2023 – A Methodology to Model the Cracks and Defects in CFRD to Assess the Slope Stability

Reza Mahinroosta

The development of cracks at Concrete-Faced Rockfill Dams (CFRD) affects the hydraulic gradient and phreatic line in the dam body, and seepage flow downstream. The crack modelling is required in seepage analysis to determine these values for assessing internal erosion and slope stability. Due to the concentration of the flow in the crack, the Darcy equation cannot be used. This paper proposes a methodology to model the nonlinear behaviour of cracks in the concrete slab considering their width and location. The method is meticulous on the one hand, which considers the nonlinear flow rule in the crack, and simple on the other hand, in which only boundary condition is produced instead of modelling the crack itself. For instance, in the location of the crack at the face slab, a flow boundary condition, referred to as the cubic flow law, was applied, applying an appropriate value for the geometry of the crack. The method was used to determine the phreatic line in a CFRD assuming different widths and elevations of the cracks, followed by slope stability assessment. The crack width ranged from 0.5 mm to 2 mm. The results showed that the crack width significantly affects the phreatic line. The lower crack width is associated with the phreatic line being lower than the crack location, while higher crack width results in the phreatic line being higher than the crack location. It was found that the phreatic line level increases with the crack elevation on the face slab up to some certain level and then decreases. The phreatic line does not necessarily start at the crack location.

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