Large-scale field model testing of the effects of soft rock water content on the bearing performance of tunnel-type anchorages

Due to the elevation of tunnel-type anchorages (TTAs) is close to or even much lower than the reservoir water level in the Three Gorges Reservoir area of China, some TTAs are in a water-soaked state due to the high groundwater level. Nevertheless, the influence of the water content of soft rock on the bearing performance of a TTA has not been fully explored. Hence, two large-scale field models buried in soft rock with different water contents were developed to investigate the effects of water on the deformation evolution, ultimate bearing capacity, load transfer efficiency, and progressive failure characteristics of TTAs. The model tests show that the water content of the rock mass increases from 5.36 to 7.39%, and the ultimate bearing capacity of the TTA decreases by approximately 22.8%. The load transfer efficiency of TTAs decreases with increasing rock mass water content. There will be great relative slip along the interface between the floor of the plug body and the surrounding rock during the bearing of TTAs with different rock mass water content; the TTA preferentially fails along this interface. Additionally, the ground surface cracks are mainly tensile and shear cracks. Although an increase in water content significantly reduces the ability of a rock mass to resist deformation, a change in water content does not affect its movement mode or failure characteristics. The influence of water is mainly manifested in the increase in rock mass deformation and decrease in the ultimate load-carrying capability, crack initiation load, and load transfer efficiency of TTAs.