Evolution of ground freezing temperature field under sudden seepage with stable flow rate and discriminate method of seepage

In the research field of artificial ground freezing,most of studies about the coupling of groundwater flow and temperature field focus on constant seepage conditions,limited studies consider sudden seepage with stable rate flow.To analyze the evolution law of temperature field under sudden seepage with stable ratio,the model test on single-row pipe freezing was established and carried out in this study.The evolution law of frozen curtain and temperature field under sudden seepage with stable ratio was obtained.The model test results show ① when the velocity of sudden seepage (vs)close to the critical closure velocity (vc),the temperature in the upstream and downstream unfrozen areas changes linearly with time.However,when vs>vc,the unfrozen area temperature changes with time as a quadratic function.This trend becomes obvious as the increase of seepage velocity; ② with the increase of vs,the frozen curtain shape changes from eccentric frozen curtain to independent eccentric frozen column at the end of experiment.Also,the study demonstrates that ① the effect of sudden seepage on temperature field can be divided into the direct effects in unfrozen area and indirect effects in frozen area; ② based on the frozen curtain shape and temperature field distribution characteristics,the freezing process can be divided into four stages:continue expansion stage,decelerating expansion stage,inhibition development stage and total damage stage; ③ before seepage occurs,the temperature gradient of the soil is distributed as a trigonometric function.After seepage occurs,the temperature gradient peak in upstream will increase rapidly,and the position of peak will move to the frozen area.The temperature gradient in downstream will level off.According to the above results,the most important measure to ensure engineering safety and reduce cooling consumption after seepage occurs is to assess the occurrence of sudden seepage in continue expansion stage and decelerating expansion stage.Therefore,the assessment method based on the double criteria of temperature and temperature gradient was proposed. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.