Study on Dynamic Modulus and Damping Characteristics of Modified Expanded Polystyrene Lightweight Soil under Cyclic Load

In recent years, expanded polystyrene (EPS) lightweight soil has been widely used as subgrade in soft soil areas because of its light weight and environmental protection. This study aimed to investigate the dynamic characteristics of sodium silicate modified lime and fly ash treated EPS lightweight soil (SLS) under cyclic loading. The effects of EPS particles on the dynamic elastic modulus (E(d)) and damping ratio (λ) of SLS were determined through dynamic triaxial tests at various confining pressures (σ(3)), amplitudes, and cycle times. Mathematical models of the E(d) of the SLS, cycle times, and σ(3) were established. The results revealed that the EPS particle content played a decisive role in the E(d) and λ of the SLS. The E(d) of the SLS decreased with an increase in the EPS particle content (EC). The E(d) decreased by 60% in the 1–1.5% range of the EC. The existing forms of lime fly ash soil and EPS particles in the SLS changed from parallel to series. With an increase in σ(3) and amplitude, the E(d) of the SLS gradually decreased, the λ generally decreased, and the λ variation range was within 0.5%. With an increase in the number of cycles, the E(d) of the SLS decreased. The E(d) value and the number of cycles satisfied the power function relationship. Additionally, it can be found from the test results that 0.5% to 1% was the best EPS content for SLS in this work. In addition, the dynamic elastic modulus prediction model established in this study can better describe the varying trend of the dynamic elastic modulus of SLS under different σ(3) values and load cycles, thereby providing a theoretical reference for the application of SLS in practical road engineering.