Deterioration and Cavity of Surrounding Rocks at the Bottom of Tunnel Under the Combined Action of Heavy-Haul Load and Groundwater: An Experimental Study

Abstract

In China, the first tunnel was built in accordance with the 30-ton heavy-haul railway standard. Based on the change in water and soil pressure obtained from long-term on-site monitoring, the cavity mechanism of the surrounding rock at the bottom of a heavy-haul railway tunnel under rich water conditions was explored in this study. The cavity characteristics and degradation depth of the three types of surrounding rock under different axial loads and hydrodynamic pressures were analyzed through laboratory tests. The structural defects at the bottom of the tunnel and local cracks in the surrounding rock were determined to provide a flow channel for groundwater. The dynamic load of heavy-haul trains causes groundwater to exert high hydrodynamic pressure on the fine cracks. The continuous erosion of the bottom surrounding rock leads to a gradual loss of surrounding rock particles, which would further exacerbate with time. The cohesive soil surrounding rock is noticeably affected by the combined action of heavy-haul load and groundwater in the three types of surrounding rock, and the surrounding rock cavity is characterized by overall hanging. In the simulation experiment, the particle loss of the surrounding rock reached 1,445 g, which is 24.2% higher than that of the pebble soil surrounding rock and 40.8% higher than that of sandy soil surrounding rock. The findings of this study could be helpful for developing methods for defect prediction and treatment of heavy-haul railway tunnels.

Dynamic Response and Service Life of Tunnel Bottom Structure Considering Hydro-Mechanical Coupling Effect under the Condition of Bedrock Softening

“…Figure 2 shows the design lining section of the grade-V surrounding rock. and numerical simulations [23,24,[26][27][28], but these studies have not considered groundwater. Therefore, this paper combines groundwater and bedrock softening, and establishes a three-dimensional numerical model considering train load-tunnel-groundwatersurrounding rock-bedrock softening.…”

“…Indraratna et al [25] through a series of undrained cyclic triaxial tests, found that the softening of surrounding rock is due to the upward migration of water and fine particles in the soil, which eventually leads to the softening and fluidization of the uppermost part of the soil sample. Li et al [26,27] studied the evolution law of the voiding of surrounding rock with different soil qualities (cohesive soil, pebble soil, and sandy soil) for a tunnel base using field monitoring and model tests, and they found that the cohesive soil was most affected by the train load and groundwater. Chai [28] used the finite difference software FLAC3D to study the dynamic response and structural damage of a tunnel base structure with different degrees of bedrock softening.…”

“…In general, some researchers [7][8][9][10][11][12][13][14][15][16][17] have made some progress in the study of the dynamic response of railway tunnel base structures under ideal conditions, but they have ignored the effect of bedrock softening. In order to consider the influence of bedrock softening, scholars have conducted some studies through laboratory experiments [19][20][21][22]25] and numerical simulations [23,24,[26][27][28], but these studies have not considered groundwater. Therefore, this paper combines groundwater and bedrock softening, and establishes a three-dimensional numerical model considering train load-tunnel-groundwater-surrounding rock-bedrock softening.…”