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

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 4 wt% 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 8 wt% contaminated sand types was lower than that of clean ones. Furthermore, Gmax of both sand types were not sensitive to adding more crude oil (≥ 8 wt%). 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 4 wt% contaminated samples of both sand types in comparison with specimens containing 8 and 12 wt% of crude oil.