Investigation On Flow Characteristics Of Wet Concrete Conveyed By Compressed Gas And Anti-blocking Of Pipeline Vibration

Currently,the technology of concrete spraying mainly includes dry shotcrete and wet shotcrete.Because wet spraying has many advantages such as low rebound rate,low dust concentration and high concrete strength after spraying,it has been gradually promoted in actual engineering.There are two mainstream transportation methods of wet shotcrete,namely pumping and compressed gas transportation(hereinafter referred to as air conveying).Compared with the pumping method,the method that uses compressed air to transport concrete through pipelines has the advantages of simple system structure,high construction efficiency and convenient pipeline cleaning,but there is a problem that the pipeline is easy to block.Therefore,in order to solve the above problems,field test,numerical simulation,laboratory experiment and other methods are used to conduct research in this paper.The main research contents are:firstly,the concrete spraying effect of various working conditions on the site,the flow characteristics of the mixture during the air-conveyed concrete transportation process in the pipeline,and the blocking mechanism and flow characteristics were systematically analyzed and studied;secondly,a method for solving pipeline blockage was proposed and corresponding simulation exploration was carried out;then,a distributed pipeline vibration anti-blocking device was developed,and subsequent indoor tests were carried out using this device,and apply it to the air-conveying onsite spray test to detect the improvement effect of its vibration and anti-blocking.Finally,the influence of the stiffness coefficient of the tension spring in the vibration anti-blocking system on the vibration response of the pipeline is explored through numerical calculation methods.The main research results of this paper are as follows:(1)Considering many factors such as the length of the conveying pipeline,the inner diameter of the pipeline,and the material of the pipeline,the air-conveying onsite wet spraying concrete test was carried out systematically,and the spraying effect and spraying quality of concrete under various working conditions were obtained.Through the analysis of the test results,it is concluded that the current problems of the air conveying wet spraying method and the main factors affecting the effect of the air conveying wet concrete spraying have laid the foundation and direction for the followup research.(2)The analysis of concrete flow characteristics in the pipeline is carried out based on the method of computational fluid dynamics,and the influence of different working condition parameters on the flow of concrete in the pipeline is obtained,and the mechanism of concrete blockage in the pipeline is qualitatively analyzed.(3)Based on the actual engineering,a numerical calculation model for the secondary air refilling of the pipeline was established,and the influence of the air filling angle,the air pressure of the secondary air filling and the air filling position on the concrete flow in the conveying pipeline was respectively explored.At the same time,the working conditions of multi-point secondary aeration are considered.First,the effective influence range of single-point secondary aeration is explored,and then the influence of the number and spacing of secondary aeration points on the flow of concrete in the pipeline is explored.Finally,the optimal layout plan of the gas filling pipe is present.(4)A distributed pipeline vibration anti-blocking device was invented.Based on this device,an indoor vibration anti-blocking test of concrete conveying hoses was carried out,and the law of pipeline vibration under the action of excitation force was obtained.On the basis of the vibration response under the action of a single pneumatic hammer,the influence law of the system air pressure,the number and arrangement of pneumatic hammers on the vibration response of the pipeline are respectively explored.5)Based on the dynamic model of the pipeline system,the law of pipeline vibration attenuation under the action of excitation force was obtained,and the results of the indoor vibration test were verified;at the same time,the stiffness of the tension spring in the distributed vibration anti-blocking system was explored The influence of the coefficient on the vibration of the pipeline,and the functional relationship between the stiffness coefficient and the vibration response is established.The research results of this paper can provide an important reference for solving the problem of pipe blockage during the process of wind conveying concrete.Finally,the device was applied to the on-site concrete spraying experiment,and the effect of the device on improving concrete sticking to the wall and the anti-clogging in the pipeline was explored.The results showed that the device can effectively solve the problem of pipeline blockage during the process of spraying wet concrete by compressed gas.There are 106 figures,20 tables and 136 references in this paper.