ROCK STABILITY ASSESSMENT IN PRELIMINARY SITE INVESTIGATIONS--GRAPHICAL METHODS

Abstract

The report deals with the assessment of stability in highway rock cuttings. Simple graphical methods based on stereographic projection of scaled or unscaled field data are outlined. They are considered adequate for the identification of potential problems. Plotting of the data using a simplified composite net and contouring after using a Dimitrijevic counting net are recommended. Stability assessment overlays for each each of the 3 common failure mechanisms, plane, wedge and toppling, can be constructed from stability assessment nets. Use of the overlays with the plotted and contoured field data considerably simplifies stability assessment. Methods of optimisation of the design slope and the sensitivity of slope stability to variations in design slope azimuth, dip and friction angle of the rock, are readily apparent. The report recommends that such a stability assessment should be carried out in all intended highway excavations in rock. Nets necessary for assessment are included and a summary example of an assessment is given. (Author/TRRL)