岩溶管道结晶堵塞水动力-化学反应耦合模拟对比研究

Numerical simulation of crystallization blocking in tunnel drainage pipes based on dynamic mesh and level set

岩溶隧址区含水层内的高矿化度地下水渗入排水管道中,由于温压条件的改变,会导致渗流结晶从而堵塞排水管道。为定量化研究隧道排水系统结晶堵塞过程,本文首次构建了考虑管道水动力场、浓度场和化学反应场耦合的排水管岩溶水结晶堵塞模型,采用动网格和水平集方法定量刻画隧道排水系统结晶堵塞过程,开展模拟对比研究,分析温度、流速和溶液浓度等因素对结晶堵塞的影响程度。结果表明:(1)两种方法均能实现结晶堵塞过程的模拟预测,其中动网格方法建模简单,且求解精度高;水平集方法可追踪拓扑结构的变化,模拟管道完全堵塞的过程;(2)纵管内流速普遍大于横管,横管内CaCO3晶体浓度高于纵管,因此结晶堵塞主要发生于横管中;(3)温度和溶液浓度与结晶速率呈正相关关系,管内流速与结晶速率呈负相关关系。本文构建的考虑水动力-化学反应耦合的结晶堵塞数值模型可为岩溶隧道堵塞早期识别与安全评价提供技术支撑。

The complex hydrogeological conditions in karst areas lead to frequent water seepage and water gushing disasters in tunnels,which often require supporting drainage systems to prevent and control water hazards.When the karst groundwater with high salinity enters the tunnel drainage pipe,the solubility of soluble salt ions in water changes with the variation of external temperature and pressure conditions,forming saturated solution.Ions crystallize and precipitate,sticking to the inner wall of the drainage pipe,which will contribute to decreasing its flow area.If not treated,in the long run,the drainage pipe will be blocked,resulting in the increase of water pressure in the tunnel lining.Consequently,it is likely to occur a series of tunnel water hazards such as water leakage,water gushing,mud outburst,lining damage,etc.,which may seriously threaten the safety of tunnel construction and operation.For quantitative research on the crystallization blocking process of tunnel drainage system,we constructed the blocking model of karst water crystallization in drainage pipes for the first time,coupling with the pipeline hydrodynamic field,the concentration field and the chemical reaction field.Meanwhile,with methods of dynamic mesh and level set,we quantitatively expounded the crystallization blocking process in the tunnel drainage system.We also carried out a comparative study on different simulation technologies to analyze the influence of such factors as temperature,velocity,solute concentration,etc.on the blocking of crystallization.The results show that:(1)Both of the two methods can simulate and predict the crystallizing process,among which the dynamic mesh method is simpler and its solving accuracy is relatively higher,and the level set method can be used to simulate the further deposition after the topological shape has been changed(i.e.,completely blocked).(2)Crystallization blocking mainly occurs in the transverse tube,where more crystalline precipitates are developed,because the flow velocity in the longitudinal tube is generally higher than that in the transverse tube,and the CaCO_(3) crystal concentration in the transverse tube is higher than that in the longitudinal tube.(3)Temperatures and solution concentrations are positively correlated with the crystallization rate,while the flow rate is negatively correlated with it.(4)Given the coupling of hydrodynamic reaction with chemical reactions,the numerical model of crystallization blocking can provide technical support for the early identification and safety evaluation of geological hazards of karst tunnels.