Research On Hollow Grouting Bolt Support Technique For The Tunnel With Soft Surrounding Rock Tunnel

Although the ordinary mortar bolt can play a supporting effect in the soft surrounding rock tunnel,it often meets the problems of insufficient anchorage force and difficulty.To control the deformation of surrounding rock,the ordinary mortar bolt can be replaced by hollow grouting bolt.The latter not only has the supporting force of the bolt,but also has the effect of the grouting pipe,which can improve the supporting effect of the weak surrounding rock.At present,there are few systematic studies on the hollow grouting bolt,and the theoretical analysis and application research need to be further studied.The research on the hollow grouting bolt relying on the engineering background and the actual excavation way of the tunnel was rarely studied.In this paper,the supporting characteristics of hollow grouting bolt are studied.Through the finite difference software FLAC3D,the supporting effect is simulated and analyzed.And the mechanical model of hollow grouting bolt,the type of hollow grouting bolt,the support mechanism of hollow anchor bolt,and the influencing factors of the grouting effect of hollow grouting bolt are also discussed.The research shows that:(1)Under the condition of grade V surrounding rock,with the burial depth 7.33?13.77m,the support effect of hollow grouting bolt to the vault is fine,the maximum displacement is not more than 8mm,the axial force of the vault bolt is distributed between 150?200kN.The hollow grouting bolt in the side wall has less displacement and the axial force.The hollow grouting bolt has good reinforcement effect on the original stratum,and the surface settlement can be controlled to no more than 2mm.(2)Under the condition of grade V surrounding rock,with the burial depth 7.33-13.77m,the hollow grouting bolt has lower vault settlement and surface settlement than the ordinary mortar bolt,and can reduce the settlement of the vault and the surface about 50%of the deformation value,hso supporting effect is good in weak surrounding rock tunnel.(3)Under the condition that the buried depth is 28.39m,the maximum value of the vault settlement is up to 1.93cm and the circumference converges to 2.66cm when the tunnel passes through the fault zone.The maximum axial force of the arch roof bolt reaches 260.68kN when crossing the fault zone,and the maximum value of the axial force of the arch shoulder bolt reaches 178.14kN,and the maximum value of the arch anchor bolt's axial force reaches 162.93kN.(4)In the soft surrounding rock tunnel with deep 57m,it is suggested that the length of the hollow grouting bolt is about 3M,which support effect of support is good.The effect of bolt support is not fully used when it is longer than 3m;when the longitudinal bolt row spacing is increased from 100cm to 125cm,the settlement of the vault has a rapid increase,and 50?100cm can be used as a reasonable bolt spacing.When the lateral spacing is less than 125cm,the axial force of bolt is smaller.Under the condition of soft surrounding rock,the reasonable spacing between anchor rods is less than 125cm.(5)In the soft surrounding rock tunnel with deep 57m,when the length of bolt is less than 4m,the deformation control is unfavorable.Increasing the length of the bolt can significantly reduce the axial force of the bolt and increase the ability to resist tension fracture.