How does the water-rock interaction of marly rocks affect its mechanical properties in the Three Gorges reservoir area, China?

Marly rock is a sensitive rock group of landslides in the Three Gorges reservoir area, China. It is composed predominantly of carbonate and clay minerals, water-rock interaction (WRI) of which could activate landslides in the reservoir area. To study the mechanism by which WRI affects the mechanical properties of marly rock, samples were collected from two boreholes (depth 301.78 and 307.14 m) and slope surface. Then, laboratory tests were designed to study the quantitative relationship between mineral contents and mechanical properties of intact rock, to analyze both change process of mineral composition and microstructure under short-term and long-term WRI. Finally, the change in mechanical properties and its effect on slope stability are suggested. This study indicates that the uniaxial compressive strength and Poisson ratio can be estimated by linear regression equations: (1) sigma (c) = 8.959 x (C/Q) - 0.744 x CM + 58.516; (2) mu = 0.014 x (C/Q) - 0.001 x CM + 0.234. The chemical reactions of WRI mainly included dissolution and ion exchange. On the slope surface, dissolution mainly acts on calcite, illite, dolomite, feldspar and other minerals dissolved in water. Underground, both chemical reactions of dissolution and ion exchange easily approach equilibrium with long-term seepage. Small-size minerals and micropores damage the stable microstructure of marly rock. These changes of minerals and microstructure can trigger shallow slope failure and develop deep creep deformation along some crash zones in the reservoir shoreline.