Objective Installing isolation piles between small-clearance shield tunnels is an effective measure to control their mutual influence. The construction difficulty of MJS (metro jet system) flexible isolation piles is relatively low, but the isolation effect is still unclear, necessitating in-depth research on this subject.

Method Based on a small-clearance metro interval tunnel project in Suzhou, the project overview is introduced. By determining the monitoring scheme, two on-site monitoring sections are selected; no isolation piles are set at monitoring section 1, and MJS isolation piles are constructed at monitoring section 2. Soil pressure gauges and steel bar stress gauges are pre-embedded in the entire ring segments of the leading tunnel at both two monitoring sections. The additional earth pressure and additional internal forces (including additional axial force and additional bending moment) of the leading tunnel induced by the follow-up tunnel during shield excavation are monitored and comparatively analyzed.

Result & Conclusion  Under the parallel condition of small clearance tunnels, flexible isolation piles can effectively smooth the loading/unloading process of additional earth pressure on the leading tunnel induced by the shield construction of the follow-up tunnel, and reduce the additional axial force in the leading tunnel segments, but with less significant influence on the additional bending moment.