A sensitivity study of influencing factors of collapsibility properties for coarse-grained saline soil as an embankment filler

Coarse-grained saline soil is often used as an embankment fill material for the construction of a subgrade of high-speed railway in coarse-grained saline soil areas. As the soluble salt in saline soil dissolves easily in water, when coarse-grained saline soil is used as embankment fill material, it can readily cause embankment collapse with water around. This study aims to investigate the effects of gradation, salt content, soil density, and other factors of collapsibility properties for coarse-grained saline soil as an embankment fill material, and find the quantitative relationship between particle content and collapsibility coefficient due to different particle shapes. Eighty-nine soil samples of typical natural coarse-grained saline soil were selected from an existing subgrade of a high-speed railway line. By the use of the large-scale sedimentation test instrument for the coarse-grained saline soil, the indoor collapsibility test of the single-line method was carried out, to obtain the collapsibility coefficient of each sample. The test results show that with the increase in P5 ( >5 mm) particle content, the skeleton effect of coarse particles in the soil gradually becomes more apparent, making it difficult for the soil to be compressed and therefore reducing the collapsibility coefficient gradually. The contents of the fine-grained soil and soluble salt content are directly proportional to the collapsibility coefficient of the coarse-grained saline soil. Besides, the sensitivity of the gravel soil indexes on the collapsibility coefficient is analysed and discussed, including the effect of the particle shape of the soil. In particular, the lab test results suggest that for angular sandy gravel, when soluble salt content is less than 0.7%, with the increase in P2 particle content, the collapsibility coefficient decreases linearly. However, for rounded sandy gravel, when soluble salt content is more than 0.7%, natural gravel saline soil presents a low collapsibility coefficient that shows the soil hardly collapses.