Lyme Regis Environmental Improvements Phase IV Presentation by Chris Hill CEng FICE Dean & Dyball Civil Engineering Project Manager
Project Timeline Contract award – May 2012 • Start date - September 2012 • Site set up - through September and October 2012 • Detailed design by URS - September 2012 to March 2013 • Ecological works & site investigations - September 2012 to February 2013 • Main construction works - April 2013 to April 2014 • Landscaping - May to August 2014 •
Contract Details NEC3 Option C Design & Construct • Tender based on a well developed reference design • Won convincingly on quality • 116 week programme with planned Completion 29/04/14 •
Key Construction Stages Ecological surveys & mitigation • Site clearance • Treatment of invasive plant species • Ground investigations • Installation of new instrumentation • Monitoring • Trench drains • Foreshore haul route • Seawall • Rock armour • Soil nails • Drainage • Dowel piles • Large diameter piling • Landscaping •
Ecology & Environment World Heritage Site • Site of Special Scientific Interest • Special Area of Conservation • Area of Outstanding Natural Beauty • Jurassic Coast designation • Rock ledges • An abundance of protected species including • dormice Japanese Knotweed • Other controlled plant species • Asbestos • Disused tip • Old gas works •
Ecological Surveys & Mitigation
Site Clearance
Trench Drains
Foreshore Haul Route 5m wide and built from gabions and stone fill • Designed to protect the rock ledges, offer some protection from the tide and to allow • construction vehicles to travel along the foreshore
Seawall Stops further erosion by preventing waves hitting • the coastal cliff Recurve profile to deflect waves • Provides a pedestrian walkway, a splash wall, • seating and access for maintenance and emergency vehicles Reinforced ready mix concrete – in the order of • 7000m3 Built in the inter-tidal zone • Straight and curved 8m long panels, up to 6m high • Follows the profile of the existing wall • Demands an extremely high standard of • workmanship To be backfilled with stone from the haul route •
Seawall – 60 years ago
Seawall Foundation The seawall foundation needs to be sufficiently deep to prevent the new wall being • undermined by tidal scour This means founding the wall on a harder limestone band – not on the weaker mudstone • A lot of work has taken place to identify the level of these harder bands •
Rock Armour 400T of 3-6T rock armour from the Mendips • Designed to protect the eastern end of the new seawall • from further ‘outflanking’ Placed in position by a large excavator with a grab • Delivered to site early to be used as temporary works •
Soil Nails Approx. 2500 steel bars drilled into the coastal cliff to pin the • unstable material near the surface to deeper more stable material Bars are grouted into position, steel mesh is placed on the • surface of the slope and bars are tensioned with a cover plate and nut Nail heads will be recessed into the slope and covered over • prior to landscaping
Soil Nail Installation Methods
Drainage 20-25m long drilled drains installed just above the new • seawall to intercept ground water and allow it to escape before it destabilises the ground Gravity drainage to collect the run off from the trench • drains and to replace the existing over-land pipes
Piling 8m long 300mm diameter dowel piles on • East Cliff to enhance the stability of the cliff above the soil nails, protect the new seawall and to ensure that landslips cannot progress inland Dowel piles are filled with grout and • reinforced with a steel tube Up to 25m long 750mm to 1200mm • diameter piles below Charmouth Road Car Park and through the allotments to prevent landslips progressing inland but also positioned to allow the SSSI site to be preserved Larger piles filled with concrete and • reinforced with a steel cage
Piling Installation Methods
Landscaping The coastal slopes will be sprayed with a hydroseed • mix to prevent erosion and to quickly establish native grassland Planting areas on the flatter parts of the slope will • have native scrub planting and deterrent species along property boundaries New footpath leading from Charmouth Road Car Park • to the seawall
Artwork Geological timeline • concept under discussion Stone insets or curb • stones marking the timeline QR codes used to provide • easy access to web sites
Thank You
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