Crystallization rate model of tunnel drainage pipes in karst areas

The crystallization blockage of the tunnel drainage pipes in karst areas often threatens the normal construction of tunnels and affects operation of drainage systems. Based on basic theory of CaCO3 crystallization, this study analyses the law of the crystalline scale formation rate of tunnel drainage pipes in karst areas through three mass transfer mechanisms: convective mass transfer, molecular diffusion and wall ion reactions, obtains the calculation model of crystalline scale formation rate of drainage pipes, and verifies model by simulating crystalline scale formation tests of tunnel drainage pipes. The results show that factors such as the flow rate of karst water, the inner diameters of tunnel drainage pipes, the molecular diffusion coefficient, the dynamic viscosity of karst water, the molecular diffusion coefficient of calcium carbonate, the temperature of karst water, and the slopes of tunnel drainage pipes have certain influences on the crystallization of the tunnel drainage pipes in karst areas, and they promote or inhibit the formation of scale layers on the inner walls of the tunnel drainage pipes in karst areas by affecting the efficiency of convective mass transfer, molecular diffusion and wall ion reactions; under different test conditions, the average relative errors between the calculated results of the crystalline scale formation rate of drainage pipes and those of the pipes in the test group are 9.1%, 13.7%, 14.2% and 16.1% respectively. Considering the scouring effect of water flow on crystalline scale layers, although there are certain errors in the results, this does not affect the overall results