基于雷诺数的砂砾石管涌过程判别

Discriminating piping process in sandy gravels based on Reynolds number

管涌破坏是发生堤坝险情乃至溃决的主要原因。传统渗流力学涉及管涌机理、发展过程及控制措施,对管涌过程定量判别及非线性特征研究尚显不足。开展不同级配砂砾石管涌试验,指出细颗粒含量及均匀程度是影响砂砾石管涌破坏的主要因素;分析管涌破坏过程中水流状态变化规律,提出了基于雷诺数Re的管涌过程判别方法。试验结果表明:砂砾石管涌过程可定量分为孕育阶段(Re<0.85)、形成阶段(0.85≤Re≤5.00)、发展阶段(5.00<Re≤50.00)和破坏阶段(Re>50.00)。孕育和形成阶段,可动细颗粒启动并缓慢调整,水力坡降与渗流速度呈线性关系,黏阻力占主控作用,渗流运动符合达西定律;发展和破坏阶段,渗流通道形成并逐步扩展,可动细颗粒快速流失,渗流速度变化较大,惯性力占主控作用,水力坡降与渗流速度呈远离平衡态的非线性关系,层流逐渐向紊流过渡,可用二次方程描述。研究结果可为管涌险情预报和应急处置提供决策依据。

Piping is one of the main reasons of dike and dam break in defective reservoirs.Traditional seepage theories focus on piping mechanism,developing process and controlling measures,yet seldom shed light on quantitative discrimination and nonlinear characteristics of overall piping process.Groups of laboratory tests of piping process in different grading sandy gravels were conducted,and the judging method of overall piping process was proposed by the analysis of fluid regime changes based on the Reynolds number,which shows that fines content and uniformity are main influence factors of piping failure.The whole process of piping in sandy gravels can be quantitatively divided into four stages,that is,incubation(Re<0.85),formation(0.85≤Re≤5.00),evolution(5.00<Re≤50.00)and destruction(Re>50.00).During incubation and formation stages,removable fine particles are started up and adjusted,and the relationship between hydraulic gradient and seepage velocity is linear.Viscous drag force plays an important role,and seepage flow conforms to the Darcy’s law.However,during evolution and destruction stages,seepage pathway is gradually formed and developed,and removable fine particles run off rapidly.Meanwhile,the seepage velocity changes increasingly,and the relationship between hydraulic gradient and seepage velocity is nonlinear,which shows the inertial force plays a leading role.Laminar flow gradually transfers into turbulent flow,which can be described by a quadratic equation.The research findings can provide the base for piping scientific forecast and emergency disposal.