复杂地层内地铁联络通道冻结施工冻胀控制研究

A Research on Frozen-heave Control of Freezing Method Applied to the Subway Connected Aisle in Complex Strata

针对地铁联络通道冻结施工时常面临的冻胀过大且冻胀率较难测定的施工难题，依托杭州某复杂地层内越江隧道联络通道冻结施工实例，采用数值分析不同假定冻胀率对冻土体内力和主隧道变形的影响，通过冻土体内力变化制定出冻土体的临界冻胀率，同时对主隧道竖向变形进行监测，并结合主隧道计算竖向变形反馈出实际冻胀率，最后根据实际冻胀率和，临界冻胀率的比较，采取相应施工措施。研究结果表明：此类地层联络通道冻结施工时，冻土体临界冻胀率为2％，可采用可观测的主隧道竖向变形监测来反馈冻土体的实际冻胀状态，当冻结和暗挖阶段主隧道竖向变形量分别小于7．5mm和4．88mm时，实际冻胀率为1％。2％，冻胀对冻结效果的影响尚在可控范围内，故除常规泄压孔减胀措施，无需再采用加强减胀措施。

Aiming at the problems that frost heave is excessive and the frozen-heave factor is difficult to measure, which is always encountered in the freezing construction of subway connected aisle, this paper, based on a project case in Hangzhou which applies freezing method fo the connected aisle of a cross-river tunnel in complex strata, analyzes the influence of different frozen-heave factors on the internal force of frozen soil and the deformation of main tunnel by numerical analysis. And then, the critical frozen-heave factor is determined according to the internal force change of frozen soil. Simultaneously, combining with calculated value, the monitoring concerning the vertical deformation of tunnel is conducted to give feedback whether the actual frozen-heave factor exceeds the critical one, so the corresponding measures can be taken timely. The findings indicate that the critical frozen-heave factor of frozen soil is 2% in the freezing construction of connected aisle in this type of strata, and the actual frozen-heave state of soil can be reflected by the monitoring of vertical deformation in the main tunnel, which is less than 7.5mm and 4.88mm respectively in the stage of freezing and subsurface excavation when the actual frozen-heave factor keeps between 1% and 2%. Meanwhile, the influence of frost heave on freezing effect can be controlled, so no more strengthening measures for frozen-heave reduction are needed but the conventional measures of relief holes.