深厚表土层变断面钻井井壁竖向稳定临界深度的有限元计算

在给出了深厚表土层钻井井壁竖向稳定性有限元基本理论的基础上，结合工程实例，计算出该钻井井壁的竖向稳定临界深度为635 m（其钻井井壁全深为645.3 m），表明该钻井井壁在下沉到底时存在竖向失稳的可能性.通过增加横向约束的方法，井壁的竖向稳定性可得到有效地改善.同时研究了井壁的质量、井壁上下端的约束条件和井壁底接触面积等因素对钻井井壁竖向稳定临界深度的影响.结果表明：井壁的质量与钻井井壁竖向稳定临界深度成反比；井壁上下端的约束条件对井壁的竖向稳定性影响较大；井壁底与岩面的接触面积越大，井壁的竖向稳定性越强.

Numerical simulation on vertical stability critical height of variable cross section drilling shaft in deep alluvium

Based on finite element theory of drilling shaft lining vertical stability in deep alluvium,a critical height of variable cross section drilling shaft's vertical stability was calculated by finite element method.Its critical height of vertical stability is 635 m(its total height 645.3 m).Therefore it is instability with the shaft lining sinking to bottom.Adding horizontal restriction improves drilling shaft lining's vertical stability.At the same time,the factors that influence the drilling shaft's vertical stability critical height were analyzed.The drilling shaft lining's weight is inverse ratio with its vertical stability critical height.The different boundary conditions influence its vertical stability.And the vertical stability is better with the interface area increasing at shaft bottom.