Coupled Thermo-Hydro-Mechanical Analysis of Valley Narrowing Deformation of High Arch Dam: A Case Study of the Xiluodu Project in China

General studies examining reservoir bank deformation during its impoundment primarily consider the coupling effect between the seepage field and the stress field, but thermal field variation in the bedrock and its effect are rarely considered. In this paper, a case study concerning a 285.5 m high arch dam project, where a valley narrowing deformation occurs after the initial impoundment, is implemented. An analysis of in situ measurement is given to interpret the causes of the unique hydro-thermal phenomenon of the project. Possible reasons for the valley narrowing deformation pattern are discussed. A numerical model based on the thermo-hydro-mechanical (THM) coupling theory of porous medium is used to calculate the evolution processes of the thermal, seepage, and stress fields of the area after impoundment of the reservoir. The simulated deformation trend and pattern of the river valley are consistent with the monitoring data. The results demonstrate that water infiltration after impounding cools the bedrock and the temperature decrease makes the bedrock contract, which induces the narrowing deformation of the valley. Factor analysis of the hydrothermal field shows that temperature variation is the main cause of long-term deformation. Thus, it shall be considered as a key factor in terms of structural safety assessment. Furthermore, sensitivity analysis of the hydraulic conductivities of rock strata suggests that future development of the deformation can be eased off if the anti-seepage method is adopted on the bedrock.