MECHANICS ANALYSIS ON METRO STATION CONSTRUCTION BY ENLARGING LARGE-DIAMETER SHIELD TUNNEL WITH PBA METHOD

The contradictory between the construction of metro station and shield tunnel may be high effectively and safely solved by enlarging shield tunnel with shallow buried and undercutting method. Taking Jiangtai Station of Beijing Metro line 14 as an experimental project, Pile-Beam-Arch (PBA) method is put forward to enlarge the shield tunnel with an outer diameter of 10m. This method is more conducive to structural stability and construction safety than other excavation methods. A detailed description of simulating the shield advancement and enlarging shield tunnel process is stated. The results show that the ground settlement mainly occurs in the shield advancement, and the settlement is less in the enlarging process due to the effect of perfusion piles and arches. The critical condition is excavating the first layer soil and demolishing the small blocks. The key segments work together with arches, beams, pillars and perfusion piles to form a complete mechanics system. In the process of the structure converting from the complete rings to opening rings causes the structural internal force redistribution; therefore it is important to quickly connect the arches and the key segments as a whole. The study proves that the scheme is feasible in mechanics performance and construction operation.