Study on voiding process and deterioration mechanism of heavy-duty railway tunnel basement under weak surrounding rock

Based on Taihang Mountain Tunnel of Wari Railway, the evolution process of basement voiding and the deterioration mechanism of the surrounding rock of heavy-duty railway tunnels under the condition of weak surrounding rock are studied by comprehensively using field measurement, laboratory test, and discrete element simulation methods. By laying fiber grating water and earth pressure sensors on site, the measured data of the surrounding rock of the basement under the combined action of train load and groundwater were obtained. It was found that the earth pressure of the arch bottom increased by 181.1 kPa within two years of operation, and the water pressure under the track rose from 117.35 to 286.86 kPa, indicating that the surrounding rock at the bottom was gradually damaged and deteriorated. Then, an indoor model is constructed to simulate the deterioration process of three typical surrounding rocks due to long-term scouring by dynamic water flow. The results show that the particle loss of sandy soil, pebble soil, and clay surrounding rock is 13.75 kg, 10.9 kg, and 0.3 kg, respectively, and shows obvious differences in erosion resistance characteristics. Finally, the PFC particle flow model is established, and the contact chain evolution and particle loss process within 360 days of operation are analyzed. The deterioration degree of the surrounding rock of sandy soil is 162.5%, that of pebble soil is 87.5%, and that of clay is 37.5%. The research shows that the weak surrounding rock deteriorates obviously under the coupling action of water-load, and the type of surrounding rock has the main influence on the voiding range and velocity. The results can provide a theoretical basis for tunnel structure operation and maintenance, and disease control under similar geological conditions.