The granitic rock mass which exists along at (code: E18, 14.5) of the highway Semenyih-Sg.Long (SSL), Selangor state in Malaysia contains a number of major discontinuities, and several sets of minor discontinuities. Therefore, the rock engineering problems of high steep rock slopes are somewhat complicated. The orientation of the major discontinuities were as follows (dip-direction/dip-angle) : J1:36°/66°; J2:152°/60°; J3:79°/88°; J4:117°/66° and the free-face is ff5:105°/70°. Based on the data analysis, the following types of key blocks were determined: type I (keyblock) is the JPs 1000 and JP1100, and type II (potential keyblock) is JPs 1110. The result showed that the maximum safe slope angle (MSSA) is 70° for the type I (keyblock) and MSSA is 72° for the type II (potential keyblock). The cut slope along at the highway Semenyih-Sg.Long (SSL) is not stable because the cut slope angle is 80° that is greater than 70° and 72° within fresh granite, and contains these discontinuities, therefore there is a need for installation of a proper support system in order to maintain the long term stability of this rock slope.
1. INTRODUCTION
The highway Semenyih-Sei.Long (SSL) is one of the largest highways in Selangor, Malaysia. The granitic rock mass which exist along at the highway SSL contains a number of major discontinuities, and minor discontinuities, [3], [13]. Therefore, the rock engineering problems of high steep rock slope in the highway SSL are somewhat complicated. In the natural state, these rock slopes are not in a stable condition. When the rock-mass is excavated, for example for a highway, some blocks will develop sliding according to structural planes, and then a chain reaction may occur, which may lead the collapse of whole slope. The block theory is a method to analyze rock mass stability. The reason for the rock mass collapse is due to structural blocks sliding over each other at discontinuities. Previous research on the stability problem of discontinuous rock slope using block theory include determination of sliding modes and safety factors of sliding block by Hoek and Bray [13]. The assessment of kinematic feasibility, sliding and volumes of blocks using inclined stereographic projection by [5] and [6], and vector analysis by [7]. The block theory developed and continouosly extended by shi et.al. [1], [8], [10] can be thought of as a comprehensive procedure of static analysis for stability evaluation of the rock slopes in discontinouos rock massa. The application block theory for stability analysis of rock slope by [2], [4] and [14], [15], [16] and [9] has been illustrated. The block theory is used to identify different block types that exist at highway SSL cut slope faces and is a planning tool for the slope stability. The main purpose of this study is to determine a safe angle for the rock slope for the case of the highway SSL Selangor Malaysia. The block theory is used to determine the Maximum Safe Slope Angle (MSSA) for the rock slopes. The MSSA is a useful planning tools for the cut rock slope stability analysis.
