Analysis Of UHPC Strengthening Mechanism And Strengthening Effect Of Tunnel Lining

Over the years,the construction of tunnels in our country has developed rapidly.At the same time,a large number of existing tunnel linings will suffer from carbonization,cracking,falling off and other diseases under the long-term effects of man-made and natural actions.In view of the above problems and the ultra-high performance of UHPC,a new method for applying it to tunnel lining strengthening is proposed,and a numerical test of UHPC strengthened tunnel lining under bending state and UHPC strengthened tunnel lining under complex force conditions is carried out,which reveals the bending bearing performance of UHPC strengthened tunnel lining,determines the quantitative method of lining safety evaluation and strengthening effect,and provides a practical new idea for the actual strengthening design of the project.The main results of this paper are as follows:(1)Based on the existing research results,the appropriate UHPC,concrete,and UHPC-NC interface constitutives and parameters have been determined.Through the four-point bending test of UHPC strengthened concrete beams,the strengthening mechanism and ultimate bearing capacity of different UHPC-NC interface strength and crack depth are discussed,the influence of the failure mode,and further analyze its strengthening effect.The results show that under the premise that the UHPC-NC interface has a certain bond strength,the UHPC strengthening layer can not only significantly increase the ultimate bearing capacity of the composite beam,but also effectively improve the section stiffness and structural ductility.It is worth noting that the excessive UHPC-NC interface strength will sacrifice the partial extension of the composite beam,and the limit carrying capacity of the composite beam is more sensitive to the crack development in the early stage of crack development,so the UHPC strengthening layer should be applied as soon as possible in the actual engineering strengthening to make it more safe to operate.(2)The numerical model of UHPC strengthened tunnel lining under the action of stratum is further established,and the influence of different UHPC-NC interface strength,crack position and depth on the strengthening effect of UHPC strengthened tunnel lining is analyzed.The results show that: in addition to significantly improving the safety factor of the lining structure,the UHPC strengthening layer can also make the lining structure more evenly stressed,making full use of the high compressive strength and low tensile strength of concrete materials to avoid waste of material performance.(3)Combined with the reality of the tunnel lining of Yuntaishan,the strengthening effect of UHPC strengthened tunnel lining is analyzed,and the validity and applicability of UHPC strengthened tunnel lining are verified from the angle of the safety factor of lining structure,displacement field and yield proximity of surrounding rock respectively,which opens up a new road and new method for the design of tunnel lining strengthening in the actual project.