Baseline rockfall rates and rockfall protection in Virginia

Current approaches to rockfall hazard and risk mitigation have been dominated by a model in which rockfall is treated as a global slope stability phenomenon which is mainly triggered by precipitation, freeze-thaw, or root wedging. The methods implemented by many public agencies and private entities developed from this conceptualization. These methods, such as the Rockfall Hazard Rating System, Key Block and Key Group Analysis, and remote sensing using LIDAR or digital images, are best applied to the end-members of slopes, such as pure engineered soil or structurally simple and consistent rock slopes. Slopes exhibiting complex structure, slopes that cross formations or fault zones, or faults that consist of mixed zones of soil and rock can not be accurately assessed by these methods. Our new data on rockfall patterns in the Valley and Ridge Province of Virginia show that a large component of rockfall is triggered neither by climatic, seismic, or other events, but depends heavily on the structural and lithological characteristics of the rock mass. Understanding this pattern offers the potential for a more rational, cost-effective, and safer design philosophy for all types of rockfall. Rock mass indices that take into account the structural and lithological aspects of a rock slope provide a more reliable tool for predicting rockfall behavior than those in current use. Indices such as the Rock Mass Rating System (RMR), the Norwegian Geotechnical Institute's Tunneling Index (Q), or Geological Strength Index (GSI) correlate particularly well with rockfall hazard. The three papers included within this Dissertation focus on specific aspects of this new rockfall protection philosophy. The first paper is a case study of a failed slope in Bath County, Virginia, where traditional methods of slope analysis failed. The second paper focuses on the failure of the Rockfall Hazard rating System to adequately ensure the safety of the traveling public and presents the theoretical basis for rockfall patterns and presents a new suggestion for roc slope management. The third paper focuses on the structural and lithological controls on rockfall and explores the possibility of using rock mass strength indices as proxies for rockfall.