"Sewer Network Analysis"

The word sewerage is made from sewer. The word sewer indicates the usable water which is received from kitchen, bathroom and outfall from toilet/W.C. Every large or small city was held at sea, river and lake and it was planned at initial stage of the project planning, that the dirty water of homes and industries was dumped in that water source easily. Many years passed the dirty water from these utilities are dumped in the nearest source and that source water was make too poisons. Many aquatic life is survive in water and when dirty water is mixed with water source the biological cycle was affected and fishes and other animals population was decreases.

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In that case population of human is also increases continuously and after that level of water source was decreases and we faced many problems continuously. Then sewer network is introduced. Outlet from all homes are connected to lateral lines means the water of kitchen, bathroom and water closet are connected to 100 mm/150 mm dia. UPVC pipes and these pipes are connected to lateral line pipes i.e. 200 mm to 350 dia. of DWC pipes and that lateral line pipes are connected to main line pipes which is 1400 mm dia. Dia. of pipe may differ for different projects.

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The main line pipes are passing through street line, Highway side and railway crossings and that lines are reached to STP area and firstly connected to Intake area .Fluid has the nature, that can changes shape whenever   source is available there and if no any obstructions it will continuously flow through their gravity. Some areas network lines are easily passes and water is reached at STP area, but some area may create more difficult to laying. Houses are made from upper and lower portion, many obstructions are there and also their co-ordinates are not similar to passing the network line. In that case a new structure introduced, whose name is SPS (Sewerage Pumping Station). Water is reached at SPS, Where large capacity pump is available (Some are working and minimum one or two pumps are standby), they reached the water through that.

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Making Procedure of Sewer Lines:-

     (1.)  TBM is fixed through nearest co-ordinate.

     (2.)  We got GL(Ground Level) & IL (Invert Level) from the drawing.

    (3.)  Find the depth of excavation from GL-IL(Subtract IL from GL) and excavate the required area and also follow the instruction of excavation i.e. embankment will provided, step cutting will also provided,trenches will make , shooring & shuttering with their supporting arrangements.

 

    (4.) For excavation, approx 300 mm step cutting is required both side for each 2 metre depth. It may be vary as per site condition.

Pipe with sand cover(Photo:Ritesh Raj)

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     (5.)Always prefer only road cutter machine with allowed depth is required.

    

     (6.)  In drawing also showing how much local sand bedding is required for DWC pipe laying. It will 100 mm, 150 mm and 200 mm depend upon drawing.In the case of precast RCC pipe minimum 200 mm PCC is required or it may be vary as per diameter of pipe or depth of pipe.

    (7.)  After sand bedding/PCC bedding we are laying the pipe and each pipe is connected to another pipe through a ring rubber socket (gasket ring), its main purpose is the leakage prevention.

   

Pipe with sand cover(Photo:Ritesh Raj)

    (8.)  After pipe laying we are covered the pipe through local sand/PCC or the sand which are mentioned in the drawing. The pipe is fully covered through sand/PCC.

    (9.)  Then we will start the backfilling. For backfilling test MDD & OMC will required and it will obtained from laboratory testing.Must consider each layer thickness is not more than 200 mm. Only soil will filled there.No any debris will mixed with soil is used in backfilling.With the use of water sprinkling, plate compacter and hand rammer will complete the process of compaction of backfilling. In that situation when top level is comes, will utilized there baby roller or roller.Now we are making the road in the motarable condition, because public movement will easily and convenient.

DWC Pipe Stockyard(Photo:Ritesh Raj)

    (10.) After backfilling and before road restoration, we have done hydrotest/smoke test and it is mendatory for all sewer network condition in the case of manhole and pipe.

 

    (11.)For sometimes road is left for settlement and then we start the road restoration as per technical specifications, Contract and drawing provided us.

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   Note:-

    (1.) Manhole is provided at junctions of each street and where the length is approx 30 m or more houses is available there and as per drawing.

    (2.) The distance between one manhole to another manhole is known as condict.

Brick Manhole (Photo:Ritesh Raj)

    (3.) Each manhole have two, three and more risers and they are safely laid one upon another and gap is filled through joint filling material exmple-sika latex powder with the ratio of 1:4:6 (where 1 is sika latex powder, 4 is water and 6 is cement) or 1:3 cement mortar (where 1 is cement and 3 is sand).

Sand bedding (Photo:Ritesh Raj)

    (4.) During the  excavation of pipe laying and manhole erection always consider the nature of the soil.If water comes during excavation due to their low water level, then we have firstly applied brick soling.

    (5.)At bottom of manhole PCC is required, then base raft of the manhole is provided and then riser of manhole will laid there.In the case of no any provision as per site condition, we are applying cast-in-situ for manhole.For cast-in-situ minimum M-30 grade concrete is required.

Sand Bedding (Photo:Ritesh Raj)

 

    (6.)After the manhole erection outer  and inner portion of gap will filled through rich cement motar and also cement mortar will applied at the junction of pipe and manhole.

    (7.) Benching will make at the inner portion of the manhole and their slope will provided approx 1:12, through which no any obstruction in flowing of water.

    (8.) Cover of manhole is 560 mm approx or given in drawing.

Sand Bedding (Photo:Ritesh Raj)

    (9.) In each riser 6 mm plastic encapsulated on 16 mm dia. round bar of steel bar (known as  isrungs) available, through which no any obstruction when any needed to a person going inward of the manhole suppose cleaning difference between two rungs is approx 300 mm.

    

    (10.) Present scenario used manhole is only precast. Few years ago manhole is made from brick.

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(11.)

  
                                               

Sl. No.	Depth of Manhole	Diameter of Manhole	Diameter of Precast Slab	Type of Manhole
1	0.91 m to 1.67 m	910 mm	1560 mm	Flat
2	1.68 m to 2.29 m	1220 mm	1870 mm	Flat
3	2.30 m to 9.00 m	1520 mm	2170 mm	Conical
4	2.30 m to 9.00 m	1820 mm	2470 mm	Conical

Above records are taken from precast manufacturing company. These above mentioned manhole is mostly uses in sewer network lines or it may change for different projects. In the case of conical shape manhole upto 1000 mm dia. of RCC pipe, 1520 mm is required.

(12.) Before uses at site manhole and pipes inspection certificate is required and that will done through reputed third party agencies.

(13.) Present time uses pipes in network lines is DWC (Double Wall Corrugated) for smaller dia. i.e. 200 mm to 450 mm and RCC pipes for higher dia.

(14.) For house connection UPVC pipe 100 to 150 mm dia pipe is used.

UPVC Pipe (Photo:Ritesh Raj)

(15.) Length of each pipe is 6 metre for UPVC pipes, DWC pipes (PN 8) and HDPE pipes. In the case of RCC pipe it will 2.5 metre.

HDPE Pipe (Photo:Ritesh Raj)

(16.) Where these pipes (DWC & RCC) is not used, HDPE pipes is used, where HDD(Horizontal Directional Drilling) method will apply. Some details of HDPE pipes is following:-

Sl. No.	Inner Dia. Of Pipe	Outer Dia. of Pipe	Thickness of Pipe	Type of Pipe
1	180 mm	200 mm	10 mm	PN6
2	220 mm	250 mm	15 mm	PN6
3	280 mm	315 mm	20 mm	PN6
4	310 mm	355 mm	20 mm	PN6

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HDPE Pipe Joint (Photo:Ritesh Raj)

(17.) During the house connection we are making the house connection pit of different sizes as described in drawing, is used and the wall will plastered both sides inner and outer where cover is precast making.

(18.) Which cement and steel will used also mentioned in technical specification and drawing.

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Written By- 

Ritesh Raj

Email Id-rajritesh.motiharirr@gmail.com