基于FLAC^(3D)对输电线路锚杆基础的模拟分析

Simulation Analysis on Transmission Line Anchor Foundation Based on FLAC^(3D)

锚杆作为岩土工程中广泛应用的结构构件,一直是工程师和研究人员关注的热点。FLAC^(3D)内置的Cable、Pile等线性结构单元可考虑锚杆的结构属性和摩擦特性,是较为常用的锚杆建模方式;Pile单元的轴向行为特性采用一维模型描述,粘结摩擦特征采用法向和剪切向耦合弹簧模拟,但一维线性模型很难对锚杆截面形态带来的影响进行充分考虑。为研究截面尺寸对锚杆数值模拟的影响,构建一种Pile结构单元与实体网格单元组合形成的锚杆,用Pile结构单元模拟钢筋,用实体网格单元模拟注浆体,网格单元强度参数参考Pile单元耦合弹簧的强度参数取值,构建模型后与单独采用Pile结构单元构建的模型进行了对比分析。根据数值模拟结果,单独的Pile单元锚杆模型的极限抗拔力远小于组合锚杆。经过分析发现,FLAC^(3D)软件在考虑锚杆与岩土体耦合时假定锚杆的每个节点都位于某个FLAC^(3D)网格域内(该域被称为寄宿域),锚杆节点到寄宿域各网格点的距离作为权重因子进行插值,锚杆单元节点与寄宿域网格点之间的相互联结方式、寄宿域网格节点特性等直接影响到计算结果,虽然软件计算前需设置Cable、Pile等结构单元的界面尺寸、锚固剂周长等参数,但软件对桩结构单元的体积和尺寸效应如何考虑暂时未找到相关论述。

As a structural member widely used in geotechnical engineering,anchor rod has always been the focus of engineers and researchers.The cable,pile and other linear structural elements built in FLAC^(3D)can simulate and analyze the anchor rod,which is a more commonly used modeling method of anchor rod.The axial behavior of pile structural unit is described by a one-dimensional model,and the bond friction characteristics are simulated by normal and shear coupled springs.However,it is difficult for one-dimensional linear model to fully consider the influence brought by shape of anchor rod section.In order to study the influence of section size on numerical simulation of anchor rod,this paper builds an anchor rod formed by combining pile structural unit and solid grid cells,uses pile unit to simulate reinforcement,solid grid cells to simulate grouting body,with grid cell strength parameters referring to the strength parameters of pile unit coupling spring.After the model is established,the paper makes a comparative analysis on the model constructed by pile unit alone.The numerical simulation results show that the ultimate pull-out force of single pile unit anchor rod is much smaller than that of combined anchor rod.Analysis results are as follows:When considering the coupling between anchor rod and rock-earth mass,FLAC^(3D) software assumes that every node of anchor rod is located in a FLAC^(3D) grid domain(this domain is called the boarding domain).The distance between the anchor node and each grid point in the boarding domain is interpolated as the weight factor;the mutual connection mode between the anchor rod element node and the grid point in the boarding domain,as well as the characteristics of the grid node in the boarding domain,directly affect the calculation results.Although the software needs to set the interface size,anchorage agent perimeter and other parameters of cable,pile and other structural units,the software has not found relevant discussion on how to consider the volume and size effect of pile structural units.