| In order to make up for the lack ofvisualized numerical simulation of radon migration in relevant research at home and abroad,solve the problem that soil radon convective velocity is always taken as a parameter that can be neglected in radon migrationresearch,make up for the lack of research on calculation methods and influencing factors of radon convection velocity,improve the understanding of radon convection velocity.Based on the above purpose of the research,this thesis is to explore the visualized numerical simulation of soil radon migration,construct the physical modelsofthe soil cover and layered soil which areabove the foundation rock,combined with the theory of radon migration,obtain the results of visualized numerical simulationof radon migration,through the expression,solution and programming of the mathematical model,and mainly study the impact of convection on radon migration.This thesis also puts forward the calculating methodsof soil radon convection velocity,and conducts the reliability analysis of calculation results.Combined with statistical methods,the main influencing factors of radon convection velocity are analyzed,and the relationship between soil radon convection velocity and soil medium type is also studied.The results of the study showed that:1.The results of visualized numerical simulation showed that:in the soil cover which is above the foundation rock and contains anomalies,there exists an area rich in radon in each horizontal section,whose range decreases as its depth from the earth surface decreases.2.Convection has an important effect on the radon migration;that is vertical convection velocity promotes radon's ability to migrate towards the earth surface;horizontal convection velocity will laterally deflect the radon migration and it will have an effect on the distribution of radon in horizontal section.3.The soil radon's ability to migrate to the near surface increases with the increase of soil porosity;the increase of the thickness of soil cover,however,is not conducive to the process of radon migration to the near earthsurface.4.The reliability of calculation results of radon convection velocity is evaluated;radon convection velocityin Yanqing District of Beijing are positively correlated with the related coefficient of soil porosity rate,Person=0.543,p=0.007<0.05;in the area of high permeability,the related coefficient of radon convection velocity and gas permeability,Person is 0.337,which is of high coincidence degree;among all the test points,it is positively correlated with the measured atmospheric temperature,which is consistent with the theoretical analysis.5.The average calculated value of radon convection velocity in Shenzhen City is 3.91×10-6m/s,which in Yanqing District of Beijing is 1.83×10-6m/s.Shenzhen survey area is higher than that of Beijing.6.The average soil radon convective velocity in the White-Loess,Dolomitic Gray Mountain loess,Hai Tuo Mountain meadow and Clay soil is respectively:2.02×10-6m/s,2.60×10-6m/s,1.73×10-6m/s and 1.33×10-6m/s.In terms of soil texture,the convective velocity of radon in sandy soil is slightly higher than that in sandy clay mixed soil.The conclusion drawn in this thesis is as followed:1.The results of visualized numerical simulation results of radon migration and distribution can be obtained based on radon migration theory combined with corresponding physical and mathematical models and program implementation.2.Vertical convection can promote the vertical migration of radon while transverse convection can deflect radon's migration.3.Solution method can be used to calculate the theoretical value of radon's convection velocity,by which the results can be more reliable and verification results are all consistent with the theoretical analysis.4.The soil radon convective velocity is under the comprehensive influence of soil porosity,soil permeability,soil type,atmospheric pressure and temperature. |
PDF Full Text Request