Experimental Study on Freeze-Thaw Characteristics of Weathered Arsenic Sandstone Soil Improved by Microbial-Induced Calcium Precipitation

Severe soil erosion in arsenic sandstone areas not only reduces the local vegetation and deteriorates the ecological environment, but also the debris formed by weathered arsenic sandstone constantly migrates into the Yellow River and other rivers, becoming the main source of coarse sediment in the middle and upper reaches of the Yellow River. Therefore, the microbial-induced calcium precipitation technique was applied to arsenic sandstone and its weathered soil to cure and improve their water disintegration. On the basis of the mineralization and cementation for weathered soil of arsenic sandstone, macroscopic mechanical properties tests combined with microstructural tests of pore sizes were conducted to study the property changes and deteriorative mechanisms of the weathered soil after freeze-thaw cycles in the salt corrosion environment. The test results indicated that the strength of the soil-mineralized specimens decreased after freeze-thaw cycles in the salt corrosion environment, and the internal pores changed continuously with different sizes of pores developing or transforming into each other. The attenuation in the intensity properties of soil-mineralized specimens in the salt corrosion environment was greater than that in the deionized water environment, and the attenuation in the intensity properties of soil-mineralized specimens in the composite salt environment was greater than that in the single salt environment. After five rounds of freeze-thaw cycles in the mixed salt environment, the soil-mineralized specimens were damaged and the freeze-thaw resistance was reduced to 0.125 6, and simultaneously, the freeze-thaw resistance of the soil-mineralized specimens in the deionized water environment was reduced to 0.416 7 in the same period, a difference was nearly three times; the porosity of the soil-mineralized specimens increased as a result of the frost heave action, wet-dry action and the destruction of inter-particle connections, and the cumulative ratio of change in different types of pores increased with the round of freeze-thaw cycles. The reduction in strength of the soil-mineralized specimens was actually a macroscopic reflection of the reduction in the mechanical properties of the internal skeleton. The macroscopic strength dropped constantly reducing with the resistance to frost heaving of pore skeleton of the soil-mineralized specimens. As the potential deformation resistance of soil-mineralized specimens was released, the volume expansion coefficient and pore shrinkage coefficient of ice continued to increase. Due to the frequent internal bonding damage and weak deformation ability of the pore skeleton, the mixed salt had the highest expansion coefficient and the lowest shrinkage coefficient.