Geotechnical data mapping is important during the pre and post civil engineering construction particularly near or inside the geohazard area. Subsurface ground instability reflects difficulty of engineering investigation task especially to determine the possible subsurface ground instability zone for rehabilitation, maintenance and monitoring purposes. This study applied a seismic refraction method to investigate a geotechnical data for preliminary geotechnical and engineering geology assessment due to subsurface ground instability. The method used a concept of seismic waves generated by one of several types of energy sources and detected by arrays of sensitive devices called geophones. The data was processed by Optim software for generating subsurface velocity distribution (primary velocity, vp) and interpretation with supported by existing borehole information. The result obtained three main velocity layers with possible subsurface ground instability zone which consisted of top soil/residual soil (350 – 600 m/s) 0 – 4 m, weathered zone with a possible mixtures of soil, boulder and rock fractured (500 – 1900 m/s) 2 – 23 m and fresh rock/bedrock (> 2300 m/s) from 6 m depth. The thickness and width of subsurface ground instability zone varies within the survey line from 3 – 20 m and 75 m respectively with a primary velocity of 700 – 1800 m/s. The seismic refraction survey produces a good relationship results compared to the borehole information in term of stratigraphy and geomaterials features. This study proved that the seismic refraction method was a good geophysical technique to be integrated in geotechnical mapping assessment since its covers a large area which extends the borehole data. The application of seismic refraction method can increase the effectiveness of geotechnical data in term of cost and time since it can determine the subsurface information in two dimensional (2-D) profiles rapidly by employing fewer workers compared to others conventional mapping techniques. In addition, this geophysical method used a surface technique that can reduce the site damageability during the data acquisition stages which can contribute the development in a sustainable build environment.
geohazard, seismic refraction, subsurface ground instability, geophysical, primary velocity, geomaterials