Temperature Field Distribution and Numerical Simulation of Improved Freezing Scheme for Shafts in Loose and Soft Stratum

This paper examines the engineering background of the main shaft of Ruihai Mining Group Company in Laizhou City, with a focus on the loose permeable stratum located in the frozen section of the shaft. Field measurements and data collection, including brine temperature and surface subsidence values, were conducted using temperature and hydrological boreholes. The distribution of the frozen wall temperature field was then numerically simulated using finite element analysis, and the results were compared and analyzed with field data. Scanning electron microscopy (SEM) was used to qualitatively describe the microstructure of the soft rock in the frozen section under different freezing schemes. Based on the formation of the frozen wall, a new construction scheme for freezing and excavating the internal and external circles of the vertical shaft in the loose permeable stratum is proposed. This involves the implementation of "inner and outer double-circles of freezing holes" and a comparison of the freezing effect of the temperature field before and after the improvement. The results indicate that the new freezing scheme can accelerate the freezing rate of the surrounding rock of the shaft, and reduce the time required for closure by more than 10 days. After applying the improved scheme for 60 days, the temperature is lowered by 4–5 ℃ compared to the original scheme, and the thickness of the frozen wall is approximately 4.8 m, significantly thicker than before. These findings demonstrate the effectiveness of adding an inner circle of freezing holes in achieving the lowest temperature which contributes to subsequent shaft excavation. The new scheme holds significant implications for the safe construction of shaft excavation in complex hydrogeological areas.