Construction Technology for Shield Tunnelling Under-passing in Proximity to Operation Metro Tunnels in Water-rich Pebble Stratum

Abstract

Objective In the process of shield construction under-passing the existing metro line in water-rich pebble stratum, irregular settlement of the overlying soil mass beyond control range may occur, potentially leading to issues such as underground water gushing and ground collapse. Therefore, it is necessary to research the construction technology for shield under-passing in proximity to operation metro tunnel in water-rich pebble stratum. Method Taking the case of shield under-passing existing Chengdu Metro Line 4 at the newly-built Fengxi Avenue Station on Chengdu Metro Line 17, on the basis of introducing project overview, four land subsidence monitoring points and four deep soil mass settlement monitoring points are selected to analyze the stratum settlement variation law during shield excavation process. A three-dimensional finite element model is created using MIDAS GTS, simulating the reinforcement construction with a combination of 38 m super-long pipe shed and oblique angle grouting. The pre-reinforcement effect on Line 4 tunnel is analyzed. Based on this, the timing for ground tracking grouting is determined, and its effectiveness is further analyzed. Result & Conclusion The reinforcement measures effectively enhance the overall integrity of structure bottom soil mass, improve the structural loading conditions, and successfully control the structural settlement of Line 4.

Keywords

• metro shield tunnel
• water-rich pebble stratum
• shield under-passing
• soil mass reinforcement
• long-large pipe shed
• ground surface tracking grouting