隧道分部开挖的围岩松动区演变分析

Evolution of loosened zone of surrounding rock for tunnels constructed by multi-partition excavation method

以乌蒙山二号四线铁路隧道为工程背景,通过数值模拟手段对比研究分部开挖与一次成洞的松动区形态和大小差异,再结合现场测试结果,分析隧道分部开挖的松动区演变规律。结果表明:一次成洞松动区范围要普遍大于多部开挖的最终松动区范围,最大径向松动深度高出12.6%,最小径向松动深度高出41.2%;在松动区分布形态上,一次成洞表现为左右基本对称,多部开挖具有一定的不对称性,且多部开挖基本是从拱顶到边墙部位依次减小,而一次成洞则呈"拱顶>拱脚>拱肩>边墙"的分布形式。多部开挖时,先挖部分的松动区随着后续开挖部的推进有所增加,后挖部对先挖部的影响表现为:"上下关系"强于"左右关系";另一方面,左右对称位置后挖侧松动区略大于先挖侧,说明先挖部对后挖部亦有劣化作用;其最终松动区是各开挖部相互影响和发展的结果,体现过程相关性。

Based on Wumengshan No.2 railway station tunnel with four tracks,numerical simulation is performed to comparatively study the differences of loosened zone between multi-partition excavation and full face excavation.Based on the field monitoring data,the evolution of loosened zone by multi-partition excavation is analyzed.The results indicate that:from the viewpoint of thickness of loosened zone,the full face excavation makes it greater than the multi-partition excavation does,with the maximum value being 12.6% greater and the minimum value being 41.2% greater.From the viewpoint of distribution of loosened zone,the full face excavation makes it generally symmetrical,but the multi-partition excavation does not.Besides,for the multi-partition excavation,the thickness of loosened zone decreases from the crown to the side wall,but for the full face excavation,the thickness has a distribiotion of 'crown > arch toe > arch shoulder > side wall'.For the multi-partition excavation case,the loosened zone near the earlier excavated part will increase owing to the later excavation of other parts.This influence of 'up and down position' is greater than that of 'left and right position'.Furthermore,for the left and right position,the loosened zone near the later excavated part is little greater than that near the earlier excavated part.This makes it clear that the earlier excavation has deteriorating effect on the later excavated part.The final loosened zone is the result of excavation interaction of all parts,so it is highly process-related.