Abstract:

In order to clarify the influence of fine-grained soil content on the salt expansion characteristics of coarse-grained sulfate saline soil embankment fill material, sand and gravel saline soils with sulfate salt contents 1% and 3% were investigated. A series of cooling and salt expansion tests was carried out to examine salt expansion characteristic of coarse-grained sulfate saline soil under conditions of increasing fines content. On this basis, PFC^3D discrete element method was adopted to simulate salt expansion of coarse-grained sulfate saline soil, and typical soil skeleton of coarse-grained saline soil during salt expansion process was analyzed combining microscope tests results. The result shows that with the increase of the content of fine-grained soil, the salt expansion/ frost heave of coarse-grained sulfate saline soil first increases, then decreases and increases finally. The boundary fines content varies with the salt content and soil type. Sand and gravel soil samples with 1% and 3% salt content would produce the largest salt expansion or frost heave at 15% and 10% fine-grained soil contents respectively. The initial expansion temperature of sand and gravel soil with 3% salt content is basically kept about 20℃. The initial expansion temperature of soil samples with 1% salt content varies greatly with the fines content and soil types, and there exists an obvious limit of fines content. When the content of fine-grained soil is lower than the limit value, the initial expansion temperature is about 0.5–2 ℃, when higher than the limit value, the initiation temperature is about 4–12 ℃. A typical state model of the coarse-grained soil skeleton in the salt-expansion state and the fines content limit of the coarse-grained sulfate saline soil as the embankment filler are given.

Key words: roadbed engineering, coarse-grained saline soil embankment fill material, salt expansion, fine-grained soil content