高应力地下洞室顶拱深部变形及受力特性研究

Research on Deep Deformation Characteristics of Roof Arch and Loading Variation of Unboned Pre-stressed Cable at Large Underground Cavern with High Geostress

为探讨高应力条件下顶拱深部围岩出现的收缩受力特征,采用位移分析法讨论上游侧顶拱在开挖过程中产生的收缩变形,根据弹塑性理论定性分析顶拱深部收缩变形产生机制;采用回归分析讨论了收缩变形区无黏结锚索预应力特征及其与围岩变形的关系。研究表明,围岩变形在顶拱呈显著空间分异特征,收缩应变出现在上游侧,沿厂房轴线的分布范围与钻孔深度成正比。收缩应变集中在距洞壁10 m范围内,量值随深度增加而递减。开挖引起应力重分布使顶拱深层产生拱效应区,上游侧顶拱深层围岩位于"拱座",其受力为沿顶拱径向加载,产生收缩变形;下游侧顶拱为卸荷松弛区。收缩变形区与洞室尺寸相关,在开挖初期收缩变形区向深部演化,相对浅部围岩收缩应变减弱,甚至转为拉伸应变。锚索预应力变化经历3个阶段,"0"承载期、"阶跃"增长期及收敛期。收缩区范围超过锚索加固深度时,预应力接近锁定值,钢绞线只承受预拉荷载。锚索预应力损失率主要受深部围岩拉伸应变影响。

In order to explore the characteristics of those deformation induced deep in surrounding rock of the roof arch, a Displacement Analysis on the distribution features was carried out, as well as the development. Based on the elastic-plastic theory, the mechanism of deep shrinkage deformation of top arch was qualitatively analyzed. Then the loading variation of Unboned Pre-stressed tension stress, where the shrinkage occurrs, was discussed by analyzing the correlation between Pre-stressed tension stress and rocks strain. The research shows that rocks strain is in strange asymmetric distribution during the early excavation, the shrinkage strain appears in the upstream side, and the distribution range along the powerhouse axis is directly proportional to the drilling depth. Shrinkage strain occurrs in the range of 10.0 m far away from the wall, and is weaken in depth. The stress redistribution caused by excavation causes the arch effect area in the deep layer of the crown arch. The deep surrounding rock of the crown arch on the upstream side is located in the "arch seat", and its stress is loaded radially along the crown arch, resulting in shrinkage deformation. The downstream side crown is the unloading relaxation area. The shrinkage deformation zone is related to the size of the cavern. At the initial stage of excavation, the shrinkage deformation zone evolves to the deep, and the shrinkage strain of the surrounding rock in the relatively shallow part decreases, or even turns to tensile strain. The variation of cable stress go through three stages, including “0” load bearing, rising in step, and convergence. The value of the cable stress was approximate to pre-stressed tension one and the steel strand only bears the pretension load when the depth of Shrinkage zone beyond the anchor depth. The pre-stress loss rate was mainly affected by tensile strain of reinforced rock mass.