冻结法在富水砂层暗挖施工中的应用

以采用冻结法作为联络通道暗挖辅助工法的西安地区某地铁联络通道工程为研究对象,基于实测数据及数值模拟,进行湿陷性黄土地区富水砂层冻结法暗挖施工的土体温度场、应力场及冻胀融沉规律研究。结果表明:积极冻结期,越靠近冻土帷幕内侧、周围布置冻结管越多,冻结壁的发展速率越快;积极冻结期土体降温梯度随径向深度增加而增大;泄压孔对冻土帷幕的冻胀力释放及冻胀位移控制具有显著作用,其压力突变可作为冻土帷幕交圈闭合的判别依据;以冻土最慢发展速率计算得出的积极冻结期偏于保守,同时"成冰公式法"可用于湿陷性黄土地区富水砂层冻结法施工中冻土帷幕平均温度的估算;土体开挖后,冻土帷幕在联络通道内壁上会发生向联络通道内侧的位移;土体开挖后联络通道内壁冻胀位移的有限元计算结果存在3类误差,即度量范围误差、地应力平衡误差和开挖尺寸误差,前2类误差可通过调整有限元计算结果的度量范围进行减小。

Application of AGF in Underground Excavation Construction of Water-Rich Sand Layer

A subway cross passage project in Xi’an was taken as the research object,which adopted the artificial ground freezing(AGF)as the auxiliary construction method for the underground excavation of cross passage.Based on the measured data and numerical simulation,the temperature field,stress field,frost heave and thaw settlement regularity of the soil mass in the AGF construction of the water-rich sand layer in a collapsible loess area were studied.Results show that in the active freezing period,the closer is to the inner side of the frozen soil wall,and the more frozen pipes are arranged around it,the faster the development rate of the frozen wall will be.During the active freezing period,the cooling gradient of soil increases with the increase of radial depth.The pressure relief hole plays a significant role in releasing frost-heaving force and controlling frost-heaving displacement of the frozen soil wall.The sudden change of pressure in the pressure relief hole can be used as a criterion for judging the closure of frozen soil wall.The active freezing period calculated by the slowest development rate of frozen soil tends to be conservative.At the same time,the average temperature of frozen soil wall in construction of water-rich sand layer by AGF method in collapsible loess area can be estimated by"ice forming formula method".After soil excavation,the frozen soil wall on the inner wall of cross passage will move to the inner side of the cross passage.There are three kinds of errors in the finite element calculation results of the frost-heaving displacement of the inner wall of the cross passage after soil excavation,namely,the error of measurement range,the error of geo-stress balance and the error of excavation size.The first two kinds of errors can be reduced by adjusting the measurement range of the finite element calculation results.