Design of Ultimate Pit Slope for a Proposed Opencast Limestone Mine in the Hilly Region of Northern India

Abstract

This paper presents the investigation conducted for the design of ultimate pit slope of a proposed limestone opencast mine in the hilly region of the state of Himachal Pradesh in northern India. The limestone rock mass at this project-site was classified as good with Bieniawski’s basic RMR varying from 60 to 72. The intact rock was weak to medium weak with uni-axial compressive strength in the range of 16–37 MPa. The kinematic analysis suggested plane and wedge types of failure conditions. Based on the stability analysis, the overall slope angles of 43º and 35º were suggested for ultimate pit depths of 100 and 150 m respectively. The bench height and bench slope angle were suggested at 10 m and 80º respectively. In addition to above, it was suggested that a minimum distance of 150 m be maintained between the cliff bottom and the crest of ultimate pit slope. Further, it was suggested that the above slope designs could be used as an initial estimate and after the mining was actually started the slope design could be revised, if required based on the actual geotechnical exposures and the response of rock mass.