ROCKFALL CONTROL IN WASHINGTON STATE

The mountainous and rugged terrain of Washington State presents major and ongoing rockfall problems along transportation corridors. Rockfall control in Washington focuses on rockfall containment, identification, and prevention or minimization. Washington State Department of Transportation (WSDOT) has developed ditch design criteria for containing rockfall, which have been in use since 1963. The criteria address ditch design and rockfall fence placement for both rock and talus slopes. Rock slope design is a critical element of rockfall control in Washington. All new and upgraded construction of rock slopes is first evaluated for kinematic feasibility of rockfall. If applicable, cut-slope orientations are also based on kinematics. Highly fractured rock masses and those with random discontinuity orientation are designed using a nonlinear failure criterion. Controlled blasting methods are required on all WSDOT projects. Slope irregularities are kept to an absolute minimum and the use of midslope benches for a rockfall catchment has been eliminated. Commonly used stabilization methods are shotcreting, rock bolting and dowelling, slope trimming and scaling, and wire mesh. A priority rating system is also in use to direct proactive mitigation work in areas of high rockfall hazard around the state. In addition, WSDOT and Washington State University are developing an expert-type computer system, the unstable slope management system (USMS), for statewide use.