Decision to Terminate Excavation for Slurry Walls in Dam

Abstract

The studied earth dam, which has been in operation for over 40 years, was founded on residual soil and weathered rock layers that had not been adequately treated for seepage resistance prior to construction. Currently, a slurry wall is being constructed along the dam core to improve stability, using trench excavation methods with hydraulic grab and hydromill machinery. This article develops a systematic decision-making criterion for determining the stopping depth of excavation, based on borehole data, geological interpretations from actual excavation, machine performance records, and expert opinions. These factors are integrated into a quantitative index consisting of three main components: machine performance data (30%), excavated material characteristics (40%), and design information (30%). The recommended stopping criteria are set at 75 out of 100 points for normal-depth Slurry walls, and 85 out of 100 for deeper walls. To date, the implementation results from 50 out of 65 construction panels have confirmed the appropriateness of the stopping criteria, which have subsequently been adopted as a guideline for cutoff wall excavation in other related projects. The index helps improve construction quality control, reduces the risk of unnecessary deep excavation, and enhances the long-term stability of the dam. Moreover, it serves as a practical guideline for similar earth dams with comparable foundation conditions.