预应力锚杆内力传递分布规律与时空效应

为了得到预应力锚杆在基坑开挖过程中受力分布特性,结合西宁火车站综合改造项目,对桩锚支护结构在不同阶段锚杆的受力特征进行现场内力测试试验,试验测得了锚杆轴力和摩阻力随时间及空间分布规律,分析了锚杆支护过程边坡潜在滑移面的动态演化规律,探讨了预应力锚杆自由段与锚固段相互关系,结果表明:未锁定时,受力增加了预应力锚杆的初始应力,对其受力不利,应严格予以控制,锁定后,锚杆摩阻力沿锚固段渐进式减小,摩阻力不断向后传递,但摩阻力峰值并未出现改变;锚杆锚固作用使得边坡潜在滑移面向深部转移,同时,滑移面剪出口沿坡脚向上转移,剪出口位于距基坑底部约H/3处;预应力锚杆自由段长度越长受力越好,但应以超出预估可能出现最终滑移面一定深度最为经济合理,在满足锚固力要求的情况下,锚固段长度存在一临界值,超过临界值则浪费。

Distribution characteristics and time-space effects of internal force of prestressed anchor rod

This paper aims to study the distribution of forces along the prestressed anchor rod during the excavation of foundation pits. A filed experiment is carried out to investigate mechanical behavior of anchor rod through a comprehensive reconstruction project at Xining Railway Station. The temporal and spatial distribution of axial forces and frictional forces is obtained. The development of potential slip plane is analyzed, and the relation between free part and anchored part of the prestressed anchor rod is discussed. The results show that, if unanchored, the initial stress of the prestressed anchor rod will be increased which is unfavorable. If anchored, the shear stress decreases steadily along the anchored part and then transports backward, but the maximum shear stress doesn’t change. The potential slip plane of slope moves deeper inward due to the effects of anchor rod. At the same time, the exit of the slip plane moves upwards from the foot of the slope, and locates at about one third the height from the bottom of the pit. On one hand, the prestressed anchor rod with a longer free length has better mechanical performance, however the one with a certain length that is enough to prevent the potential slip of slope is more economical and reasonable. On the other hand, the anchored length of the anchor rod, which provides sufficient anchoring force, is better to be short so that the anchor is economical and efficient.