Influence of Chemical Stabilization on the Flexural Fatigue Performance of Subgrade Soil

The chemically-stabilized subgrade (CSS) soil layer in a pavement structure can undergo flexural fatigue as a result of a high number of loading cycles and brittleness of the stabilized soil. The type and amount of chemical stabilizing agents are generally selected based on the results of unconfined compressive strength (UCS) and/or resilient modulus (M_r) tests. The UCS and M_r tests help characterize the compressive behavior of the soil and do not specifically assess the flexural behavior of the CSS layer under cyclic loads. This study aims to evaluate the fatigue life of the CSS layer and compare it with other common indicators such as UCS and M_r. For this purpose, a series of UCS, M_r and four-point flexural fatigue (FPFF) tests were conducted on CSS soil samples. The materials tested in this study consisted of six blends of a lean clay stabilized using cement kiln dust (CKD) and hydrated lime. The CKD was mixed with the soil at 5, 10, and 15% by weight of dry soil. The hydrated lime was mixed with soil at 3, 6, and 9% by weight of dry soil. It was found that while increasing the amount of stabilizing agent resulted in higher UCS and M_r values, it had an adverse effect on the fatigue life of CSS. The specimens containing 5% CKD and 3% lime showed the highest fatigue lives compared with other mixes. It was concluded that the strain endured by the material at the peak load (strain at failure) plays an important role in the fatigue life of the CSS. CSS samples with a high strain level at failure possessed a high fatigue life while those with a lower strain at failure failed after a relatively low number of loading cycles.