Controlled diesel-mixed soils for roadway embankments: laboratory and ultrasonic characterization

Abstract

Soils contaminated with hydrocarbons is a repetitive site condition that may occur at locations adjacent to underground fuel tanks and other facilities. The main purpose of this study is to characterize and assess possibilities of reusing contaminated soil in useful applications such as roadway embankments. Accordingly, controlled amounts of diesel were mixed with clays and sands using percentages ranging from 0 to 13.5%. Unconfined compression, direct shear, California bearing ratio, and other tests were conducted on the diesel-mixed soil, along with the ultrasonic test. The ultrasonic test provided measures for the pulse wave velocity and received frequency, which was correlated with other soil parameters such as elastic modulus, resilient modulus, and California bearing ratio. From the main outcomes, it was found that small amounts of diesel can help improved soil shear strength. For instance, adding 5% diesel increased the soil cohesion by 63% and the unconfined compressive strength from 0.14 to 0.21 N/mm2. In sands, the California bearing ratio increased by almost double by adding 5% diesel, which is essential for roadway embankments especially in remote locations. Damping coefficient of soil was determined at different levels of diesel using the ultrasonic wave decay envelops. The ultrasonic waves were analyzed using fast Fourier transform to determine useful correlations between the wave frequency and the diesel content starting from 0 to 13.5%, and it was realized that an uncomplicated ultrasonic test can be acceptably used to assess static and dynamic properties of clean as well as contaminated soils.