Anti-floating stability study of working shafts in pipeline tunnels within water-rich soft soil strata

Abstract Ensuring the anti-floating stability of pipe-tunnel working shafts adjacent to rivers in water-rich soft soil strata is a critical challenge throughout both the construction and long-term operation periods. Current research primarily focuses on conventional anti-floating measures for general underground structures, overlooking the potential of utilizing the soil-cement mass from base pressure grouting as a structural counterweight, particularly for deep circular shafts subjected to fluctuating groundwater levels. This study proposes a novel passive anti-floating measure, the counterweight method, which involves pressure grouting the soil beneath the base slab. A three-dimensional finite element model, validated against field monitoring data, was established to systematically investigate the effects of four key parameters: groundwater level, grouting replacement ratio, grouting depth, and retaining structure embedded depth. The results demonstrate that the proposed method effectively balances buoyancy forces. A 15.4% increase in the anti-floating safety factor was observed when the groundwater level dropped from flood to the lowest level. While the grouting replacement ratio had a minor impact, increasing the grouting depth and embedded depth by 8 m enhanced the safety factor by 6.78% and 4.82%, respectively. A multivariate regression design formula was derived for rapid stability assessment during the operation period. This research provides a cost-effective technical solution and a reliable design tool for assessing and ensuring the anti-floating stability of deep working shafts in complex hydrogeological environments.