排水管道颗粒物沉积-悬浮规律及其状态更替机制研究

The drainage pipe is critical infrastructure of urban. In long-term run, the deposition of suspended particles and the resuspension of sediment usually occur in drainage pipe, and that has caused the corrosion of pipe, the reduction of flow capacity and the pollution of receiving water. Studying the dynamic migration process of particles in drainage pipe, and exploring the inherent laws and mechanisms of the two major migration processes of deposition and suspension of particles, are the important ways to solve the deposition problems of pipeline. This project will adopt the methods of theoretical analysis, simulation test and mathematical model calculation. Firstly, the deposition and scour suspension processes of particles in drainage pipe are studied. On this basis, two kinds of mathematical models of deposition and suspension processes are established, and the calculation methods of macro parameters such as maximum deposition location and deposition rate are obtained. Then the two laws are revealed, one for the deposition of suspended particles, and the other for the scour suspension and transportation of sediments in drainage pipeline. Next, the replacement process of deposition-suspended state of particles in drainage pipe is studied from the microscopic perspective. The research and analysis methods of three deposition states and three suspension-movement states of particles are explored, and the critical parameter variation of the six states is obtained. Then the replacement mechanism of deposition-suspension state of particles is revealed by establishing a mathematical model. The implementation of the project can provide theoretical support for the quantitative assessment of the deposition and scour suspension processes, the prediction of particulate state, and the further technical measures.

排水管道系统是城镇重要的基础设施，在长期运行中极易发生悬浮颗粒物的沉积和沉积物的冲刷再悬浮现象，引发管道腐蚀，降低过流能力，造成受纳水体的污染。研究颗粒物在排水管道内的动态迁移过程，探索颗粒物沉积、悬浮两个主要迁移过程的内在规律和机制，是解决管道沉积问题的重要途径。本课题拟通过理论分析、模拟试验和数学模型计算，从宏观角度研究排水管道颗粒物沉积、悬浮两个过程，建立沉积、悬浮两类数学模型，获得管道内最大沉积位置、沉积率等宏观参数的计算方法，揭示排水管道内颗粒物沉积规律和冲刷悬浮及输送规律。从微观角度研究排水管道颗粒物沉积-悬浮状态的更替过程，探索颗粒物三种沉积状态、三种悬浮移动状态的研究分析方法，获得六个状态临界参数的变化规律，建立模型揭示颗粒物沉积-悬浮状态更替机制。课题的实施将为排水管道中沉积和冲刷悬浮过程的量化评估、颗粒物状态的预测判断以及采取技术性措施提供有力的理论支撑。

城市排水管道内发生不同程度的沉积堵塞，使得管道排水能力下降，造成城市内涝、受纳水体污染等诸多问题。本项目研究了排水管道中颗粒物的沉积和冲刷悬浮过程，建立管道内悬浮颗粒物沉积数学模型，确立了输送通量、沉积率和沉积临界流速等参数的计算方法；雨水管道变输送通量条件下，计算沉积量、平均/最大沉积速度和易沉积点等参数；建立排水管道内沉积物冲刷悬浮及输送数学模型，计算冲刷量、冲刷率和冲刷临界流速等参数，并验证准确性；采用临界流速来量化分析不同沉积状态、冲刷悬浮状态的临界条件。主要结论如下：排水管道中颗粒物的沉积和冲刷悬浮过程均受到颗粒粒径、密度、管壁粗糙度、水流流速和悬浮固体浓度影响，与颗粒本身受到的重力、管壁摩擦力和水流剪切力等有关。当流量增加时，管道中的易沉积点从管道前部向后迁移，流量减小时则相反。随着水流悬浮固体初始浓度降低，管道的平均沉积速度逐渐下降。叠加效应下，管道中可能同时存在沉积和冲刷的过程，两者交替占据主导地位。根据计算的沉积率，对四种常用管材管道的“沉积状态”进行了划分：当管道内的沉积率达到0.5%～1.5%时，颗粒物开始从“不沉积”转变为“少量沉积”状态，对应的流速为沉积临界流速；当沉积率达到9.5%～10.5%时，颗粒物开始从“少量沉积”转变为“大量沉积”状态。建立石英砂、沸石颗粒的沉积临界流速计算模型，将模型计算值和试验实测值进行对比，两者差异率在-4.50%~5.50%范围内。参照冲刷率，对四种管道中的“冲刷状态”进行划分：当冲刷率达到0.5%～1.5%时，颗粒物开始从“不冲刷”转变为“少量冲刷”状态，此时流速为冲刷临界流速；当冲刷率为9.5%～10.5%时，颗粒物开始从“少量冲刷”转变为“大量冲刷”状态。经拟合，建立两种颗粒的冲刷临界流速计算模型。经验证，模型计算值和试验实测值的差异率在-4.80%~7.50%范围内，一致性较好。研究结果为排水管道中沉积、冲刷悬浮过程的量化评估，颗粒物状态的预测判断，及进一步采取技术性措施提供理论支撑。