锚杆临界锚固长度简化计算方法

假定锚固体与周围岩土体之间剪应力呈倒三角形分布，计算出锚固体顶端弹性位移；基于锚杆抗拔承载机制及变形特性分析，锚固体周围岩土体变形分析采用与抗拔桩类似的剪切位移模型，得到锚固体周围紧贴锚固体表面岩土体的位移；然后根据锚固体与周围岩土体之间的位移协调原理，推导出了锚杆临界锚固长度的简化计算公式。工程算例对比分析结果表明，其计算结果与实测值吻合较好，且计算公式简单易记，取值明确，适用于工程设计中估算锚杆临界锚固长度。

A simplified method for calculating critical anchorage length of bolt

On the supposition that the distribution of shearing force in inverted triangular form between anchorage-body and surrounding soil, the displacement of the top of anchorage-body was calculated. Based on the analysis of pull-out bearing mechanism and deformation characteristics of bolt, which is similar with anti-floating pile, a displacement of shear mode between anchorage-body and surrounding soil was used to calculating the displacement of the surrounding soil. Then, a simplified method for calculating the critical anchorage length of bolt was deduced according to the displacement coordination between anchorage-body and surrounding soil. Comparative analysis results of two engineering examples show that the calculated values by the presented method agree well with the measured data. Furthermore, the calculation formula is a simple and easily remembered one and it has a specific value range. And it is appropriated to estimating the critical anchorage length of bolt in engineering design.