高流速卵石地层地铁联络通道人工冻结温度场研究

Subway Cross Passage Artificial Freezing Temperature Field in Pebble Stratum with High Velocity Flow

地铁联络通道的开挖经常受到地下水干扰,人工地层冻结法凭借其优秀的封水性和适应性成为富水地层联络通道施工的首选工法。依托北京地铁12号线苏州桥站~人民大学站区间1#联络通道冻结工程,通过现场实测研究地层温度场和泄压孔压力的发展规律,分析冻结帷幕的交圈特征,确定高流速地层冻结壁薄弱位置。结果表明:盐水去回路温度在冻结初期迅速下降,而后降速减缓并最终稳定在-28℃以下;测温孔中土体与管片交界处的温度高于土体内部,渗流上游冻结壁温度高于下游,这些区域应当重点监测;冻结至59 d时,利用基于实际降温速率的分阶段冻结壁厚度计算方法求得不同截面位置处的冻结壁最小厚度为2495.2 mm,同时泄压孔压力已全部释放并保持稳定,冻结壁不再发展,满足联络通道开挖要求。研究成果能为高流速地层的人工冻结参数选取和监测提供理论支持。

The excavation of subway cross passage is often disturbed by groundwater,and the artificial ground freezing method has become the preferred method for the construction of cross passage in water-rich stratum by virtue of its excellent water sealing and adaptability.Relying on the freezing project of 1#cross passage between Suzhou Qiao Station and Renmin University.Station of Beijing Metro Line 12,the development law of stratum temperature field and the pressure of depressurization hole was studied through field monitoring.The closure characteristics of freezing curtain were analyzed to determine the weak position of freezing wall of high flow velocity stratum.The results show that the temperature of brine decreases rapidly in the early stage of freezing,then the rate of decrease slows down and finally the temperature stabilizes below-28℃.The temperature at the junction of soil and tunnel lining in the thermometric holes is higher than that inside of the soil,and the temperature of the freezing wall at the upstream of the seepage is higher than that at the downstream,so these areas should pay more attention to monitor.When freezing to 59 d,based on the actual rate of decrease in temperature,the calculation method of the freezing wall thickness in different stages is used to obtain the minimum thickness of the freezing wall in different section is 2495.2 mm.At the same time,the pressure of depressurization hole has been fully released and kept stable,the frozen wall no longer develops,and meets the requirements of cross passage excavation.The research results can provide theoretical support for the selection of artificial freezing parameters and monitoring in high flow velocity strata.