Study On The Rational Arrangement Of System Bolt And Lock Bolt In Bulk Surrounding Rock Of Highway Tunnel

The bulk surrounding rock loses its bearing capacity because of its loose structure,low strength and vulnerability to external disturbance.In the actual construction,the system bolt grouting support for bulk surrounding rock tunnel is often caused by the difficulty of drilling,the disturbance to the surrounding rock,the quality of grouting,the increase of construction procedure,the lag support ring and so on,which leads to the increase of dome settlement or even collapse.Many scholars believe that the system bolt should be removed in the soft surrounding rock and the feet-lock bolt support should be strengthened.Based on the background of 200 m buried deep bulk rock tunnel in Songshan tunnel,this paper studies and analyzes the arrangement of system anchor and lock foot anchor in bulk rock of highway tunnel It reads as follows:(1)According to the relevant literature,this paper analyzes the properties of bulk rock and the supporting characteristics of anchor bolt.In combination with the problems existing in the actual construction process,it is proposed to cancel the grouting of anchor bolt in the whole ring system in the tunnel of bulk rock,and to set up grouting anchor bolt at the joint of steel arch frame such as arch shoulder,arch waist and arch foot,and the bolt end is welded with the steel arch frame to fix the new bolt supporting method with locking feet.(2)According to the report of tunnel geological survey,the experimental section of tunnel bulk rock is determined by field advance geological forecast and surrounding rock classification,and the physical parameters of surrounding rock are calculated through the above information,which is used as the basis for numerical simulation of surrounding rock basic parameters.(3)FLAC3D finite difference method software is chosen as the numerical simulation tool to determine the simulation parameters and the simulation contrast scheme.(4)Based on the comparison and analysis of each simulation scheme,it is determined that on the basis of the new type of anchor bolt support mode,8 anchor bolts of grouting system are set up locally in the arch roof or 1.5 m reinforcement rings are formed by strengthening the advance small pipe grouting,Then the stress,displacement,plastic zone and mechanical state of anchor rod of surrounding rock and lining structure of the two support methods are analyzed to confirm the stability of the support scheme.(5)Based on the field comparison test,the deformation and stress change of surrounding rock at key points were monitored,and it was confirmed that under the condition of 200 m buried depth of highway tunnel,grouting of anchor bolt is cancelled,grouting locking bolt is installed at the joint of arch shoulder,arch waist,arch foot and so on.Then the stress,displacement,plastic zone and mechanical state of anchor rod of surrounding rock and lining structure of the two support methods are analyzed to confirm the stability of the support scheme.