使用塑料冻结管的液氮冻结温度场试验研究

温度场分析是判断冻结土体性状进而反映冻结效果的重要手段,而盾构出洞液氮冻结加固中使用塑料冻结管对温度场的分布有较大影响。为获得使用塑料冻结管液氮冻结温度场的分布规律,以相似理论为基础,使用塑料冻结管进行上海淤泥质黏土的液氮冻结物理模拟试验,得出结论如下:沿塑料冻结管长度方向,冻结管壁的温度差别较大,造成不同位置冻结壁的发展范围不均匀,在冻结循环的末端管壁温度最高,冻结效果相对较差。冻结形成冻结区内的温度分布曲线较陡直,而在冷却区的温度分布曲线较平缓,其温度梯度较使用钢管的液氮冻结时小。在土层性质确定的情况下,液氮灌注状况、冻结管间距、冻结时间是影响液氮冻结效果的主要因素。冻结过程中,采用较小的冻结管间距,可以加快冻结速度,缩短冻结时间,发挥液氮冻结优势。研究结果表明,塑料冻结管可以应用于液氮冻结加固施工,研究成果可以为液氮冻结的工程应用提供有益的参考。

EXPERIMENTAL STUDY OF TEMPERATURE FIELD OF LIQUID NITROGEN FREEZING BY PLASTIC FREEZING PIPE

The distribution of temperature field,an essential method to judge the frozen ground and to reflect the freezing effect,will be affected when freezing pipes are used in liquid nitrogen freezing of shield tunneling setting out.In order to obtain distribution law of temperature field,the liquid nitrogen freezing model test based on the similarity theory is carried out,which is using plastic freezing pipes in Shanghai mucky clay.Conclusions are drawn as follows:Firstly,the freezing pipe wall temperature is great difference along its longitudinal direction,which will lead to an uneven distribution of frozen wall in different positions.The frozen wall have poor effect in the end of freezing system,where the freezing pipe wall temperature is higher.Secondly,the temperature distribution curve in the frozen region is more steeply than in temperature dropping area.And the temperature gradient in the frozen region of liquid nitrogen freezing by plastic freezing pipe is smaller than in steel tube freezing.Thirdly,the main influence factors of liquid nitrogen freezing effect include liquid nitrogen perfusion status,frozen pipes space and freezing time in the determination soil layer.The advantage of liquid nitrogen freezing can be found in the freezing process,such as accelerating freezing speed,shorting freezing time.The results indicate that the plastic freezing pipe can be used in liquid nitrogen freezing.The conclusion drawn from the study can provide valuable references for the practice.