Influence of weathering process on small-strain shear modulus (Gmax) of hydrocarbon-contaminated sand

Abstract

The engineering characteristics of hydrocarbon-contaminated soils have been concentrated so far. However, besides influential effects of weathering on hydrocarbon-contaminated soils, a substantial majority of these studies have been devoted to short-term analyses. By the same token, the present paper aims at comparing short- and long-term effects of light crude oil contamination on maximum shear modulus (Gmax) of two sand (Ottawa and Firoozkooh sand). To this aim, a series of bender element tests was conducted on both newly and aged contaminated sand samples under similar circumstances so as to characterize short- and long-term influences of the hydrocarbon contamination on Gmax. In the short term, Gmax of Firoozkooh sand was more sensitive to the contamination compared to Ottawa sand; however, the tendency of their responses was almost similar so that presence of 4wt% of crude oil into both sand types could greatly increase the value of Gmax, and adding further contamination made markedly negative changes in Gmax to some extent that Gmax of both 8wt% contaminated sand types was lower than that of clean ones. Furthermore, Gmax of both sand types were not sensitive to adding more crude oil (≥ 8wt%). Generally, in the long term, weathering process could obviously increase the value of Gmax of both sand types such that the changes were more detectable during the first 6 months, and more importantly, the majority of these alterations took place in the first 2 months. Additionally, in contrast to short-term findings, contaminated Ottawa sand samples were more sensitive to weathering process, and the degree of weathering effects on Gmax was more observable in 4wt% contaminated samples of both sand types in comparison with specimens containing 8 and 12wt% of crude oil.