Study On Mechanical Performance Of High Ductility Tunnel Lining Under Active Fault Dislocation

With the rapid development of transportation construction in mountainous areas in western China,the number of tunnels crossing active faults is increasing.The permanent deformation of the stratum caused by the creeping slippage of the active fault may cause cracking,destruction and even overall collapse of the tunnel lining structure,seriously endangering the tunnel structure safety.The study on the dislocation failure mechanism of tunnel crossing active faults and the countermeasures against faults has become one of the important technical problems to be solved urgently in the construction of tunnels in the western mountainous areas.The study of the dislocation failure mechanism and anti-disruption measures of tunnels crossing active faults has become one of the important technical problems to be solved urgently in the construction of tunnels in mountainous areas in the west.At present,most of the research on the anti-breaking measures of the tunnel structure is about adopting measures such as flexible connection and setting of the shock-absorbing layer,and there are few studies that attempt to improve the anti-breaking performance of the lining structure material.In this paper,based on a highway tunnel project across an active fault zone in Yunnan Province,a model test,theoretical analysis and numerical simulation are used to carry out a study on the mechanical response and anti-breaking performance of high ductility lining under the action of an active fault.The main research contents and results are as follows:(1)Uniaxial compression and uniaxial tensile tests were carried out on the polyvinyl alcohol fiber strengthened engineered cementitious composites(PVA-ECC)to determine the axial tensile and compressive properties of ECC materials.Based on the test results and the existing research results,a constitutive model that can accurately reflect the tensile and compressive properties of ECC materials was determined.On this basis,the numerical model of the R / ECC beam was established based on the general finite element software,and the numerical simulation of the ECC beam four-point bending test was conducted.By comparing the numerical simulation results and the test results,the effectiveness of the ECC material damage constitutive was verified.(2)Based on a highway tunnel project across an active fault in Yunnan Province,a numerical model of reverse fault-rock-tunnel interaction was established.The finite element analysis method was used to study the deformation and damage characteristics of RC lining and ECC lining under different displacement distances,different fault widths,fault dip angles and surrounding rock conditions.The influence rules of two types of linings affected by different reverse fault characteristics were clarified,and the anti-fault properties of the two lining structures were compared and analyzed.The numerical simulation results show that: under the action of reverse fault displacement,the increase of fault displacement distance obviously increases the local stress of the lining and aggravates the damage of the lining.The fault fracture zone is a buffer area for lining deformation.A wider fault width delays the development of local damage to the lining and increases the limit lining distance.The greater the fault dip angle,the greater the vertical displacement component under the same reverse fault offset distance,and the more obvious the local tensile deformation of the lining,resulting in the reduction of the limit displacement distance of the lining,which reduces the resistance of the lining to fault resistance.The higher the strength of the rock mass above and below the fault,the stronger the rock mass’ s restraint effect on the tunnel,so that the lining deformation area was more concentrated,the local deformation was more intense,and the destruction of the lining structure was accelerated.Under different reverse fault characteristics,the deformation characteristics and damage failure rules of RC lining and ECC lining are similar.However,the deformation adaptability,crack resistance and anti-breaking performance of ECC lining are obviously better than RC lining.Under the above reverse fault conditions,the limit error distance of ECC lining failure was more than 3 times that of ordinary RC lining under the same conditions.(3)A dislocation simulation calculation model for crossing normal fault tunnels was established by using a numerical analysis method.The influence of fault width,fault dip angle and surrounding rock conditions on the stress of RC lining and ECC lining is studied,and the damage and failure laws and anti-breaking properties of the lining under different normal fault characteristics and dislocation conditions were discussed.In addition,the influence of fault form on tunnel lining was further analyzed.The results show that under different displacement distances,fault widths and surrounding rock conditions,the regularity of RC lining and ECC lining affected by normal fault displacement is similar to that of reverse fault displacement.As the dip angle of the normal fault increases,the limit stagger distance that the lining can bear has increased.The tensile failure characteristics of the lining under normal fault displacement are more obvious.Therefore,under the same conditions,the lining was affected more by the normal fault displacement than the reverse fault,which was manifested by the smaller limit displacement of the lining.ECC lining can better exert its advantages of strong crack resistance and good tensile toughness under normal fault fault action,so it shows significantly better deformation adaptability and anti-breaking performance than RC lining.Under the normal fault conditions involved in this article,the limit displacement distance when the ECC lining fails was more than 3 times that of the common RC lining under the same conditions.