Deformation behaviors and meso–structure characteristics variation of the weathered soil of Pisha sandstone caused by freezing–thawing effect

The deformation behaviors of soil caused by freezing–thawing (F–T) effect play a key role in determining the damage for engineering structures in seasonal frozen soil regions. Based on the laboratory tests, investigations were made into the deformation behaviors of the weathered soil of Pisha sandstone, as well as the meso–structure characteristics variation before and after F–T effect. The F–T tests demonstrate that there exists an initial frost heave moisture content (IFHMC) and an initial thawing settlement moisture content (ITSMC) in the soil. When the moisture content of the soil below the IFHMC and the ITSMC, the frost heave and the thawing settlement phenomenon will not occur. On the contrary, the soil will expand during the thawing process. Once the moisture content exceeds the value of IFHMC and ITSMC, the frost heave ratio and thawing settlement coefficient increase with moisture content. The frost heave ratio displays a growing trend with dry density, while the thawing settlement coefficient decreases first and then increases with dry density. There is a critical dry density that corresponds to the minimum value of thawing settlement coefficient. With the decreases of freezing temperature, the unfrozen water amount in soil drops, and the frost heave ratio and the thawing settlement coefficient increase gradually, presenting a non–linear increasing development tendency. The meso–structure tests show that some changes occurred in the pore structure and soil particles of the specimen. The larger moisture content of the specimen is, the more sensitive to the pore structures change and soil particles position variation.