Experimental Research For Comparing Swelling And Shrinkage Of Expansive Soil

The most obvious characteristics of expansive soil are swelling and shrinkage. Most literatures focus on researching the single property, and it is not common about comparing the two together to study. In engineering design, swelling property of expansive soil is taken more seriously than shrinkage property. Therefore it is necessary to concentrate on swelling-shrinkage mechanism and relation-difference between them. Swelling and shrinkage equation have been deduced based on theoretical analysis. Laboratory tests have illuminated some relevant laws on the swelling and shrinkage process of expansive soil. At last the comprehensive contrastive analysis between swelling and shrinkage property was taken to reveal the inherent unity and difference between the two, and the engineering significance was also expounded.Firstly, theoretical analysis mainly involves dissertation about swelling (shrinkage) process and swelling (shrinkage) equation. Swelling process includes two stages, namely porous filling and granular expanding. And the theoretical swelling equation was established based on "intergranular expansion (electrical double layer)" and "lattice expansion". Shrinkage process consists of evaporation, water migration, crack production and so on. Empirical equation of shrinkage was got through existing shrinkage curve, and the micro impetus leading to shrinkage is capillary force, which is equal to matrix suction at macro level.Secondly, laborstory tests contain basic soil test, swelling test, and shrinkage test, making relevant laws about swelling-shrinkage property clear. Swelling test results show that swelling process divides into three stages including rapid expansion, moderative expansion and slow expansion. Swelling ratio and swelling force decrease with the increasing initial water content, and swelling force increase with the increasing initial dry density. The entire swelling process of expansive soil divides into "porous filling" and "granular expanding", and "granular expanding" also consists of water-absorption stage, expansive stage and stabilization stage, through which swelling equation has been estabilished. Shrinkage test results indicate that evaporation process can be divided into rapid evaporation stage, moderative evaporation stage and slow evaporation stage in view from the shrinkage time-history curve, and linear shrinkage ratio increase with the increasing initial water content. Rapid shrinkage stage, moderative shrinkage stage and residual shrinkage stage make up the entire shrinkage process. During rapid shrinkage stage, pore water is runing off. The residual pore water and loosely bound water loss in the moderative shrinkage stage. And the residual shrinkage stage mainly contains moisture diffusion. Matrix suction makes soil mass shrink, the maximum of which is nearly1MPa measured by experiment. Two types of soil from Chengdu and Weifan respectively were tested in laboratory tests, the experimental results of which agreed with each other.Finally, contrastive analysis between swelling and shrinkage property makes clear that the inherent unity of them is the change of soil mass structure caused by water content variation, from which equilibrium water content of Moisturizing Method has been obtained. The difference between swelling and shrinkage property mostly focuses on state of water, movement direction of water, change of soil mass structure, soil strength change and so on, through which the deformation and failure mechanism of expansive soil slope can be explained clearly in order to serve engineering construction bitterly.