Syphon Project - Copy 4e5g1x

INTRODUCTION; Syphon is a cross drainage work, i.e a structure which is constructed at the crossing of a canal and a natural dam. So as dispose of drainage water without interrupting the continuous canal super piles. In whatever way the canal is aligned, such drainage work generally become unavailable. In order to reduce the cross drainage work, the artificial canals are generally aligned along the ridge lines called water shed. When once the canal reaches the watershed, line across drainage work are generally not required, unless the canal aligned is deviated from the watershed line. However before the watershed is reached, the canal which takes off from the river has to cross a number of drains, which drove from the watershed towards the river. A Cross drainage work is generally a costly construction and most be avoided as far as possible, Since the watershed canal crosses minimum number of dams.  The number of cross drainage work may also be reduced by diverting one dam into another and also by the alignment of canals. So that it crosses below the junction of the drains. PURPOSE OF DEG SYPHON  The purpose of siphon is to drain liquid from the reservoir by liquid flow that es over a higher level than the liquid surface in reservoir.  A canal conveying water from the hand work has to run for large distance and has to maintain the water levels appropriately as designed along its length.

DRAINAGE SYPHON

 It has to run through terrains which generally would have a different slope than the canal. The surrounding areas would invariably have its own discharge system ranging from small stream to large rivers.  The has to carry the water across these water bodies as well as artificial obstacles like railway or roads.  Hence to prevent the hindrance of mobility of water as well as mobility of people or vehicles. We prepare a design for a structure known as Siphon. FUNCTIONS OF SIPHONS;  The siphon has been recognized for ages. A siphon is created by a tube or other type of conduit filled with the liquid to be siphoned, thereby creating a continuous and closed path.  In any siphon the discharge end of the conduct must be lower than the level of the fluid in the source reservoir. Atmospheric pressure of the reservoir surface becomes the driving force pushing the fluid through the tube to the lower point of the discharge.

DRAINAGE SYPHON

TYPES OF SIPHON; Depending upon the level of discharge it is of following types; Aqueduct

Siphon Aqueduct

 Aqueduct;- When the high flood level(HFL) of the drain is sufficiently below the bottom of the canal such that the drainage water flows freely under gravity, then the structure is known as Aqueduct.  Siphon Aqueduct;- In siphon aqueduct the high flood level(HFL) of the drains is much higher above the canal bed and the water runs under siphonic action through the aqueduct i.e. known as siphon aqueduct. DETAILED DESCRIPTION AQUEDUCT AND SYPHON AQUEDUCT;In these works, the canal is taken over the natural drain, such that the drainage water runs below the canal either freely or under siphoning pressure. When the HFL of the

DRAINAGE SYPHON

drain is sufficiently below the bottom of the canal, so that the drainage water flows freely under gravity, the structure is known as the aqueduct. However, if the HFL of the drain is higher than the canal bed and the water es through the aqueduct barrels under syphonic action, the structure is known as siphon aqueduct.

In this type of works, the canal water is taken across the drainage in a through, as shown in fig. An aqueduct is just like a bridge except that instead of carrying o road or a railway, it carries a canal at its top. An aqueduct is provided when sufficient level difference is available between the canal and the natural drainage the canal bed level is sufficiently higher than the torrent level. In Sirsa, a city near Roper in Punjab, an excellent aqueduct having 20 spans of about 13m each have been constructed to carry a canal having a bed width of 28 meters and a discharge of about 4300 cumecs. A difference of 3.3meters was available between the bed level of the canal and that of torrent in this case. In this case of a siphon Aqueduct, the drain bed is generally depressed and provided with a

DRAINAGE SYPHON

pucca floor as shown in figure on the upstream side, the drainage bed may be ed to the pucca floor either by a vertical drop (when the drop is of order of 1m) or by a glacis of 3.1m (when the drop is more).The down-stream rising slope should not be steeper than 5:1. In this type of cross-drainage work, the canal remains open to inspection, and the damage caused by floods are rare. However, during heavy floods, the foundation of the work may be susceptible or waterway of the work may be chocked with debris, trees etc. SUPER AGE AND SYPHON;In these works, the drain is taken over the canal such that the canal water runs below the drain either freely or under siphoning pressure. When the FSL of the canal is sufficiently below the bottom of the drain through. So that the canal water flows freely under gravity, the structure is known as super age. However, if the FSL of the canal is sufficiently above the bed level of the drainage through, so that the canal syphon or syphon. A super age is thus the reverse of an aqueduct, and similarly, a siphon is reverse of an aqueduct, and similarly, a siphon is reverse of an aqueduct syphon. However in these type of cross drainage work the inspection road cannot be provided along the canal and separate bridge is required for the

DRAINAGE SYPHON

road way. For effective economy, the canal may be flumed, but the drainage through is never flumed. In the case of siphon, the canal bed is depressed and a ramp is provided at the exist so that the trouble of silting is minimized. VARIOUS TYPES OF AQUEDUCTS AND SYPHON AQUEDUCTS;These are mainly divide into three types;TYPE-I TYPE-II TYPE-III TYPE-I ;In this type, the sides of the aqueduct are earthen banks with complete earthen slopes. The length of the culvert through which the drainage the water has to under the canal should not only be sufficient to accommodate the water section of the canal but also the earthen banks of the canal with aqueduct slopes

TYPE-II ;In this type, the canal continuous in its earthen section over the drainage, but the outer slopes of the canal

DRAINAGE SYPHON

banks are replaced by retaining walls, thereby, reducing the length of the drainage culvert by that much extent.

TYPE-III ;In this type, earthen section of the canal is discontinuous and the canal water is carried in a masonry or a concrete though. The canal is generally flumed in this case, so as to find economy in the construction. The culvert length or width of aqueduct is maximum in type-I and minimum in type-III. An intermediate value exists in type-III.

SELECTION OF SUITABLE TYPE;The selection of a particular type out of three types of aqueducts or siphon-aqueducts lies on the consideration of economy. T he cheapest of three types at a particular place shall be the obvious choice. SIGHT LOCATION FOR SYPHON The following points should be considered while selecting the site of a cross-drainage work:  At the site, the drainage should cross the canal alignment at right angles. Such a site provides good

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flow conditions and also the cost of the structure is usually a minimum.  The stream at the site should be stable and should have stable banks.  For economical design and construction of foundations, a firm and strong sub-stratum should exit below the bed of the drainage at a reasonable depth.  The site should be such that long and high approaches of the canal are not required.  The length and height of the marginal banks and guide banks for the drainage should be small.  In the case of an aqueduct, sufficient headway should be available between the canal trough and the high flood level of the drainage.  The water table at the site should not be high, because it will create De-watering problems for laying foundations.  As far as possible, the site should be selected d/s of the confluence of two streams, thereby avoiding the necessity of construction of two cross-drainage works.  The possibility of diverting one stream into another stream upstream of the canal crossing should also be considered and adopted, if found feasible and economical.

DRAINAGE SYPHON

 A cross-drainage work should be combined with a bridge, if required. If necessary, the bridge site can be shifted to the cross-drainage work or vice versa. The cost of the combined structure is usually less. Moreover, the marginal banks and guide banks required for the river training can be used as the approaches for the village roads. SELECTION OF SUITABLE TYPE OF CROSSDRAINAGE WORK The following factors should be considered while selecting the most suitable type of the cross-drainage work.

1. RELATIVE LEVELS AND DISCHARGES: The relative levels and discharges of the canal and of the drainage mainly affect type of cross-drainage work required. The following are the broad outlines: 1. If the canal bed level is sufficiently above the H.F.L. of the drainage, an aqueduct is selected.

DRAINAGE SYPHON

2. If the F.S.L. of the canal is sufficiently below the bed level of the drainage, a superage is provided. 3. If the canal bed level is only slightly below the H.F.L. of the drainage, and the drainage is small, a siphon aqueduct is provided. If necessary, the drainage bed is depressed below the canal. 4. If the F.S.L. of the canal is slightly above the bed level of the drainage and the canal is of small size, a canal syphon is provided. 2. PERFORMANCE: As far as possible, the structure having an open channel flow should be preferred to the structure having a pipe flow. Therefore, an aqueduct should be preferred to a syphon aqueduct. Likewise, a super-age should be preferred to a canal siphon. In the case of a syphon aqueduct and a canal syphon, silting problems usually occur at the crossing. Moreover, in the case of a canal syphon, there is considerable loss of command due to loss of head in the canal. The performance of inlet-outlet structures is not good and should be avoided. 3. PROVISION OF ROAD: An aqueduct is better than a super-age because in the former, a road bridge can easily be provided along with the canal trough at a small extra cost, whereas in the latter, a separate road bridge is required. 4. SIZE OF DRAINAGE: When the drainage is of small size, a syphon aqueduct will be preferred to an aqueduct as the latter involves high banks and long approaches. However, if the

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drainage is of large size, an aqueduct is preferred. 5. COST OF EARTHWORK: The type of cross-drainage work which does not involve a large quantity of earthwork of the canal should be preferred. 6. FOUNDATION: The type of cross-drainage work should be selected depending upon the foundation available at the site of work. 7. MATERIAL OF CONSTRUCTION: Suitable types of material of construction in sufficient quantity should be available near the site for the type of cross-drainage work selected. Moreover, the soil in sufficient quantity should be available for constructing the canal banks if the structure requires long and high canal banks. 8. COST OF CONSTRUCTION: The cost of construction of cross-drainage work should not be excessive. The overall cost of the canal banks and the cross-drainage work, including maintenance cost, should be a minimum.

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9. PERMISSIBLE LOSS OF HEAD: Sometimes, the type of cross-drainage is selected considering the permissible loss of head. For example, if the head loss cannot be permitted in a canal at the site of cross-drainage, a canal syphon is ruled out. 10. SUBSOIL WATER TABLE: If the subsoil water table is high, the types of crossdrainage which requires excessive excavation should be avoided, as it would involve De-watering problems. 11. CANAL ALIGNMENT: The canal alignment is sometimes changed to achieve a better type of cross-drainage work. By changing the alignment, the type of cross-drainage can be altered. The canal alignment is generally finalized after fixing the sites of the major cross-drainage works.

DATA-REQUIREMENT 6.1- For any type of cross drainage work some data is required which is common to all types of cross drainage works. A location map for the work with results of subsurface exploration conducted at site, cross sections of the stream, upstream and downstream of the proposed site, should be prepared, as given in 6.2 to 6.9. 6.2- An index map to a suitable scale showing the recommended location of the cross drainage structure, the alternative sites of crossings investigated and rejected, the existing communications, the general topography of the country and the import?& habitations in the vicinity. . J 1

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6.3- A catchment area map to a suitable scale, with contour markings at suitable intervals showing the main drainage channel front its sources together with all its tributaries. The map should also show the various locations of rain gauge stations, gauging sites, etc, as also the general soil types and land use (that is forests, cultivated and uncultivated areas). The hydrological observation sites should also be marked. Existing, under construction or proposed embankments and flood management measures should also be shown. 6.4 A detailed survey plan of the drainage channel to suitable scale showing important topographical features extending considerable distances, downstream and upstream, of the proposed site of crossing and either of its banks. I 6.5- A site plan to a suitable scale showing & details of the site selected and extending upstream and downstream, of the centre line of the proposed crossing and covering its approaches to sufficient distances, so as to demarcate levels, cadastral survey plot numbers, important topographical features like depressions near the proposed alignment of canal, general sub-soil water levels (with slope, if possible), etc. 6.5.1- The other requirements for the plan at 6.5 are: a) b) 4 d j e) 0 g) reference to the position of the benchmark used as datum with its full description and reduced level; the lines and identification numbers of the cross sections and longitudinal sections of drainage channel taken within the scope of site plan and exact locations of their extreme points; the locations of the

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various trial pits and/or. Borings with tilter identification numbers; The contour of the drainage channel at intervals between 0’5 m to 1’5 m depending upon the terrain. This interval region be greater in mountainous regions; The direction of flow of water; The angle of direction of crossing; and Cross alignment of canal further upstream for some distance beyond the limits of cross drainage works. 6.6- A cross section of the drainage channel at the proposed site of the crossing to appropriate vertical and horizontal scales indicating the following information: a) Cross section covering the bed and banks of the channel portion and the ground levels beyond the banks covering the entire flood plane, or from ridge to ridge at close intervals to sufficient distances on either side showing all uneven features and habitations, if any; b) Nature of the soil in bed, banks and approaches, with trial pit or bore-hole sections showing the levels and natures of the various strata down to stratum suitable from foundation considerations and front considerations of safe bearing capacity of soil; c); Lowwater level; and d). &High flood level. 6.7- Longitudinal section of the drainage channel covering a reasonable reach to suitable scale, showing the location of the cross drainage work, with levels of the observed flood, the low water and the bed levels at suitably spaced intervals along the line of the deep water channel. 6.8 A note giving the salient features relating to the catchment area, the meteorological conditions experienced thereon, besides the following other points: a) b) 2 Any predictable (future) alteration

DRAINAGE SYPHON

in the land use; Storages in the catchment (artificial or natural) 6.8- A note giving the salient features relating to the catchment area, the meteorological conditions experienced thereon, besides the following other points: a) b) 2 Any predictable (future) alteration in the land use; Storages in the catchment (artificial or natural). and embankment breaches that have occurred in the past; Short duration intensity and frequency data in respect of rainfall in the catchment; Liability of the site to seismic disturbances; Likelihood of heavy sediment charge or floating timber, Particulars of foundation exploration data incidental to design requirements; and Recuperation tests, where foundation depth is more than 3 m below the water table and where the strata are pervious. 6.9- A note giving the salient design features of structures existing upstream or downstream of the proposed site. 63.1 Presence of dams, barrages, weirs, etc, on the natural drainage channel in the vicinity either upstream or downstream, may affect the hydraulic characteristics of the natural drainage channel, like obliquity and concentration of flow, scour, silting of bed, change in bed levels, flood levels, etc. These effects should be considered in the design of the cross drainage work. 6.10- For preparing the design of a cross drainage structure, the following specified hydraulic data should -- also be made available.

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6.10.1 Canal 1. 2 3. 4. 5. 6. 7. 8. 9. 10. 11. Full supply discharge, Q; Bed width; Full supply depth; Water surface slope; Bed level; Bed slope; Full supply level; Top of bank level; Cross section of canal showing Natural Ground Level; Subsoil water level; and Nature pf bed material and value of ‘n’ (rugosity coefficient in Manning’s formula). i’ 6.10.2 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. IS 7784 (Part 1) : 1993 Drainage Channel Extent and nature of drainage area (catchment’ area); Maximum annual rainfall and the period (years) of data; Maximum intensity of rainfall with year; Maximum observed flood discharge at the site; Maximum flood level; Water surface slope; Site plan of proposed crossing including contours; Log of borehole or trial pit data; Type of bed load of drainage channel; Longitudinal section of the stream for suitable distance upstream and downstream of the canal depending upon site conditions; Cross section of the drainage channel for a distance 100 m to 300 m upstream and downstream, at intervals of 10 m to 50 m; Waterways provided in road and railway bridges or other hydraulic structures on the drainage channel; Spring water level at the crossing site in May and October; and Silt factor. 7 DESIGN FLOOD FOR DRAINAGE CHANNEL 7.1 Design blood for drainage channel to be adopted for cross drainage works should depend upon the size of the canal, size of the drainage channel and location of the cross drainage. A very long canal, crossing a drainage channel in the initial reach, damage to which is likely to affect the canal supplies over a large area

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and for a long period, should be given proper weight age. 7.2- Cross drainage structures are divided into four categories depending upon the canal discharge and drainage discharge. Design flood to be adopted for these four categories of cross drainage structures is given in Table 1. Category structure

A B

of Canal Estimated discharge in drainage cumec/sec discharge in cum/sec 0-0.5 All discharge 0.5-15 0-150 Above 150

C

15-30

0-100 Above 100

D

Above 30

0-150 Above 150

Frequency of design flood

1 in 25 years 1 in 50 years 1 in 100 years 1 in 50 years 1 in 100 years 1 in 100 years As Note 2

STRUCTURAL DESIGN OF SYPHON A simply ed one-way siphon of effective span 4 m is ed on masonry wall of 230 mm thickness. 2

Design the siphon. Take live load equal to 14.715 KN/m 2

and floor finish equal to 1KN/m . The materials are M 20 grade concrete and HYSD reinforcement of grade Fe 415. SOLUTION

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Assuming o.35% steel, a trial depth can be found out by using deflection criteria. Service stress = 0.58 f

y



= 0.58 415 2

=240 N/mm Modification factor = permissible

span d

ratio



= 1.4 20 = 28 required

d



4000 28

=142.85 mm. D=d

required

+cover+dia of bar/2

=142.85+15+

10 2

(assume 10 # bar)

=162.85 mm. Assume an overall depth =170 mm. 



Self weight/dead load = D 1 unit weight of RCC =0.17

×

1

× 2

=4.25 KN/m 2

Floor finish = 1.00 KN/m 2

Live Load = 14.715 KN/m Total Load = 4.25+1.00+14.715

25

DRAINAGE SYPHON 2

=19.96 KN/m ×

Factored Load=19.96

1.5 2

=29.94 KN/m Maximum moment =

W  L2 8

=

29.94  4 2 8

=59.88 KNm. Maximum shear =

W L 2

=

29.94  2 2

=59.88 KN.

DESIGN FOR FLEXURE Assume D=170 mm Effective depth (d) =D-clear cover-diameter/2 D=170-15-5 =150 mm M u 59.88 10 6  bd 2 1000 150 2

=2.66

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





4.6 M u  fck bd 2 fy



f ck 

 1 1

 t  50 

p

   



=50

4.6 59.88  10 6   1 1 20 1000 150 2  415   20 

     

=0.910 A

streq uired

=

=

pt  b  d 100

0.910  1000  150 100 2

=1365 mm Provide 10 mm bar pt  b 

  dia 2 4

Astrequired

So spacing =

0.910  1000 

  10 2 4

1365

=

= 50 mm. Provide 10 mm# 50 mm c/c Half of the bars are bent up 0.1L =0.1

×

4000

= 400 mm

DRAINAGE SYPHON 2

Remaining bars provide =785.4 mm area 100 As 100  785.4  b d 1000 170

= 0.462 > 0.12…….ok I.e. remaining bars provided minimum steel, Thus half of the bars may be bent up. Distribution steel =

0.12  1000 170 100 2

=204 mm 2

Provide 8 mm# @ 240 mm c/c =209.43 mm CHECK FOR SHEAR Depth = 150mm 100 As 100 1413.71  b d 1000 150

= 0.94 From IS code 0.75

0.56

1.00

0.62

By interpolation

0.56 + c

 0.62  0.56    1.00  0.94  1.00  0.75  2

=0.5744 N/mm

For 170 mm thick slab c

K =1.26

×

0.57

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=0.72 Actual shear =

59.88 10 3 1000 170

=0.352 < 0.72……… (Safe) CHECK FOR DEVELOPMENT LENGTH 0

Consider L = 8 # for continuing bars A

st

 785.4mm 2

. st

1

Assume, Mu =0.87 fy A (d-0.42 x xu  xu max

=0.48 d =0.48

150

=72 mm.  415  785.4  150  0.42  72 10 6

u1

M =0.87 =33.96 KN.m V

u

 59.88

1.3

KN

M u1  L0  Ld Vu 1.3 

i.e.

33.96  10 6 8 59.88  103

≥

#

47



39 # 737.27 #

≤

18.90 mm ………. (O.K.)

CHECK FOR DEFLECTION Basic

span d

ratio =20

u max

)

DRAINAGE SYPHON

t



p

100  1570.8 1000  150

=1.04 Service stress =0.58

×

415

×

1365 1570.8 2

=209.16 N/mm Modification Factor=1.42 Permissible

span d

ratio= 20

×1.42

=28.4 Actual

span d

ratio =

4000 150

=26.66<28.4 ……… (O.K.) CHECK FOR CRACKING Maximum spacing permitted for main reinforcement =3 ×160

=480 mm or 300 mm, i.e. 300 mm

Actual spacing =170 mm (O.K.) Maximum spacing permitted for secondary reinforcement =5

×160

=800 mm or 450 mm, i.e. 450 mm

Actual spacing = 240 mm ….. (O.K.) For trying the bent up bars at top, provide 8 mm # @ 240 mm c/c.

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CONCLUSION  The comparative study for the project reveals that not only the selection of type of CDs for a particular crossing plays a vital decisive discriminatory role, but also the design of the structural with various alternatives with respective to (i) suitability of

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foundation

vis-à-vis

various

foundation

strata, (ii) transitions (iii) u/s and d/d protection works (iv) post construction operation and maintenance

etc.

does

equally

challenge

the

hydraulic engineers exposure to the veracity of the job’s complex nature.  The aqueduct which we have designed is found to be the

most

stable

and

economical

structure

as

compared to the any other cross drainage work. Here we have not provided any inspection road but in future, if required, then we can design and provide an inspection road.

References • Irrigation Engineering

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• By Prof N N Basak • Tata Mcgraw-Hill • Irrigation Engineering & Hydraulic Structures • By Prof. Santosh Kumar Garg • Khanna Publishers For Deg • By Prof. H. J saha • Internet Websites • http://www.uap-bd.edu/ • Lecture Notes By: Dr. M. R. Kabir • Professor and Head, Department of Civil Engineering Department ,University of Asia Pacific (UAP), Dhaka