Engineering geological assessment of rock slopes in former quarry sites for housing development

Former quarry sites usually have high, steep with overhanging and potentially unstable rock slopes. The rock slope faces formed during quarry operation have a high potential for slope failure hazards. The purpose of this study is to evaluate the stability of the rock slopes and classify the failure modes based on kinematic analysis of rock blocks formed by the rock joints and discontinuities. The slopes studies were located in former quarry sites in Palm Walk, Mayang Kiara and Goodview Heights in Hulu Langat, Selangor. They were mostly classified as slightly to moderately weathered rock. The rock joints data was collected using the scanline survey technique. Application software, DIPS (Version 5.1) and Stereonet (Version 10.0) were used for joints plotting and analysis. Rock samples were also collected and Point Load Test (PLT) and Uniaxial Compressive Strength (UCS) test were conducted. Based on discontinuity survey and rock strength data, Rock Mass Rating (RMR) of the rock mass was determined. The joints survey showed that there were six joint sets for Palm Walk, six for Mayang Kiara and five joint sets for Goodview Height rock slopes. The PLT ranged from 5.34 to 8.76 MN/m2 and the UCS ranged from 24 to 52 MN/m2. The RMR classified the rock as poor to fair rock. The kinematic analysis for the rock slopes showed that Slope A at Palm Walk was potentially unstable with two wedge sliding and two toppling failures. Slope B at Palm Walk was potentially unstable with one plane sliding and two toppling failures. For Mayang Kiara, the kinematic analysis showed that there was no indication of potential any failure to occur. For Goodview Heights, the kinematic analysis showed that both Slope A and B were potentially unstable with three wedge sliding, three plane sliding, and three toppling failures. The study showed that it was possible to analyse the potential for rock slopes instability at the former quarry sites in order to assess the hazards posed to the residents in the vicinity of the study sites. The results of this study can be useful to analysis hazards at these sites and the same technique could be applied in other similar sites.