Study On Applicability Of Construction Schemes For Expressway Tunnel Shafts Under Different Working Conditions

As the expressway tunnel becoming larger,longer and deeper,ventilation in the tunnel is becoming more and more difficult.Shaft ventilation is one of the commonly used ventilation methods in tunnel engineering.The construction scheme is subject to the hydrogeological conditions of the tunnel site.The shaft diameter and excavation depth are affected by many factors.Therefore,under different geological and engineering conditions,the construction scheme adopted by the shaft engineering is not the same.Based on the smoke shaft of the Yingerling Tunnel in the Hebei section of Rongwu Expressway,the general finite element analysis software Midas GTS NX was applied in this paper.The three-dimensional shaft model was used to simulate the construction process of the Yingerling tunnel smoke exhaust shaft.Based on the simulation results,combined with the actual site survey data,the applicability and safety of the construction scheme are analyzed;and it provides a certain reference value for the shaft engineering under similar geological and engineering conditions.The main research contents and conclusions are as follows:(1)Numerical simulation of the actual construction scheme of the smoke shaft of Yingerling Tunnel is carried out,and the stability of shaft surrounding rock and initial support during construction is evaluated based on the simulation results.The results show that the stress concentration of the surrounding rock at the junction of the bottom of the shaft and the connecting transverse hole is obvious,and the plastic zone is prone to occur.The support strength should be strengthened during the construction;the maximum vertical direction of the surrounding rock around the shaft during the excavation of the shaft Both displacement and horizontal displacement are within the normal control standard of surrounding rock displacement;the surrounding rock stress of the shaft section is positively correlated with the excavation depth,but the maximum stress value is lower than the uniaxial compressive strength of the surrounding rock;Significant stress concentration will occur at the rock grade change,and the support strength should be appropriately strengthened during the construction process.Based on the above analysis,the construction plan of the smoke shaft of Yingerling Tunnel is applicable to the shaft construction under its geological conditions and has certain safety.(2)Based on the construction scheme of the smoke shaft of Yingerling Tunnel,the control variable method is applied to select the two diameters of shaft excavation diameter and depth,and the application of the construction scheme of the smoke shaft of Yingerling Tunnel under different working conditions is studied.When the control variable is the diameter of the shaft,three cases with shaft diameters of 5m,7.5m and 10 m are selected.The stability analysis of the surrounding rock and initial support during the construction process is studied by comparative analysis.The analysis results show that: Under similar geological conditions,when the shaft excavation depth is less than 100 m,the construction scheme of the smoke shaft of Yingerling Tunnel can be applied to the shaft project within 7.5m in diameter.When the control variable is the depth of the shaft excavation,the depth of the shaft is selected as In the three cases of 100 m,300m and 500 m,the stability of the surrounding rock and initial support during the construction process was studied by comparative analysis.The results show that: Under similar geological conditions,when the shaft diameter is less than 5m,the construction scheme of the smoke shaft of Yingerling Tunnel can be applied to the shaft project within 300 m of excavation depth.