Evolution of temperature field and frozen wall in sandy cobble stratum using LN2 freezing method

Abstract

There is high risk of water inrush and ground collapse when tunneling in sandy cobble stratum in confined aquifer. Among various methods, artificial freezing method is an effective method to pre-reinforce the soft ground to prevent water inrush and ground collapse during tunneling. This paper mainly focuses on application of artificial freezing method using liquid nitrogen in sandy cobble stratum in confined aquifer. The R1 metro tunnel in China’s Jinan city, a well-known City of Springs, is used as a case study. In order to prevent water inrush and ground collapse accidents in the shield machine reception process, liquid nitrogen is applied as a freezing method in the sandy cobble stratum near the reception shaft. First, the heat transition of water in soil associated with liquid nitrogen vaporization is analyzed. Then, a three-dimensional (3D) model is built and the freezing process is simulated. Considering the temperature change of gas nitrogen along the freezing pipe when flowing, the distribution of temperature field and the growth of frozen wall associated with freezing time is obtained. The numerical simulation results show that the freezing method using liquid nitrogen in the sandy cobble stratum can meet the requirement of shield machine reception in sandy cobble stratum rich in groundwater.