Effects of light crude oil contamination on small-strain shear modulus of Firoozkooh sand

Abstract

The geotechnical properties of hydrocarbon-contaminated soils have been greatly concentrated so far due to its effectiveness and significance in various aspects of engineering applications. In this regard, several hydrocarbon contaminants and diverse soil types were considered in the literature aiming at evaluating physical, chemical and engineering characteristics of hydrocarbon-contaminated soils including particle size, hydraulic conductivity, compaction and compressibility, internal friction and cohesion as well as shear strength. Meanwhile, small-strain shear modulus of hydrocarbon-contaminated soils ($G_{max}$ or $G_0$) has not been precisely focused. In this paper, bender element (BE) test was employed to examine the effects of a hydrocarbon (light crude oil) on shear wave velocity and the resultant $G_{max}$ of Iranian silica sand, Firoozkooh sand. In this connection, various methods of determining shear wave travel time in BE test were firstly evaluated, and the most reliable ones (start-to-start method and cross-correlation function) were employed to analyse the results. The values of $G_{max}$ were found highly sensitive to crude oil contamination and confining pressure so that $G_{max}$ increased after uniformly mixing oven-dried sand with 4 wt.% of crude oil under various confining pressure; however, the degree of induced changes diminished as confining pressure grew. Moreover, adding more crude oil up to 8 wt.% substantially decreased the value of $G_{max}$ to an amount slightly higher than that of the clean sand. Beyond this oil content (≥8 wt.%), $G_{max}$ followed a status of scattering and there was not significant alteration to be cited. The analytical results obtained by BE test about the hydrocarbon-induced alteration on $G_{max}$ could be confirmed by the microstructure observations via scanning electron microscopy.

Keywords:

• Hydrocarbon-contaminated sand
• small-strain shear modulus
• shear wave velocity
• Firoozkooh sand
• bender element test

Acknowledgment

The authors wish to greatly acknowledge the beneficial supports in doing this research provided by Silica Sand MFG Company, West Oil and Gas Production Company (WOGPC) of Iran, Soil Mechanics Industry of Iran (SMI), and also International Institute of Earthquake Engineering and Seismology (IIEES). The authors also express their deep appreciation and thanks to Dr. Jahangir Khazaei for his beneficial supports during the present research.