Experimental study on the water retention properties of sulfate saline soils during the cooling process

Abstract

The water retention properties of sulfate saline soils during cooling were investigated by theoretical derivation as well as by nuclear magnetic resonance (NMR) tests and matrix suction determination tests by the contact filter paper method. The equations for calculating the free water content of sulfate saline soils during the cooling process and the amount of salt crystallization were derived based on the law of conservation of mass. The free water content of sulfate saline soil during the cooling process was determined by the NMR test. The reliability of the derived calculation equation was verified, which laid the foundation for the subsequent processing of the test data for matrix suction determination. The study showed that when the soil pore solution is saturated with sodium sulfate, the free water content in the soil decreases as the temperature decreases, accompanied by the crystallization process, and that the matrix suction of the soil increases as the temperature decreases. For silty clay without salt, the effect of temperature on its matrix suction is small. Use of either the serial filter paper method or the parallel filter paper method to measure the matrix suction has no effect on the matrix suction soil-water characteristic curve. The parallel filter paper method can exponentially reduce the test time compared with the serial filter paper method. Salt crystallization has no effect on the matrix suction soil-water characteristic curves (SWCCs) of sulfate saline soils. The matrix suction SWCCs of silty clay soils without salt can be employed to calculate the matrix suction of sulfate saline soils during the cooling process.