Abstract
Reservoir impoundment is a complicated problem in hydraulic engineering. It’s related to different scientific phenomena in different scales, such as valley width contraction near the dam, reservoir bank slope deformation, and reservoir-induced earthquake in the basin-scale. Pore pressure increases as water level rises up, and causes material degradation and strength reduction in several ways. The effective stress law made a remarkable success in describing the mechanical behavior of saturated soil, but its application is still limited in rock materials, especially when it comes to elasto-plastic constitutive relation. A generalized effective stress concept in elasto-plastic model for fractured rock is presented and applied in the slope deformation assessment during reservoir impoundment. The observed slope deformation during impounding process is introduced and explained. The additional plastic deformation induced by the increasing fracture pressure is the main factor of slope deformation. A case study is provided of the left bank slope of Jinping-I high arch dam. The results show that the Drucker-Prager criterion embedded with the concept of effective stress describes accurately the measured values of slope deformation, and this method is efficient and useful in the deformation and hazard assessment of hydraulic engineering projects.
1. INTRODUCTION
A number of high arch dams have been designed and constructed in Southwest China in recent years, including Xiluodu arch dam (285.5m high), Xiaowan arch dam (292m high), Jinping-I arch dam (305m high), Dagangshan arch dam (210m high) et al. The rock slopes in the dam sites are characterized by large-scale, high geostress and developed fractures. Although high safety factors are achieved in the optimized schemes of the dams, the impounding deformation of slopes and its influence to the dams are still of great significance. Typical hydraulic catastrophes related to the impounding process include the Vajont dam, the Malpasset dam and some other cases. The Vajont dam suffered from a reservoir-induced landslide and the catastrophic consequences, which occurred 3 years later after the initial impoundment [1-3]. The failure of the Malpasset dam was attributed by some investigations to the seepage forces in the fractures of foundation [4-6]. The dam heel cracking of Kolnbrein arch dam was also during the initial impoundment [7].
