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，人孔盖经常被人孔中的高压压缩空气吹走，这是由于流量调节（例如，水管系统下游端泵站的闸门关闭）。为了检验防吹措施的有效性，必须建立污水管系中有空气质量的溢流径流模拟模型。首先，提出了城市污水管系中人孔处有空气质量的溢流径流模拟模型。在这个模型中，考虑了空气的可压缩性。其次，该模型应用于雨水管与检修孔水力模型的径流试验，并将模拟模型模拟的气压过程线与实测的气压过程线进行比较。结果表明，本文提出的模拟模型能很好地模拟人孔内气压随时间的变化。第三，通过水工模型径流试验，研究了井盖吹胀的机理。结果表明：（1）井盖上的气孔对降低人孔内的气压有一定的作用;（2）侧管（也称为空气管道）附接到人孔的壁，具有高效率以降低人孔中的空气压力;（3）在井盖被人孔外排出的径流水碰撞吹走之前，待人孔内的空气几乎全部排出后，井盖恢复到正常位置。

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.