Study On Experiment And Numerical Simulation Of Collision-rebound Of Wet-mix Shotcrete

Compared with the dry-mix concrete,the material ratio control of the wet-mix shotcrete technology is accurate,and the strength and quality of the spray layer are higher.It is the main development direction of the shotcrete process of the anchor spray roadway.However,due to the limitation of the wet spraying process and the operation conditions of the roadway,the rebound caused by the construction of the wet-mix shotcrete is more harmful in the deep roadway and narrow range.Among them,the rebound seriously affects the support strength,resulting in a decrease in the proportion of coarse aggregate,and at the same time,the uneven distribution of aggregate at the interface is likely to cause structural defects,increasing the risk of shrinkage,cracking and debonding at the interface.What' s more,the materials are sputtered to produce dust,the flow entrainment and air flow disturbance cause the spattered dust particles to diffuse to the working surface,increase the dust concentration of the working surface,and the high silica content of the spray dust,which causes serious damage to the physical and mental health of workers.This thesis is mainly aimed at the special field of underground wet-spray concrete operation.From the layer of concrete aggregate particle and the particle flow spray,the theory and experiment of the rebound of concrete aggregate particles,the coupling simulation of the particle flow spray and the new concrete rheology affects the performance of the rebound of concrete is done,respectively.A comprehensive and systematic study on the whole process of wet-spraying concrete wall slamming,adhesion,rebound and deposition is also done.The research content mainly includes the following three aspects:1.By constructing the experimental platform of shotcrete collision-rebound,combined with the theory of viscoelastic mechanics,using high-speed camera to analyze the movement process of wet-spraying concrete aggregate particle rebound.Through the single-particle aggregate collision-rebound experiment,based on the particle velocity change and energy dissipation law are analyzed,and the aggregate particle rebound calculation model is established to obtain the aggregate rebound dynamics criterion.2.Through the analysis of the working principle of the wet spray machine,the nozzle structure,the jet parameters,the concrete flow characteristics and the injection characteristics,using the finite element and discrete element coupling method,combined with the corresponding control equations and the relevant theoretical knowledge of high pressure wind transport.The dynamic pressure and velocity variation of gas phase(continuous phase),the trajectory and distribution of particles(discrete phase),the velocity field distribution of particles with different particle sizes and the mechanical behavior of particle collision are obtained,which reveals the factors affecting the stability of wet-mix shotcrete.3.Combined with different types of concrete additive components,the rebound test of wet-sprayed concrete based on different types and different admixtures was carried out to investigate the rheological characteristics of fresh concrete affect the shotcrete characterisitcs.The variation of rheological properties(yield stress,plastic viscosity,gas content,bleeding rate,etc.)of fresh concrete affects the rebound characteristics and the relationship between the rebound and the energy dissipation law.On this basis,the multiple linear regression equations of the rheological properties and the rebound rate of the shotcrete are obtained.