PLUMBING-SEWERAGE SYSTEM ASSIGNMENT 1

Group 1: Amit Moza, Anwesha Samantha, Pallav P.Baruah, Reaspreet Singh Nayyar, Kanika Sachdeva

M.B.E.M. 1 Yr. ,S.P.A. Delhi

Types of materials used for sewerage infrastructure system for

pipes and their suitability

Following factors should be considered before selecting material for manufacturing

sewer pipes:

1. Resistance to corrosion:

Sewer carries wastewater that releases gases such as H2S. This gas in contact with

moisture can be converted into sulphuric acid. The formation of acids can lead to the

corrosion of sewer pipe. Hence, selection of corrosion resistance material is must for

long life of pipe.

2. Resistance to abrasion:

Sewage contain considerable amount of suspended solids, part of which are inorganic

solids such as sand or grit. These particles moving at high velocity can cause wear

and tear of sewer pipe internally. This abrasion can reduce thickness of pipe and

reduces hydraulic efficiency of the sewer by making the interior surface rough.

3. Strength and durability:

The sewer pipe should have sufficient strength to withstand all the forces that are

likely to come on them. Sewers are subjected to considerable external loads of

backfill material and traffic load, if any. They are not subjected to internal pressure

of water. To withstand external load safely without failure, sufficient wall thickness

of pipe or reinforcement is essential. In addition, the material selected should be

durable and should have sufficient resistance against natural weathering action to

provide longer life to the pipe.

4. Weight of the material:

The material selected for sewer should have less specific weight, which will make

pipe light in weight. The lightweight pipes are easy for handling and transport.

5. Imperviousness:

To eliminate chances of sewage seepage from sewer to surrounding, the material

selected for pipe should be impervious.

6. Economy and cost :

Sewer should be less costly to make the sewerage scheme economical.

Material for sewer pipe:

1. Asbestos cement sewer :

These are manufactured from a mixture of asbestos fibers, silica and cement.

Asbestos fibers are thoroughly mixed with cement to act as reinforcement.

These pipes are available in size 10 to 100 cm internal diameter and length up to

4.0 m.

These pipes can be easily assembled without skilled labor with the help of special

coupling, called Ring Tie Coupling or Simplex joint.

The pipe and joints are resistant to corrosion and the joints are flexible to permit

12 deflection for curved laying.

These pipes are used for vertical transport of water. For example, transport of

rainwater from roofs in multistoried buildings, for transport of sewage to grounds,

and for transport of less foul sullage i.e., wastewater from kitchen and bathroom.

Advantage:

These pipes are light in weight and hence, easy to carry and transport.

Easy to cut and assemble without skilled labor.

Interior is smooth (Mannings n = 0.011) hence, can make excellent hydraulically

efficient sewer.

Disadvantage:

These pipes are structurally not very strong.

These are susceptible to corrosion by sulphuric acid. When bacteria produce H2S,

in presence of water, H2SO4 can be formed leading to corrosion of pipe material.

2. Plain Cement Concrete or Reinforced Cement Concrete:

Plain cement concrete (1: 1.5: 3) pipes are available up to 0.45 m diameter and

reinforcement cement pipes are available up to 1.8 m diameter. These pipes can be

cast in situ or precast pipes. Precast pipes are better in quality than the cast in situ

pipes. The reinforcement in these pipes can be different such as single cage

reinforced pipes, used for internal pressure less than 0.8 m; double cage reinforced

pipes used for both internal and external pressure greater than 0.8 m. elliptical cage

reinforced pipes used for larger diameter sewers subjected to external pressure; and

Hume pipes with steel shells coated with concrete from inside and outside. Nominal

longitudinal reinforcement of 0.25% is provided in these pipes.

Advantage:

Strong in tension as well as compression.

Resistant to erosion and abrasion.

They can be made of any desired strength.

Easily molded, and can be in situ or precast pipes.

Economical for medium and large sizes.

These pipes are available in wide range of size and the trench can be opened and

backfilled rapidly during maintenance of sewers.

Disadvantage:

These pipes can get corroded and pitted by the action of H2SO4.

The carrying capacity of the pipe reduces with time because of corrosion.

The pipes are susceptible to erosion by sewage containing silt and grit. The

concrete sewers can be protected internally by vitrified clay linings. With protection

lining they are used for almost all the branch and main sewers. Only high alumina

cement concrete should be used when pipes are exposed to corrosive liquid like

sewage.

3. Vitrified Clay or Stoneware Sewers :

These pipes are used for house connections as well as lateral sewers. The size of the

pipe available is 5 cm to 30 cm internal diameter with length 0.9 to 1.2 m. These

pipes are rarely manufactured for diameter greater than 90 cm. These are joined by

bell and spigot flexible compression joints.

Advantage:

Resistant to corrosion, hence fit for carrying polluted water such as sewage.

Interior surface is smooth and is hydraulically efficient.

The pipes are highly impervious.

Strong in compression.

Disadvantage:

Heavy, bulky and brittle and hence, difficult to transport.

These pipes cannot be used as pressure pipes, because they are weak in tension.

These require large number of joints as the individual pipe length is small.

4. Brick Sewers:

This material is used for construction of large size combined sewer or particularly for

storm water drains. The pipes are plastered from outside to avoid entry of tree roots

and groundwater through brick joints. These are lined from inside with stone ware

or ceramic block to make them smooth and hydraulically efficient. Lining also makes

the pipe resistant to corrosion.

5. Cast Iron Sewer :

These pipes are stronger and capable to withstand greater tensile, compressive, as

well as bending stresses. However, these are costly. Cast iron pipes are used for

outfall sewers, rising mains of pumping stations, and inverted siphons, where pipes

are running under pressure. These are also suitable for sewers under heavy traffic

load, such as sewers below railways and highways. They are used for carried over

piers in case of low lying areas. They form 100% leak proof sewer line to avoid

groundwater contamination. They are less resistant to corrosion; hence, generally

lined from inside with cement concrete, coal tar paint, epoxy, etc. These are joined

together by bell and spigot joint.

6. Steel Pipes :

These are used under the situations such as pressure main sewers, under water

crossing, bridge crossing, necessary connections for pumping stations, laying pipes

over self-supporting spans, railway crossings, etc. They can withstand internal

pressure, impact load and vibrations much better than CI pipes. They are more

ductile and can withstand water hammer pressure better. These pipes cannot

withstand high external load and these pipes may collapse when negative pressure

is developed in pipes. They are susceptible to corrosion and are not generally used

for partially flowing sewers. They are protected internally and externally against the

action of corrosion.

7. Plastic sewers (PVC pipes):

Plastic is recent material used for sewer pipes. These are used for internal drainage

works in house. These are available in sizes 75 to 315 mm external diameter and

used in drainage works. They offer smooth internal surface. The additional

advantages they offer are resistant to corrosion, light weight of pipe, economical in

laying, jointing and maintenance, the pipe is tough and rigid, and ease in fabrication

and transport of these pipes.

8. High Density Polyethylene (HDPE) Pipes:

Use of these pipes for sewers is recent development. They are not brittle like AC

pipes and other pipes and hence hard fall during loading, unloading and handling do

not cause any damage to the pipes. They can be joined by welding or can be jointed

with detachable joints up to 630 mm diameter. These are commonly used for

conveyance of industrial wastewater. They offer all the advantages offered by PVC

pipes. PVC pipes offer very little flexibility and normally considered rigid; whereas,

HDPE pipes are flexible hence best suited for laying in hilly and uneven terrain.

Flexibility allows simple handling and installation of HDPE pipes. Because of low

density, these pipes are very light in weight. Due to light in weight, they are easy for

handling, this reduces transportation and installation cost. HDPE pipes are non-

corrosive and offer very smooth inside surface due to which pressure losses are

minimal and also this material resist scale formation.

Co-ordination Problem in installing of sewage system

Any sewage system includes installation of components like underground pipes,

manhole chambers, pumps, and finally a sewage treatment plant. All these

components have to be installed either alongside other facilities or need the inputs

from other disciplines like civil works for their installation. Moreover, since the

sequencing of the activities is very critical, co-ordination between various agencies is

of paramount importance if the job has to progress smoothly. Following problems can

crop up if proper co-ordination and sequencing of activities is not closely followed.

1. The sewage system co-ordination begins at the design stage itself. While a

sewage system is to be designed by a specialist who is usually other than the

architect, close co-ordination needs to be maintained between the two for optimum

and correct design conditions. The exchange of information on the levels or RLs at

site with the design RL of building floors has to be carried out effectively so that a

sewage system is designed for such levels only. The slope of the sewer lines can only

be determined based on this co-ordination. Sometimes, when site conditions are such

that certain minimum levels have to be maintained, the levels of building floors and

other facilities may have to be worked out on the basis of sewage outlet level or else

the use of pumps might become necessary which may be not be desirable. Such

instances can be avoided if proper co-ordination and flow of information is

maintained during design stage.

2. The sewage pipes have to come down the building, usually inside a shaft for

which scaffolding needs to be installed. In case the civil works guy completes his

outer finishing and removes the scaffolding, the pipeline job shall unnecessarily get

delayed due to re-installation of scaffolding. The scaffolding for sewage pipeline

coming down the building can be installed while external jobs are being carried out.

In case the same is not coordinated with the civil works, the same shall have to be

taken only after the finishing of civil works on ground are completed.

3. The inspection chambers or traps for sewage or waste-water pipes coming down

from the building have to be constructed around the building on the ground. Usually

these have to be constructed on the filled up soil which is backfilled for excavation of

foundations. If proper co-ordination is not maintained with civil works for effective

compaction of the backfill, entire chambers swill settle in the long run and sewage

system shall become defunct.

4. Close co-ordination is also required to be kept with road works as sewage

systems sometime need to be laid underground across the road. Therefore, the

sewer line must be laid in a way that no repair work becomes necessary on road. This

is required for construction of manholes too, especially in case the manholes are

coming on the road itself.

5. Similarly, sewer lines have to be laid underground with many other services like

water supply, electrical cables, rain water harvesting drains etc. Which line or

service has to be laid at what level and what shall be the sequencing of laying these

service has to be closely coordinated with different agencies carrying out these jobs

so that the service do not cross each other or fault with each other.

6. Co-ordination is also required while the manpower is being planned by different

agencies for their respective jobs and such jobs are interdependent. For example,

while sewage pipes are being laid in the floors of the building, the manpower of the

sewage guy must be so planned that the work always follows the civil work so that

fronts can be made available to the plumbing guy. The pace of plumbing must not

outstrip the pace of associated civil work to avoid idling of plumbing manpower.

Therefore, deployment of manpower of the plumbing guy has to be carried out in

close co-ordination with the civil guy or any other inter dependent or associated

service.

7. The sewage transport (sewer) have to be laid in co-ordination with the sewage

treatment plant work too so that both the jobs are completed in such a way theta no

idling of manpower or machines occurs. In case the sewage is to be disposed to a

public service sewer, then co-ordination with state or development authorities is a

must.

Sewage System Construction Process and Equipment

Excavation, shoring and timbering in trenches cement concreting and

refilling

All sewage pipes when below the ground should be leak proof.

Process of laying the sewer pipes involves:

Excavation: The top turf and or other soil is kept aside. Turf being carefully kept

for use in reinstatement. The excavation shall be carried out with manual labour or

with suitable mechanical equipment as

The excavation must be done keeping in mind:

a. The width of trench at the bottom must have 200 mm wide clearance on the

either side of the trench.

b. Excavation below the water table must be done after dewatering the trenches.

c. Concreting:

Bedding/Encasing Stoneware Pipes

W = D+X, Where D is the External Diameter o f t h e pipe

300 up to Trench Depth of 1200

400 Trench Depth more than 1200

T = 100 for pipes under 150, 1/4th Internal dia subject to a

Min. of 150 mm and max. 300 mm for pipes more than 150 Dia

MWL = Maximum water level

(a) For all diameters, up to an average depth of 120 cm, width of trench in cm =

diameter of pipe + 30 cm.

(b) For all diameters for depths above 120 cm, width of trench in cm = diameter of

pipe + 40 cm.

(c) Notwithstanding (a) and (b) the total width of trench shall not be less than 75 cm

for depth exceeding 90 cm.

2. Laying: Where the pipes are laid on soft soil with maximum water table lying at

invert level of the pipe, the pipes shall be bedded in cement concrete with thickness

and mix as

Specified, projecting on each side of the pipe to the specified width of the trench. The

pipes with their crown level at 1.20 m depth and less from ground shall be covered

with 15 cm thick.

The pipe shall be carefully laid to the alignments, levels and gradients shown on the

plans and sections. Great care shall be taken to prevent sand etc. from entering the

pipes. The pipes between two manholes shall be laid truly in a straight line without

vertical or horizontal

Undulation. The pipes shall be laid with socket ends facing upstream. The body of

the pipe shall for its entire length rest on an even bed of concrete and places shall be

excavated in the concrete to receive the socket of the pipe.

Jointing: Tarred gasket or hemp yarn soaked in thick cement slurry shall first be

placed round the spigot of each pipe and the spigot shall then be slipped home well

into the socket of the pipe previously laid. The pipe shall then be adjusted and fixed

in the correct position and the

The remainder of the socket shall be

filled with stiff mixture of cement

mortar in the proportion of 1:1 (1

cement: 1 fine sand). When the socket

is filled, a fillet shall be formed round

the joint with trowel forming an angle

of 45 degree with the barrel of the

pipe.

Refilling: In cases where pipes are not bedded on concrete special care shall be taken

in refilling trenches to prevent the displacement and subsequent settlement at the

surface resulting in uneven street surfaces and dangers to foundations etc. The

backfilling materials shall be packed by hand under and around the pipe, and

rammed with a shovel and light tamper. This method of filling will be continued up

to the top of pipe. The refilling shall rise evenly on both sides of the pipe continued

up to 60 cm above the top of pipe so as not to disturb the pipe. No tamping should be

done within 15 cm of the top of pipe.