Study On Unsaturated Properties Of Inland Sulphate Saline Soil

As a problematic soil, saline soil has many particular engineering characteristics and can cause many engineering problems such as salt heaving and collapsibility. These engineering properties are closely related to soil water content, and soil suction under different water content. This thesis selected saline soil of Gansu Jiuquan area, measured the soil water characteristic curves (SWCCs) of saline soil samples of different dry densities using vapour equilibrium technique and the Ku-pF apparatus, and studied the unsaturated properties of sulphate saline soil in Northwest of China.The mathematical equation to represent saline soil-water characteristic curve is essential to the strength and constitutive features of the unsaturated soil. Widely used models at home and abroad were selected to fit the measured results. What’s more, according to The Fredlund(2001) physical-empirical model, the SWCCs over the entire soil suction range was predicted from grain-size distribution and physical properties of saline soil. Through experimental testing and analysis, the following conclusions have been draint.(1) Because of the existence of osmotic suction, saline soil has a gentle slope at the transformation stage of SWCCs, soil suction at the same water content is higher than the general soil, and water content capability thus enhanced.(2) At low suctions stage, soil density has an obvious influence on SWCCs of saline soil. The performance of low density soil samples corresponds to a smaller value of the intake suction, higher rate of water loss, and a poor water holding capacity. At high suction stage, density has no impact on soil water characteristic curve, soil samples of different densities of soil-water characteristic curve tends to coincide.(3) Soil particles have a significant impact on SWCCs. Fine-grained soil samples have higher intake values, very slow water loss rate and a high water content or water-holding capacity than coarse grained soil samples at the same suction state.(4) With the continieus decrease in the water content, the unsaturated hydraulic conductivity of saline soil is decreased. The sample with high-density has higher un-saturated hydraulic conductivity than the low-density sample. The fine-grained sample has a more high unsaturated hydraulic conductivity, and a good water holding capacity than the coarse-grained soil.(5) The salt content has a great influence on soil water-holding capacity, because the presence of salt can cause increased soil solute suction. At low suction state, the soil with high salt content present a strong water-holding capacity. When the soil suction increases to exceed a certain value, The water content of various soils with different salt contents become closer at the same, indicating a neglegible influence of salt content(6) Widely used models at home and abroad were contrasted to fit the experimental results. It is found that Fredlund and Xing(1994) model could well reflect the relationship between water content and soil suction in saline soil.(7) Based on grain-size distribution and physical properties of saline soil, the theory and method of Fredlund physical-empirical model, the SWCCs of saline soils with different dry density over the entire suction range was used to establish. The research results may provide a theoretical support and a beneficial reference for further research of saline soil’s engineering properties.