土钉抗拔承载力计算方法

Calculation method of pull-out bearing capacity of soil nail

土钉抗拔承载力是影响土钉设计的关键指标,规范给出的计算方法具有较大的随意性。土钉的极限抗拔承载力受到钉土界面强度、土钉周围土体强度、上部土压力以及土钉杆体材料等因素的影响,本文根据不同情况把土钉拉拔的破坏方式分为4种:(1)沿钉土界面上发生的圆柱形剪切破坏;(2)沿土钉周围土体内部发生土体形剪切破坏;(3)破坏面部分位于钉土界面部分位于土钉周围土体的复合剪切破坏;(4)由于土钉杆体材料屈服发生的破坏。基于摩尔库伦准则,假定土体中侧向压力沿土钉杆体方向线性变化,本文推导了发生土体剪切破坏、复合剪切破坏时的土钉抗拔极限承载力计算公式,通过计算实例表明在大多数粘性土中土钉极限抗拔的破坏方式为土体剪切破坏。

Pull-out bearing capacity of soil nail is a key parameter of soil nailing design, the calculation method supplied by the standard is too romantic. Pull-out bearing capacity of soil nailing is primarily controlled by interface strength of soil and nail, soil strength around the soil nail, soil press from upper soil and material strength of soil nail. Based on the different conditions, the styles of soil nail pull-out failure can be classified as column shear failure on the interface between soil nailing and soil, soil shear failure around soil nail, composite shear failure and material yield failure of soil nail. Based on Mohr-Coulomb criterion and the hypothesis that the lateral soil press along soil nail is linear, the calculation formula of pull-out bearing capacity of soil nail are developed when soil shear failure around soil nail and composite shear failure happen. Two engineering cases illustrate that the soil shear failure around soil nail happen in most cohesive soil.