Study of the rock foundation stability of the Aizhai suspension bridge over a deep canyon area in China.

Suspension bridges have good spanning ability and seismic resistance. They avoid the need for tall piers and reduce the amount of foundation excavation. Therefore, suspension bridges are the first choice when building large-span bridges. Recent expansion of highways in the high mountainous region of western China has led to the widespread construction of large-span suspension bridges. Mountainous areas with deep canyons feature complex topographic and geological conditions, such as constricted construction sites, extensive unloading of rock masses and problematic stability of high and steep slopes, that adversely affect foundation stability and complicate surveys and analyses. In this paper, the Aizhai suspension bridge was used as a case study, and four key issues related to bridge foundation stability were analyzed. The results suggest that a comprehensive geological investigation is needed to develop a full understanding of the geological conditions, particularly unloading and dissolution-related geologic defects, in rock masses. The stability problem in the bridge foundation rock masses occurs primarily in the high and steep slopes on both banks of the canyon. The design load did not cause significant deformation in the rock mass. If proper reinforcement measures are taken to ensure the stability of the slope rock mass, the foundation rock mass will be stable. In addition, no significant interaction was observed between the structures. A tunnel-type anchorage can resist strong pullout forces via the “clamping effect” provided by the surrounding rock. Because tunnel-type anchorages are rarely used, the rock mechanics of the surrounding rocks have not been fully studied. Therefore, the pullout capacity of these anchorages may have been seriously underestimated. [ABSTRACT FROM AUTHOR]