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WATERWAY DESIGN for RLYBRIDGES and WEIR for RAT
A CASE STUDYA CASE STUDYCHENNAICHENNAIGUDUR SECTIONGUDUR SECTION
S.RLYS.RLY
Presented By
Sri D . Stanley
ADEN / SW /DHONE SCR
Sri S . Shanmughom
AXEN / MC / TVC SR
Guided By
Shri G.Bansal,Professor
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INTRODUCTION
Design of water way for Rly Bridges have been carried out
in the following circumstances.
1. Construction of New Lines
2. Doubling and Gauge Conversion
3. Rebuilding / Rehabilitation of Bridges
4. HFL raises above DL
5. Water over flowing the track
6. During Floods and breaches of track and Bridges
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Breach in embankment
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BR.NO.245
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DESIGN OF WATERWAY OF RLY BRIDGES
Criteria for design - based on catchment areafor catchment area < 25 Sq.Km
Using Improved Rational Formula
by IMD,RDSO and CWC( RBF-16)
for catchment area > 25 Sq.Km
Using Synthetic Unit Hydrograph Methodby IMD,RDSO and CWC ( Sub-zonal Report )
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CASE STUDY in S.RLY
Flash Flood on 15/16-Oct-2001. ( Rain fall =245mm )
MAS GDR Section @ Km.114 to Km.118
Touched the bottom of Girder @Br.239(6x12.2mGB )
Water crossed DL @ Br.No.240 (7x12.2m GB
Water Level above BOS @ Br.No.245 ( 2x1.83mRCC Slab-DN Line & 1x4.57PSC Slab UP Line
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Estmation of Q 50 Discharge forBr.244 and 245
Lattitude = 130
58 N , Longitude 790
54 ESub Zone 4(b)
Length,L = 1.5 Km
Height of Ridge above bed level ,H= 29.50 22.565 = 6.935m
Time of Concentration TC = (1.53/6.935)0.345
= 0.78 hours
R 50 ( 24 hours ) = 320mm
From graph short duration ratio for TC = 0.3
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ISOPLUVIAL MAP
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0.850.780.6825134
0.860.790.7013530.870.800.7152.52
0.880.810.722.501
60 - 18030 - 60< 30ToFrom
( in Minutes )( Sq.Km. )
Time of Concentration
catchment
Area
Sl.No.
Areal Reduction Factor
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Run off Coeffecient Constant(K)
0.498Hilly soil / Barren areas5
0.456Black cotton / Plain &Barren
//Submontene/Plateau areas
4
0.415Red soil / Clayey /Cultivated Plains / Tall
crops / wooded areas
3
0.332Alluivium / Silty / Coastalareas
2
0.249Sandy Soil/Arid Areas1
Value of K Description of CatchmentS.No
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Contd
Intensity of Rain fall , I= 0.30 * 320 / 0.78 = 123mm/hour
Catchment area ( A ) = 1.22 Sq.Km
,Areial Reduction Factor,F = 0.81
Run off Coeff,C = 0.415 *( 32* 0.81 )0.20 = 0.795
Using Improved Rational FormulaQ 50 = 0.278 * C*I*A = 0.278 * 0.795*123*1.22
= 33.18Cumecs.
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Capacity of Br.No.245( Exg 2 x 1.83m RCC Slab DN
and 1x 4.57 PSC slab UP )
B.O.S = 24.705 , Bed Level = 22.565
HFL = 24.800,Std VC = 0.600 + 3.180 * 0.60/269= 0.610m
Max Allowable HFL = 24.705 0.610= 24.095Max depth pf flow , DF = 1.53m
Wetted area , W A = ( 2*1.83 + 0.90 ) *1.53 =
6.98m2
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Wetted perimeter , WP = 4.56 + 2 * 1.53 = 7.62m
Hydraulic Mean radius , R = 6.98 / 7.62 = 0.92mSlope , S = 1 in 220
Velocity, V = (1 / 0.03) * ( 0.92) 0.67 * ( 1/220)0.50
= 2.12m/secDischarge, Q = 0.9 * 2 * 1.83 * 1.53 * 2.12
= 10.68 cumecs ( DN line Br. Capacity
I.e. < 33.18 cumecs ( Q 50 )
HFL Discharge of Br.245 ( UP line )
Similarly HFL Discharge = 25.94 cumecs < 250
VC available ( UP ) = 25.435 24.800 = 0.635
> 0.620m
VC (DN ) = 24.705 24.800 = -0.095 m
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Proposed 2 x 4.57m PSC slabBr.245Probable HFL = 24.165DF = 24.165 22.565 = 1.600m
Q = 0.90* 2 * 4.57 * 1.56 * 2.57 = 33.8 cumecs > Q 50VC available ( UP ) = 25.435 24.095 = 1.340 > 0.620m
VC (DN ) = 25.045 24.165 = 0.880 m > 0.620m
Free Board Available = 26.225 0.675 24.165 =1.385
I.e > 1.0m Hence OK
Hence It is proposed to rebuild Br.245 as 2 x 4.57 PSCslab ( UP & DN )
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Details of breaches of Tanks
16Damaragunta Tank ( RAT )11
140Kotambedu Tank10
25Chilamanuru Tank9
70Sangavaram Tank8
66Bhatlakanupuru Tank7
12Vengamamba puram Tank5
120Sagatooru Tank4
638Machavaram Tank3
60Mummayapalem Tank2
296Nemallapudi Tank ( RAT )1
Length of thebreach
Name of the TankSl.No.
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Estmation of Q 50 Discharge forBr.239 and 240
Latitude = 130 57 N , Longitude 790 47 E
Sub Zone 4(b)
Length,L = 32.47 Km,Lc=17.05 kmR 50 ( 24 hours ) = 340 mm
Catchment Area =250 SQ KM
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Computation of Equivalent slope
27.087180.58
118.790.1513732.75
1288.56
207.16103.5
8
61.7928032.554
591.2963.5841.799.36030.553463.0321.7921.7921.254021.252
000018.2101
Lix(Di-
1+Di
Di-
1+Di
Ht
Abov
Datm
(Di)
Length
(Li)
Redcd
levl
Dist
Fm Br
Sl No
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Tp=0.376(L*Lc/SQRT(S))0.43
S=1288.567/32.7^2=1.2 m/km : Tp=5.62 hrs=5.5 hrs
qp = 1.215/(tp)0.691 = 0.374cumcs / sq.km
W 50 = 2.211 / ( qp )1.07 = 6.33 hours
W 75 = 1.312 / ( qp ) 1.003 = 3.518 hours
WR 50 = 0.808 / ( qp )1.053 = 2.276 hours
WR 75 = 0.542 / ( qp ) 0.965 = 1.40 hours
TB = 7.621 * ( tp )0.623 = 22.04 hours
QP = qp * A = 0.374 * 250 = 93.50 cumecs
TM = tp + tr / 2 = 6 hours
Determination of Synthetic Unit
graph Parameters
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Unit Hydrograph
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l Estimation of Base FlowQb = 0.536 / ( A ) 0.523 = 0.03 cumecs / sq.km
Total base flow = 0.03 * 250 = 7.50 cumecs
Estimation of design storm duration :
Design storm duration , TD = 1.1tp=1.1*5.5
= 6 hoursEstimation of point rain fall & aerial rain fall
6 hour point rain fall coeff = 0.6950 year 6 h point rain fall = 0.69 * 340
Ariel fraction factor = 0.82
50 year 6hour aerial rain fall = 0.69 * 340 * 0.82= 192 mm
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Time distribution of Aerial Rain fall and Estimation of
Effective Rain fall units
0.00
0.410.40
1.55
3.09
9.62
1 houreffective
rain fall( in cm )
0.38
1.161.15
2.30
3.84
10.37
1 hour rainfall incriment
( in cm )
0.75
0.750.75
0.75
0.75
0.75
Designloss rate(
in cm /hour )
19.201.006
18.820.98517.660.924
16.510.863
14.210.742
10.370.541
StormRain
fall
DistCoeff
Duration (
inhour)
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Estimation of 50 yr Flood Peak
56.00
70.00
84.00
93.50
76.00
UGordinates(
cumecs )
1327.93Total22.400.409
28.700.418
259.563.097
899.479.626
117.781.555
Direct Runoff ( cumecs
)
1 hr effectiverain fall ( in
cm )
Time( inhours )
Q50 = 1327.93 + 7.50 = 1335 cumecs
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HFL Discharge of Br.No.239
( 6 x 12.2m ) GB & Br.No.240( 7 x 12.20mGB )HFL = 25.225 , BL = 18.900
DF = 25.225 18.9 = 6.325
WA =( 6 * 1.2.20 + 5 *1.60 ) * 6.325 = 513.2sq.m
WP = 6 * 12.19 + 5 * 1.60 + 2 * 6.325 = 93.79 m
R = 513.2/93.79 = 5.47 m
V = ( 1/ 0.03 ) * (5.47 ) 0.67 * ( 1 / 975 ) 0.50 = 3.32m/sec
HFL , Q = 0.9 * 6 * 12.2 * 6.325 * 3.32 = 1380 cumecsVC available ( DN ) = 25.475 25.225 = 0.250m < 1.50m ( Std VC )
Similarly HFL discharge of Br.No.240 ( exg 7 x12.20m GB ) = 1346.67cumecsTotal HFL = 1380 + 1346.67 = 2726 . 67 >> 1335 cumecsVC available ( DN ) = 25.860 25.575 = 0.285m
< 1.50m ( Std VC )
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Capacity of Br.No.239
( 6 x 12.2m ) GB & Br.No.240 ( 7 x 12.20m GB )Probable,HFL = 23.270 , BL = 18.900Depth of Flow , DF = 23.270 18.9 = 4.370m
WA =( 6 * 1.2.20 + 5 *1.60 ) * 4.370 = 354.58sq.mWP = 6 * 12.19 + 5 * 1.60 + 2 * 4.370 = 89.88 mR = 354.58 /89.88 = 3.945 mV = ( 1/ 0.03 ) * (3.945 ) 0.67 * ( 1 / 975 ) 0.50 = 2.67m/secQ = 0.9 * 6 * 12.2 * 4.370 * 2.67 = 767 cumecs
VC available ( DN ) = 25.475 23.270 = 2.20m > 1.50m ( Std VC )VC is available ( UP ) = 25.505 23.270 = 2.235mSimilarly capacity of Br.N0.240 ,Q = 0.9 * 7 * 12.2 * 3.300 * 2.26 = 573.60 cumecs
Total HFL = 767 + 573.60 = 1340 > 1335 ( Q 50 )
VC available ( DN ) = 25.860 23.270= 2.590m > 1.50m ( Std VC )VC ( UP ) = 25.800 23.270 = 2.530 > 1.50m ( Std VC )
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Catchment Area of tanks
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Flow pattern of Breached tanks
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Water way design of surplus weir for RAT
RAT Is a tank , a breach / damage / substandard
maintenance or an act of negligence or omission indue operation of which result in danger to anyrailway in the opinion of responsible railway officernot less than DEN.
Nemalla pudi Tank ( RAT ) Catchment area = 52.80 sq.m.Q 50 Discharge = 52.80 * 1335.43/ 250 = 278 cumecs.
Design depth of flow( H ) = 1.03 m = 1.03/0.305=3.37FT.Q = 2 * L * H 1.50 ( FPS units ).
Length of Weir required.L = 278 * 35.31 / ( 2 * (3.37 )1.50 ) = 790 ft = 790 * 0.305 = 240m.
Existing weir length = 42m.Hence Additional weir length is required.with 1.03m designed depth, 240 42 = 198m.
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Additional length of weir required
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Proposals & Conclusions1. Adequacy of waterway should be checked for all minor
bridges and major / important bridges, if it is affected by
RAT / RAW
2. The catchment area of RAT s and connected upper tanks
should be studied and length of surplus weir to be checked
for adequacy.
3. The ADEN in charge of the section should conduct joint
inspection with the engineers of state irrigation department
regarding the stability of bunds ,water way etc beforeonsoon as per guide lines specified in the relevant manuals
and codes.
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References
1. Flood Estimation Methods for catchments
< 25 sq.km in area ( RBF 16 ) by RDSO
2. Flood Estimation Report Eastern Coast Region
( Sub Zones 4 a,b, &c ) CWC and RDSO
3. IRS Code for sub structure and foundations
4. IRS Bridge Manual
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Acknowledgements
we are very much thankful to IRICEN Institute in
providing the well equipped library and computer centre as well as in the hostel premises also. For this we extend our sincere
thanks to the Director, IRICEN and faculty members.
We are very much grateful to our project guide shri G. Bansal , professor /Bridges, IRICEN ,Pune for his valuable
guidance in preparing the project work entrusted to us.
We extend our sincere thanks to the Chief BridgeEngineers office( Flood Section ) / Southern Railway and state
irrigation dept , GUDUR for providing us the records for the
case study.
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THANK YOU