基于改进Terzarghi方法的桩网地基桩土应力计算

Calculation of pile-soil stress in pile-net composite foundation based on improved Terzarghi method

桩土应力比是桩网复合地基承载力和沉降计算的重要参数,其与地基的固结沉降相关,具有明显的时变特性。已有基于Terzarghi土拱模型的松动土压力计算理论是在滑动面土体均达到极限状态的假定上讨论的,不适用于桩网地基小变形条件下桩土应力的计算。为此,在Terzarghi模型的基础上,相对位移面摩阻力传递函数采用等刚度理想弹塑性模型,结合土体单元的平衡方程与变形协调方程,导出了桩土应力及土拱高度理论解,系统分析了桩土应力及拉膜效应随各设计参数的定量变化规律。分析结果表明,改进方法与现有土拱效应模型相比适用性较好,随着桩土差异沉降增加,土拱高度和桩土应力比逐渐增大,土拱率呈双曲线形减小,同时拉膜效应逐渐发挥。增加填筑荷载对土拱效应有显著削弱作用,桩土应力比随桩距增大而减小,随黏聚力增大而增大。结合改进方法与已有现场实测数据,分析了桩土应力的时变特性,验证了该方法的合理性,可为桩网地基桩土应力计算提供参考。

The pile-soil stress ratio is an important parameter for calculating the bearing capacity and settlement of the pile-net composite foundation,which is related to the consolidation settlement of the foundation and has obvious time-varying characteristics.The calculation theory of loosening earth pressure based on Terzarghi soil arch model is discussed on the assumption that the soil of sliding surface reaches limit state,and it is not suitable for the calculation of pile-soil stress under the condition of small deformation of pile-net foundation.Therefore,on the basis of Terzarghi model,the equivalent stiffness ideal elastic-plastic model is adopted for the transfer function of relative displacement surface,and the theoretical solutions of pile-soil stress and soil arch height are derived by combining the equilibrium equation of soil element with the deformation coordination equation.The quantitative variation of pile-soil stress and the membrane effect with each design parameter is analyzed systematically.The results show that the improved method is more applicable than the existing arching algorithm model.With the increase of pile-soil differential settlement,the arching height and pile-soil stress ratio gradually increased,and the arching ratio decreased in hyperbolic shape,while the membrane effect works gradually.The arching effect is significantly weakened by increasing the filling load,and the pile-soil stress ratio decreases with the increase of pile spacing and increases with the increase of cohesive force.Based on the improved method and the field measured data,the time-varying characteristics of pile-soil stress are analyzed,and the rationality of the method is verified.The method proposed can be used as a reference for the calculation of pile-soil stress on the pile-netted foundation.