Abstract:The Wangxia rock body(W2-2) is a dangerous body of rock located on the left side of the Three-Gorges section of the Yangze River in Wushan county. It suffered evident deformation during the monsoon of 2010; emergency monitoring was immediately conducted and two forecasts were made successfully. The evolution of W2-2 is similar to that of other common dangerous rock bodies. In this study, geological investigations and in-situ monitoring are used to determine the dynamic processes involved in the deformation-evolution of W2-2. Results show that, in general, falling of sliding masses into the river was induced by continued rainfall, and that infiltrated rainwater weakened the intensity of the soft mudstone foundation. The plastic flow was thus strengthened, and bottom deformation of the rock body occurred. As a result, tensile cracks were generated in the overlying sandstone layer. In addition, a fracture was widely developed in the rock body because of the effect of river water. Ultimately, rainfall occurring during the period from October 10 to 15, 2011 led to integral collapse of the W2-2 on October 21. Evolution of the deformation and failure of W2-2 included four stages:initial cumulative deformation, uniform deformation, accelerating deformation, and threshold-accelerated deformation. The accelerating point and the threshold-accelerated point are thus considered to be effective indicators for use in forecasting, and the accelerating point is identified to be representing the threshold between the stability and instability of the rock body.
