锦屏一级水电站左岸高陡边坡卸荷岩体采用压力分散型无黏结预应力锚索作为主要支护方式,由于锚索吨位大、间距小,卸荷岩体在锚固力作用下出现较大压缩变形,相邻锚索相互影响导致锚固预应力损失,群锚效应显著。为研究卸荷岩体中的群锚效应,根据相似理论制作了卸荷岩体相似材料模型,进行了群锚加固物理模型试验,结合试验数据和Mindlin解分析了岩体的位移、变形、锚固力叠加效应及锚索预应力损失。研究结果表明卸荷岩体中的群锚效应主要包括:①锚索引起的应力叠加对卸荷岩体具有显著的压缩效应;②锚索张拉造成邻近锚索的预应力损失。最后通过试验分析和理论推导得出了群锚作用下岩体的位移及锚索预应力损失率的计算方法。研究认为,合理设置锚索间距和适当增加锚索长度能有效地减小群锚效应造成的锚索预应力损失,并在实际工程中得到了验证。

Pressure-distributed unbonded prestressing anchor cable is the major support for the strongly unloading rock mass in the left-bank high and steep slope of Jinping Hydropower Station. Large anchoring force and small spacing of the anchorage gave rise to notable compressional deformation of the rock mass; the mutual influence of anchor cables led to massive prestress loss. A physical model test on the anchoring of unloading rock mass was carried out to examine the displacement and deformation of rock mass as well as the superposition of anchoring force and prestress loss in association with Mindlin’s solution. The anchor group effect mainly includes 1) the compression of unloading rock mass posed by stress superposition; 2) the prestress loss of anchor cable caused by tensions on adjacent ones. Furthermore, the calculation methods of rock mass displacement and prestress loss rate were obtained via experimental analysis and theoretical derivation. Reasonable spacing of anchor cables and appropriate increase of anchor cable length can effectively reduce the prestress loss caused by group anchor effect.