盾构通过后横向风道暗挖法受力分析

Mechanical analysis of transverse air duct mining techniqueafter shield tunnlling

北京地铁17号线区间隧道采用盾构先行通过后横向暗挖风道的施工工艺,上层风道跨越盾构隧道开挖至端墙,下层风道开挖至临近盾构隧道。在上层风道二衬结构保护下,倒挂井壁开挖盾构隧道两侧土体,施工竖井二衬,保留盾构隧道范围内的下层风道侧墙及底板不施工,以保证后期施工安全。因需要进行多次受力转换,采用荷载-结构法对二衬结构进行各阶段内力分析。采用地层-结构法对开挖风道、竖井、拆除管片进行各阶段变形及应力分析,结果表明地表沉降满足不超过6cm的要求。监测结果反映地表沉降达到9.91cm,主要原因为竖井开挖到底后遇到承压水,未及时封底,导致支护结构无法闭合成环形成整体受力体系,竖井底部土体无法对底板提供支撑,最终导致地表沉降超标。

The Beijing metro line 17 adopts the construction process of transverse mined air duct after shield tunnelling.The upper air ducts cross the shield tunnel and are excavated to the end wall,while the lower air ducts are excavated close to the shield tunnel.Under the protection of the secondary lining structure of the upper air duct,the soil on both sides of the shield tunnel were excavated by the upside down shaft lining method,the secondary lining of the shaft was constructed,and the side wall and bottom plate of the lower air duct within the scope of the shield tunnel were not constructed to ensure the safety for later construction.Due to the need for multiple force conversion,the load-structure method was used to analyze the internal force of the secondary lining structure at various stages.The ground-structure method was used to analyze the deformation and stress of each stage of the excavation of air ducts,shafts,and removal of segments.The results show that the surface settlement meets the requirement of no more than 6 cm.The monitoring results show that the surface settlement reach to 9.91 cm,which was mainly due to the fact that after the shaft was excavated to the bottom,the bottom was not sealed in time due to encountering confined water,so that the supporting structure could not be closed into a ring to form an overall stress system,and the soil at the bottom of the shaft could not provide support for the bottom plate.This resulted in the surface settlement exceeding the standard.