Investigation at the First of Three Sites
Washington State Route 12 bisects the Cascades in southern Washington. Several portions of the highway were identified for potential rockfall mitigation as part of the White Pass Unstable Slopes Corridor Project. In 2005, Landslide Technology (LT) was retained by WSDOT to evaluate three sites and develop rockfall mitigation plans.
LT geologists performed geologic field reconnaissance, mapped geologic structural features (i.e. rock discontinuities such as joints, fractures, faults, etc.), conducted kinematic analyses of the rock discontinuity data, modeled stability failure modes, and conducted laboratory testing to determine physical and engineering properties of representative samples.
The results of the investigations and analyses were used to develop rockfall mitigation measures including tree cutting, hand and mechanical scaling, cable lashing, bolting key rock blocks, draped mesh, modified cable net fences, concrete barriers, improved ditch/fallout areas, and controlled blasting. LT completed final design on the measures and prepared Special Provisions to supplement the WSDOT Standard Specifications. Construction was completed in the summer of 2006.