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.