多排管局部冻结冻土壁温度场特性

上海地铁一区间隧道因施工联络通道发生工程事故导致隧道坍塌,修复工程中部分采用四排局部垂直冻结形成冻土墙,用于抵挡水土压力和嵌固完好隧道。针对冻结深度深以及冻结土层为扰动的粉质黏土、砂质粉土并承受较高承压水头这些特点,工程中对冻结壁温度场发展进行实时监测。从冻结深度、厚度方向上分析多排局部冻结排内和排外温度发展特征,并分析计算出积极冻结期排内冻土壁交圈时间、发展速度。鉴于目前计算冻土帷幕厚度公式并不适用于计算多排管冻结,引入双排管计算公式,并利用作图法推导出平均温度计算公式。利用这2个公式,分析多排局部冻结冻土壁特征,计算出积极冻结期结束时冻土壁厚度和平均温度,以及整个冻结期排外冻土壁单侧发展厚度和发展速度。

CHARACTERS OF TEMPERATURE FIELD IN FROZEN SOIL WALL WITH MULTIROW FREEZE-TUBES AND LIMITED DEPTH FREEZING

An interval shield tunnel in Shanghai encountered tunnel lining collapse due to construction of the cross-passage.The limited depth freezing method with four rows of freeze-tubes placed in vertical holes drilled from the surface was applied as an aid to recover the collapse tunnel to form a frozen soil wall,which was used to resist the soil and water pressure and fix the undamaged tunnel lining between the undamaged tunnel and the collapsed tunnel.Due to the frozen soil containing disturbed sands and silts subjected to high groundwater pressures,the in-situ monitor of the development and changing features of the temperature field in the frozen soil wall was applied to supervise the construction.By analyzing the monitored data,the differences of the temperature fields inside and outside of the rows of the freeze-tubes are discussed in two ways,from vertical and horizontal directions,respectively.The time of frozen soil wall closure and the velocity of the growth are calculated during the primary freeze period.In view of the fact that the present formula to calculate the frozen curtain thickness and the average temperature are not applicable to calculate the multi-row freezing;the double-row formula is introduced,and an average temperature formula by graphing method is deduced for the first time.By these two formulast,he characters of the temperature field in the frozen soil wall are analyzed.The thickness and the average temperature of the frozen soil wall are calculated at the end of the primary freeze period.The single side thickness and the growth velocity of the frozen soil wall are also calculated during the freezing period.