防护网与液氮冻土墙复合基坑支护技术研究

Key Technology of Composite Foundation Pit Supporting Structure of Protective Net and Liquid Nitrogen Frozen Soil Wall

结合一个具体的工程算例,对一种防护网与液氮冻土墙复合基坑的支护结构进行了温度场、位移场和应力场的数值分析,比较了低温盐水冻结和液氮冻结两种情况下温度场演变规律的差异,同时判断了该新型支护结构的安全性,主要得出:液氮冻结形成所需冻土帷幕的时间要比盐水冻结早许多;液氮冻结的冻结效果优于盐水冻结,所形成的冻土帷幕强度比盐水冻结大;计算出来的位移场值均很小;其主应力最小值也都很小,最大值为0.92 MPa;最大剪应力为0.17 Mpa;计算得出拉、压、剪应力值的安全系数均远大于2.由此最终得出的结论为:该工法安全可靠,可为今后类似工程提供重要的参考依据.

In the report, a specific engineering was used as an example to perform the numerical analysis of temperature field, displacement field and stress field of a protective net and liquid nitrogen frozen soil composite foundation pit support structure, the two conditions of low temperature brine freezing and liquid nitrogen freezing were compared, and the difference of temperature field evolution law and the safety of the new supporting structure were also judged. The results indicated that the frozen soil curtain required for liquid nitrogen freezing formation is much earlier than brine freezing;the freezing effects of liquid nitrogen freezing are better than that of salt water, the frozen soil curtain is stronger than the brine;the calculated displacement field values are small;the maximum and minimum principal stresses are also small, the maximum value was 0.92 MPa, the maximum shear stress was 0.17 Mpa;The safety factors of the tensile, compressive and shear stress values are much greater than 2, which shows that the safety reserve can be guaranteed. The method is safe and reliable, and can provide an important reference for similar projects in the future.