The sewers are generally designed as open channels except when it is specially required to design them as conduits carrying sewage under pressure as in the case of inverted siphons. Thus various empirical formulae which are used for the design of open channels are used for the design of sewers. The following empirical hydraulic formulae are commonly used for the [...]
In this article we will discuss about the velocity of flow in sewers. Minimum Velocity of Flow in Sewers - Self Cleansing Velocity: A sewer should be so designed that the solid matter present in the sewage is not deposited at the bottom of the sewer and thus clogging of the sewer is prevented. The deposition of the solid matter [...]
Based on the cross-sectional shapes the sewers may be classified as: 1. Circular Sewers 2. Non-Circular Sewers. 1. Circular Sewers: Sewers of circular section are most commonly used. These are best suitable for diameters up to 1.5 m. The various advantages of circular sewers are as indicated below: (i) A circular section gives the least perimeter for a given area, [...]
The various steps involved in the laying and testing of sewers are: 1. Setting out Sewer Centre Line 2. Alignment and Gradient of Sewers 3. Excavation of Trenches, Timbering and Dewatering 4. Laying and Jointing of Pipe Sewers 5. Testing of Pipe Sewers 6. Backfilling of Trenches. Step # 1. Setting out Sewer Centre Line: This is the first step [...]
There are three types of installation or construction conditions for underground conduits, viz.: (i) Trench condition, (ii) Embankment condition, and (iii) Tunnel condition. Trench condition exists when the conduit is installed in a relatively narrow trench (not wider than twice the external diameter of the conduit) cut in undisturbed soil and then covered with earth backfill up to the original [...]
In addition, the following special equipments and devices are used for cleaning sewers: 1. Portable Pump Set 2. Manila Rope and Cloth Ball 3. Sectional Sewer Rods 4. Sewer Cleaning Bucket Machine 5. Dredger 6. Roding Machine with Flexible Sewer Rods 7. Scraper 8. Hydraulically Propelled Devices. 1. Portable Pump Set: In cases where sewers are blocked completely and sewage [...]
The various forces exerted on a sewer are explained as follows: 1. Internal Pressure of Sewage 2. Temperature Stresses 3. Forces due to External Load. 1. Internal Pressure of Sewage: Most of the sewers are designed to run partially full in which case sewage flows through sewers under gravity and hence no internal pressure is exerted by the sewage on [...]
The sewers may be of the following types: 1. Brick Sewers 2. Cement Concrete Sewers 3. Asbestos Cement Sewers 4. Stoneware or Vitrified Clay Sewers 5. Cast Iron Sewers 6. Steel Sewers 7. Plastic Sewers 8. Fibre Glass Reinforced Plastic (FRP) Sewers 9. Pitch Fibre Sewers. Type # 1. Brick Sewers: Bricks have been used for the construction of sewers, [...]
Following method is followed for the design of sewers: 1. Zone Formation 2. Sewer Network 3. Sewage Quantity 4. Flow Velocity 5. Sewer Section 6. Grade of Sewers. 1. Zone Formation: The whole town or city in which sewerage system is to be provided is divided into different zones. The layout of sewers is plotted along the roads, and the [...]
Fig. 5.3 shows the common egg-shaped sewer cross-section. The calculation of areas and the wetted perimeters of these sewers at various depths of the sewage involve tedious calculation works. Curves of the hydraulic elements of the standard forms of the egg-shapped sewers are prepared in the same way as for circular sections. The design work can be easily done by [...]