Impact Analysis and Deformation Control Measures for Zero-Distance Deep and Large Excavation Adjacent to Both Sides of an Existing Subway Station

Based on the demand for three-dimensional urban development， the number and scale of subway superstructure projects are gradually increasing， which has a significant impact on existing subway stations and tunnels during the construction process in Tianjin’s soft soil areas. Taking the existing subway station topping project of Tianjin Subway Line 5 as a case study， the paper analyzed the entire excavation process， including pre-excavation dewatering， based on the measurement data. It further studied the impact of deep and large excavations with simultaneous two-sided excavation on existing subway stations and tunnels. A deformation control method for existing structures during construction by refining the dewatering scheme was proposed. The study showed that： 1） Simultaneous deep and large excavations on both sides exerted a huge impact on the existing subway station and tunnel structures between them. The vertical displacement of the existing structures risked exceeding the alarm value or even the control value. Additionally， the vertical and horizontal deformation patterns differed significantly between the existing structure and the new diaphragm wall： during the excavation process， the main structure of the station experienced continuous heave， while the diaphragm wall initially settled but transitioned to heave upon reaching the final excavation depth， with both structures ultimately reaching a similar heave value of approximately 11.0 mm. In terms of horizontal deformation， the newly constructed diaphragm wall exhibited progressively increasing outward displacement as excavation progressed， whereas the station structure showed an initial increase followed by a gradual reduction in horizontal displacement， resulting in a final horizontal displacement of the diaphragm wall that was more than twice that of the station structure. 2） The influence of dewatering in the excavation on the main body of the existing structure and the new diaphragm wall had a large difference. By formulating a refined dewatering scheme， controlled pre-settlement of the station structure could be achieved before excavation. This approach effectively minimized construction-induced heave of the existing station while ensuring compliance with deformation control standards for the new diaphragm wall and supporting structures， thereby guaranteeing construction safety.