超浅埋暗挖隧道管幕冻结法积极冻结方案试验研究

Experimental study on active freezing scheme of freeze-sealing pipe roof used in ultra-shallow buried tunnels

港珠澳大桥珠海连接线拱北隧道口岸暗挖段,作为富水地区超浅埋暗挖隧道,采用管幕冻结预支护体系。以实顶管内"圆形主力冻结管"和空顶管内"异形加强冻结管"的不同组合方式形成实顶管单独冻结模式、实顶管与空顶管协同冻结模式和实顶管为主与空顶管为辅的冻结模式三类管幕冻结法积极冻结方案,结合设计方案要求,通过测点温度–时间曲线和冻土帷幕厚度两种不同分析方法,对以上方案进行了分析和验证。结果表明实顶管单独冻结模式不能在60 d内形成2 m厚冻土帷幕,实顶管与空顶管协同冻结模式30 d内即可形成2 m厚冻土帷幕,实顶管为主与空顶管为辅的冻结模式下异形冻结管滞后12 d和39 d开启60 d内均可形成2 m厚冻土帷幕,且异形冻结管开启后1～3 d即可达到管间封水要求。

The excavated section of Gongbei Tunnel of Zhuhai Link of Hong Kong-Zhuhai-Macao Bridge is an ultra-shallow buried tunnel located in water-rich area,and a new pre-support system named freeze-sealing pipe roof(FSPR) is first adopted.Based on the diverse combinations of "circular master freezing-tube" within the solid jacking pipes and "profiled enhancing freezing-tube" within the empty jacking pipes,three kinds of active freezing modes are proposed,i.e.,solid jacking pipes,combination of solid jacking pipes and empty jacking pipes,and combination of solid jacking pipes as the principal and empty jacking pipes as the complement.The above three freezing modes are analyzed and verified by means of two different analysis methods of temperature-time curve and thickness of frozen curtain according to the requirements of the design program.The results show that the first freezing mode cannot form a 2 m-thick frozen soil curtain in 60 d,the second one can form 2 m-thick frozen soil curtain within 30 d,and the third one can also form 2 m-thick frozen soil curtain in 60 d under lagged running of profiled enhancing freezing-tube of 12 d or 39 d;and the requirements of sealing water between jacked pipes can be achieved after 1 to 3 d when the profiled enhancing freezing-tube is started to work.