Design of sewers

Here you will get all information about sewer design, its type & various tests carried out on it for any leakage or any obstruction present and of improper joints.

1. .   DEPARTMENT OF CIVIL ENGINEERING   A PRESENTATION ON D E S I G N O F SEWER SYSTEM Name Roll no. 1.Kumathe Shushant A. 26 2.Kumbhar Swapnil A. 27 3.Kumbhar Vaibhav S. 28 4.Kyadagi Vivek N. 29 5.Lande Atul V. 30 G u i d e - M r . M a n o j M o t a ( A s s t . P r o f essor ) SHARAD INSTITUTE OF TECHNOLOGY COLLEGE OF ENGINEERING YADRAV(ICHALKARANJI) DIST.-KOLHAPUR. 416112

2. A s e w e r i s piped system to transport wastewater (and sometimes storm water) from the source (household, industry , runoff ) to a treatment facility. The hydraulic design of sewers and drains, means finding out their sections and gradients ,is generally carried out on the same lines as that of the water supply pipes Howeverthere are two major differences between characteristics of flows in sewers and water supply pipes. Design of sewers

3. F i g . 1 : G e n e r a l s e w e r s y s r e m

4. Sanitarary sewer- carries only sanitarary and domestic sewer Separate sewer – carries only disposal water Combined sewer – carries by weather flow plus storm water Partially combined sewer – carries dry weather flow plus a portion of WWF House sewer- carries sewage from house or building to street or public sewers Lateral sewer-collect sewage directly from houses C lassifi c a t i o n o f s e w e r s

5. Large network of underground pipes, mostly in urban areas. Collection of Blackwater, brownwater,greywater and stromwater. The system contains three types of sewer lines: 1 ) Main line (primary): the centre of the system, all other lines empty into it 2 ) B ranch lines (secondary): extend from the main Wastewater is transported to a centralised treatment facility by gravity. Depending on topography , sewer pumping stations are necessary. It must be designed to maintain “ self cleansing” velocity that no particle accumulate. Design principal

6. 1 . Chezy’s F ormula v = c(Ri)^(1/2) Where, v= is the mean velocity(m/s) c= is the chezy coefficient (m^1/2) R= is the hydraulic radius (- water depth ) (m) I= is the bottom slope(m/m) Constant (c) is very complex. Depends on size , shape and smoother roughness of the channel the mean depth etc. C can be calculated by using Bazin’s formula Hydraulic Formulae

7. C =157.6/[1.8+(k/R^1/2)] Where, K=Bazin’s constant R= hydraulic radius 2.Bazin’s formula

8. V = K/N R^2/3.S^1/2 W h e r e V= Velocity of flow (m/s) k= conversion factor of 1.486( ft /m)^1/3 N= manning coefficient Rh= hydraulic radius(m) S= slope of the water surface 3 . Manning Formula

9. The flow velocity in the sewers should be such that the suspended materials in sewage do not get silted up i.e., the velocity should be such as to cause automatic self cleansing effect. T he generation of such a minimum self cleansing velocity in the sewer at least once a day is important because if certain deposition takes place and is not removed, it will obstruct free flow ,causing further deposition and finally leading to the complete blocking of sewer. Minimum Velocity

10. To calculate minimum velocity of flow following formula is used. V= [(8k/f)(es-e)/e.g.ds]^(1/2) where, V=minimum velocity of flow in m/s. K= size of solids in sewage varying between 0.06mm F= Darcy’s coefficient of friction (normally 0.03 ) Self clearing velocity

11. es= specific gravity of solid material flowing in sewage , varies between 1.2 to 2.65 e= specific gravity of liquid in sewage (genrally1) g= gravitational acceleration cont. ds= dia of solid particles in mm S e l f c l e a n i n g v e l o city :

12. Due to variation in discharge , the depth of flow varies , and hence the hydraulic mean depth (r) varies. Due to the charge in the hydraulic mean depth , the flow velocity gets gets affected from time to time. It is necessary to check the sewer for maintaining a minimum velocity of about 0.45m/s at the time of minimum flow (assumed to be 1/3 average flow) Effects of flow variation on velocity in a sewer

13. The designer should also ensure that velocity of 0.9 m/s is developed at the time of maximum flow and preferably during the average flow periods also. Moreover, can should betaken to see that at the time of maximum flow , the velocity generated does not exceed the sourcing value.

14. Circular sewer Non circular sewers 1.Rectangular shape section 2.Semi-circular shaped sewer 3.U-shaped section sewer Forms of sewer F i g . 2 : N o n c i r c u l a r s e w e r s

15. Circular section has least perimeter and maximum R for given area so it is most efficient . It requires minimum quantity of material , making it economical too. Having uniform curvature , it prevents the possibility of deposition. They are easily manufactured. Significance of circular sewers

16. The testing of sewer is necessary as any leakage, improper joints, straightness or obstruction of sewer may occur during laying of sewers. The defect may be removed or required after detection . So there are various tests by which these defect may be detected. Testing of sewer

17. Water test Air test Smoke test test for obstruction Test are:-

18. This test is carried out for sewer lines between two manholes. Plugging is done by rubber plug at its lower end . Rubber plug is connected with air blown . The upper end of sewer is plugged with a connection to the funnel. Water test :

19. The head varies with the material of sewer. In case of cast iron sewer , the head should be at 9m. The acceptable loss or head loss should not exceed 2lit/cm of length of the sewer. To perform this test sufficient amount water should be available. W a t e r t e s t :

20. Air test : When sufficient amount of water is not available,then air test is to be carried out. Air is pumped into the pipeline , usually via a handpump with a control valve,until the reading on the manometer is around 125-150mm. The setup is then left for 5-10 minutes to allow for temperature stabilisation within the pipe before the pressure is reduced to exactly 100mm on the manometer scale

21. Smoke test : The purpose of smoke testing is to find potential points of inflow and infiltration in the sanitary sewer system that could lead to high flows during a storm. Smoke testing forces smoke-filled air through a sanitary sewer line. The smoke under pressure will fill the main line plus any connections and then follow the path of any leak to the ground surface, quickly revealing the source of the problem.

22. Reference Enviromental Engineering http://youtube/r08aMKFkH5U https://www.slideshare.net/mobile/bibhabasumohanty/hydraulic-design-of-sewer