Study On Settlementdeformation Of Expansive Clay Under Low Embankmentwith Soaking In Yun-Gui Area

Expansive soils are widely distributed in our country, with the construction of high-speed railway, the standards of railway construction and the control of subgrade settlement are more and more stringent, he swelling-shrinking defor-mation for expansive soil has an important influence on settlement of the rail-way embankment in the area of expansive soils. For low embankment, the Overlying load is small, the characteristic of swelling-shrinking may lead to engineering accident due to that it makes the railway line irregularity. For most field tests, many studies are focused on the swelling-shrinkage characteristics for expansive soil foundation under rigid foundation and stability of expansive slope. The study focused on the swelling-shrinkage characteristics for expansive soil foundation under flexible foundation exists rarely, such as railway em-bankment and highway embankment. For the study of calculation theory of swelling-shrinking deformation for expansive soil foundation, many scholars put forward calculation methods considering one or more factors. Because of the special character of expansive soil, the Theoretical calculation methods exit defects more or less at present. This article relies on the construction of Yun-Gui railway, the studies at home and abroad are investigated in the early stage, some test methods which are laboratory soil test of intact expansive soil, measuring settlement of railway line and field wetting and drying test under low embank-ment are applied. According to field test data and theoretical calculation, the article focuses on studying the characteristics of swelling-shrinking deformation for expansive soil foundation under low embankment and the calculation meth-ods of swelling-shrinking deformation.The contents and conclusions in the article include the following areas in detail:(1)The article analyzes current research systematically at home and abroad, through investing the information about the characteristics of swelling-shrinking deformation for expansive soil foundation. The studies of field swell-ing-shrinking test for expansive soil foundation and swell-shrinking calculation methods are highlighted.(2)Laboratory soil test of intact expansive soil is adopted to study that the soil in Mile area belongs to medium-strong expansive soil. To obtain the basic physical parameters and swelling-shrinking deformation calculation parameters of the intact expansive soil in Mile area, some soil samples are carried out for physical test and swelling-shrinking test.(3)In the field, we carry out large-scale wetting and drying test under low embankment to study macroscopic characteristics of swelling-shrinking about expansive soil foundation. During soaking, the expansion of expansive soil foundation under low embankment increases rapidly. As time flies, expansion rate slows and finally the expansion stabilizes. During drying the contraction of expansive soil foundation under low embankment goes through the period of rapid contraction, the period of contraction rate slowing down and finally stabi-lizes.(4)According to the data for wetting and drying test under low embankment, modified direct simulation method is adopted to calculate the expansion and contraction about expansive soil foundation, through comparing different swelling-shrinking calculation methods about expansive soil foundation. The correction coefficients of swelling-shrinking deformation about(5)Expansive soil foundation in Mile area are defined (The correction co-efficient of swelling deformation is 0.7, The correction coefficient of shrinking deformation is 0.6).