Research On Supporting Effect Of Advanced Small Conduit In Soft Rock Tunnel

In order to avoid the phenomenon of the instability and landslides when the soft rock tunnel excavate,the arch shell is formed on the cross section of the tunnel by adopting the pre-reinforcement technology of small conduit grouting to effectively suppress the large deformation of the surrounding rock.Based on the characteristics of advanced small conduit grouting reinforcement technology,this paper relies on She Zui 1# tunnel project,it is mainly studied in the reinforcement mechanism of advanced small conduit,support effect,support parameters and the effect of combination with different construction methods by using theoretical analysis and numerical simulation method.Firstly,the Winkler elastic foundation beam theory is used to establish the mechanical model of the advanced small conduit in the process of tunnel excavation,the preliminary parameter method is used to solve the two kinds of relatively the most unfavorable mechanical model of the small conduit,and combined with engineering examples,advanced small conduit in the process of tunnel excavation is studied mechanical effects.Sencondly,using finite difference numerical simulation technology,the three-dimensional simulation of the tunnel under the conditions of no advance small tube grouting and small advance tube grouting is carried out,from the three perspectives of deformation of surrounding rock,stability of tunnel face,and initial supporting stress,the effects of grouting reinforcement of advanced small conduit are analyzed;and from the perspective of small conduit stress,the theoretical results and numerical results are compared.The results show that the control effect of the excavation of unsupported vault settlement is particularly obvious by using the small grouting pre-reinforcement technology,it can restrain the stress relaxation of the surrounding rock in front of the tunnel face and effectively keep the soil in the state of being pressed in three directions in the front,in the longitudinal direction of the tunnel face played a greater constraint,the longitudinal displacement of the tunnel face is reduced and the stability is enhanced,it can weaken the stress concentration of the tunnel arch and improve the stress state of the initial support structure;although theoretical analysis and numerical simulation are different in the results,the overall trend of the bending moment of advanced small conduit is basically the same.Thirdly,taking the vault settlement as the standard,the influence of small grouting conduit parameters is analyzed,and the correlation analysis of the parameters is further carried out on the basis of the sensitivity of each reinforcement parameter.Finally,a comprehensive analysis of the soft rock tunnel plastic zone and surrounding rock deformation under different construction methods is carried out,during the process of tunnel excavation,the vault settlement,the out-of-plane deformation of the tunnel face and the plastic zone range from the small to the large are followed by three step and seven step excavation method,core-keeping ring cut method,and full section method.From the point of view of tunnel safety construction,the combination of advanced small conduit and different construction methods are analyzed with the measurement of the vault settlement at the front of the tunnel face.