Long-term uplift of high-speed railway subgrade caused by swelling effect of red-bed mudstone: case study in Southwest China

A high-speed railway must support fast-moving vehicles and have strict low-deformation requirements. However, many high-speed railways encounter the problem of abnormal subgrade deformation caused by expansive rocks. In this study, the Neijiangbei station of the Chengdu-Chongqing high-speed railway in Southwest China, where the subgrade has undergone continuous and stable uplift during the construction and operation periods, was considered as an example. The Jurassic red-bed mudstone widely distributed in this area is a typical expansive rock, and its swelling effect is the main cause behind the uplift of the subgrade. Results of water-absorption tests, disintegration tests, and expansion tests indicate that the red-bed mudstone is characterized by easy disintegration, slow water absorption, and long-term swelling. A decoupling analysis method for the seepage and swelling of red-bed mudstone was proposed to simulate the water infiltration through the fissures and the temporal and spatial changes in the swelling. Using monitoring data, an inversion analysis of the high-speed railway subgrade uplift was conducted, and the subgrade deformation was predicted. The results suggest that the main changed area of the moisture-content field in the rock formation was a small area near the fissure layer. The moisture content of the mudstone increased rapidly in the first few years of infiltration and increased slowly over subsequent decades. Correspondingly, the subgrade uplift increased rapidly in the first few years after excavation owing to the swelling of the mudstone; thereafter, the growth rate decreased, but the subgrade uplift maintained long-term continuous growth for several decades.