Pipeline design. concrete for life

Transcription

1 Pipeline design concrete for life

2 Pipeline Design

3 Pipeline design - hydraulic Graph showing relative velocity and discharge in a circular pipe for any depth of flow Proportional depth of flow PROPORTIONAL DISCHARGE PROPORTIONAL VELOCITY Proportional velocity and discharge in pipes flowing part full 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.

4 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 Therefore Actual discharge Average velocity 0.67 x x cubic metres/sec 3.0 metres/sec

5 Pipeline design - hydraulic Hydraulic flow charts For Pipes Flowing Full Ks = 0.3mm (Colebrook-White) Water 15 0 C

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

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

8 Pipeline design structural design Introduction This section is based on BS EN : 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 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 min 300mm Bc Bc Bc

9 Pipeline design structural design 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: Bc Bc Bc Y 300 DN 45 Y 180 Y Y Bedding class F B S Description 45 o granular bed 180 o granular bed 360 o granular bed Bedding factor ¼ Bc Bc+200min 1¼ Bc Bc+200min ¼Bc 120 ¼Bc ¼DN min ¼DN min Bedding class A unreinforced A reinforced Description 120 o unreinforced concrete cradle 120 o reinforced concrete cradle Bedding factor 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/mm 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 , 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

10 Pipeline design structural design Crushing test loads Crushing test loads in kilonewtons per metre of effective length for concrete pipes. * Denotes classic size. + Not kitemarked. Nominal Size DN EN 1916 / BS :2002 Minimum crushing load (Fn) kn/m * * * * * * * * * * * Notes: 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.

11 Pipeline design structural design 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: Fm > We x Fse Fn. Where Fm = Bedding factor We = Total external load (See BS EN ) Fse = Factor or safety taken as a minimum of 1.25 (see note below) Unreinforced pipes (DN 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 BS proof loads permitting continued use of the current Fse = 1.25

12 Pipeline design structural design Depth of cover charts Class 120 Pipes under fields Fse = 1.25 DN Bc Bd mm mm mm Cover Depth (m) DN = Nominal diameter Bc = External diameter Bd = Trench width Class B Class S

13 Pipeline design structural design Depth of cover charts Class 120 Pipes under main roads Fse = 1.25 DN Bc Bd mm mm mm Cover Depth (m) DN = Nominal diameter Bc = External diameter Bd = Trench width Class B Class S

14 Scotland Sales and Works CPM Group Ltd, 101 Main Street, Newmains, Wishaw, Lanarkshire, ML2 9BG Tel: Fax: Pollington Works CPM Group Ltd, Pollington, Goole, East Riding of Yorkshire, DN14 0DU Tel: Fax: Leek Sales and Works CPM Group Ltd, Barnfields, Leek, Staffordshire, ST13 5QG Tel: Fax: Scotland Sales and Works Technical Offices CPM Group Ltd, CPM House, Heath Mill Road, Wombourne, Wolverhampton, West Midlands WV5 8AP Tel: Fax: Pollington Works Head Office Sales and Works CPM Group Ltd, Mells Road, Mells, Nr Frome, Somerset, BA11 3PD Tel: Fax: Technical Offices Leek Sales and Works Head Office Sales and Works