Discontinuity Controlled Cut-Slope Failures on Weathered Low Grade Metamorphic Rocks along the East-West Highway, Grik to Jeli

Abstract

This paper describes the occurrence and mechanism of discontinu ity-contro lled cut-slope fa ilures within the res idual soil zone and the underlying weathered metased imentary and metamorphic rocks, drawing on the experi ence gained from investigati ons of a number of landslides observed on th e cut- slopes of the East-West Highway. These s lope failures highlighted the important influence that discontinuities in res idual so ils and weathered rocks can have on s lope stab ility. The slope movements recognised in the metasedimentary and metamorphic rock slopes along the East-West Highway are: - A) movements of rock-soil cover through: (i) movement of loose soil and weathered fragments, and ii) rotational sliding movements or slumps, B) movements of loosened blocks (rockfalls), C) movement of intact rocks a long predeterm ined planes (s lides), D) progressive complex movements. Slope fail ures are found to be largely controlled by the unfavourable orientation of discontinuities with respect to the slope face compounded by the weathered nature of the rock and the infiltration of water and continuous traffic flow that triggered movement down slope. The occurrence of landslides in slopes, which have been investigated and engineered, may be the result of inadequate attention to structural features in the weathered rock mass during site in vestigations and construction (design).