Study On Surrounding Rock Stability And Support Structure Of Diversion Tunnel In Central Yellow River Diversion Project

At present,the level of tunnel construction in China has been greatly improved,but there is a lot of reliance on engineering experience,and there is a lack of necessary theoretical support for how to balance engineering reliability and economic rationality.In this paper,taking the middle Yellow River water project 2 # no pressure diversion tunnel as an engineering example,according to the modern support theory,considering the joint bearing effect of surrounding rock and supporting structure and surrounding rock load release,FLAC 3D finite difference software is adopted to establish the reasonable three-dimensional numerical model,simulation of the tunnel excavation process,the primary support and secondary lining,the stability of the diversion tunnel during the construction was analyzed and evaluate the supporting effect.At the same time,the typical tunnel section of type IV surrounding rock is selected as the research object to study the influence of the change of supporting parameters on the stability of surrounding rock of the tunnel,and the supporting effects under different supporting schemes are compared and analyzed to obtain the general rules.The following conclusions are drawn:(1)during the construction of the diversion tunnel,under the combined action of the surrounding rock and the supporting structure,the deformation of each part of the surrounding rock can meet the requirements of the code.The deformation at the side wall of the surrounding rock is large after the initial support of the type IV surrounding rock tunnel section,so it should be monitored emphatically so as to take effective support measures in time.After the initial support of the type V surrounding rock tunnel section,the surrounding rock floor is seriously deformed,so sealing measures should be taken as soon as possible to form a closed support and ensure the stability of the surrounding rock.(2)the stress concentration is obvious at the connection between the side wall and the bottom plate of the lining structure in the type V surrounding rock tunnel section,and the maximum compressive stress value is greater than the compressive strength of C25 concrete.Therefore,the lining structure should be reinforced to increase the structural strength of the connection.(3)the increase in the thickness of concrete shotcrete plays an obvious role in limiting the deformation of the side wall and arch roof,but the role in restraining the development of the plastic zone gradually weakens.The improvement of strength grade of shotcrete has no obvious effect on limiting the deformation of surrounding rock and the development of plastic zone.(4)the increase in the length of the system bolt plays an obvious role in limiting the deformation of side wall and the development of the plastic zone of the surrounding rock.However,when the length of the bolt reaches 2m,the range of the plastic zone is basically unchanged.The decrease of the spacing of the system bolts has little effect on the deformation of the arch roof and the development of the plastic zone.Only when the distance between bolts decreases to 1.25 m,the deformation of surrounding rock at the side wall will be significantly limited.(5)the increase in the thickness of the secondary lining concrete plays a certain role in limiting the deformation and plastic zone development of the surrounding rock,but when the thickness reaches 40 cm,the range of deformation and plastic zone of the surrounding rock remains basically unchanged.The improvement of the strength grade of the secondary lining concrete has no obvious effect on limiting the deformation of the surrounding rock and the development of the plastic zone.