Pipeline Beding Design

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Pipeline design

CPM Concrete Drainage Systems

Pipeline Design

CPM Concrete Drainage Systems Pipeline design - hydraulic Graph showing relative velocity and discharge in a circular pipe for any depth of flow

0.1 0.2 0.40.3 0.80.70.60.5 1.11.00.90 1.2

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PROP

ORTIO

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ISCHA

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TIONAL V

ELOCITY

Proportional velocity and discharge in pipes flowing part full

Prop

ortio

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epth

of f

low

For calculating transitional flow, using the Colebrook-White equation, a roughness factor of Ks = 0.3mm is recommended as a realistic figure for newly installed concrete pipelines. However, research has indicated that for mature foul sewers of any material the Ks value may rise well above this figure and the Water Services Association publication Sewers for Adoption 5th Edition recommend the following: Foul and combined sewers Ks = 1.5mm (minimum velocity should be 0.75m/ see at one third design flow) Surface water sewers Ks = 0.6mm (minimum velocity should be 1m/sec at full pipe flow) Hydraulic flow charts have therefore been included for the three roughness coefficients Ks of 0.3, 0.6 and 1.5mm.

CPM Concrete Drainage Systems Pipeline design - hydraulic Example on use of flow charts

Design of surface water sewer Pipeline length Difference in level between inlet and outlet Design discharge

200m 1m 4 cubic metres/sec (4,000 litres/sec)

to determine the size of pipe when: a. flowing full b. the proportional depth of flow is 0.6 (i.e. 60% full) Solution Hydraulic gradient Ks for surface water sewer 1 in 200 (or 0.005) 0.6mm a. Pipe flowing full: Refer to Hydraulic Flow Chart for Ks = 0.6mm. The intersection of the horizontal discharge line of 4 cubic metres per second with the vertical hydraulic gradient line of 1 in 200 gives: Pipe diameter Average velocity 1350mm 2.8 metres/sec b. Pipe flowing 60% full: Refer to the graph showing Relative. Velocity and Discharge in a Circular pipe for any Depth of Flow. The intersection of the horizontal proportional depth line of 0.6 with the proportional discharge and velocity curves gives: Proportional discharge Proportional velocity 0.67 1.07 Therefore Actual discharge Average velocity 0.67 x 4 1.07 x 2.8 2.68 cubic metres/sec3.0 metres/sec

CPM Concrete Drainage Systems Pipeline design - hydraulic Hydraulic flow charts For Pipes Flowing Full Ks = 0.3mm (Colebrook-White) Water 150C

CPM Concrete Drainage Systems Pipeline design hydraulic Hydraulic flow charts For Pipes Flowing Full Ks = 0.6mm (Colebrook-White) Water at 15C

CPM Concrete Drainage Systems

Hydraulic flow charts For Pipes Flowing Full Ks = 1.5mm (Colebrook-White) Water at 15C

CPM Concrete Drainage Systems Pipeline design structural design

Introduction This section is based on BS EN 1295-1: 1998 Structural Design of Buried Pipelines Under Various Conditions of Loading. This standard gives guidance on the nationally established methods of design. For the UK this is detailed in A Guide to Design Loadings for Buried Rigid Pipes published by HMSO 1987 and Simplified Tables of External Loads on Buried Pipelines published by HMSO 1992. The charts give the maximum depth of cover for single pipelines laid in a narrow trench where there will be relief of load due to friction at the fill/trench wall interface and where the pipe is laid in wide trench conditions. Where special conditions apply, e.g. multiple pipelines in a single trench, pipelines supported on piles, trench backfilled with lean concrete and delayed removal of trench sheeting, the charts may not be applicable and advice should be sought from our Technical Department or reference made to the full publication. Whilst the normal recommendation in the UK is to have a minimum of 1.2m cover (measured from the top of the pipe barrel to the finished road surface) under roads and 0.9m elsewhere, it is sometimes necessary to lay pipes at less cover and the charts have been prepared with a minimum cover of 0.6m in Roads and Fields, etc. However, special precautions should be taken to minimise the risk of mechanical damage during future excavations and reinstatement of other services, agricultural machinery, etc. The charts are based on the loadings likely to be encountered when installation, including reinstatement, is complete and care must be taken to ensure that the concentrated load due to construction traffic does not exceed the design surcharge loads given. For a full structural analysis contact our Technical Department who can provide detailed calculations and recommendations on bedding design.

Bd Bd Bd

H H H

Bc

min300mm

Bc Bc


Bedding class and factors The load-bearing capacity of a concrete pipeline is dependent both on the strength of the manufactured pipe and on the support provided by the bedding. The bedding factor (Fm) is the ratio of the strength of the laid pipe to its laboratory crushing test strength. The higher the bedding factor the greater is the load carrying capacity of a given pipeline. The methods of bedding normally used with concrete pipes are:

Y

300

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45

Bc

Y

300

180

DN

Bc

Y

300Y

Bedding class F B S Description 45o granular bed 180o granular bed 360o granular bed Bedding factor 1.5 1.9 2.2 1 Bc

Bc+200min

120

DN min

300

Bc

1 BcBc+200min

120Bc

DN min

300

Bedding class A unreinforced A reinforced Description 120o unreinforced concrete cradle 120o reinforced concrete cradle Bedding factor 2.6 3.4

Notes 1. Concrete cradles may extend to sides of trench. 2. Transverse steel to be 0.4% min of section at x-x (Fm 3.4). 3. Minimum strength concrete of 20N/mm2. 4. Allow concrete to gain sufficient strength prior to trafficking. 5. Maintain pipeline flexibility by leaving gaps at pipe joints filled with compressible material. 6. Bedding beneath and at sides of pipe to be well compacted. 7. Bedding/backfill directly above pipe to be lightly compacted. 8. Dimension Y: minimum of 1/6Bc or 100mm under barrels, and 50mm minimum under sockets whichever is greater (400mm maximum). In rock etc. use 1/4Bc and 150mm minimum under sockets.

Key

Granular bedding material

Selected backfill material

In-situ concrete

Nominal size of pipe DN

Pipe bedding requirement mm

225 to 525 10, 14 or 20 nominal single size or 14 to 5 graded or 20 to 5 graded 600 and above 10, 14, 20 or 40 nominal size crushed rock or 14 to 5 graded or 20 to 5 graded or 40 to 5 graded


Crushing test loads Crushing test loads in kilonewtons per metre of effective length for concrete pipes.

Nominal Size DN

EN 1916 / BS 5911-1:2002 Minimum crushing load

(Fn) kN/m

225 27 300 36 375* 45 400 48 450* 54 500 60 525* 63 600 72 675* 81 700 84 750* 90 800 96 825* 99 900 108

1000 120 1050* 126 1125+ 135 1200 144 1350* 162 1400 168 1500* 180 1600 192 1800 216 2000 240 2100* 252 2200 264 2400* 288 2500 300 2800 336 3000 360

* Denotes classic size. + Not kitemarked. Notes: 1. 2.

Pipes of higher crushing strengths than those above can be manufactured in certain diameters. Details of required strengths should be sent to the Sales Office at Mells. CPM Group do not make all of the sizes listed above.


Safe supporting strength For a safe design the supporting strength of an installed pipeline must exceed the total external design load where the supporting strength is the product of the pipe crushing strength and the bedding factor and the total external load is the sum of the trench load, surcharge load and for pipes greater than DN600 the equivalent water load. A minimum bedding factor required can be calculated from:

We x Fse Fm > Fn. Where Fm = Bedding factor We = Total external load (See BS EN 1295 1) Fse = Factor or safety taken as a minimum of 1.25 (see note below)

Unreinforced pipes (DN225-600 inclusive) = 1.25

Reinforced pipes manufactured to BS EN 1916, the Fse increases to 1.5, However in order to maintain design continuity and to cater for schemes designed prior to the implementation of BS EN1916, CPM will continue to test reinforced pipes to BS5911 100 proof loads permitting continued use of the current Fse = 1.25


Depth of cover charts Class 120 Pipes under fields Fse = 1.25

DN = Nominal diameter Bc = External diameter Bd = Trench width Class B Class S

DN Bc Bd

mm mm mm

Cover Depth (m)

1.0 2.0 3.0 4.0 5.0 6.0 7.0 0.7 225 295

Wide 0.85 300 410 Wide 1.05 375 495 Wide 1.15 450 530 Wide 1.20 525 675 Wide 1.35 600 770 Wide 1.45 675 860 Wide 1.50 750 940 Wide 1.60 825 985 Wide 1.90 900 1100 Wide 2.10 1050 1265 Wide 2.20 1125 1345 Wide 2.30 1200 1450 Wide 2.50 1350 1620 Wide 2.70 1500 1740 Wide 2.81 1600 1920 Wide 3.10 1800 2090 Wide


Depth of cover charts Class 120 Pipes under main roads Fse = 1.25

DN Bc Bd

mm mm mm

Cover Depth (m)

1.0 2.0 3.0 4.0 5.0 6.0 7.0 0.7 225 295

Wide 0.85 300 410 Wide 1.05 375 495 Wide 1.15 450 530 Wide 1.20 525 675 Wide 1.35 600 770 Wide 1.45 675 860 Wide 1.50 750 940 Wide 1.60 825 985 Wide 1.90 900 1100 Wide 2.10 1050 1265 Wide 2.20 1125 1345 Wide 2.30 1200 1450 Wide 2.50 1350 1620 Wide 2.70 1500 1740 Wide 2.81 1600 1920 Wide 3.10 1800 2090 Wide

DN = Nominal diameter Bc = External diameter Bd = Trench width Class B Class S

Scotland Sales and Works

Pollington Works

Leek Sales and Works

Technical Offices

Head Office Sales and Works

SSccoottllaanndd SSaalleess aanndd WWoorrkkssCPM Group Ltd, 101 Main Street, Newmains, Wishaw,Lanarkshire, ML2 9BGTel: 01698 386922 Fax: 01698 387167

PPoolllliinnggttoonn WWoorrkkssCPM Group Ltd, Pollington, Goole,East Riding of Yorkshire, DN14 0DUTel: 01405 860591 Fax: 01405 863606

LLeeeekk SSaalleess aanndd WWoorrkkssCPM Group Ltd, Barnfields, Leek,Staffordshire, ST13 5QGTel: 01538 380500 Fax: 01538 380510

TTeecchhnniiccaall OOffffiicceessCPM Group Ltd, CPM House, Heath Mill Road, Wombourne,Wolverhampton, West Midlands WV5 8APTel: 01902 356220 Fax: 01902 356221

HHeeaadd OOfffificcee SSaalleess aanndd WWoorrkkssCPM Group Ltd, Mells Road, Mells, Nr Frome,Somerset, BA11 3PDTel: 01179 812791 Fax: 01179 814511

[email protected]

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Pipeline Beding Design

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