Abstract：Weathering，being a natural process that decreases rock strength，stiffness and durability，is specially concerned in investigation and design of rock engineering. Runyang Bridge is the longest suspension bridge in China and the third longest one in the world by now. Weathering strongly affects the quality of the bedrock of granite and therefore controls the siting and designing of the bridge foundations. Systematical geological analyses and a set of field and laboratory tests were carried out. It is found that the lithology and the geological agents，including vertical tectonic moving，fracturing，unloading，river eroding and infiltration，are the main factors affecting the granite weathering and the various distribution of weathered rockmass at the bridge site. The study indicates that the granite is susceptible to weathering and unloading，and in early chemical weathering stage. The main geotechnical issues due to weathering and correlated countermeasures about selection of bridge type，site and design of the tower foundations，determination of bedrock parameters and control of further weathering of bedrocks are further discussed.
