Determination of geothecnical properties by using seismic refraction velocities. A case study in Luanda (Angola)

Abstract

Seismic refraction is a prospecting geophysical method, which measures the terrain response in reaction to a P compression wave, mechanically produced at the surface and propagating across. The physical parameter in use, in the case, is the wave propagation velocity, Vp, which travel across the subsurface rock material and reflcts to the surface in function of the material’s density it fids on its way down. That way, indexes associated to the parameter will measure and reveal the geomechanic characteristics of the terrain under study. Those indexes, whilst keeping some correlations with the geological nature of the rock in different horizons, allow to infer also their depths and thickness. The present study has the scope of showing a methodology to map geotechnical parameters using seismic reflction, and it has been noticed that the longitudinal velocities also computed are correlated with penetration resistance values, measured by Standard Penetration Tests (SPT). The dynamic parameters were chosen to be presented in 2D maps, in order to give either, a better representation of their characteristics, as well to allow for a continuous geotechnical interpretation over the entire area of study. The latter, is an area of silty/sandy soils located in the city of Luanda (Angola).