新建小净距变电所隧道对正洞既有隧道的影响

Influence of Newly Built Short Distance Substation Tunnel on Existing Tunnel

新建与既有隧道小净距且平行的变电所隧道,研究此变电所隧道台阶法开挖过程中既有正洞隧道的位移、二衬内力变化及周边围岩塑性区的变化.通过大型通用有限元软件ANSYS模拟既有隧道,模拟变电所隧道的整个开挖过程,并进行分析.数值分析结果表明:变电所隧道的开挖将改变正洞隧道周边围岩压力,导致二衬位移增减,拱顶及仰拱发生位移较大,二衬结构的内力增大,各内力最大值均分布在左拱脚,故应对二衬拱顶、仰拱及左拱脚重点监控;整个开挖过程正洞周围未产生塑性屈服区域;值得注意的是,变电所隧道上台阶的开挖对正洞二衬位移及内力的影响明显大于下台阶的开挖,因此上台阶开挖过程应重点监控二衬各力学指标变化情况,必要时应采用改变施工参数、施工方法、加固既有隧道周围土体等施工措施.

The displacements of the existing main tunnel,the changes of the internal forces of its second lining and the changes of the plastic zones of its surrounding rock were carefully investigated as a substation tunnel parallel to the existing tunnel with a small clear distance was being newly dug with the top heading and bench method.The commercial software ANSYS was adopted for simulating the whole excavation processes of both the exiting main tunnel and the substation tunnel at work.The excavations of the substation tunnel will change the surrounding rock pressure of the main tunnel,resulting in the increase and decrease of the displacements of the second liner.The excavation of the substation tunnel will change the surrounding rock pressure of the main tunnel,resulting in an increase or decrease in the displacement of the second lining.The vault and invert have larger displacements,and the internal force of the second lining structure will increase.The maximum values of the internal forces are distributed on the left arch foot,therefore,monitoring should be focused on the second liner vault,invert and left arch foot.During the entire excavation process,there is no plastic yield area around the main tunnel.It is worth noting that the excavation of the upper bench of the substation tunnel exerts greater influence on the displacement and internal force of the second lining of the existing main tunnel than the excavation of the lower bench.Therefore,the changes of the mechanical indicators of the second lining should be the focus of monitoring in the excavation process of the upper bench.And,changing the construction parameters and methods and strengthening the soil around the existing main tunnel can be adopted in engineering when necessary.