Discontinuity Significance Index and Electronic Data Collection for Rock Slope Stability Studies

Abstract

The advent of microcomputer technology has made possible the computerized collection and analysis of many types of geotechnical data in the field. Data collected in this way may be quickly transferred to mainframe computers for detailed analyses or analyzed near the site utilizing microcomputer programs. In particular, a computerized system for the collection of geologic structure data related to rock slope stability was developed by C. F. Watts while a doctoral student in engineering geology at Purdue University (Watts et al., 1982). In slope stability studies, discontinuity orientation data are often represented on stereonet projections and rectangular dip plots. Traditionally, such orientation plots have treated all discontinuities equally. In reality, many discontinuities have physical characteristics which make them far more significant to stability than other discontinuities. The discontinuity significance index (DSI) was developed to permit the ranking of discontinuities within a particular rock mass in terms of their potentials for instability. The DSI values incorporate such field data as discontinuity length, degree of dip, roughness, continuity, hardness of adjacent rock, and water conditions. They may be quickly calculated near the field site by microcomputer and depicted on orientation plots. The development of the DSI concept is described along with potential variations. A case history is briefly examined in which clusters having the highest DSI values were identified for a rock mass. Those discontinuities later contributed to a rock slope failure that partially closed the adjacent highway.