Classifying Ground Rippability and Weathering Grades in a Sedimentary Rock Geological Environment Using Seismic Refraction Survey

An in-depth understanding of the ground subsurface is crucial for foundation design and excavation works and for avoiding potential hazards during land development.In this regard, the ground rippability and weathering grades are some of the ground information needed. While geotechnical works are preferred, their limited horizontal coverage and high cost are often constraints that limit their use.

To counter this, a geophysical survey is employed for its wider area coverage and cost-efficiency. Therefore, this study used the seismic refraction method to assess the rippability and weathering grades in a sedimentary rock geological setting (interbedded sandstone, siltstone, and shale) as a preliminary ground assessment.

A seismic refraction survey was carried out using Aktiebolaget Elektrisk Malmletning (ABEM) Terraloc Pro 2, where the survey line was 115m long. Rippability was obtained by correlating seismic values with the Caterpillar D10R rippability table. Meanwhile, the weathering grades of the ground were determined by correlating the study area with another study area of a similar geological setting.

Within the 39m penetration depth, three layers can be classified from the ground’s P-wave velocity values and D10R Caterpillar rippability chart, which include rippable, marginal, and non-rippable layers. A break in the continuous ground layers could be seen, causing lower velocity values to be sandwiched between high velocities, which signified the presence of fracture. The weathering grades were also successfully classified from the seismic velocity values.

Using seismic refraction method, this study successfully employed seismic velocity values in determining the rippability and weathering grades of interbedded sedimentary rock without borehole record.