Impact of petroleum hydrocarbon on shear wave velocity of Brahmaputra river sand

The geotechnical characteristics of hydrocarbon-contaminated soils have been an issue of major concern for its inevitable impacts on our surroundings from engineering as well as environmental viewpoints. The impact of hydrocarbon on various geotechnical properties of diversified soils have been reported in the literature. Nevertheless, shear wave velocity (Vs) of hydrocarbon-contaminated soils has not been precisely focused. This paper aims to investigate the shear wave velocity of crude oil contaminated silty sand by performing a series of bender element tests. The key influencing parameter is crude oil content (2, 4, 6, 8, 10, and 12%) in addition to frequency, confining pressure, and depth of contamination. The test results have been discussed for the values obtained within the consistency range of frequency. The results revealed that, petroleum contamination moderately increases the shear wave velocity initially up to a critical amount of crude oil and thereafter falloffs sharply. This critical value has been introduced as the transition point in the Vs profile. The effect of depth of hydrocarbon contamination has been explained in terms of contamination depth ratio (β). In a saturated state, shear wave velocity follows a non-linear trend with increasing depth of contamination and for β > 0.6, no substantial change was observed. There also exists a zero change point at which the positive and negative influences of crude oil contamination get counter-balanced and no net change in shear wave velocity of contaminated sand with respect to clean sand was observed. Beyond this point, the value of Vs drops below that of virgin sand.