The usefulness of seismic, resistivity, and vegetation surveys for predicting subsurface strength characteristics of granitic rock was evaluated in the Idaho batholith. Rock strength varies inversely with degree of weathering and fracture density. Rocks that have weathered or altered to the point where they contain lays (referred to here as highly weathered rock) are particularly susceptible to mass failure following disturbance. Eleven of 12 zones identified as highly weathered were predicted by the surveys along a proposed road centerline. Using the same criteria, 10 other zones would have been predicted to contain highly weathered rock, but did not. Preconstruction geophysical and vegetation surveys may efficiently narrow the number of sites requiring additional surface exploration, or drilling for drainage location, or location of sites requiring road stabilization structures.
Clayton, James L. 1983. Evaluating slope stability prior to road construction. Res. Pap. INT-307. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 6 p