突发定渗流作用下冻土温度场演化规律及判别方法

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

在人工冻结法工程中,关于地下水与冻结温度场的耦合性研究主要着眼于恒定渗流工况,而对突发定渗流工况鲜有研究。为了分析突发定渗流作用下温度场演化规律,基于相似理论建立模型试验系统,开展了单排管冻结模型试验研究,得到了突发定渗流条件下冻结壁及温度场的演化规律。试验结果显示:①突发定渗流速度vs接近恒定渗流条件下极限交圈流速vc时,上、下游未冻区温度随时间呈线性变化,当vs>vc时未冻区温度随时间呈二次函数型变化,vs越大该变化趋势越显著;②随着vs的增大,试验末期冻结壁形态逐步由偏心冻结壁向独立偏心冻土柱过渡。研究表明:①突发定渗流对温度场的作用可划分为未冻区的直接作用和冻土区的间接作用;②基于突发定渗流发生后的冻结壁形态和温度场分布特征,地层冻结过程可划分为:持续扩展、减速扩展、发展抑制、全面损伤4个阶段;③渗流发生前,土体温度梯度呈三角函数分布,渗流发生后,上游温度梯度峰值将会迅速增大,峰值位置向冻土区移动,下游温度梯度逐步趋平。根据上述研究结果发现在地层冻结过程的持续扩展和减速扩展阶段完成突发定渗流的判定,对保证工程安全、减少冷量消耗最为关键,并提出基于地层温度和温度梯度分布双准则的突发定渗流判定方法。

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 show①when 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;②with 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 that①the effect of sudden seepage on temperature field can be divided into the direct effects in unfrozen area and indirect effects in frozen area;②based 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;③before 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.