Safety Analysis of the Left Bank Excavation Slopes of Baihetan Arch Dam Foundation Using a Discrete Element Model

This paper presents a safety analysis study of the left bank excavation slopes of the Baihetan arch dam foundation, using a complex discrete element model developed with the 3DEC software. The Baihetan hydroelectric project is currently under construction in southwest China and consists of a 289-m-high arch dam, two underground powerhouse caverns, located in each bank, and several underground tunnels. It will be the second largest hydroelectric project in China and in the world after the Three Gorges project, reaching a total power capacity of 16 GW. The actual excavation geometry of the left bank was represented in the model using a set of ordinary photographs taken at the site. The main geological structures found in the left bank during the geotechnical surveys, and the excavations were also inserted in the model. The unfavourable configuration of the geological structures in the left bank can lead to the development of potential failure mechanisms in the rock mass that may affect the stability of the dam foundation. The safety evaluation analysis was performed by the progressive reduction of the shear strength parameters of rock discontinuities, until the failure condition is reached. This study revealed the development of local failure mechanisms in the rock mass, in the downstream excavation slopes, involving large sub-vertical faults and sub-horizontal shear bands. A parametric analysis was also performed to evaluate the effect of the variation of cohesion and friction angle values of the sub-horizontal shear band involved in one of the failure mechanisms identified. This study confirmed the need in continue monitoring the downstream excavation slopes, since some rock block instabilities have already been detected during excavations.