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Welcome
Demonstration of the Self Erecting, Low Cost Flood Barrier
The ‘SELOC’ Flood Barrier
John Greenwood
Reader in Geotechnical Engineering
School of Architecture, Design and the Built Environment
Nottingham Trent University
Peter Atchison
Director
PAGeotechnical Ltd, Corby
Steve Corbet
Technical Director
Aecom Group (Faber Maunsell Ltd)
Project team:
Current approaches to Flood Defence
Permanent walls hold back the floods but we lose the river views
(Nottingham in old photographs 1944-1974, Douglas Whitworth 1991)
Current flood defence systems
Ironbridge flooding
Demountable barrier
Demountable barrier, Shrewsbury
(Ref. Environment Agency – Stokes and May 2004)ICE Tilt Dam
A low cost, self erecting flood barrier.The idea:-
Cover
Protective slab
tie
Geomembrane Backfilled trench
Float
Flood waters
The flood and wave barrier – construction sequence
Site selection and investigation
Trench planned
d =width =depth =height of protection
d
d
d
Trench excavated
Flexible geosynthetic membrane, (typical width = 3d) placed against sides and base of trench.
Ties connected to membrane.
d
d
d
d (tie)
d (tie)
Trench backfilled.
Most of arisings compacted back into trench
Protective stabilising slab placed on trench fill.
Suitable rigid covers attached to membrane
Suitable float attached to each cover
(if needed for buoyancy)
Ties attached to covers and linked to membrane in trench
Operation checked between closed and open conditions
Note, in simplest form, covers hinge on the geomembrane.
Coarse gravel placed to allow easy access of water to float.
Barrier is now ready for action
As water level rises, float responds and barrier rises restrained by the tie.
As water level falls again, barrier returns to horizontal rest position
The flood and wave barrier.- Resting position
After flood,
barrier returns to horizontal rest position.
Use as walkway?
Lea Marston TrialsFunded by Stimulating Innovation for Success (SIS)
Site Surveying and setting out (4th Sept, 2007)
Initial Trial at Lea Marston Trial – Excavation starts (10th Sept)
Trough cut out in slope, Trench excavated, reference plywood/timber edge installed
Membrane (Seaman XR5) prepared
40 mm pipe inserted through cut outs in fold in membrane to attach ties
Trench backfilled with natural soil
Paving slabs placed for additional stability
Plywood covers attached – Gate hinges used in trial
Membrane folded over polystyrene floats held by batons. Ties attached.
Covers fixed ready for actionGround elevation change at ends of barrier compensated by horizontal
alignment change to permit free operation of covers.
Ready to pump water in
Successful retention of 600mm of water
A successful initial trial
The basics of the design(Patent no EP 1880058 granted 31 Dec 2008)
Tie
Cover - Decking or polymer
Float (if required)
Permeable block
Backfilled trench
Tie attached to rod through seam
Geomembrane
Slab
Edge kerb
Mechanical hinge or membrane hinge
The barrier at rest – used as a walkway
Design of the self erecting barrier as a retaining structure(Student exercises)
Total vertical pressure
d
d
d
Effective vertical pressure
Effectivehorizontalpressure
WaterPress.
Effect.vert.press.
Effect. horiz. press.
Total vert. press.
Water pressure
d(b - w)2dwdw +db Kad(b - w)
2dw
d(b-w) dw dbKpd(b-w)
dw
B
caW
E
DC
A
Pw3Pa
wl
Pp
Pw6
Pw5
Pw4
Pw1
Pw2
wl
‘ACTIVE’ FORCES
GRAVITY FORCES
‘PASSIVE’ FORCES
BUOYANCY FORCES
Consideration of flows beneath the barrier
E
D
A
B
C
Flow line
h = d
Impermeable boundary
Equipotential
If k=10-5 m/sec, under head, d= 0.9m, Flow q= 14 litres/hr per m run.
Trench depth may be increased in very permeable ground
Current demonstration - production version
conceptual cover design in polyethylene using Rotarymould process.
Hinges slot in to kerb unit
Timber pattern for covers
The team consider kerb options
Rotary moulded covers and hinge units
The kerb and hinge assembly
Test loading of the rotary moulded covers and hinge units at NTU
Lea Marston Site Demonstration – September 2009Trench excavated,- Straight section with end walls
Seaman XR5 Membrane – tie attachments
Membrane and ties positioned in trench
Ready for backfill
Backfilling commences
Natural soil backfilled and compacted
Bedding for paving slabs
Paving slabs positioned
Kerbs and covers positioned
End wall construction
Battens fixed to hold membrane to covers
Ties fixed
Site Demonstration
• Developments and Applications
Self erecting barrier used to increase effective height of existing (or new) flood embankment
Membrane may be extended below embankment to intercept groundwater flows in more permeable strata
Basic Design – possible use of decking as Barrier covers
• Flood protection where cost or visual intrusion precludes conventional flood defences
• Low cost alternative to demountable barriers
• Increase the effective height of existing or new flood banks (No additional fill or loading)
• Secondary protection of local areas for ‘at risk’ cities such as Hamburg or New Orleans
• Temporary water storage
• Low cost protection of low lying agricultural land
• Protection around ‘hazardous’ storage tanks
• Control of drainage – Diverting flood waters to safe storage areas
• Help resist tsunami wave forces
Applications
SELOC Flood Barrier – Advantages• Control of (flood) waters at low cost
• ‘Low tech’ site construction – re-use of on-site materials
• Self erecting (no dependence on mobilised manpower)
• Preserves waterside landscape
• Membrane intercepts and reduces groundwater seepage
• Full professional technical support. Each ‘at risk’ site carefully assessed by Consulting Engineers (AECOM) and SELOC applied only if it is the appropriate solution.
• Can be designed to suit scale of flood protection (200 – 1000mm+) and protective surfacing provided to suit the location (walkway/driveway etc,)
• Varied applications - (Flood protection, water storage, tsunami protection etc.)
• European Patent
‘Working Together’
Engineering in Harmony with the Environment!
Thank you for your interest todayThe project team is grateful to the Environment Agency (Harvey Twivey) for
making the site and pumping facilities available for the trials at Lea Marston.The financial support under the ‘EMDA’ Innovation Fellowship Scheme is
acknowledged with thanks.We appreciate the support of our organisations and in particular the site help
and project input provided by:
NTU – Anton Ianakiev, Steve Goodman, Alan Chambers, Mark FlanaganAECOM – Pete Jones (Site trial coordination), Dave CartwrightPAGeotechnical – David Plumtree, Neil SalvedgeRototek – Stuart Wright.
[email protected]@pageo.co.uk (Peter Atchison)[email protected]
