河间隐伏型岩溶裂隙含水系统演化的数值模拟

Numerical simulation for the evolution of covered karst fissure system between rivers

为揭示隐伏型岩溶含水系统在不同边界条件与介质特征下的发育状况,基于地下水渗流和碳酸盐岩溶蚀理论构建耦合裂隙网络渗流与碳酸盐岩溶蚀的岩溶裂隙网络溶蚀扩展模型,模拟再现了河间隐伏型岩溶含水系统平面上发育演化过程。结果显示:岩溶系统发育过程中流量变化呈现三个阶段:第Ⅰ阶段为缓慢层流阶段,流量增速为2.2×10^-6 mL⋅(s⋅a)^-1,持续时间与初始水头差呈对数关系;第Ⅱ阶段为极快速紊流阶段,流量增速为5.5×10^2 mL⋅(s⋅a)^-1,持续时间与初始水头差呈线性关系;第Ⅲ阶段为快速紊流阶段,流量增速为26 mL⋅(s⋅a)^-1。优势裂隙的存在使得岩溶裂隙网络溶蚀演化加快,非均质系统进入极快速紊流阶段所用时间较均质系统缩短了53%,裂隙溶蚀扩展的速度加快了12.5%。

Initial media characteristics and boundary conditions of a karst system determine its evolution process.The purpose of this study is to reveal the development of a concealed karst aquifer system under different boundary conditions and medium characteristics.Based on groundwater seepage and carbonate dissolution theory,we construct a karst fissure network dissolution propagation model of coupled fracture network seepage and carbonate dissolution,and conduct simulation on the evolution process of the concealed karst aquifer system between rivers.The results show that the flow changes during the development of the karst system have three stages.The first stage is a slow laminar flow with a flow rate increase of 2.2×10^-6 mL⋅(s⋅a)^-1,with a duration logarithmically related with the initial head difference.The second stage is a very fast turbulent with a flow rate increase of 5.5×10^2 mL⋅(s⋅a)^-1,and the duration is linearly related with the initial head difference.Stage Ⅲ is a fast turbulent with a flow rate increase of 26 mL⋅(s⋅a)^-1.The existence of dominant cracks accelerates the dissolution of karst fracture network.The time for the heterogeneous system entering the extremely fast turbulence phase is 53%shorter than that of the homogeneous system,and the dissolution rate of cracks is accelerated by 12.5%.