Wetting Induced Swelling And Soil-water-volume Characteristics Of Expansive Soils Under Low Stresses

As a special clay,the properties of expansive soil are different form those of common clay due to its expansion characteristics.In the actual projects,it is feasible to ignore the volume change of common caly with less expansion under different saturation conditions.However,the expansive soil is prone to swelling and shrinking when the water content changes,which will induce great damages to the light building,subgrade,airport,channel slope and dam.Two types expansive soils were investigated,one from the middle route project for south to north water transfer in Handan,Hebei Province,and the other from the slope of a seasonal frozen area in Heilongjiang Province.A series of experiments were carried out to study the expansion characteristics of the strong expansive soil,such as swelling force tests,natural swelling force tests and moistening deformation tests.The soil-water characteristic curves of the saturated middle expansive soil were studied using consolidation tests,shrinkage tests,isostatic temperature and pressure control method tests,and pressure plate tests.The main achievements are as follows:（1）Through the experimental study of the swelling force and the natural swelling force,it was found that the swelling force peaks with the initial water content.The natural swelling force increases approximately logarithmically with the increase of the water content increment.（2）Through the experimental study of moistening deformation,it was found that free and loading moisten swelling ratio,respectively,increase rapidly with the increase of water content in the early stage of moistening.What’s more,both of them increase linearly with the increase of water content in the later stage of moistening.By data fitting,it was concluded that the ratio of the increase rate of moisten swelling ratio with loading to that without loading decreased logarithmically with the vertical stress in the later stage.（3）Through the experimental study of shrinkage characteristics,it was found that the radial shrinkage rate of medium and strong expansive soil changes linearly with the water content in the second stage,whereas,the vertical shrinkage rate of them changes nonlinearly.For the medium expansive soil,the initial value of water content for the vertical shrinkage curve are equal to that of the radial shrinkage curve in the second stage,but for the strong expansive soil,the both are not similar.Taking account of these factors,the e-ωshrinkage curve model proposed by Peng et al was suggested to modify the volume change of SWCC in the full suction range.（4）Through the experimental study of drying soil-water characteristic curves,it was found that the threshold values(ψ_cr)that obtained from theω-ψcurve in the no-load state is same to that from low vertical stress state.The initial dry density and low vertical stress only influence the pore ratio of the samples,but they don’t affect the pore structure of the sample.Therefore,theω-ψcurves under different dry density and low vertical stress conditions are similar in the later stage.（5）Through the experimental study of volume change in drying SWCC,it was found that the e-ψcurve under low vertical stress condition includes two processes,namely,consolidation process and drying process.The two processes are independent,and the coupling effect between them could be neglected.The volume change in consolidation process can be modified using the data from the consolidation tests.The volume changes of the drying process could be modified using parameters of the e-ψcurves without loading.An improved model was proposed to describe the relationship between void ratio and suction in low vertical stress state.The improved model was used to predict the volume change in low vertical stress condition,and the results are in good agreement with the measured data.