Abstract
Large storage dam projects may modify geo-environmental conditions in many ways. The reservoir impoundment of the 285.5 m high Xiluodu arch dam located on the Jinsha River (China) caused large-scale canyon deformations, including significant canyon contraction and uplift movements from reservoir to downstream valley. The dam experienced subsequent tilting towards upstream and raised a safety concern of the project. A Thermo-Hydro-Mechanical (THM) mechanism is proposed for this extraordinary behavior. Due to reservoir impounding and seepage, significant temperature drops and fluid pressure increase within the underlying geothermal limestone aquifer in a synclinal basin are primary root causes. Finite element THM simulations successfully reproduce these unique deformations. Recent observations of large quantities of thermalized discharge water downstream and high pore pressure in the limestone layer provide further support for the proposed mechanism. Furthermore, refined numerical modeling is adopted to evaluate the safety of Xiluodu dam subjected to potential larger canyon contractions. We conclude that these unprecedented phenomena are dominantly the consequence of THM response to regional hydrogeological evolution following the build-up of a large reservoir. The accumulated canyon contractions at the current stage would not pose a direct threat to the dam safety, but a tripled situation may cause severe safety issues.
Highlights
Large storage dam projects may modify geo-environmental conditions in many ways
The construction of the Xiluodu arch dam, a large hydropower station located on Jinsha River, introduced substantial canyon deformations with unique characteristics
The relevant mechanisms proposed in previous studies, including the ancient landslide reactivation, saturation-induced rock strength degradation, reservoir loads, and excavation induced unloading, are all incapable of providing a comprehensive explanation for the large-scale canyon deformations and uplifts at the base monitored in Xiluodu dam site
Summary
The reservoir impoundment of the 285.5 m high Xiluodu arch dam located on the Jinsha River (China) caused large-scale canyon deformations, including significant canyon contraction and uplift movements from reservoir to downstream valley. From the onset of reservoir impoundment in May 2013, largescale canyon deformations were observed, featuring a uniform contraction along the transverse river direction, and uplifts both at the dam base and over several kilometers of the downstream valley floor. This unusual behavior of valley deformation had brought forward a wide range of spirited discussion on its root-cause mechanism, which gave an impetus for the current investigation
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