design of sanitary sewers

7/30/2019 Design of sanitary sewers

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5th December, 2009

HYDRAULIC DESIGN OF SEWERS


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DESIGN PERIODS

Sewers: 30 years

Sewage Pumping Stations

Civil Structures: 30 years

Equipment:phases of 15 years

Sewage Treatment Plants:phases of 10 to 15 years

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POPULATION FORCASTS AND WATER

DEMAND FORCASTS

City/ Town Level

Wards Level

Sewerage Zone Level

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In well developed Urban areas, sewage flows may

be as high as 90% of water supply due to industrial wastes

contribution.

Generally average sewage flow may be taken as 80% of

water supply. However sewers should be designed for at

least 100 lpcd.

(CPHEEO manual on Sewerage)

PER CAPITA SEWAGE FLOW

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PEAK FACTORS

(Ratio of Maximum to Average Flow)

Contributing

Population

Peak Factor

Up to 20,000 3.0

20,000 to 50,000 2.5

50,000 to 7,50,000 2.25

Above 7,50,000 2.0

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INFILTRATION OF GROUND WATER

Units Minimum Maximum

l/Ha.d 5,000 50,000

l/km.d 500 5,000

Lpd/manhole 250 500

Approximately Infiltration can be assumed to be about 10 to

15% of average sewage flow.

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MANNINGS FORMULA

General form,V = (1/N) x ( R S)

For Circular Conduits,

V = (1/N) x (3.968 x 10-3

)D

S

And Q = (1/N) x (3.118 x 10-6)D8/3 S

Where, Q = Discharge in lps;

S = Slope;

D = Internal Dia of pipe in mm;

R= Hydraulic radius (A/P) in mm;

V= Velocity, in m/sec;

N= Mannings coefficient of roughness

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COEFFICIENT OF ROUGHNESS N

Material Condition N

Stoneware Pipe a) Good 0.012

b) Fair 0.015

Reinforced

Cement Concrete

a) Good 0.011 to 0.013

b) Fair 0.015

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Minimum size of public sewer - 150mm

Minimum velocity for present peak flow - 0.6m/sec

Maximum velocity to avoid erosion - 3.0m/secTrial full flow velocity - 0.75 to 1.0 m/sec

Minimum depth of cover over crown - 1.0 m

Depth of flow - 0.8D at ultimate peak flow

(CPHEEO Manual on Sewerage)

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DESIGN PARAMETERS


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Manholes to be provided at;Every change in alignment, gradient, diameter

Head of all sewers

Junction of sewers

Intermediate locations with spacing not greater that 30m

on manually cleaned manholes.

90 to 150m spacing for900 to 1500mm dia mechanicallycleaned sewers

150 to 200m spacing for 1.5 to 2.0m dia mechanically

cleaned sewers.

MANHOLE SPACING

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DEPTH OF FLOW WITH SIZE OF SEWER

Size (mm) d/D

Upto 400

> 400 upto 900

> 900mm

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SEWER 3 software of the World Bank


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HYDRAULIC ELEMENTS OF CIRCULAR

SEWERS RUNNING PARTIALLY FULL

d/D a/A p/P r/R For N/n=1.0 N/n For variable N/n

v/V q/Q v/V q/Q

(1) (2) (3) (4) (5) (6) (7) (8) (9)

1.00 1.000 1.000 1.000 1.000 1.000 1.00 1.000 1.000

0.90 9.949 0.795 1.192 1.124 1.066 0.94 1.057 1.002

0.80 0.858 0.705 1.217 1.140 0.988 0.88 1.003 0.869

0.70 0.748 0.631 1.185 1.120 0.838 0.85 0.952 0.712

0.60 0.626 0.564 1.110 1.072 0.671 0.83 0.890 0.557

0.50 0.500 0.500 1.000 1.000 0.500 0.81 0.810 0.405

0.40 0.373 0.436 0.857 0.902 0.337 0.79 0.713 0.266

0.30 0.252 0.369 0.684 0.776 0.196 0.78 0.605 0.153

0.20 0.143 0.295 0.482 0.615 0.088 0.79 0.486 0.070

0.10 0.052 0.205 0.254 0.401 0.021 0.82 0.329 0.017

0.00 0.000 --- --- --- 0.000 --- --- ---20


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Qaverage= 0.0094 cumec,

Peak factor = 2.5

Actual Qpeak= 0.0094 x 2.5 = 0.0235 cumec

Try 150mm size;

From Table, forvfull= 0.908m/sec, Grade 1 in 90

Qfull= 0.0161cumec

< Actual Qpeak0.0235 cumec

150mm size not adequate

ADEQUACY OF PIPE SIZE AND VELOCITY

AT PEAK FLOW..(1)

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AT PEAK FLOW..(2)

Try 200mm size

From Table, ForVfull= 0.898 m/sec; Grade 1 in 135

Qfull= 0.0282 cumecFord/D = 0.5, q/Qfull= 0.4050 for N/n variable;

q = 0.4050 x 0.0282 = 0.0114 cumec

< 0.0235

200mm size is inadequate

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A Q AC O S A OC


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AT PEAK FLOW..(3)Try 300mm size

From Table, ForVfull= 0.902 m/sec; Grade 1 in 230

Qfull= 0.0638 cumec

Ford/D = 0.5, q/Qfull= 0.4050 for N/n variable;

q = 0.4050 x 0.0638 = 0.0259 cumec

> 0.0235

300mm size is adequate.

Actually q/Qfull= 0.0235/0.0638 = 0.368From diagram, forq/Qfull= 0.368, d/D = 0.48

From diagram, v/Vfull= 0.78

vactual

= 0.902 x 0.78 = 0.703 m/sec

> 0.6m/sec OK 25

DESIGN OF SEWER SYSTEM


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DESIGN OF SEWER SYSTEMLine Location Manholes Ground

level at

starting

manhole

Length Area Served (ha) Population Sewage

flow

mld

Ground

water

infiltration

mld

From To Increment Total

1 2 3 4 5 6 7 8 9 10 11

1. Street R.8.5 R.8.4 38.275 120 0.80 0.80 240 0.054 0.016

2. Street R.8.4 R.8.3 37.960 116 1.2 2.0 600 0.135 0.040

3. Street R.8.3 R.8.2 36.873 114 1.40 3.40 1020 0.230 0.068

4. Street R.8.2 R.8.1 36.895 116 0.90 4.30 1290 0.290 0.066

5. Street R.8.2 R.8.1 36.420 75 0.70 5.0 1500 0.34 0.10

Peak flow Diameter

mm

Slope Discharge lps Velocity mps Total

fall m

Invert Elevation m

mld lps Q Full Q Actual V Full V Actual Upper end Lower end

12 13 14 15 16 17 18 19 20 21 220.205 2.37 150 0.008 14 2.37 0.75 0.57 0.96 37.125 36.165

0.5112 5.92 150 0.008 14 5.92 0.75 0.72 0.93 36.135 35.205

0.873 10.10 150 0.008 14 10.10 0.75 0.82 0.91 35.175 34.265

1.10 12.73 150 0.008 14 12.73 0.75 0.86 0.93 34.235 33.305

1.29 14.92 200 0.005 24 14.92 0.70 0.74 0.38 34.275 33.89526


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SEWER 3

WORLD BANK

SOFTWARE


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ECHOING INPUT VARIABLE

Title of the Project: WRR75n

Name of the User: CHAWATHENumber of Pipes: 20

Number of Nodes: 21

Minimum Velocity, m/sec: 6

Maximum Velocity, m/sec: 3

Minimum Allowable Cover, m: 2.44

Maximum Allowable Cover, m: 7

Number of Existing Pipes:Number of Commercial Diameters: 10

Number of Excavation Layers: 5

InFiltration Rate in percentage: 1

Maximum Allowable Slope as X (1:X): 30

Minimum Allowable Slope as X (1:X): 1000

Diameter Progression Considered? (Y/N): Y

Manning 'n' to be kept constant? (Y/N): N

Lay Pipe Parallel to Ground? (Y/N): Y

Provide Drop if Min Cov Violates? (Y/N): N

Lowest/Mean/Highest/Auto Dia? (L/M/H/A): L

Type of Backfill: Saturated TopsoilUnit Weight of BackFill Soil kg/sq m: 1840


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PIPE DATA

Pipe No. From Node To Node Length m Manning n Diameter mm Min. Vel. m/sec Max. Vel. m/sec

1 1 2 106.00 0.0130 0.6 3.00

2 2 3 121.00 0.0130 0.6 3.00

3 3 4 106.00 0.0130 0.6 3.00

4 6 5 121.00 0.0130 0.6 3.00

5 5 4 131.00 0.0130 0.6 3.00

6 4 7 167.00 0.0130 0.6 3.00

7 8 7 106.00 0.0130 0.6 3.00

8 9 8 137.00 0.0130 0.6 3.00

9 10 9 152.00 0.0130 0.6 3.00

10 7 11 152.00 0.0130 0.6 3.00

11 12 11 106.00 0.0130 0.6 3.00

12 13 12 106.00 0.0130 0.6 3.00

13 14 13 152.00 0.0130 0.6 3.00

14 11 15 182.00 0.0130 0.6 3.00

15 18 17 121.00 0.0130 0.6 3.00

16 17 16 191.00 0.0130 0.6 3.00

17 16 15 106.00 0.0130 0.6 3.00

18 15 19 121.00 0.0130 0.6 3.00

19 19 20 152.00 0.0130 0.6 3.00

20 20 21 182.00 0.0130 0.6 3.00

O A A


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NODE DATANode No. Flow lps Elevation m Peak Factor Pumping (Y/N/F) Minimum Cover (m)

1 113.300 152.40 1.00 2.44

2 84.960 150.88 1.00 2.44

3 56.640 148.44 1.00 2.44

4 141.600 146.30 1.00 2.44

5 113.280 149.83 1.00 2.44

6 113.280 149.35 1.00 2.44

7 169.920 143.26 1.00 2.44

8 113.280 144.78 1.00 2.44

9 133.280 147.83 1.00 2.44

10 226.560 149.35 1.00 2.44

11 198.240 141.73 1.00 2.44

12 113.280 143.26 1.00 2.44

13 198.240 144.78 1.00 2.44

14 254.880 147.83 1.00 2.44

15 198.240 138.68 1.00 2.44

16 85.960 140.21 1.00 2.44

17 56.640 141.43 1.00 2.44

18 113.280 142.65 1.00 2.44

19 56.640 137.46 1.00 2.44

20 141.600 136.55 1.00 2.44

21 0.000 135.64 1.00 2.44

COMMERCIAL DIAMETER DATA


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COMMERCIAL DIAMETER DATA

Pipe Diameter Maximum

d/D

Trench

Width m

Unit Cost Rs. /m

length

Strength (km/m)

Internal External

500.0 550.0 0.5 0.85 550.0 2300.00

600.0 650.0 0.5 0.95 650.0 2400.00

800.0 850.0 0.5 1.15 850.0 2500.00

1000.0 1050.0 0.67 1.35 1050.0 2600.00

1200.0 1250.0 0.67 1.55 1250.0 2700.00

300.0 350.0 0.67 0.65 350.0 2200.00

150.0 200.0 0.75 0.5 200.0 2000.00

200.0 250.0 0.75 0.55 250.0 2100.001300.0 1350.0 0.75 1.65 1350.0 2800.00

1500.0 1550.0 0.75 1.85 1550.0 2900.00

EXCAVATION COST DATA


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EXCAVATION COST DATA

Depth of Excavation in m Unit Rate Rs/cub m Vol

From To

0.00 3.00 1.00

3.00 6.00 2.00

6.00 9.00 3.00

9.00 12.00 4.00

12.00 50.00 6.00

PIPE DETAILS


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PIPE DETAILSPipe No. From Node To Node Peak Flow (lps) Length (m) Diameter mm Pipe Slope Ground Slope Existing

Pipe

1 1 2 113.413 106.00 500.0 67 69.6

2 2 3 198.458 121.00 500.0 47 49.73 3 4 255.155 106.00 500.0 47 49.6

4 6 5 133.393 121.00 500.0 73 79.6

5 5 4 266.787 131.00 500.0 86 85.8

6 4 7 623.683 167.00 800.0 190 54.8

7 8 7 473.593 106.00 600.0 68 69.6

8 9 8 360.200 137.00 500.0 44 44.9

9 10 9 226.787 152.00 500.0 96 99.7

10 7 11 1267.366 152.00 1000.0 98 99.6

11 12 11 566.966 106.00 600.0 50 69.5

12 13 12 453.573 106.00 600.0 67 69.6

13 14 13 255.135 152.00 500.0 47 49.8

14 11 15 2032.771 182.00 1200.0 222 59.8

15 18 17 113.393 121.00 500.0 97 99.2

16 17 16 170.090 191.00 500.0 152 156.6

17 16 15 256.136 106.00 500.0 67 69.5

18 15 19 2487.345 121.00 1200.0 148 99.3

19 19 20 2544.042 152.00 1200.0 142 166.1

20 20 21 2685.783 182.00 1200.0 127 200.0

PIPE LEVEL DETAILS


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PIPE LEVEL DETAILSPipe No. Ground Elevation Crown Level Invert Level Execution Depth

U/S (m) D/S (m) U/S (m) D/S (m) U/S (m) D/S (m) U/S (m) D/S (m)

1 152.4 150.9 150.0 148.4 149.4 147.8 3.1 3.1

2 150.9 148.4 148.4 145.8 147.8 145.3 3.2 3.2

3 148.4 146.3 145.8 143.6 145.3 143.0 3.0 3.3

4 149.4 147.8 146.9 145.3 146.4 144.7 3.1 3.1

5 147.8 146.3 145.3 143.7 144.7 143.2 5.5 3.1

6 146.3 143.3 141.7 140.8 140.8 140.0 3.1 3.3

7 144.8 143.3 142.3 140.8 141.7 140.1 3.1 3.1

8 147.8 144.8 145.3 142.2 144.8 141.7 3.0 3.1

9 149.4 147.8 146.9 145.3 146.4 144.8 3.5 3.1

10 143.3 141.7 140.8 139.3 139.8 138.2 3.2 3.5

11 143.3 141.7 140.7 138.5 140.0 137.9 3.2 3.8

12 144.8 143.3 142.3 140.7 141.6 140.0 3.0 3.2

13 147.8 144.8 145.4 142.2 144.8 141.6 5.9 3.2

14 141.7 138.7 137.1 136.2 135.8 135.0 3.0 3.7

15 142.6 141.4 140.2 139.0 139.7 138.4 3.0 3.0

16 141.4 140.2 139.0 137.7 138.4 137.2 3.1 3.1

17 140.2 138.7 137.7 136.1 137.2 135.6 4.1 3.1

18 138.7 137.5 135.8 135.0 134.6 133.8 3.7 3.7

19 137.5 136.6 135.0 134.0 133.8 132.7 3.8 3.8

20 136.6 135.6 134.0 132.5 132.7 131.3 4.4 4.4

PIPE MISC DETAILS


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PIPE MISC DETAILS

Pipe No. Dia. Mm d/D Partial Velocity (m/sec) Pipe Slope Remarks

1 500.0 0.39 1.60 67

2 500.0 0.48 2.13 47

3 500.0 0.55 2.31 47

4 500.0 0.40 1.55 73

5 500.0 0.61 1.81 86

6 800.0 0.67 1.74 190

7 600.0 0.66 2.39 68

8 500.0 0.66 2.62 44

9 500.0 0.63 1.74 96

10 1000.0 0.59 2.63 98

11 600.0 0.67 2.82 50

12 600.0 0.64 2.37 67

13 500.0 0.55 2.31 47

14 1200.0 0.75 2.23 22215 500.0 0.43 1.40 97

16 500.0 0.61 1.36 152

17 500.0 0.61 2.04 67

18 1200.0 0.75 2.73 148

19 1200.0 0.75 2.80 142

20 1200.0 0.75 2.95 127

NODE DETAILS


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NODE DETAILSNode No. Node Type Peak Factor Peak Flow (lps) Ground Elevation (m) Excavation Depth (m) Pumping Provided (Y/N)

1 REF 1.00 113.300 152.40 3.0

2 1.00 84.960 150.88 3.1

3 1.00 56.640 148.44 3.2

4 CONF 1.00 141.600 146.30 3.0

5 1.00 113.280 149.83 3.1

6 REF 1.00 113.280 149.35 5.5

7 CONF 1.00 169.920 143.26 3.1

8 1.00 113.280 144.78 3.1

9 1.00 133.280 147.83 3.0

10 REF 1.00 226.560 149.35 3.5

11 CONF 1.00 198.240 141.73 3.2

12 1.00 113.280 143.26 3.2

13 1.00 198.240 144.78 3.0

14 REF 1.00 254.880 147.83 5.9

15 CONF 1.00 198.240 138.68 3.0

16 1.00 85.960 140.21 3.0

17 1.00 56.640 141.43 3.1

18 REF 1.00 113.280 142.65 4.1

19 1.00 56.640 137.46 3.7

20 1.00 141.600 136.55 3.8

21 TAIL 1.00 0.000 135.64 4.4

RELATIVE SIZES AND LEVELS OF


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Outgoing sewer size to be at least equal

to the size of the largest of incoming sewers.

Sewers to be continuous.The crown of the outgoing sewer not to be higher

than that of incoming sewers.

Hydraulic flow line in the outgoing seer not to behigher than that in the incoming sewers.

RELATIVE SIZES AND LEVELS OF

INCOMING AND OUTGOING SEWERS AT

MANHOLE

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design of sanitary sewers

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