Constructing a cut-off dam inside a water-filled circular tunnel with backfill grouting

Abstract

This study employs laboratory model tests for backfill grouting and numerical analyses (coupled analysis of the discrete element method and computational fluid dynamics, DEM-CFD coupling analysis) to investigate the feasibility of constructing a cut-off dam inside a water-filled circular tunnel using the backfill grouting method from the ground surface. Several improved backfill methods were studied to enhance the effectiveness of the cut-off dam. These methods include: (a) adding an additional backfill grouting hole between the double-row cut-off dam and applying pressurized grouting; (b) adjusting the number of backfill grouting holes per row of the cut-off dam; (c) simultaneously grouting the double-row cut-off dams to minimize the formation of interface fissures and voids; (d) adjusting the grout hole spacing of the double-row cut-off dams to reduce the volume of backfill material. Additionally, pressurized mortar grouting is a critical mass to ensure the water tightness of the cut-off dam. The implementation of these backfilling arrangements improves the effectiveness and watertight of the cut-off dam, thereby reducing the construction time and cost. The findings of this study can serve as a reference for water-filled tunnels and subsequent rehabilitation works in the future.