软弱地层联络通道冻结法施工温度及位移场全程实测研究

研究软弱地层联络通道冻结法施工的冻结温度场、解冻温度场、冻胀融沉发展规律,是解决其冻胀及工后融沉预测与控制的前提。以软土隧道联络通道冻结法工程为背景,对冻结温度场、解冻温度场、地表变形、深层土体冻胀融沉及温度变化规律等进行了全程实测,对冻结壁的形成及解冻全过程进行了分析。结果表明:冻结过程温度变化规律可分为温度快速下降、降温减慢、降温速度加快、土体温度稳定、维护冻结等5个阶段。解冻期间,土体温度经历快速回升、0℃附近稳定、温度持续回升3个阶段。冻结圆柱交圈是产生迅速冻胀的临界时间点,冻胀主要发生在冻结18~45 d;联络通道解冻15 d,部分土体温度达到0℃附近,冻土进入相变阶段,因此应在15 d后开始融沉跟踪注浆;入土深度越大土体相变阶段持续时间越长,粉土融沉主要发生在解冻前2个月,其完全解冻需要100 d左右,此为跟踪注浆至少应持续时间。深部土体温度、冻胀融沉位移均随深度增大呈线性递增。实测拱顶冻结壁处最大冻胀及融沉位移分别是对应地表冻胀、融沉量的3.6倍、4.9倍。地表冻胀融沉槽为联络通道中线两侧符合拟正态分布规律,其影响范围约为隧道底部埋深的1.2倍。

Whole range monitoring for temperature and displacement fields of cross passage in soft soils by AGF

Studying the temperature fields of freeze-thaw and development laws of frost heave and thaw settlement in the construction of cross passage in soft soils by artificial ground freezing method (AGF) is the premise to solve the problem of frost heave and thaw settlement. Taking the construction of cross passage in soft soils by AFG as the engineering background, the variation rules of freeze-thaw temperature, ground surface deformation, frost heave and thaw settlement of the deep soils are monitored during the whole range, then the variations of temperature and deformation of the frozen wall are analyzed. The results show that the process of freezing can be divided into five stages by temperature: rapid drop of temperature, slow drop of temperature, accelerated drop of temperature, temperature stability and freezing maintenance. But during the thawing period, the variation of soil temperature can be divided into three stages: rapid rise of temperature, temperature stability around 0℃ and sustainable rising. The frozen cylinder closed is the critical time to produce rapid frost heave, and frost heave mainly occurrs during 18 to 45 days after the start of freezing. After thawing for 15 days, the temperature of soils partly reaches that close to 0℃, then comes into the phase transformation stage. Therefore, in order to control the thaw settlement, tracing compensation grouting should be taken after 15 days from the starting of thawing. The soil phase transition process lasts longer as the soil is deeper. The thawing settlement of silt mainly occurs in the first two months since thawing, and it completely thaws for about 100 days. This is also the minimum time that should be continued for tracking compensation grouting. The temperature and displacement of frost heave and thaw settlement in deep soils increase linearly with the increasing depth. The maximum displacement of frost heave and thaw settlement at the dome of frozen wall are respectively 3.6 times and 4.9 times those of ground surface. The frost heave and thaw settlement slots of the ground surface are vertical to the center line of the cross passage, and both sides are in line with the normal distribution. The influence range is about 1.2 times the depth of the bottom of the tunnel.