| The cracks of the reinforced concrete segment are the most important factor affecting the safety,durability,and refinement of tunnel structures.This thesis aims to investigate the formation of cracks in subway tunnel segment and dissect the damaging mechanisms of the segment structure.To repair micro-cracks in the initial stage of the tunnel segment,high-performance repair materials with high strength,low shrinkage,fast curing and high groutability are developed.Meanwhile,to address the problem of huge segment volume and operation difficulty,the huge volume segment specimens are replaced by the inclination beam and plate.The mechanical and fatigue tests before and after crack repair-reinforcement are carried out by means of inclination beam test.In addition,numerical calculations are carried out using the finite element software.The main research contents are as follows:(1)Based on the investigation and analysis of the crack characteristics of subway concrete in different sections,the cause of cracking and leakage are explored.The cracking mechanisms of concrete segments during the construction period of the subway tunnel are elucidated through the experimental research and theoretical calculation.(2)To repair the longitudinal structural cracks of the subway segment,the water-based epoxy resin modified repair materials with a high performance is developed by taking advantage of the special properties of the exposy resin repair materials.The micro-pore structures of the repair materials with different pozzolanic ratios are tested by scanning electron microscopy,infrared spectroscopy and X-ray diffraction.In addition,the adhesive,compressive and flexural strength,durability,expansion and shrinkage of the developed repair materials are also investigated.When the polymer cohesion ratio is 0.5,the repair materials display the highest fluidity and the shortest setting time.After repaired by the polymer,the mortar or concrete matrix possesses a higher bond strength.The bond strength of the concrete matrix increases by 10% ～40% at 28 days of curing,while the mortar base at the same curing age increases by 10% ～30%.The bond strength of the epoxy polymer-based repair material is lower in a dry environment than in a wet environment.Also,the shrinkage rate of the epoxy polymer is lower than that of the ordinary mortar,which decreases with the increase of the polymer content.Besides,the sulfate resistance of the polymer-modified composite is increased by 35%～55% compared with the ordinary mortar.The total pore volume and average pore diameter of the modified composite are smaller than that of the ordinary cement paste.(3)To repair the micro non-structural cracks of the segment,the acrylic copolymer emulsion modified repairing materials are developed.The fluidity,flexural strength,compressive strength and bonding strength of the repair materials with different poly-ash ratios are studied.It is found that the ratio of the poly-ash ratio and sand-ash ratio has a negligible effect on the setting time of the repair materials.As the ratio of the poly-ash ratio increases,the flexural strength of the repair materials decreases gradually.After repaired by acrylic polymer,the mortar or concrete matrix has a high bond strength.The bonding strength of the repair material is smaller in a wet environment than in a dry environment.With increasing the content of the modified mastic,the shrinkage of mastic decreases.The chloride penetration resistance of the repairing materials is stronger than that of the ordinary mortar,and their sulfate resistance increases first and then decreases with increasing the ash ratio.The results show that acrylic emulsion participates in the hydration reaction,giving rise to a more compacted structure.Based on the analysis of the pore structures,it can be concluded that the addition of acrylic emulsion is able to significantly reduce the harmful pores.(4)The inclination beams and plates are used to simulate the segment to avoid the difficulties in testing the semgment because of its large size.The epoxy resin modified repair material(HPM),HPM and GFRP are used to repair and strengthen the specimens.The mechanical behaviors of specimens with different reinforcement ratios and different cross-sections are evaluated before and after reinforcement.The secondary crack position of the specimens after repaired by HPM,HPM,and GFRP is not in the original position,indicating that HPM has a strong bonding with the concrete matrix.At the same time,HPM and GFRP repaired plate specimens can fully take advantage of the high tensile strength of GFRP cloth.After repaired by HPM,the initial cracking load of L12,L14,B12 and B14 is increased by 11%,13%,11%,and 18 %,respectively.For the same type of specimens,a higher reinforcement ratio leads to a more significant increase in the initial cracking load.After the specimens are reinforced by HPM and GFRP strip,the initial cracking load of L12,L14,B12,and B14 is increased by 39%,33%,22%,and 36%,respectively.Their ultimate load is increased by 8.3%,4.4%,5.9%,and10.5%,respectively.The ductility of the HPM reinforced beam specimens decreases to a certain extent,with a larger reinforcement ratio leading to a more significant decrease in performance.In contrast,the ductility of the plate specimens experiences undiscernable changes.(5)The fatigue performance and residual bearing capacity of the inclination beams and plates repaired by HPM and GFRP are tested.The results show that at a fatigue stress level of0.74,and the fatigue life of PB12-2 after repair is increased by 90.7% compared with that of the unreinforced PB12-1.At a fatigue stress level of 0.77,the fatigue life of PB12-2 after repair is increased by 150.1% compared with that of the unreinforced PB14-1.Interestingly,the fatigue life of the plate with a larger reinforcement ratio is improved more significantly,demonstrating that the repair material could restrain the decrease of rigidity and the damage of the concrete,which has a more signficant improvement on the inclination beam with a low reinforcement ratio.The mid-span displacement of the specimen after 5000 cycles of fatigue is still smaller than that of the reinforcement specimen.The PB14-2 specimen has the smallest mid-span displacement.At the initial stage of reinforcement,the reinforcement material has a protective effect on each specimen.As for the beam,a larger reinforcement ratio leads to a larger residual bearing capacity.It should be noted that the ductility of the specimen undergoing the fatigue test is better than that of the specimen subjected to the static test.(6)The finite element software is used to simulate the inclination plate test to verify the consistency of the experiments.The calculation results are found to be consistent with the test results.The HPM and double layer of GFRP are added to beam B12-4,while the HPM and single layer of CFRP are added to B12-5.Under a load of lower than 40 KN,the load-displacement curve of B12-4 and B12-5 basically coincides with each other.When the load is above 40 k N the stiffness of B12-5 is higher than that of B12-4,and the ultimate bearing capacity of B12-5 is most significantly increased.Compared with B12-1,B12-2 ～ B12-5respectively have a 6.2%,12.4%,40%,and 26.5% reduction in the difference of effective peak value of plastic strain.The demonstrates that the specimens strengthened with HPM+2GFRP have the highest stability.(7)The finite element software is also used to calculate the simple support plate,inclination plate,and segment specimens.The results show that the ultimate load of the simple support plate and the inclination plate is 91.7% and 101.7% of the segment,respectively.Meanwhile,their ductilities are 96.9 % and 102.2% of the segment,respectively.Moreover,the effective plastic strain of the inclination plate is more similar to that of the segment,indicating that the simulated inclination plate is more in line with the actual load bearing of the segment.The bearing capacity of the strengthened simple support plate and inclined plate is 82.6% and 84.1% of the strengthened segment,respectively,while their corresponding ductility is 90.0% and 86.1% of the strengthened segment,respectively. |
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