Study On Mechanical Behavior Of PVA-ECC Lining Under Concentrated Load

With the rapid development of traffic construction in China,the number of operating tunnels has increased dramatically and the problem of cracking and seepage of tunnel linings has become increasingly prominent in recent years,which is limited by the inherent defects of traditional concrete materials.In order to fundamentally solve the problem of lining cracks,it is urgent to develop new materials with better crack resistance and impermeability to replace traditional concrete materials.Engineered Fiber Reinforced Cementitious Composites(ECC)have attracted wide attention due to their high toughness,excellent crack resistance,remarkable strain hardening characteristics and good durability,but their application in tu nnel lining is relatively lagging.For preliminarily evaluating the adaptability of ECC lining in mountain tunnels,the mechanical characteristics of ECC lining are studied by means of indoor model test and the numerical simulation.The main contents and co nclusions are as follows:(1)A lining horizontal loading device was developed,and four 1/5 scale lining models of NC lining,RC lining,ECC lining and steel reinforced R/ECC lining were designed to carry out model tests on bearing and deformation performance of lining under vertical load.The test results show that compared with the traditional NC lining and RC lining,the use of PVA-ECC delays the generation of lining cracks,effectively controls the development of cracks,and significantly improves the crack resistance and crack control ability of the lining.The PVA-ECC lining exhibits a basic bearing capacity comparable to that of the conventional RC lining,which significantly improves the ductility and toughness of the lining,while the R/ECC lining has better crack control effects,and the bearing capacity,ductility and toughness are more improved.The ECC and R/ECC linings are flexible supports with initial stiffness less than conventional concrete linings but with better overall life stiffness sta bility.The smaller the formation stiffness,the more obvious the effect of PVA fiber in crack arresting and toughening in ECC and R/ECC lining,and the lining shows stronger deformation ability.(2)Based on the total strain crack model,a numerical calc ulation model for tunnel lining is established.The reliability of the numerical calculation model of the lining is verified by comprehensive comparison of numerical values and experimental results.On this basis,the load direction,material properties,f ormation stiffness and size effect are investigated,and the sensitivity analysis of the parameters of the lining stress performance is carried out.The calculation results show that the failure modes of various types of linings under different load direct ions are caused by the loss of bearing capacity due to the formation of three plastic hinges.The horizontally loaded lining damage site is more concentrated,showing higher bearing capacity and initial stiffness than vertical and oblique loading.Improvin g the tensile properties of ECC materials helps to improve the load-bearing and deformability of the lining.The change of formation stiffness obviously affects the deformation behavior of the lining after peaking.To be specific,the greater the formation stiffness,the sharper the load-displacement curve,and the larger the model size,the significantly higher the lining peak load and its corresponding displacement.At full size,the effect of formation stiffness on the mechanical behavior of the lining i s similar to the 1/5 model.Overall,material properties and formation stiffness are key factors influencing the mechanical response of the lining.