Abstract: This paper presents a case history of a deep excavation support design project for a a river crossing tunnel in Jiangsu Province. The deep excavation supporting method of the diaphragm wall + internal support+ bottom reinforcement by using N-JET grouting is proposed. A three-dimensional numerical model is established by using the numerical simulation method to study the impact of deep excavation on the supporting structure and surrounding structures. The results show that, after the excavation, the displacement and stress of the supporting structure are small, the maximum horizontal displacement of the deep layer of the north diaphragm wall and the east and west diaphragm walls are 13.4 mm and 7.2 mm respectively, The maximum axial force on the supporting structure is about 14 868 kN, the maximum stress on the diaphragm wall is about 1.31 MPa, and the surrounding surface settlement is small, which verifies the effectiveness of the excavation support method and can ensure the smooth construction of the deep and large deep excavation project. The results can provide a good reference for the design and construction of similar projects.

Key words: Large and Deep Excavation, Excavation Support Structure, Numerical Simulation, Stability Analysis