深厚表土中冻结壁与井壁相互作用的数值分析

冻结壁对井壁的作用力构成了深厚表土中冻结井外层井壁的外载；其增长规律与冻结壁与井壁之间的聚苯乙烯泡沫板压缩性能密切相关。为研究深厚表土中冻结井外壁外载的取值方法,以华东某冻结凿井工程为背景,基于冻土的弹塑性及蠕变本构方程,开展了冻结凿井过程中冻结壁与井壁相互作用的数值分析。结果表明：冻结壁对井壁的流变作用力极为显著；泡沫板的存在及其压缩性,可显著降低冻结壁作用力,尤其是弹塑性及流变作用力P_epc的数值,并影响其增长速度及增长规律；随着泡沫板压缩性降低直至泡沫板取消,冻结壁作用力由低速、近似线性增长,变为高速、非线性增长,从而易对井壁的早期安全构成威胁。因此,冻结凿井工程设计与施工中,应针对冻结壁的流变变形特性,审慎地研究确定泡沫板的材质及厚度。

Numerical analysis of interaction between freezing wall and shaft lining in deep alluvia

The load of outer shaft lining during freeze sinking mainly originates from the interaction between the freezing wall and the outer shaft lining, whose growth greatly relates with the compressibility of polystyrene foam board between them. In order to study the load in deep alluvia, taking a freeze sinking project in East China as the background, the interaction between the freezing wall and the shaft lining is studied by adopting the elastic-plastic and creep constitutive models for frozen soils. The results show that there is significant rheological interaction between the freezing wall and the shaft lining. The existence of foam board and its compressibility significantly reduce the value of the interaction pressure, especially P_epc and affect its growth rate and growth rule. During the gradual decrease of compressibility of foam board until the cancelation of foam board, the interaction pressure first approximately linearly grows at low speed, then gradually nonlinearly grows at high speed, and it will pose a threat to the early safety of shaft lining. Therefore, in the design and construction of freeze sinking, the foam materials and thickness should be carefully studied and determined based on the rheological characteristics of freezing wall.