关键词: 孤石群地层, 气垫式泥水盾构, 双模盾构, 洞内改造, 环流系统

Abstract: In-service air-cushioned slurry shields operating in high-density boulder group strata frequently experience sharp declines in advance rates, abnormal cutter damage, muck accumulation in the chamber, and chamber-pressure fluctuations. To overcome these challenges, an in-tunnel, insitu dual-mode reconfiguration scheme was proposed. Supplemental geological investigations, cross-hole computed tomography, chamber inspections, and analyses of tunneling parameters were conducted to investigate the coupled failure mechanisms involving rock fragmentation, muck discharge, and chamber-pressure control in strata containing large, high-strength boulders. The results indicate that the boulders could not be adequately fragmented into sizes suitable for discharge through the slurry system. Consequently, oversized rock fragments accumulated in the chamber and obstructed the discharge passages, disrupting slurry circulation, destabilizing chamber pressure, and causing frequent shield stoppages. To address these problems, the cutterhead grating is optimized, the shield-body structure is reconfigured, a screw conveyor is integrated, a dual-channel muck-discharge system is developed, and the slurry circulation system is upgraded. These modifications transformed the original air-cushioned slurry shield into a dual-mode shield designed to operate primarily in earth pressure balance (EPB) mode and secondarily in slurry mode. Representative tunneling sections before and after reconfiguration were compared to evaluate tunneling performance, equipment reliability, and construction safety. During post-reconfiguration verification, the shield operated in EPB mode, with muck discharged mechanically through a screw conveyor and a belt conveyor. The results show the following: (1) the average advance rate increased from 0.43 to 5.20 m/d, corresponding to an approximately 12-fold increase; (2) the abnormal cutter damage rate decreased by more than 70%, muck accumulation in the chamber was largely eliminated, and the maximum surface settlement was limited to 18 mm; (3) techno-economic analysis showed that the ratio of reconfiguration time to the estimated reduction in construction duration was approximately 1∶11.9, while the combined monthly costs of the major construction items decreased by more than 90%; and (4) adaptive reconfiguration of the entire machine and system integration of an in-service slurry shield were technically feasible under the spatial constraints of underground tunneling. These findings provide a practical reference for improving the adaptability of in-service shield machines and overcoming tunneling challenges in highly heterogeneous strata.

Key words: boulder group strata, air-cushioned slurry shield, dual-mode shield, in-tunnel reconfiguration, circulation system