Abstract：Passing through unfavorable geologic bodies and strata interface is the one of the most difficult problems during subsea tunnel construction. So tunnel geological forecast ahead，grouting reinforcement schemes and construction method optimization are important issues to guarantee the safety of subsea tunnel construction. The control of strata settlement induced by tunnel construction especially for some unfavorable geologic bodies is one of the key techniques during tunnel construction. How to control strata settlement is not only important to the safety during construction period，but also is crucial to long-period safe tunnel operation. According to the characteristics of subsea tunnel，the essence of the inrush of water during subsea tunnel construction is disclosed from the view of the connectivity of strata interface，strata settlement and cave-in，etc.. By using in-situ measured data，numerical simulation and theoretical analysis method，the mechanism of integral deformation of upper strata due to tunnel excavation is then expounded；and subsequently settlement control standard and its determination method for different strata are proposed. The relation between surface crack space and strata displacement is presented to offer guidelines to water inflow prediction. The relation between the thickness of grouting circle and strata settlement is also given to determine the optimal grouting circle thickness for unfavorable geologic bodies. Besides，combined with the characteristics of large-span cross-section of subsea tunnel，tunnel construction technology and monitoring schemes are therein shown. Finally，construction techniques that are used for tunnel passing through unfavorable geology bodies are indicated. The application of above-mentioned technological schemes and measured data are proven to be successful in passing through the weathered slot F1 of Xiamen Xiang¢an subsea tunnel.
