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

在城市暴雨污水管道系统中，井盖经常被井盖内的高压压缩空气吹走，这是由于在大雨期间，由于流量调节（例如，管道系统下游端泵站的闸门关闭），水流从明渠过渡到加压流造成的。为了检验缓解这种吹气现象发生的对策的有效性，必须建立污水管道系统中含大量空气的附加流的径流模拟模型。首先，建立了城市污水管道系统沙井处空气附加流的雨水径流模拟模型。在这个模型中，考虑了空气的可压缩性。其次，将该模型应用于带有人孔的雨阴沟水工模型的径流试验，并将模拟模型模拟的气压线与观测结果进行了对比。结果表明，所建立的模拟模型能较好地模拟井口内气压的时间变化。第三，通过水工模型径流试验研究井盖吹胀机理。结果表明：(1)井盖上的气孔具有一定的降低井盖内气压的作用；(2)附在人孔壁上的侧管（又称风管），效率高，可降低人孔内的气压；(3)在井盖与从井口排出的径流水碰撞被吹走之前，井盖在井口内的空气几乎全部排出后恢复到正常位置。

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.