Seepage characteristics of core rockfill dam foundation with double cutoff walls in deep overburden: A case study

Some high rockfill dams, built on deep overburden, utilize double concrete cutoff walls for seepage control, thereby introducing increased complexity to seepage characteristics in the dam foundation. This study focuses on a core rockfill dam located on the Dadu River in China, investigating the impact of dam body and foundation permeability coefficients on the percentages of hydraulic head reduction by the double cutoff walls. A multifactor sensitivity analysis, based on finite element method, is conducted to analyze this influence. Subsequently, an inversion model, integrating support vector regression and whale optimization algorithm, is proposed to identify parameters that align with seepage monitoring data. Results indicate that the permeability coefficients of the surface bedrock and the main grouting curtain exert the most significant influence. Parameters derived from the inversion model yield finite element calculations consistent with monitoring data. Moreover, upstream water level minimally affects the distribution of hydraulic head reduction percentages by the double cutoff walls. And the seepage gradient (G) in the dam foundation overburden remains below the permissible limit, with its relationship to the upstream water level (L) fitted as G = -1.03318 + 6.96E - 4 x L.This study may offer valuable insights for the construction and operational management of similar projects employing double cutoff walls.