the aggregate of underground pipelines and sewers receiving and draining waste waters away from population centers and industrial enterprises and toward the appropriate treatment facilities; the principal element of a sewerage system.
An urban sewer network consists of pipe networks draining city blocks, buildings and groups of buildings, and streets, sewage mains, and pressure lines. The lines of the sewer network running within individual buildings are connected to the network of that group or block of buildings through special drainage outlets. Pumping stations are built to pump the sewage water to treatment facilities. Manholes are provided for inspection and repairs. Industrial enterprises may have several sewer networks for removing effluents of different composition (for example, strong acid and strong base).
Depending on topography, ground conditions, composition of the effluents, and sequence of construction, networks may be perpendicular, transverse, parallel, zonal, or radial. Whenever possible, sewer networks are designed to use a gravity-fed system to transport household and industrial effluents. The hydraulic calculations necessary in designing a sewer network consist in determining the diameter of the pipes and their load and the rate of flow of the effluents. The network should be deep enough (depending on the depth of soil freeze) to protect the pipes against damage by surface transport. This comes to about 2 m for the middle zone of the USSR.
The choice of pipelaying material depends on the composition of the effluents and groundwaters and on the purpose of the pipeline. A gravity-fed sewer network is made from ceramic, asbestos-cement, concrete, and reinforced-concrete pipe; the large-diameter mains are made from reinforced-concrete pipe or prefabricated sections of reinforced concrete. Metal, asbestos cement, and reinforced-concrete pipes are used for pressure lines. Pipes can also be made from synthetic materials. Careful fitting of the joints in laying the pipe helps ensure water tightness and long life.
IU. M. LASKOV