Comparison between results of seismic refraction and standard penetration test (SPT) to study shallow geological subsurface in an urban area of Brasília, Brazil

Abstract

The most common procedure for an engineering project/construction is the use of direct survey, borehole and Standard Penetration Test (SPT). This provides punctual information of the geology at the site, and many boreholes are necessary along the construction site, representing a significant amount of the budget for the construction and to help develop a better geological understand/map of the site. The use of geophysical methods allows to study the subsurface by indirect means, with low cost, and enable to cover large areas if compared to direct surveys. Geophysical methods are increasingly being used in engineering works, however, in Brazil the use in engineering projects is still scarce. In this work was used shallow seismic refraction method to study the shallow subsurface in an area along the future track of the subway system of Brasília, Brazil. The refraction results (P-wave) were compared with previous existing data from Standard Penetration Test (SPT), and soil profile description. The seismic was used to study the subsurface geology, and SPT data were used to compare the seismic results. We observed a good correlation for the depths obtained through each method, mostly in the north portion of the line, when the SPT was near the line, indicating that its results are influenced by the same mechanical parameters, related to soil strength. Our results motivate the use of seismic refraction as a tool to optimize the direct investigation methods for better geotechnical characterization of the medium.