格栅碎石桩加固软基的机理及计算方法

格栅碎石桩是碎石桩应用于软土地基加固的特殊形式．为了保证软土地基中碎石桩的承载力，对格栅的强度应有一定的要求，即格栅受到的环向拉力不能达到或超过其抗拉强度极限值，否则会导致格栅失效，影响加固效果．基于弹性力学的基本假定通过受力分析提出了计算碎石桩中应力及格栅环向拉力的简化算法，采用有限元模拟法与简化算法分别对算例进行分析，阐述了两种算法所得结果的异同点，验证了简化计算法的可行性，进而分析了各种因素对碎石桩及格栅中应力的影响．研究表明基础刚度对碎石桩及格栅中应力的分布有较大影响；格栅的存在对于提高碎石桩的承栽力效果显著；当上部荷载增大时格栅受到的环向拉力有可能达到其极限抗拉强度．

Mechanism and Calculation Method of Geogrid Gravel Pile in Soft Soil Foundation Improvement

Geogrid gravel pile is a particular form of gravel pile used in soft soil foundation improvement. In order to ensure the bearing capacity of gravel pile in soft soil foundation,the strength of geogrids should meet certain requirements ,namely, the loop tensile stress of the geogrids should not reach or exceed its tensile strength limit. Otherwise,it will lead to failure of the geogrid and even of foundation of the gravel piles. Based on the basic assumptions of elastic theory and force analysis ,a simplified method was established to calculate the gravel pile stress and the loop tensile stress of the geogrids. Meanwhile,a finite element method （FEM）was applied. The analyzing results with the proposed method and with FEM were compared, which proved the feasibility of the proposed method. Furthermore ,the influences of factors on stresses in the gravel pile and the geogrid were analyzed. Analyzing results show that the foundation stiffness has a great impact on the stress distributions of the gravel pile and the geogrid. The existence of geogrid can significantly improve the gravel pile bearing capacity and the loop stress in the geogrid might reach its ultimate tensile strength when the upper load increases.