Research on expansive soil characteristics – taking Ankang Tunnel as an example

This paper takes the Ankang Tunnel as an example to conduct research on the mechanical characteristics of swelling and shrinkage deformation of expansive soil, such as the free swelling ratio, unloaded swelling ratio, axial load swelling ratio, and swelling pressure, hoping to provide guidance for the construction of similar expansive rock and soil tunnels. The research shows that: (1) The free swelling ratio of the expansive soil in the Ankang Tunnel is relatively low, at 49.7 %, with weak-medium expansiveness. (2) The unloaded swelling process of the expansive soil can be divided into the rapid swelling stage in the initial swelling stage, the swelling transition stage and the slow swelling stage in the middle swelling stage, and the swelling stable stage in the later swelling stage. (3) With the increase of the water content, the swelling pressure of the soil gradually decreases.