Study On The Mechanical Behavior Of Tunnel Lining Thickness Defect And The Reinforcement Performance Of Modified ECC

The lack of lining thickness is a common defect in the process of tunnel construction,which affects the service life and operation safety of the tunnel after completion.How to reinforce the lack of lining thickness is the current research hotspot.Polyethylene Fiber-Engineered Cementitious Composite(PE-ECC),as a new cement-based material for concrete reinforcement and reinforcement,has the characteristics of high toughness,high strength and high ductility.The incorporation of sulphoaluminate cement(SAC)can improve the rapid hardening and early strength performance of PE-ECC materials.In this article,a sulphoaluminate cement modified PE-ECC material is prepared by using modern composite material theory.Through the mechanical performance test and SEM microstructure analysis of materials under different mix ratios,the influence of modified components on the compressive,tensile and bending resistance of PE-ECC materials was studied,and the optimal mix ratio of materials was determined.The model test of tunnel reinforcement with insufficient lining thickness was carried out to verify its reinforcement effect.The main research contents and conclusions are as follows :(1)ABAQUS finite element software is used to establish the calculation model of defective tunnel,and the influence of the depth and angle factors of insufficient lining thickness on the displacement and stress of tunnel structure is studied.The calculation results show that with the increase of the depth and angle of the lining thickness,the vertical displacement increases,the bearing capacity of the lining decreases.The vertical displacement at 1/2 depth is 0.2 times larger than that at 1/4depth,and the vertical displacement at 7° angle is 1 times and 0.32 times larger than that at 3° and 5°.(2)The compressive,tensile and flexural properties of SAC modified PE-ECC materials at different curing ages(1d,3d,7d,28d)were studied by cube compressive test,uniaxial tensile test and three-point bending test.The results show that the S11 group modified PE-ECC material mixed with 10% SAC and silica fume reaches40.8%,66.9% and 72.6% of the 28 d compressive strength after curing for 1d,3d and7 d,respectively.The compressive strength growth rates of 3d,7d and 28 d are 64.1%,8.4% and 37.8%,respectively.At the same time,the uniaxial tensile stress-strain curve and the three-point bending load-deflection curve of each curing age show strain hardening characteristics.The multi-crack cracking phenomenon in the tensile process shows that the bonding force between the modified ECC matrix and the fiber,the bridge between the fiber and the fiber bear the tensile load together,and have good damage ductility.(3)The fracture surface of SAC modified PE-ECC specimens after failure was analyzed by SEM electron microscopy.After adding SAC and silica fume,the micro-cracks generated in the hydration reaction of PE-ECC materials were significantly reduced,and the bonding force between the matrix and the fiber and the bridging force between the fiber and the fiber were synergistically resistant to failure.Among the PE-ECC specimens mixed with 10% SAC and silica fume,the bonding between PE fiber and cement matrix material was the best(better than the other groups).In addition,the three-point bending strength of each group of materials appeared to shrink after 28 days of curing.(4)The model test of tunnel reinforcement with insufficient lining thickness was carried out.The optimal ratio of SAC modified PE-ECC material mixed with 10%SAC and silica fume was used to reinforce the insufficient lining thickness.The ultimate bearing capacity of the lining before and after 1d,3d,7d and 28 d reinforcement was 4.7%,11.2%,22.8% and 30.7% respectively.