Abstract: The average particle gradation can be obtained after sieving the local gravel-soil from the Three Gorges Reservoir area, and then its experimental particle gradation is designed with replacement method. According to the feature of gravel-soil, the water content of sample is controlled by granule soil content and sampled under the same vertical pressure. The following conclusions are drawn on the shear strength and parameter of gravelly soil with different water contents and different rock contents: with different water contents, the critical rock content with changed strength will be different; with different rock contents, c value changes little with water content, while ? value changes remarkably; the internal friction angle changes with different rock contents, probably reducing by 3° -10° or so, when gravelly soil changes from the original condition to its saturation. These conclusions uill to be a basis for estimating the carrying capacity reduction of overpass and roadbed after the Three Gorges Reservoir filling.

Key words: Three Gorges gravelly soil, weakening, water content, shear strength