Field soaking tests on the moderate-strong expansive soil ground of the high-speed railway subgrade

As the high-speed railway subgrade is constructed on the moderate-strong expansive soil ground，embankment uplift and subsidence problems commonly exist. These problems aggravate track irregularity and then affect the normal operation of high-speed rail; therefore, the treatment of expansive soil ground becomes a key technology problem. Field soaking tests on the natural moderate-strong expansive soil ground and composite ground treated by CFG pile were performed. The deformation characteristics of ground with time were investigated under in-service loading, soaking, and drying conditions, and the variations of ground moisture content with time and depth were studied. The results show that the deformation-time curves of natural expansive soil ground and GFG pile-treated ground exhibit S-shaped characteristics. The surface deformation of CFG pile-treated ground was reduced by 78.3%～124.4% as compared to that of natural ground. The transverse distribution of the subgrade deformation was approximately basin shaped during the loading and soaking stages with greater values found in the middle of the subgrade and lower values on its sides during the dehydration-induced contraction stage. The moisture content of shallow expansive soil increased rapidly during the early stage of soaking. The moisture content of deep expansive soil increased slowly and was less than 5%. After soaking, the moisture content of shallow expansive soil decreased with time and finally approached the initial moisture content. The moisture content of deep expansive soil increased slowly and was less than 10%. The CFG pile-treated expansive soil ground can effectively suppress its expansive and contractive deformation and control the up warping deformation of subgrade surface, which can meet the allowable subgrade deformation requirements of high-speed railway ballastless track. The research results can provide technical reference for the subgrade construction of high railway in moderate-strong expansive soil areas. © 2022, Central South University Press. All rights reserved.