潜孔锤冲击作用下土体变形的有限元分析

潜孔锤冲击挤密钻进过程中周围土体的变形机理是一个高度非线性问题。针对潜孔锤在土中的面-面接触问题,运用Drucker-Prager屈服准则为判据,将土体视为DP材料,通过钻具与土之间的接触及施加冲击载荷来模拟钻进过程,从而建立了潜孔锤在土中冲击挤密钻进的有限元模型。利用非线性瞬态动力学有限元分析手段,对钻进过程中冲击力对土的作用加以研究,分析了钻具周围土体的应力、应变以及钻具与土体的摩擦情况。结果表明,在冲击载荷作用下,锥形钻头前端土体应力集中,并形成应力泡,冲击功主要用于竖向压缩土体,而水平方向的挤压作用相对较小,摩擦应力在钻头锥面附近出现峰值,是影响钻进速度的主要原因之一。

Finite element analysis of soil deformation subjected to the percussion of downhole drills

The soil deformation mechanism is a complicated nonlinear problem in the percussion-extruding drilling process of downhole drills. As of the contact problem of downhole drills to soils, the author in this paper establishes a finite element analysis model that uses downhole drills for percussion-extruding drilling in soil on the basis of adopting the Drucker-Prager yield criterion, taking soil as DP materials, and simulating the drilling process according to the contact and press load of drilling tools to soils. Based on the finite element method of non-linear transient dynamics, the impact force of downhole drills to soils is studied and the stress and strain of soils around the drilling tools and the friction between drilling tools and soils are analyzed. Research results show that there are stress concentration bulbs near the cone bit, and the impact energy is mainly used to compress soils in vertical direction while the compress effect is smaller in horizontal direction. The peak value of the frictional stress is located near the bit cone surface, which is one the main factors affecting drilling speed.