Study On The Regularity Of Crystallization And Blocking Of Tunnel Drainage System In Limestone Area

With the development of China’s western development and the deepening of urban construction,all kinds of infrastructure construction also will be accelerated,traditional bridge and road construction can not meet the rapid economy development of China,a growing number of tunnels and underground construction started.While in the Midwest of China,a lot of tunnel engineering inevitably have to through limestone areas which are rich in calcium and carbonates,make the tunnel drainage pipe form insoluble carbonate crystallization easily,blocked drain pipe,affect the life of safety of tunnel structures.At present,few researches on crystallization blocking problems of tunnel drainage system in limestone area at home and abroad,this paper relies on National Key Laboratory of bridge and tunnel and Material Laboratory in mountain area of Chongqing Jiaotong University,using the method of model experiment to analyze the factors that influence the blockage of the tunnel drainage system,The main research contents are as follows:1)On the spot investigation of the ZhongLiangshan tunnel in the limestone area of Chongqing,the ion species and concentration of ions in water samples were obtained by the analysis of the water solution in the tunnel drainage pipe.Explain the phenomenon of crystallization blockage of the tunnel drainage system of tunnel in the limestone area occurs during operation theoretically,a comprehensive analysis of the main factors leading to blockage of tunnel drainage system as well as the impact of tunnel drainage tube formation of crystalline precipitates.2)CO₂ contact surface,diameter,shape,flow rate as the main research factors,by the method of multiple single factor repeat experiments through the model test,comparative observation on dry weight change of each pipeline every 5 days.to analyze and study the influence of these four factors on the formation of crystalline precipitates in the drainage pipe.3)Through consulting a large number of domestic and foreign literatures,and referring to the experimental results,this study provides some reference suggestions for the prevention and treatment of the blocking of the tunnel drainage system in the limestone area.The main results of this paper are as follows:1)Through the analysis of the causes of blocking the drainage tunnel in limestone area system from geology,engineering,plants and microorganisms and climate,it is in the interaction of these four,which eventually led to the blockage of the tunnel drainage system in limestone area.Summarizes the influence factors of tunnel drainage tube formation of crystalline precipitates,the main factors include CO₂,temperature,pressure and hydrodynamic,water solution of pH value and the influence of other ions in the groundwater,under the combined effect of these factors and interaction,leads to crystallization of the precipitation in the tunnel drainage pipe.2)Comprehensive analysis of the experimental results,under the same of experimental conditions and other environmental conditions,the lower CO₂ content,smaller drainage pipe diameter,the smooth inner surface of the pipe,faster the flow,harder crystallization to precipitate within the drainage pipe,the slower the rate of crystallization,wherein the CO₂,pipe shape,and the flow rate of these three factors are more significant."The smaller the diameter,the more difficult the crystallization to precipitate," the conclusion is the result of model experiments only derived,but in the actual project,the drainage pipe diameter is not the smaller the better,more is need to consider other factors of blockage.3)Assume that in the course of the experiment,each ion in the solution is continuously added,to predict the time of pipe blockage under the most adverse conditions in experiments by using curve fitting expression,found in the flow rate experiment,flow rate is set to 0.198m/s,the experimental device continuously running for 164 days,the experimental pipeline will be completely blocked by crystalline precipitate.4)Referring to the experimental results and domestic research data,through optimizing the tunnel prevention structure drainage system and increase the slope of the longitudinal drainage tube in a certain extent,high scale inhibition agent is added and CO₂ fixing enzyme and the pressurized equipment physical removal method,to prevent and cure the tunnel drainage system crystallization blocking.