Lyme Regis Environmental Improvements Phase IV

Presentation by

Chris Hill

Dean & Dyball Civil Engineering

Project Manager

Outline Programme

• Start date - 3 September 2012

• Site set up - through September and October 2012

• Detailed design - 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

Key Construction Stages

• Trench drains • Foreshore haul route • Seawall • Rock armour • Soil nails • Drainage • Dowel piles • Large diameter piling • Landscaping

Outline Programme

• Start date - 3 September 2012

• Site set up - through September and October 2012

• Detailed design - September 2012 to May 2013

• Ecological works & site investigations - September 2012 to February 2013

• Main construction works - April 2013 to April 2014

• Landscaping - May to August 2014

Current position – April 2013

Trench Drains

Trench Drains • Up to 4m deep, with an impermeable liner and filled with gravel • Perforated pipe at the bottom of the trench • Designed to collect ground water and prevent it reaching the unstable coastal cliff • 37T excavator and manhole / trench support equipment

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 • To prevent further erosion by preventing

waves hitting the coastal cliff • Special ‘recurve’ profile to deflect waves back

to sea • 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 • A combination of straight and curved 8m long

panels, up to 6m high • Designed to follow the profile of the existing

wall • Demands an extremely high standard of

workmanship if it is to be durable • To be backfilled with material from the haul

route

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

Seawall Methods & Equipment

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

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

Piling Installation Methods

• 300mm diameter piles installed with a mini piling rig

• Larger diameter piles installed with an 80T piling rig with a powerful auger

• Augers used to bore out the soil and rock forming a cylindrical open hole

• A steel cage or tube is inserted into the bore

• A 50T crawler crane is needed for the larger piles due to the weight of the cages

• Concrete or grout is poured. This sets forming a reinforced pile

• Larger piles are connected together using reinforced concrete beams and steel bars

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

Landscaping

• Coastal viewing area to be located just below Charmouth Road Car Park

• Planting and seating with a circular path

Our Priorities

WHAT WE WILL DO FOR YOU

• Carry out the work safely and quickly

• Cause Lyme Regis residents the minimum amount of disruption possible

• Keep you informed through this type of presentation, newsletters, press releases and the site information boards

• Maintain an open door policy at the Charmouth Road Car Park site offices so that you can speak to a member of our senior management team at any time during office hours

WHAT YOU CAN DO FOR US

• Take note of warning signs and never move or cross a site fence– particularly on Cobb gate and on the foreshore

• Read communications from the site team and ask questions if anything is unclear

• Stay safe at all times

Thank You