The impact of water ingress in terms of groundwater drawdown and settlement during tunnel construction

Abstract

Water ingress into tunnel is always one of the key concerns during tunnel construction. Excessive water ingress would result in significant groundwater drawdown and settlement, which would affect the structure integrity and stability. Thus estimation and control of water ingress would be important. It is commonly believed that the water ingress would be affect by the rock mass discontinuities during excavation, i.e. more rock discontinuities would result in higher water ingress. The objective of this dissertation is to study the relationship between water ingress and rock quality, Case study on settlement and groundwater drawdown is also discussed in this dissertation. The field data was obtained from the construction of tunnel section from Aberdeen to Sai Yin Pun under Habour Area Treatment Scheme Stage 2Aproject, The data has been interpreted to discuss the relationship between rock quality, including rock mass discontinuities, rock type and presence of faulting, and water ingress. It was concluded that the amount of rock mass discontinuities would affect the water ingress while the rock type and the presence of faulting did not demonstrate observable effect.