Observations and Computational Simulation of River Valley Contraction at the Xiluodu Dam, Yunnan, China

River valley contraction (RVC) has increased continuously at the Xiluodu Dam site since the completion of the slope excavation that commenced on December 1, 2008. Previous studies on RVC only analyzed the displacement after reservoir impoundment. Since deformation is affected by many factors, it is difficult to determine the leading causes of RVC by merely studying the displacement after impoundment. This study examines, for the first time, the complete displacement process before and after impoundment. Four models that include poroelastic, thermo-poroelastic, poroelastic-plastic, and poroelastic-creep are used to simulate the RVC displacement using COMSOL multiphysics. It is observed that the creep of the basalt formation is the leading cause of RVC. Sloped excavation causes RVC, and the subsequent reservoir impoundment accelerates the RVC by changing the creep parameters. A poroelastic-creep model with two-stage creep parameters was applied to the numerical simulation. The simulation results are in good agreement with the field observations. The predicted results show that the convergence value of RVC is 187 mm, and an additional closure of 21.5 mm will occur in the next 14.5 years. This research provides a further assessment of the RVC by providing a model that is validated by existing data and leads to an estimation of future RVC.

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