Surcharged flow simulation model with blowing of manhole covers in urban sewer pipe systems

在城市雨水下水道管道系统中，沙井井盖经常被沙井内高压压缩空气吹走，这是由于暴雨期间由于流量调节(例如，管道系统下游端的泵站的闸门关闭)导致从明渠到加压流动的流动转变造成的。为了检验减少这种吹气现象的措施的有效性，必须建立污水管道系统中空气质量超载流量的径流模拟模型。首先，提出了城市污水管道系统沙井中空气质量流量的暴雨径流模拟模型。在该模型中，考虑了空气的可压缩性。其次，将该模型应用于有人孔雨水管道水力模型的径流试验，并将模拟得到的气压过程线与实测值进行了比较。结果表明，本文提出的模拟模型能够很好地模拟出井筒内空气压力的时间变化。第三，通过水工模型的径流试验，研究了井盖的吹动机理。结果表明：(1)沙井井盖上的空气孔具有一定的降低沙井内空气压力的作用；(2)连接在沙井井壁上的横向管道(也称为风道)对降低沙井内的空气压力具有很高的效率；(3)在沙井井盖与从沙井外排出的径流水相撞被吹走之前，沙井井盖在几乎所有沙井内的空气耗尽后恢复到正常位置。

In urban storm sewer pipe systems, manhole covers have been often blown away by a high pressure of compressed air in manholes, which is caused by a flow transition from open-channel to pressurized flow due to flow regulations (e.g., a gate closure at a pumping station in the downstream end of the pipe systems) during a heavy rain. In order to examine the efficiency of counter-measures to mitigate the occurrence of such a blowing phenomenon, a runoff simulation model of surcharged flow with masses of air in sewer pipe systems must be developed.First, a storm water runoff simulation model of surcharged flow with masses of air at manholes in urban sewer pipe systems is proposed. In this model, the compressibility of the air is considered. Second, the model is applied to runoff experiments in a hydraulic model of storm sewer pipes with manholes, and the air-pressure hydrographs simulated by the simulation model are compared to the observed ones. As a restult, it is demonstrated that the simulation model proposed here can simulate very well the temporal variations of air-pressure in manholes. Third, the mechanism of blowing of a manhole cover is investigated through runoff experiments in the hydraulic model. As a result, the following are made clear : (1) air holes on a manhole cover have a definite effect of reducing the air-pressure in the manhole ; (2) lateral pipes (also called air ducts) attached to the wall of a manhole have a high efficiency to reduce the air-pressure in the manhole ; and (3) before a manhole cover is blown away by the collision with runoff water discharging out of the manhole, the manhole cover returns to their normal position after almost all the air in the manhole is exhausted.