地基-基础接触条件对复合加载模式下地基承载力特性的影响

Influence of footing-foundation contact conditions on bearing capacity behaviors of soil foundation under combined loading

为了研究地基-基础接触条件对复合加载模式下地基极限承载力及相应破坏机构的影响,在极限分析上限有限元法分析中,引入速度型刚性板单元及3结点三角形单元,分别模拟地基基础破坏时条形基础与地基的运动。根据地基-基础接触面承受法向拉应力特性,将地基-基础接触条件分成两类:能够承受一定的法向拉应力的接触条件I和不能承受任何拉应力的接触条件II,建立两类接触条件下地基与基础运动的约束列式及极限承载力数学规划计算模型,由此分析地基-基础接触条件对复合加载模式下地基承载力特性的影响,并在三维荷载空间(H,V,M)中得到相应的地基破坏包络面。计算结果表明,当竖向荷载分量值较小时两类接触条件下相应的力矩承载力及相应的地基破坏机构差异明显,而当超过竖向极限承载力的一半时,两类地基-基础接触条件下的承载力特性趋于一致。

Ultimate bearing capacity of soil foundation and its failure mechanisms are analyzed under combined loading by a strip footing,in which the contact conditions are considered between footing bottom and foundation soil.Two types of velocity elements,i.e.3-node triangular elements and a rigid-plate element,are introduced in upper bound limit analysis.The rigid-plate element is used for simulating movement of the strip footing with three components of horizontal,vertical and rotation movements.The 3-node triangular elements are used for the soil foundation.Two types of contact conditions are presented for describing contact behaviors on the footing-foundation interface.Definite tensile strength is sustained on the interface in the contact condition I,while none of tensile strength in the contact condition II.Constrain conditions are induced for movement of the strip footing and the soil foundation in the two types of footing-foundation contact conditions.A linear mathematical programming model is derived based on the upper bound limit analysis including the constraint conditions of velocity discontinuity on the interfaces of adjacent elements in the two types of footing-foundations contact conditions.Ultimate bearing capacity of soil foundation and its failure mechanisms are calculated.Based on the upper-bounds of ultimate bearing capacity,the failure surfaces are drawn in the three-dimensional load space(H,V,M).Results show that foundation bearing capacity behaviors are distinct in two types of footing-foundation contact conditions for a small value of the vertical load component V,but similar for a value of V larger than half of its maximum.