Key Parameters Analysis On Wet Spraying Machinery Nozzle And Shotcrete Quality Control Research

Shotcrete(including dry shotcrete and wet shotcrete)is a popular support method in construction of both ground projects and underground projects,such as tunnels,subways,slopes and roadway,etc.However,at present researches on the influence of nozzle structure parameters on the performance of concrete injection are insufficient.This research focuses on the influence of various parameters of nozzle structure on the evenness and dust generating,and conducts a systematic study on the flow characteristics of the concrete in the nozzle of wet spraying machinery and the quality control law,through a comprehensive research method combining theoretical analysis,numerical simulation,laboratory research and field tests.The research contains following points:First,through the study on working principle,overall structure,technical parameters,concrete flow characteristics,and pneumatic conveying theroies,the force and motion of the concrete material flow in the nozzle was analyzed and the differential equation has been established to study the motion law of the concrete material flow in the nozzle.Through the analysis of various pressure losses,the optimal pressure ratio of the concrete material flow to the air in the nozzle has been deduced,which provides the basis for the design of the wet spraying machinery nozzle and the establish of the theoretical model of the numerical calculation of flow field.Second,based on the concrete flow characteristics and nozzle technical parameters,the internal flow field of the nozzle was analyzed dynamically,and the mathematical model and numerical model of the nozzle internal flow field has been established.By using 3D modelling software SolidWorks,the mixed fluid geometric model in flow field of wet spraying machinery nozzle was established,and the mesh was divided by ANSYS ICEM.Then the flow field of the nozzle was simulated through the FLUENT software.Finally,the simulation result was introduced to Tecplot for post-processing.In order to ensure the reasonable balance between numerical calculation accuracy and computational resources,grid-irrelevant solution analysis is performed.The simulation calculation of the distribution law of the velocity in each position of the internal flow field,of turbulent kinetic energy,and of the concrete phase of the nozzle outlet cross section has been conducted.The relationship between these factors and the spray performance of the nozzle is analyzed.Third,this paper puts forward the design methord of rotating intake air misalignment angle for nozzle,with the purpose to enchance the energy change of air-concrete in mixing core.The air-concrete mixing performance in nozzle mixing flow field is studied based on the structure parameters of the wet spraying machinery nozzle.The effect of the air spraying angle in the mixing core on the mixing performance of the nozzle is analyzed when the convergence angle of the accumulating section in the front part of the nozzle is fixed.The rotational offset angle design helps to increase the mixing uniformity of the shotcrete and reduce the amount of dust at the outlet of the nozzle.In the case of ensuring the air incident angle in the mixing core is constant,the convergence angle of the nozzle convergent section is analyzed.When the convergence angle of the convergent section is less than 3°,it has little effect on spraying of concrete group;with the increase of the convergence angle,the spraying velocity of the flow decreases and the nozzle wear increases;when the convergent section convergence angle is greater than 6°,concrete outlet spraying velocity is very small,and the nozzle is easily blocked.When the convergence angle of the convergent section is 6°,the nozzle spray quality is better.Fourth,a field test study was conducted on the improved structure designed and manufactured by setting up a spray concrete impact force distribution test system.The test results and numerical simulation results have a good correspondence relationship,verifying the validity and reliability of numerical simulation.The real-time monitoring of the dust concentration at the test site found that the amount of dust generated by each nozzle sample during operation was less than the total dust and inhalable dust standards in the coal mine.When the convergence angle θ=4°,the hybrid core α=10°,β=30°,the total dust concentration and respiratory dust concentration are the minimum.The rotation angle plays a positive role in reducing the amount of dust generated in the nozzle.As the convergence angle of the nozzle convergent section increases,the dust concentration at the injection site is small.This study can enrich the theory of wet shotcrete and improve the shotcrete construction quality.