, it is discovered that there exists expansive soft rock subgrade and that the clay mineralogical composition mainly consists ofmontmorillonite and mixed-layermineral.

The results of undrained consolidated triaxial tests of expansive mudstone under different confining stress show that the stress-strain relationships have the characteristic of strain softening and the peak strength,residual strength and residual strength ratio increase with the increasing of confining stress.

The paper uses the ANSYS finite element software to simulate the expansive mudstone slope excavating under the condition of rainfall infiltration,and combined a project example to research displacement and stress change of expansive mudstone slope under the different intensity and time of rainfall.

Based on the construction practice of Tianxinshan Tunnel of 18th Contract Section of Ganlong Railway, the construction technology for the swelling wall rock section of this tunnel is introduced, which may also provide useful reference for dealing with large deformation of the tunnel caused by other reasons.