Deformation characteristics of existing tunnels induced by above-crossing quasi-rectangular shield tunnel

Quasi-rectangular shield (QRS) tunneling, a recent development in tunneling technology, offers the advantage of creating double tunnels with a single excavation. This technology causes significantly less secondary damage to the environment than traditional double shield tunneling. However, the deformation characteristics of existing tunnels caused by the QRS tunnel crossing above them are unknown. This study presents the first application of a QRS tunnel crossing above existing tunnels. It provides a comprehensive overview of the vertical displacement, horizontal displacement, segment convergence, and torsional deformation of existing tunnels when the QRS crosses above and runs parallel to the existing tunnels in the Hangzhou Metro Line 4. The measurement results indicate that the existing tunnels exhibit a maximum vertical displacement of 7.2 mm, maximum horizontal displacement of 2.3 mm, maximum segment convergence of 5.8 mm, and rotation index of up to ±10 × 10-4 at the intersection of the QRS and existing tunnels. All of the measurement results fall within the acceptable range, demonstrating the exceptional efficacy of QRS in controlling the deformations of existing tunnels. The effects of the plane position and distance between the tunnels on the deformation of the existing tunnels is also discussed. The deformation of the existing tunnels is negligible when the distance between the QRS and existing tunnels exceeds 16 m. The maximum vertical displacement, horizontal displacement, segment convergence, and zero-values of the rotation index occur at approximately 5 m in the plane position rather than at the intersection between the QRS and existing tunnels. The primary influence zone where the QRS tunnel crosses above existing tunnels is discussed.