| Railway abutments constructed in complex mountainous areas are susceptible to dynamic effects such as dynamic train loads,landslide creep and rockfall impacts.Under the prolonged action of coupled loads in service,cracks,deformation and aggregate dislodgement inevitably occur in the mortar rubble structure,seriously threatening the safe service of the mortar rubble retaining slope structure.Current research is inadequate in understanding the evolutionary mechanisms of slurry block damage under complex loading.The reason for this is the lack of accuracy in the damage assessment of mortar rubble by existing testing techniques.In order to reflect the true damage state of the material under multiple loads,the damage evolution pattern and fracture mechanism of mortar rubble need to be verified from multiple macro and micro perspectives.In this thesis,a scaled-down model of mortar rubble was produced and uniaxial compression,three-point bending,durability and microscopic scanning tests were carried out to investigate the mechanical properties,fracture modes,interfacial microscopic properties and dynamic fracture mechanical properties of slurry masonry with different aggregate types and aggregate contents.In combination with digital image correlation,acoustic emission techniques and scanning electron microscopy,the macroscopic damage evolution mechanism of mortar-rock under uniaxial compression and cyclic loading and unloading was monitored and analysed.In addition,dynamic splitting tests at the mortar-rock interface were carried out to investigate the effect of interface shape,inclination angle and other parameters on the impact resistance of slurry schist structures.Innovative work results were achieved as follows.(1)The compressive strength,flexural strength and durability performance of slurry schist with different aggregate types and ratio combinations were compared.It was found that the increase in limestone aggregate could not significantly improve the flexural strength of the structure due to the insufficient linkage strength of limestone aggregate and mortar.Granite mortar rubble has a low freeze-thaw loss rate and good durability.The optimum aggregate content of granite slabs is recommended to be around 70%,at which level the mechanical properties and durability of the slurry slabs perform well.When the aggregate content exceeded 70%,the strength of the specimens did not continue to increase.(2)The influence of the pore characteristics of the aggregate on the strength and damage mechanism of the interface of the slurry chip stone was investigated,and the damage states of the microstructure of the interface zone of different aggregates before and after freeze-thaw were compared.It was found that the bonding effect of the mortar-aggregate interface was an important factor affecting the performance of the interfacial transition zone of the slurry schist,while the magnitude of the bonding force was significantly influenced by the microscopic parameters of the interfacial zone pore size such as the porosity of the aggregate,the pore size and the number of fractal cones.The interfacial porosity of the limestone slurry schist was 30.0% and the number of fractal cones was small,resulting in a significant sidewall effect,which led to the worst interfacial bond strength of the specimens.The degree and extent of the edge-wall effect in the slurry schist is clearly influenced by the interfacial pore micro-parameters such as aggregate porosity,pore size and number of fractal cones.(3)The uniaxial compression failure mechanisms of slurry schist with different aggregate types were obtained using the digital image method.It was found that:interfacial debonding is the main damage mode of mortar rubble.The interlocking strength of the aggregate and mortar is the key factor affecting the compressive strength of the material.When basalt is used as the aggregate,in addition to interfacial damage the specimens show I-II composite fracture with deflected fracture.The early warning range for the breaking load of slurry schist is a high frequency signal from160-320 k Hz.A composite factor damage intrinsic model for slurry schist was established based on the DIC and AE strain parameters,which was fitted by the test results,and the model fitted well.(4)The effect of variation in basalt fibre content on the cyclic loading mechanical behaviour of slurry schist was investigated.The influence of the variation of fibre content on the damage evolution characteristics of slurry schist was investigated using characteristic parameters such as Felicty ratio,cyclic unloading ratio,b-value,peak frequency and RA-AF value obtained from AE monitoring.The study showed that the compressive strength,energy absorption rate and toughness of the slurry schist increased with the increase of B F incorporation,which retarded the stress degradation caused by cyclic loading.the incorporation of BF changed the fracture mode of the slurry schist,and the bridging action changed the fracture mode from tensile type to I-II composite fracture.(5)Based on the interface fracture mechanics,a dynamic fracture mechanics model of the mortar-rock binary was proposed.A dynamic fracture test at the mortar-rock interface was carried out using a Hopkins rod device(SHPB)to study the effects of interface shape,interface inclination and other factors on the dynamic fracture characteristics of slurry schist.The study shows that: when the impact angle is 0?,the specimen shows shear-extension type damage of interface fracture;when the loading inclination angle is in the range of 0°-90°,with the increase of the loading inclination angle,the dynamic splitting strength of the slurry-rock keeps increasing and the interface shows compound fracture;when the loading inclination angle is90°,the specimen changes from compound fracture to type II tensile fracture.The roughness of the interface shape has a greater influence on the dynamic splitting strength of the specimens.The rougher the interface shape,the higher the interfacial splitting strength and the higher the peak load to bring the material to damage. |
PDF Full Text Request