层状地基中锚杆拉拔荷载传递非线性分析

为了研究层状地基中锚杆拉拔受力的非线性特征，引入锚固界面剪切滑移的双指数曲线模型，基于荷载传递法基本原理，建立层状地基中锚杆荷载传递的非线性微分方程，推导锚杆轴向位移、轴力和界面剪应力的解析解，并给出层状地基中锚杆拉拔受力特性的计算方法与求解步骤。在此基础上，分析拉拔荷载作用下层状地基中锚杆的荷载-位移曲线特征、轴力与界面剪应力分布特征以及锚固体埋入位置对锚杆受力特征的影响，并以工程实例检验该方法的可行性。研究结果表明：作用荷载较小时，层状地基中锚杆的轴力和界面剪应力分布特征与均质地基中锚杆的轴力和界面剪应力分布特征基本一致；作用荷载较大时，地基土层状分布特征对锚杆拉拔受力特性具有显著的影响，锚杆轴力和界面剪应力在土层分界面处具有明显的界面效应，即二者在土层分界面处分别存在明显的转折点和跳跃点；锚固体埋入密实地基层中的范围越大，锚杆的极限抗拔荷载也越大，延性也越好，实际工程中应将锚固体尽可能地埋置于硬土层之中；在锚固界面弹性黏结、塑性变形（局部软化）以及滑移破坏的整个全历程阶段，所提方法的计算结果与工程实测的锚杆荷载-位移曲线均吻合较好，反映了锚固界面剪切滑移与锚杆受力变形的非线性特征。

Nonlinear Analysis on Load Transfer Mechanism of Bolts in Layered Ground

A novel nonlinear shear-slipping model (named biexponential model) is introduced to study the nonlinear characteristics of the mechanical and deformation of bolts in layered ground soils. The nonlinear differential equation governing the load transfer mechanism of the bolts is obtained based on the basic principle of the load transfer method. Subsequently, the analytical formulas of the displacement, axial force, and shear stress of the bolts are derived, and the computational method and procedure are obtained. Then, the mechanical and deformation characteristics including the load-displacement curve, axial force distribution, and shear stress distribution are discussed. The effect of the anchorage position on the mechanical and deformation characteristics of the bolts is also studied. The validity of the proposed approach is finally verified by engineering projects. The results show that the axial force and shear stress distributions along bolts in the layered ground soils exhibit similar features to those in uniform soils when the pullout load is relatively small. However, when the pullout load is relatively large, owing to the obvious influence of the layered properties, the axial force and shear stress distributions along the bolts in the layered ground soils have interface effects, e.g. turning and leaping points. The ultimate bearing capacity and ductility of the bolts increase with the anchorage length in the compacted and hard soils. During the full-range pullout process including the elastic bonding and plastic deformation (local softening) and slipping stages, the calculated results of the proposed approach show good agreements with the measured values in the field, and characterize the nonlinearity of interfacial shear and deformation.