Abstract: To explore the stress variation law of the existing lower shield tunnel induced by shield tunneling, a computing model of shield crossing is established. Considering the additional thrust generated by soil loss induced by additional thrust on cutterhead, shell lateral resistance, additional grouting pressure, and the excavation, the realtime surrounding rock pressure of the existing shield tunnel is calculated using surrounding rock pressure redistribution theory, and the internal force is calculated using a modified routine method. Based on case study, the bending moment, axial force, and shear stress of the lower shield tunnel during shield tunneling process are analyzed, and the influence of tunnel buried depth is investigated. The results reveal the following: (1) The horizontal additional stress around the tunnel is mainly caused by the friction of the shield shell and soil loss, whereas the vertical additional stress is mainly caused by soil loss. (2) The shield tunneling will induce vertical oval distribution of additional surrounding rock pressure, and the surrounding rock pressure distribution and internal force of the existing shield tunnel decrease, the bending moment and shear stress decrease sharply, and the axial force changes slightly after shield tunnel crossing. (3) During local passing of the upper shield tunnel, the surrounding rock pressure of the existing shield tunnel shows a balance process from left to right. (4) The additional stress increases and internal stress of segment decreases diversely with an increasing buried depth of the new tunnel.

Key words: shield tunnel, uppenetration driving, existing tunnels, additional confining pressure, internal force change