Abstract:

The expansive red clay easily expands in water due to its special water sensitivity, which is a main reason for instability of tunnel surrounding rock. In order to learn the relationship between the water content and expansion ratio of red clay to determine the influence of the water content on the stress and deformation of large cross-section expansive red clay tunnel and supporting structure, the fluctuation range of water content in surrounding rock of Qingyang expansive red clay tunnel on Yinchuan-Xi′an High-speed Railway is monitored. And then the correspondence between water content and expansibility and that between water content and shear strength are established by laboratory tests. Finally, the expansion relationship under the variation of water content and that under thermal condition are studied; the temperature stress field built in ABAQUS is used to simulate the humidity stress field; and the redistribution laws of the surrounding rock pressure, internal force and deformation of lining structure under different water contents are analyzed. The results show that: (1) When the water content tends to be saturated after excavation, the stresses of surrounding rock and supporting structure increase, the relative displacements of invert arch and arch foot increase, the relative displacements of crown, arch waist and sidewall decrease, and the integral safety factor decreases with the initial water content decrease. (2) Under the average water content of tunnel surrounding rock after excavation, 20.7%, the final safety coefficient of surrounding rock pressure is 2.2, the final safety coefficient of lining is 1.1, and the final relative displacement of surrounding rock is 0.97%. (3) The influence of water content on surrounding rock deformation is the largest, followed by that on surrounding rock pressure and lining structure. (4) The reserved deformation of the tunnel is recommended to be 150-180 mm based on the special geological conditions.

Key words: tunnel, water content, expansive red clay, numerical simulation, field monitoring, mechanical behavior