data set, then compared the results to the Brunton Compass-based readings and assessed potential sources of error. The resulting stereonets provided the basis for kinematic analyses of the rock slope. Split-FX? provided a large volume of structural data for the exposed bedrock, which was used to characterize variations in the structure along the slope and identify areas most at-risk for future rockfall. Split-FX? was also used to develop cross sections and block sizes that were the basis for CRSP modelling.