Study on the influence of water flow on temperature around freeze pipes and its distribution optimization during artificial ground freezing

Artificial ground freezing is usually used to improve ground and provide temporary support. However, the freezing process is dramatically influenced by water flow. Evidently, water flow with high velocity brings large heat energy that prevents the freezing of porous media around freeze pipes. In this paper, for safety and energy-saving, the influence of water flow on freezing process is simulated by a developed coupled hydro-thermal model considering water/ice phase transition and the positions of freeze pipes around circular tunnel are optimized through combining this model with Nelder-Mead simplex method based on COMSOL multiphysics platform. According to the evolution law of freezing band under well-distribution of freeze pipes, three kinds of potential frequently-used probability distribution functions are adopted to reduce control parameters and improve the efficiency of optimization program including normal distribution, Poisson distribution and chi-square distribution. The results show that the proposed combining simulation method is suitable for optimization of freeze pipes arrangement. The freezing time is significantly reduced no matter which one of the above distribution functions is employed through careful design.