Effect of Impounding on Bedrock Temperature of High Arch Dam Site: A Case Study of the Xiluodu Project, China

Abstract

The 300 m-level high arch dams built in China have different degrees of valley-narrowing deformation in the initial impoundment. This unexpected phenomenon may increase the long-term safety risk of high arch dams. There are several explanations for the valley-narrowing deformation phenomenon, and one of the explanations—that it is caused by a drop in bedrock temperature—is still under debate. In this paper, coupled thermo-hydromechanical (THM) simulations of the temporal and spatial evolutions of the bedrock temperature and seepage fields of the Xiluodu arch dam site were performed. The results showed that the mechanism of the bedrock temperature drop after impoundment can be divided into two types: short-term type and long-term. For the short-term type, the maximum temperature drop of 9 °C is caused by the heat exchange between the bedrock surface layer and the reservoir water during the initial impoundment. For the long-term type, the maximum temperature drop of 15 °C in front of the grouted curtain is caused by the long-term infiltration of cold water from upstream to downstream bypassing the grout curtain. The monitoring data showed that the valley-narrowing deformation mainly occurred in the initial impoundment, which corresponds to the short-term type. Notably, the valley-narrowing deformation may be overestimated if the long-term type of bedrock temperature drop is considered. Taken together, these findings demonstrate that the bedrock temperature change due to impoundment is dominated by the short-term type and can be applied to study the effect of temperature on valley-narrowing deformation after impounding.