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ROCK SLOPS STABILITY ANALYSIS <br />BY STEREONET <br />SECTION I. INTRODDCTION <br />Landslides represent a significant and widespread geologic hazard. <br />Reports of various government agencies indicate that losses to <br />buildings alone in the United States exceed $400 million per year <br />and that more than $100 million per year is spent repairing <br />landslide damage to highways and roads. Total economic losses from <br />landslides in the United States are conservatively estimated to be <br />in faxcess of $1 billion per year (Schuster and Krizek, 19'78). <br />Much of the total landslide damage is attributable to failures of <br />roc}c slopes. The stability of a rock mass depends on the <br />orientations and characteristics of weaknesses in the rock called <br />dis<:oatinuities, and generally not on the strength of the rock <br />itself. Excavations made in rock during construction expose <br />discontinuities which include such geologic structures as bedding <br />planes, foliations, joints, and faults. <br />Roc]c slope failures can be quite catastrophic. All mountainous <br />states, including Virginia, New York, California, Colorado, <br />PeniTSylvania, Oregon, and North _Carollna have had incidents of <br />property damage, personal injury, and fatalities resulting from <br />rocJt slope failures. Just in 1992, Virginia had several property <br />damage cases, at least one rock fall fatality case, and one <br />personal injury case in the courts. As the Interstate Highway <br />System continues to age, inventories of highway rock slopes and <br />analyses of problem sites become vital. Of course, rock slope <br />stability is not only of concern along highways, but also in open- <br />pit mining, quarrying, and building construction. <br />6ECTION II. HACXGROIIND THEORY <br />A. OVERVIEA OF ROCK SLOPE ANALYSIS <br />The complete stability analysis of an existing (or proposed) rock <br />slope involves five steps: understanding the geology, mapping the <br />situ, performing stereonet analyses, calculating safety factors, <br />and, if needed, planning remediation. These steps are explained <br />below and this exercise concentrates on the stereonet analyses. <br />1. Regional, local, and site geology <br />An understanding of rock slope stability at a site begins with an <br />understanding of the geology, starting with the regional <br />perspective and working down to the site. Sources of geologic <br />information include library and office research (articles, reports, <br />maps, air photos), discussions with colleagues, and field <br />reconnaissance. <br />Ste:reonet Analyses 1 Appendix A <br />m ~. 3~ <br />1jPPRo~eD 3/y4/py <br />