Study On Double-Hole Effect Of Shallow-Buried Tunnels With Small Spacing

As an economical and effective form of tunnel structure,tunnels with small spacing have been widely used in practical engineering.In the construction of tunnels in mountainous and hilly areas,in order to meet the requirements of terrain conditions,overall lines and linearity,small clear-distance tunnels with more flexible clear-distance changes are usually adopted.In the entrance and exit sections of tunnels,small-distance tunnels are usually in shallow-buried or biased state.Because of the shallow depth and small distance of the double holes,the mutual influence between adjacent caverns is obvious,and it is difficult to form a stable collapsed arch.The double-hole effect and the deformation characteristics of surrounding rock produced during the construction process are very complex.There are many factors influencing the double-hole effect of shallow-buried tunnels with small spacing during the construction process,including clear distance,buried depth,surface slope,excavation sequence,supporting methods,etc.Therefore,it is necessary to research the double hole effect of shallow-buried tunnels with small spacing under different influencing factors systematically.On the basis of previous studies,this paper systematically analyzes the influencing factors of the double-hole effect of shallow-buried tunnels with small spacing and the construction characteristics of the surrounding rock.Relying on the engineering background of the Dajinshan Railway Tunnel from Guoyao Station to Mohei Station,using numerical calculation methods,the double-hole effect of shallow-buried tunnels with small spacing are studied.The main research contents are as follows:(1)Aiming at the main influencing factors of the double-tunnel effect of shallow-buried and small-distance tunnels when the surface is level,by analyzing the distribution characteristics of the plastic zone during the construction process,the displacement field and stress field of the surrounding rock,and the deformation characteristics of the tunnel structure,The influence of the net distance,buried depth,and supporting parameters on the double-hole effect of shallow-buried small-distance tunnels when the surface is level is analyzed.(2)Regarding unbiased shallow buried tunnels with small clear distances,finite element models are established with different unbiased surface slopes as variables,and the surrounding rock characteristics under different bias conditions are analyzed.The influences of excavation sequence on the disturbance law of the sandwiched rock pillar and double-cavity effect are studied.And the effect of two working conditions of strengthening the support of the shallow tunnel and strengthening the support of the deep tunnel on the double hole effect are discussed.The research results show that the clear distance,buried depth,surface slope and supporting method all have an important effect on the double-hole effect of shallow-buried tunnels with small spacing.The smaller the net distance,the deeper the buried depth,the bigger the slope of the surface,the more obvious the double-cavity effect,and the greater the stress,the strain,and the displacement.The tunnels will keep away from each other and undergoes tensile failure and compression failure.The excavation sequence of "deeper first and then shallower" is more favorable to control the horizontal displacement inside the double tunnel,and the excavation sequence of "first shallow and then deep" is more favorable to control the settlement displacement of the vault.Strengthening tunnel support can reduce the influence of double tunnel effect on tunnel deformation.