软弱地基隧道锁脚钢管承载特性研究
Bearing behaviors of steel foot pipes for tunnels in soft foundation
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摘要: 应用有限元方法模拟了软弱地基隧道锁脚钢管承受竖向集中荷载时的受力变形过程,研究了锁脚钢管的承载特性。锁脚钢管与围岩的接触压力主要分布在钢管外端很小区域,应力应变极值出现在钢管外端附近。随着荷载的增大,应力极值处首先进入塑性状态,钢管呈拔出破坏。对比分析了围岩强度和钢管参数对锁脚钢管承载力的影响规律,结论为:对于不能穿透软弱地基的锁脚钢管,其轴向承载力十分有限,合理下插角很小;常用的42 mm小导管直径过小,横向承载能力有限,不宜用作锁脚钢管;锁脚钢管存在一个决定于围岩强度和钢管规格的合理长度,超出合理长度后承载力不再增加;锁脚钢管应全长开孔注浆,重点加固初期支护结构附近的围岩。在此基础上,提出了锁脚钢管设计施工的方法和建议。Abstract: Numerical simulations are conducted with FEM to investigate the bearing behaviors of steel foot pipes under vertical concentrated load.When a foot steel pipe bears the vertical load,mechanical effects mainly occur at the lateral zone,and the maximum stress occurs at the lateral end of the pipes.With the increase of the vertical load,the maximum stress point turns into the plastic state firstly,and the pipes are pulled out.The influencing factors for the bearing capacity of the steel foot pipes are studied,including the strength of rock and the parameters of the pipes.Some important results different from engineering experience are as follows: 1) for the steel foot pipes that can not penetrate the soft foundation,the reasonable dip angle is very small for the low axial bearing capacity;2) the steel pipes with diameter of 42 mm are unsuitable for the foot steel pipes because of the low horizontal bearing capacity;3) under given geological conditions and pipe parameters,the reasonable length of the steel pipes is certain,and extra length of pipes can’t lead to larger capacity;4) the surrounding rock near the support structure should be especially reinforced by drilling grouting holes along the whole steel pipes.Based on those results,the design and construction methods are presented.