Dealing with Uncertainty in Engineering Design for Large-Scale Gravel Soil Slopes in the Three Gorges Reservoir Zone

摘要

The objective of this paper is to first present a general formulation for analysis of uncertainties and evaluation of risks associated with large-scale slopes. The risks may be expressed in terms of the reliability of the system and the consequence. Preliminary studies regarding the mitigation of landslides in the Three-Gorge reservoir zone (TGRZ) of the Yangtze River is presented next. At the normal water level of 175 m, the Three-Gorge reservoir stretches for 665 km along the Yangtze River and extends into many tributaries. Some 684 colluvial deposits, ancient slides and hanging rock blocks, which are larger than 100,000 m~3 individually, and numerous smaller landslides have been identified. Since 2001, over 650 landslides of varies sizes and 2300 cut slopes at low elevations in the Chongqing section of the Yangtze River have been or are being stabilized. This paper deals with three subjects related to the landslides in the TGRZ. The general characteristics of the landslides and the consequences of these landslides are described first. The main causes of activation are considered to be rainfall infiltration, reservoir level fluctuations, and human activities. An attempt is then made to summarize the uncertainties in the design of the slope stabilization works against slope failure due to rainfall infiltration and reservoir level changes. The uncertainties discussed include those involved in the selection of design soil parameters and design-loading combinations, determination of pore-water pressures and potential slip surfaces, and use of analysis models. Finally a design scenario tree is developed to evaluate the landslide risk and to assist risk-investment decisions.