Sedimentary rock mass rippability assessment using seismic refraction survey

Selection an appropriate method for earth excavation is important for forecasting the project cost. Construction involving interbeded sedimentary and volcanic rocks mass may cause some uncertainties due to the heterogeneous subsurface profile. This study performed at Triassic sedimentary rock formation that may consists these types of rocks. The seismic refraction method is adopted to assess the geomaterials rippability at the proposed new spillway dam. The equipments were ABEM Terraloc MK8 consist of 5 kg of sledge hammer, 28 Hz of vertical geophone and seismograph. In order to generate the subsurface seismic tomography profile, the seismic raw data was analyzed using Optim and Surfer software. It was found that the ground composed of three layers based on primary wave velocity (Vp) at 100 to 800 m/s from 0 to 10 m depth, 800 to 1700 m/s for 10 to 20 m depth and 1700 to 3100 m/s for 20 to 30 m depth. From the borehole and trial pit results show that the top layers consists of residual soils at depth of 0 to 10 m depth followed by the weathered shale. Via comparing the seismic velocity, borehole data and caterpillar rippability chart, the excavation assessment indicates that the area is possible to rippable for soil at 0 to 20 m depth. Then after 20 m depth, the ground material is in marginal rippable. This study has demonstrated that the application of seismic refraction survey was successfully to conduct rippability assessment of interbeded sedimentary rock mass in cost effective way.