Study on Mechanical Characteristics of Close Construction of Deep Buried Ultra-Small Clear Distance Tunnel
In order to investigate the mechanical characteristics of close construction of the tunnel with the thickness of medium rock column less than 2 m without secondary lining,the deformation of surrounding rock and the stress characteristics of supporting structure of the close construction of ultra-small clear distance tunnel are studied by numerical simulation and field test.The results show that:(1)when the first tunnel is not lined with secondary lining,the influence of adjacent construction is significant,and the deformation of surrounding rock of the first tunnel caused by the construction of the second tunnel accounts for 43%of the total deformation;the excavation of the rear tunnel causes the deformation and internal force of the first branch of the front tunnel to show obvious bias effect,that is,the convergence deformation and the increase of structural internal force near the middle rock column are much larger than those on the outside.(2)The stress of the initial steel arch can be roughly divided into four stages:the excavation influence section of the first tunnel,the middle stable section,the excavation influence section of the rear tunnel and the late stable section.During the construction process,there are large tensile stresses in the left and right arch feet and invert parts of the first tunnel,which should be paid attention to during construction.(3)The deformation and internal force of the initial branch are taken as the necessary items to be measured when the first tunnel is only used for primary support.The change law of the deformation and internal force of the initial branch are grasped dynamically and the control measures are taken in time to ensure the construction safety and avoid the damage of the secondary lining structure of the first tunnel by blasting of the rear tunnel.
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