Ground settlement induced by tunneling crossing interface of water-bearing mixed ground: A lesson from Changsha, China

Abstract

Tunneling in mixed ground faces great challenges in control of shield machine, and improper operation easily trigger hazards without warning. Recently, an unexpected ground surface settlement of approximately 0.05 m was observed in the mixed ground of Changsha, China. When the shield machine advanced from the low-permeability ground to the high-permeability ground, the lag in the regulation of chamber pressure allowed the water inflow from the excavation face, hydraulic pressure loss at the tunnel face thus induced large settlement. To further investigate ground responses induced by tunneling crossing the interface of water-bearing mixed ground, a 3D fluid-solid coupling finite element model is established in this study. The results indicate obvious drawdown of the groundwater occurs when the shield machine crosses the interface of low-permeability and high-permeability ground with low chamber pressure, leading to significant ground consolidation settlement with close to the measured results. Three typical settlement development modes that are related to the relative position of the monitoring section to the interface are proposed to describe the tunneling-induced settlement in the water-bearing mixed ground. The experience of this case history provides an important lesson for the future control of shield tunneling in the water-bearing mixed ground.