bab 4 - sewerage system

8/2/2019 Bab 4 - Sewerage System

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GROUP 1NURSYAZANA BINTI ABDUL HALIMNURFATIAH BINTI SAIDINNURUL SHUHADA BINTI ABU

SEMANNURAZRAH HANEM BINTI RAHIMNORSHAHIDA BINTI ABDUL RAZAK

NOOR AIN BINTI ZAINOL ABIDIN


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ECONOMIC FACTORS

Pipes should not too long than the new sewer pipes

Should consider on construction that will occur in future Prepare the small sewer pipes for sewage flow from house or

building before entering the main sewage pipe.

DETERMINATION OF LOCATION

Find a suitable location of the pipeline so that it wont disturb thetraffic.

Sewerage pipe should be posted nearby the house or the buildingso that easily accept the sewage flow.


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The purpose of early investigation is to get someinformation for estimating the cost and to observe theequity of the project.

Some information can get from the map or the aerial

images. initial design is usually based on the estimated flow,contours, roador pipeline location and the locationwhere sewage flows from the house or building

based on this information, the quantity of pipes ofdifferent sizes can be estimated together with the cost

of dredging, repair roadsandsewer piping components required


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it needs to be done and depending onthe size and surfacecondition of atown or housing scheme.

aims to minimize construction costs byproviding a gravity flow of sewage.

is not profitable to provide sewerage

system for a verylarge areaand low population density.


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For areas with high population density, itis more economical if the area is divided intoseveral zones.

While for the area where the populationis scattered and not dense, the sewageproduced better treated individuallyusing septic tanks and absorption trenches.

If the surface area has a different level,pumping stations required to pump sewage toovercome gravity flow

Distribution area can alsoreduce design time due to a small areawith development term limits shorter thanthe saturated large areas.


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difficult to design a sewer system slightlycompared the water supply pipe design toestimate the quantityof sewage for discharge varies accordingto season, day and hour.

flow rate during the day higher than during

the night. therefore it is difficult todetermine the average daily flowrate and maximum flow rate.


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many housing schemes using a separate system inwhich sewage and storm water channeled intwo different sets of pipes.in the context of the sewerage system, dry

weather flow of sewage average flow rate during thedry season when no rain is taken into account.

however, a small part of the earth'swater will infiltrate into the sewer pipes, especially inareas prone to flooding.

it should be designed so that they can carry amaximumflow rate inflow 2/3 full to 750mm diameter sewer pipeand 1/2 full sewer pipes less than 750mm.

For this purpose, the flow rate factor introduced to

ensure maximum flow rate allowed for sewer pipes.


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sewerage system should be designed taking intoaccount the needs of present and future.

future needs means that if any provision of thelatest requirements.

for housing schemes which have the maximumnumber of units, when the design must take intoaccount only the maximum.

the main sewerage system which receives sewageand a town that is growing, when the

design must take into account the needs of thefuture. in practice, the time limit design usually does

not exceed 30 years.


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sewer pipes should preferably take theshortest route to the central treatmentplant so that its cost can be minimized.

in practice areusually installed sewer pipelines parallel to the lane behind the terrace houses

above the threshold for the road ahead to the

main sewer pipe. on the side of the road ahead for the road with no sill

in individual lots for which there is no way connectedto the housing back


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for cases that are not common it mustuse its own discretion virus to produce theshortest route.

generally be installed so thatthe sewer pipe in parallel with the road

and not across the building.The main components in the sewerage

systems are manhole.

manhole is required as a gateway intothe sewerage system for the purposeof inspection, maintenance and cleaning.


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it also serves as ameeting chamber for two or more main

sewerpipes and sewer pipes at each intersection

Themaximum distance between two manholesfor each of 150 feet of sewer pipe ofdiameter 6 inches or less 200 feet for pipediameters greater than 6 inches.


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flow velocity in the sewer pipe has a self-cleansing ability to avoidsedimentation of the solid will produce piles of silt.

if the velocity is too slow sediment solids will accumulate and causepipe blockages and prevent the passage of sewage.

deposited solids consisting of sand, organic solids, and non-organic. 1.0mm diameter sand has a specific gravity of

2.65 and 5.0mmdiameter organic solids with specific gravityof 1.2 requires a minimum velocity of 0.45 m / sec to move withthe sewage.

design for self-cleansing velocities to be in the range 0.5 - 1.0 m /sec.

flow velocity calculation is done using the empirical formula

to avoid a very steep slope of sewer pipes are designed to have aself-cleansing velocities during peak flows. for average flow, trenches are dug to deep enough.


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Although there may be a minimum flowof silt in it will be brought together in time

of peak flow.Pipe diameter (mm) Self-cleansing velocity

(m/sec)

150 250 1.0

300 600 0.75

600 0.6


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law slope aspect Maguire used to produce self-cleansing velocity.

diameter sewer pipes that are common in themarketis 4 inches, 6inches, 9 inches, 12 inches, each additional 3 inches.

Diameter(inches)

Gradient

normal minimum

4 1/40 1/300

6 1/100 1/300

9 1/160 1/35012 1/260 1/400

18 1/300 1/450

21 1/320 1/500


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After the velocity of flow isdetermined and the slope of sewer pipediameter is known to be counted

Usually a minimum diameter ofpublic sewer pipes is 6 inches @150 mm

However preferably use more

than 9 inches in diameter to avoidclogging pipes.


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The empirical formula used to calculate thevelocity of flow in the sewer pipe isChezy formula

crimp and Bruges formula

Bazin formula

Hazen-Williams formulaManning formula - commonly used in Malaysia


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all of this formula, the slopeof sewer pipes and used as the

hydraulic mean depth of flowin sewer pipes rarely achieve full flowtap features semi-liquid form of sewage.

table below showsthe guideline between flowdepth and hydraulic mean depth

Depth of flow Hydraulic mean depth

Full & D x 0.25

D x 0.30

2/3 D x 0.29

1/3 D x 0.19

1/4 D x 0.15


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from hydraulic mean depth schedule for full flow and 1/2 are the same. This means

that the flow velocity is equal to thefull flow and

maximum velocity in the pipe sewer flow to

occur during a round shell at a depthof approximately 4/5 of the diameter.maximum velocity value is more than

12.5% of velocity at full flow.


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equation

V = Cmi2

V = velocity (m/sec) m = hydraulic mean depth

C = Chezy constant I = slope of sewer pipes

Value usingKuiter formula

C = 23 + (155 x 10-5) li + 1/n

1 + ( 23 + (155 x 10-5)) n/m i

Roughnesscoefficient

Materials Value of n

Bricks 0.013 0.015Clay 0.014

Cast iron 0.013

Tract of soil 0.02

Rock channel 0.03


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Crimp and Bruges formula are describe inan equation : V = 83.45m2/3i


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Bazin formula specified in equation : V = 285.6mi

1 u / 3.28m

Where as:

Bazin coefficients are usually 0.3 to sewerpipes


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Hazen Williams are specified in equation: V = 0.85 Cm0.63i0.54

Material Value of C

Brick 274

Clay 305

Old cast iron 227

New cast iron 358


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V = (1/n) m2/3Isewer pipe is best planted at a depth to the

needs of present and future.depth of the trenches or excavation of the

pipe affects the construction costs thatdepend on soil conditions, the availability ofgroundwater and the foundations ofnearby buildings that can influence the

design and construction methods.minimum depth of excavation depends on

the type of soil and traffic loads on the pipe


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foundation for sewer pipe connections depends on whether theconnection rigid or flexible connections

rigid connection is classified as a"foundation class A 'and theflexible connection is classified as

a" foundation class B'


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sewer pipes buried inthe crushed rock compacted 15mm size.

height from the baseof crushed stone trenches is up to the center

of the pipe. the top and the sides of the pipe filled

with concrete 1:2:4 foundation of this class is used if

the sewer pipe underload traffic or300mm minimum cover can notbe provided


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the same as a foundation class, except thematerial used to fill-not necessarily fromthe concrete

minimum depth from the top of the pipeis 300mm (12 inches)


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sewer pipe inside diameteris 600mm or less, it can only be installedin straight alignment and density of only ar

ound in the manhole for sewer pipe inside diameter exceeding 6

00mm it can be installed on a

curved alignmentof the arc diameter is 50m or more

bab 4 - sewerage system

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