Finite Element Analysis Of Surrounding Rock Support Structure Of High Temperature Deep Buried Diversion Tunnel

With the rapid development of the economy in Northwest China,the water conservancy project has also been vigorously developed.The diversion tunnel has become an indispensable part of hydropower generation.At the same time,the stability of the supporting structure in the diversion tunnel project is also one of the important issues in the current research.At this stage,the diversion tunnel is getting longer and longer,the buried depth is getting larger and larger,and the engineering geological conditions are becoming more and more complicated,which makes the requirements for the stress and stability of the surrounding rock support structure of the diversion tunnel higher.Based on the water diversion tunnel project of Qizhithaal Hydropower Station,the project uses the finite element software COMSOL Multiphysics to support the surrounding rock support of high ground stress,high ground temperature and high internal water pressure.The structure was numerically simulated.The stability of the surrounding rock support structure of the tunnel after excavation,ventilation period and over-water period are analyzed.Combined with the actual geological conditions of the project site,the surrounding rock support structure of the tunnel is carried out under the condition of simultaneous temperature and seepage.The force and deformation conditions provide a theoretical basis for the rational design and safe operation of the diversion tunnel under high stress,high ground temperature and high internal water pressure.Through the above research,the following conclusions are drawn:(1)With the excavation of the deep tunnel,the earth stress received by the deep tunnel after excavation is larger.At this time,the maximum principal stress of the tunnel is mainly at the vault and arch of the tunnel.It can be seen that with the increase of the buried depth of the tunnel,the tension at the top and the arch of the tunnel is prone to tensile failure,which should be considered in the reinforcement of the later supporting structure.(2)By separately analyzing the influence of temperature and seepage on the surrounding rock support structure of the high temperature and high pressure diversion tunnel,the coupling stress and deformation of the tunnel structure under the combined action of temperature and seepage are further analyzed.The results show that when considering the influence of seepage and temperature at the same time,the trend of temperature field and seepage field is the same as that of separately analyzing seepage and temperature,but the force effect and deformation are not a simple superposition of two action fields.Under the joint action of temperature,seepage and self-weight of the supporting structure,the tunnel supporting structure is under pressure overall,and the stress at the bottom of the hole is the largest,and there is stress concentration at the arch.Therefore,in the supporting structure of the Shing Mun tunnel,the position of the arch and the bottom of the tunnel is a disadvantageous position of the supporting structure,and the stress of the area should be paid attention to.(3)By analyzing several factors affecting the stability of the supporting structure,the results show that increasing the thickness of the supporting structure and increasing the water passing temperature can reduce the temperature tensile stress of the supporting structure and reduce the stress.The deformation is beneficial to the stability of the supporting structure;and the higher initial temperature of the surrounding rock and the larger water head increase the force of the supporting structure,causing the deformation to increase,which is not conducive to the stability of the supporting structure.of.Therefore,under the influence of different factors,how to improve the bearing capacity of the tunnel support structure is a key issue to be considered.