Experimental Study On Strength And Deformation Characteristics Of Geogrid Reinforced Rubber Gravel

Traditional ballast track bed gravel particles rely only on rigid contact to transfer static and dynamic loads,which will cause the bed to enter the process of accelerated deterioration from the beginning of service,and the existing methods of delaying the deterioration of the bed filler(such as rubber mat type and cement type)have problems such as high cost and poor adaptability.Compared with traditional gravel fillers,rubber gravel mixes can reduce the vibration of the roadbed caused by train loads and thus reduce particle wear,but the high compressibility of rubber particles may lead to the potential problem of insufficient load-bearing capacity.However,there are few research results on geogrid reinforced rubber gravel mixes,and its reinforcement effect and deformation mechanism are still unclear.It is important to investigate the mechanical properties of reinforced composite and its influencing factors,in order to provide a reference for the engineering application and design method of geogrid reinforced rubber gravel mixes.It is expected to provide relevant references for the engineering application and design methods of geogrid reinforced rubber gravel mixes.In this thesis,indoor static and dynamic triaxial tests were carried out using GCTS large triaxial instrument,and three representative rubber-doped gravel specimens were reinforced with geogrid to analyze the effects of different reinforcement methods and different rubber dosing on the static and dynamic properties of the mixture,to investigate the reinforcement mechanism of geogrid reinforced rubber gravel mixture,and to conduct a systematic study on the strength and deformation properties of geogrid reinforced rubber gravel mixture.The main research contents and results include the following four aspects:(1)The static load triaxial test of unadulterated rubber specimens with two layers of grids and five kinds of vertical spacing of reinforcement was carried out to analyze the changes of stress-strain relationship curve,body change-strain relationship curve and damage pattern of specimens.The results show that the unreasonable vertical spacing of the bars will cause the influence zone on both sides of the geogrid to be too large or superimposed on each other,resulting in the weakening of the reinforcement effect of the specimens,but the effect on the elastic modulus of the specimens at the early strain stage is not significant.among the five different vertical spacings of the geogrid selected,the reinforcement effect of the geogrid is optimal when the vertical spacing d=150 mm.(2)After determining the optimal vertical spacing of two layers of reinforcement,the static load triaxial test was carried out on three representative rubber-doped specimens with different reinforcement layers to analyze the variation patterns of stress-strain relationship curves,body variation-strain relationship curves and specimen damage patterns,and the Duncan-Zhang model was modified by introducing the linear fitting parameter ψ.The results showed that: the increase of the number of layers of geogrid can significantly increase the peak stress of different rubber-doped aggregates and limit the occurrence of body variation.The shear damage patterns of the three rubber-doped gravel mixes showed consistent damage characteristics with the same number of reinforcement layers;the shear damage patterns of the specimens gradually transitioned from strain-softening to strain-hardening with the increase of rubber dosing,and the arrangement of geogrid in the specimens could also increase the ductility of the specimens.(3)Comparing the results of static load triaxial tests with different reinforcement layers,setting up graded cyclic dynamic loads,conducting dynamic load triaxial tests,and analyzing the cumulative plastic strain and change of backbone curve of three representative rubber-doped gravel mixes under different reinforcement layers.The results show that the reinforcement of the geogrid can improve the ability of the specimen to cope with the dynamic load to a greater extent,while prolonging the stabilization and creep phases of the specimen,delaying the generation of incremental damage of the specimen,and reducing the growth of the accumulated plastic strain of the specimen,and the reinforcement effect becomes more obvious with the increase of the number of reinforced layers.The increase of rubber doping will prolong the elastic dynamic strain phase of the specimen,but the high rubber doping will lead to the reduction of the specimen strength,which will cause stability problems,and will prolong the "overlap zone" at the beginning of the strain of the specimens with different reinforcement layers,which is not conducive to the performance of the reinforcing effect of geogrid.(4)According to the results of dynamic load triaxial test,the dynamic deformation characteristics of three representative rubber-doped gravel mixes under different reinforced layers are analyzed to explore the evolution form of hysteresis curve;with the increase of rubber doping,the hysteresis circle of the filler is more full and inclined under dynamic load,and the development law of dynamic elastic modulus and damping ratio is obtained by calculation.The results show that: rubber dosing is the main reason to influence the hysteresis curve form of rubber crumb,with the increase of rubber dosing,the hysteresis curve evolves to a fuller,more inclined and sparser form;reinforcement can improve the dynamic elastic modulus value of the composite and change its change trend;rubber dosing can change the nature of the filler and is the main reason to influence the damping ratio.