Research On Application And Optimization Of Prestressed Anchor Cable In Large Deformation Tunnel With High Stress And Soft Rock

The large deformation of soft rock under high ground stress is one of the most serious problems of tunnel engineering,especially when the surrounding rock is mainly composed of slate and phyllite,its occurrence and bedding strength will further affect the tunnel deformation.While the traditional support method represented by shotcrete combined rock bolt is not suitable for large deformation tunnels due to the disadvantages of passive support and scant support range,how to effectively control the large deformation is an urgent problem to be solved in the field of transportation and geotechnical domestic and foreign.As the support measure for reinforcing slopes and foundation pits,prestressed anchor cables have the advantages of considerable support range and active support,as a research hot button in related fields,prestressed anchor cables support has been successfully applied in mine roadways and achieved certain results,but the support effect of its application in large deformation tunnel engineering remains to be studied.In order to study the deformation characteristics of carbonaceous slate tunnels under high ground stress and the support effect of prestressed anchor cables,the following works were mainly carried out:Through the 3D modeling software Rhino and the finite difference method calculation program FLAC3 D,the 3D modeling and its transfer of the tunnel area including the geological structure are realized,according to the measured ground stress,the inversion of the ground stress in the tunnel area is carried out,and the ground stress state of the tunnel area is obtained.The results show that most mileages of the tunnel is under high and extremely high ground stress,if the support measures are unreasonable,the large deformation is very likely to occur.Using the joint plastic constitutive model(ubiquitous model),pile structural element(pile),and cable structural element(cable)in FLAC3 D to simulate the deformation of carbonaceous slate tunnel,analysis of the relationship between deformation and carbonaceous slate stratum and the support effect of traditional rock bolts and prestressed anchor cables.The results show that the rock stratum direction and dip will affect the maximum deformation and its location of the tunnel,it is beneficial to stability when the dip is small and the direction is consistent with the tunnel axis,the rock stratum strength parameters will have an impact on the amount of maximum deformation,and the influence of the internal friction angle is most significant.Compared with rock bolt support,prestressed anchor cables can reduce the scope of the surrounding rock plastic zone and improve the internal stress state of the surrounding rock,so that large deformation can be controlled,and the cables can better adapt to the deformation of the surrounding rock and is not likely to be damaged.The prestress under the anchor cable is ascertained by the reverse pull test on site,obtain the actual prestress under the anchor cable in the project,combined with FLAC3 D to evaluate the actual support effect and optimize the original design.The results show that the anchor cable prestress has a non-negligible and unavoidable loss,leading to the increase of internal force and deformation of the lining,which is not beneficial to the stability of the tunnel.Under the condition that the initial prestress of the anchor cable is certain,the final stress of the anchor cables,the internal force and deformation of the lining all decrease with the decrease of the distance between the anchor cables,proving that under the current conditions of surrounding rock and construction technology,it can be ensured that the advantages of active support can be exerted by properly densifying the arrangement of anchor cables.Starting with two aspects of numerical simulation and field test,the influence of the occurrence and strength of the carbonaceous slate stratum on the deformation mode and amount of the tunnel under the high ground stress extrusion condition was studied,the supporting theory of the prestressed anchor cables is analyzed,and the supporting effect under the theoretical and actual conditions is compared and evaluated,then for the phenomenon of prestress loss,proposing an optimized scheme for anchor cable layout,it provides a reference for the application of prestressed anchor cables in high ground stress tunnels.