Study on Unloading-wet Swelling Mechanism of Upper Arch Deformation of Mudstone Subgrade in a High-speed Railway

Abstract

Mudstone subgrade may exhibit rather complicated deformation behavior under the coupling effect of unloading and wet swelling caused by subgrade excavation. To study the deformation mechanism of mudstone subgrade, mudstones were sampled from the NO.3 branch tunnel of Badong section of Zhengzhou-Wanzhou High-speed Railway and a series of unloading and wet-swelling tests were carried out on them. We studied the long-term deformation behavior of mudstone subgrade caused by excavation based on a creep test with unloading conditions. The expansion rate of the complete mudstone cylinder samples was extremely low under the wetting and drying cycle, while that of the soil samples after the disintegration of complete mudstone was between 1% and 10% when immersed in water. Excavation unloading damage, groundwater infiltration, long-term creep deformation, dry-wet cycle, and hot-cold alternation catalyzed each other, leading to the aggravation of mudstone disintegration and the obvious increase of expansibility of underwater mudstone after disintegration. The maximum arch deformation of mudstone subgrade can be divided into three parts: the rebound deformation during short-term excavation, the creep deformation related to time and the wet-swelling deformation. Generally, the creep deformation would not converge in two years if support measures were not taken, the wet-swelling deformation could tend to a steady value after a certain period of excavation.