Influence of Microplastic Contamination on Sand Liquefaction Initiation and Post-Liquefaction Behavior

Plastics have become an essential part of human life; however, the increased dependence on single-use disposable plastic items has led to the ubiquity of microplastics (MPs) in our environment. As plastics in the environment degrade into MPs, they can spread through various means, entering the ground and causing implications for the health and well-being of the surrounding environment as well as for the properties of the soil in which the contaminants can reside. A current gap exists in the geotechnical engineering community’s understanding of the effects of MPs on the dynamic properties of soils. The influence of MPs on soil behavior under dynamic loading is assessed through a series of constant volume strain-controlled cyclic simple shear tests in conjunction with bender elements (BE). This study examines the behavior of medium-dense specimens of clean Ottawa sand and Ottawa sand mixed with 10% MPs by dry mass. The MPs utilized in this investigation are composed of polyethylene terephthalate (PET) with a particle diameter range of 50 to 100 microns. Equivalent pore pressure ratio curves vs. increasing cyclic strain percentages were developed for both clean Ottawa sand and contaminated Ottawa sand. Monotonic simple shear tests are performed on the liquefied specimens following cyclic testing. The post-liquefaction stress-strain curves of clean and contaminated sand are also developed and compared. The results determined from this study improve the assessment of the liquefaction potential of highly contaminated soils in seismic-prone areas such as dense urban communities, which can reduce the potential loss of lives and resources.