Groundwater Outburst Prediction and Warning in Tunnel Excavation below Seafloor: A Field Application to Dong-Tong Tunnel in Xiamen of China

Abstract: Groundwater outburst in underground tunnel excavation is a serious hazard in geological engineering. This problem becomes particularly critical when the tunnel is drilled under seafloor. Prediction and warning of groundwater outburst in tunnel excavation is a very challenging task because of the uncertainty of the geological and hydrological conditions at the site and the poor understanding of coupled stress field and fluid flow in fractured rock. This study uses the well documented Dong-Tong tunnel as a field example to illustrate important features to predict and warning of possible groundwater outburst. The Dong-Tong tunnel is the first below seafloor tunnel drilled in mainland China with a length of 5.9 km, connecting the Xiamen island and the Xiangan District of Xiamen City of China. To make a prediction and warning system, the extensional and shear strengthes, the permeability, and the density of fractures in the surrounding rocks and the stable groundwater discharge need to be measured first. Both in-situ measurements and non-invasive geophysical methods have been employed to obtain the petrophysical data. Secondly, a three-dimensional numerical simulation of the coupled stress field, displacement, and fluid flow will be carried out using FLAC3D. Thirdly, a data fusion technique based on MapGIS will be employed to provide possible groundwater outburst scenarios. A practical tool of predicting and warning of groundwater outburst in tunnel excavation has been developed and tested in Dong-Tong tunnel and other sites.