welcome demonstration of the self erecting, low cost flood barrier the ‘seloc’ flood barrier...

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.

John.greenwood@ntu.ac.ukPeter@pageo.co.uk (Peter Atchison)Steve.Corbet@aecom.com