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Main Road causeway - Mt Pleasant - Replacement of damaged culverts - construction of a new seawall and road repairs - Construction details

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What:
Replacement of the earthquake damaged culverts, construction of a new seawall on the estuary side of the causeway and reconstruction of the road.
Where:
Main Road causeway, between the two McCormacks Bay Road intersections.
Traffic impact:
Main Road causeway will be closed for approximately six months. There will be a detour for all traffic via McCormacks Bay Road.
When:
Monday 29 April 2013 for approximately six months. There will be further work following this project, including Main Road three laning. More information will be provided before that work begins.
Map of the Estuary of the Heathcote and Avon Rivers/Ihutai and McCormacks Bay. Seaswall to be rebuilt (blue) and Causeway road to be reconstructed and resurfaced (black): Main Road between McCormacks Bay Road intersection; Culverts to be replaced (red): two on Main Road causeway; New bridge to be built over existing culvert (yellow): one located between the two culverts to be replaced. Sourced from LINZ data, Crown Copyright reserved.

Traffic Impact

Vehicle access: Main Road causeway will be closed for six months. All vehicles will be detoured via McCormacks Bay Road; Pedestrian/cyclist access: It will not be safe for cyclists and pedestrians to use the causeway. Pedestrians and cyclists will also be detoured via McCormacks Bay Road; Water users: It will not be safe for waterway recreationalists near the culverts and along the seawall while we are working in this area. For your own safety please keep well away from the work sites.

The detour

The detour. Map data © OpenStreetMap contributors, CC-BY-SA. Map of Estuary of the Heathcote and Avon Rivers/Ihutai and McCormacks Bay. Road closure (red): Main Road between the McCormacks Bay Road intersections. Detour for all traffic (black arrows): two-way along McCormacks Bay Road between the intersections with Main Road. Also identified on the map are Mt Pleasant Road, Aratoro Place, Soleares Avenue, and Maffeys Road. 1. The western intersection: of Main Road and McCormacks Bay Road. No right turn from McCormacks Bay Road into Main Road.  2. The eastern intersection: of Main Road and McCormacks Bay Road. Also identified on the map is Beachville Road. Sourced from LINZ data, Crown Copyright reserved.

Traffic impact on McCormacks Bay Road residents and residents of adjoining side streets

  • As there will be additional traffic along McCormacks Bay Road, turning onto McCormacks Bay Road from side streets or driveways will be more difficult. Please take care and drive to the conditions.
  • Due to the increase in traffic on McCormacks Bay Road, please ensure children are safe when crossing.

Why a full road closure of Main Road causeway is the best option

In order to replace the damaged culverts and construct a new seawall at least one traffic lane along the causeway needed to be closed. Two options of managing traffic were considered:

  • A one-lane closure: Traffic heading towards Sumner would need to take McCormacks Bay Road, but traffic heading into town would be able to take Main Road.
  • A full road closure of Main Road causeway: All vehicles detoured via McCormacks Bay Road.

The advantages/disadvantages of the two traffic management options are set out:

Traffic Management Road closure One lane closure
Construction period Approximately 6 months. Approximately 8 months.
Project cost Significant savings due to shorter construction time frame as well as efficiencies due to a larger work area. More expensive due to increased construction time frame.
Safety The work site is not next to a live traffic lane which means it is considerably safer for road users and workers. As with all rebuild work safety is our number one priority. Live traffic next to the work site poses a hazard.

As the full road closure of Main Road causeway will ensure the project is safer, more efficient and will be less expensive it has been decided that the road will be temporarily closed, with a detour for all traffic via McCormacks Bay Road.

During this and other rebuild work we encourage you to 'keep Christchurch moving' by:

  • Allow extra time for your journey to account for the detour. Taking McCormacks Bay Road rather than the Main Road causeway will add 500 metres to your journey.
  • Combine activities in one trip.
  • Walk or cycle for shorter trips.
  • Use the bus visit www.metroinfo.co.nz or phone 366 88 55 for more information.
  • Find the quickest and safest routes around Christchurch at www.transportforchristchurch.govt.nz

General Impact

  • There will be increased noise, dust and vibration levels associated with this work, and the use of diggers and pumps will be necessary.
  • The work is unlikely to impact on current power, telecommunications, or gas and water services.
  • Safety is our number one priority. Safety is your responsibility too. Stay clear and stay alert – keep children and pets at a safe distance from the work site.
  • Works will take place between the hours of 7.00am to 6.00pm Monday to Friday, with Saturday work as required.
  • All works are subject to favourable weather and on-site construction conditions.
  • If during our works potholes appear in the road surface along McCormacks Bay Road, please call us on 0800 277 34 34 and we will get them repaired.

What we are doing

Map of Estuary of the Heathcote and Avon Rivers/Ihutai and McCormacks Bay showing Main Road and 1: Culverts to be replaced; 2: New bridge to be built over existing culvert; 3: Seawall to be built; 4 & 5: Causeway road to be reconstructed and resurfaced. Sourced from LINZ data, Crown Copyright reserved.
  1. Replacement of culverts at either end of the work area with new polyethylene (PE) pipes (eight weeks work).

    Culvert replacements

    Drawing of culvert replacement on Main Road causeway, showing: the Estuary; Seawall to be reconstructed; New polyethelene pipe (PE) to replace existing culvert (between the seawalls); Existing seawall; and McCormacks Bay. Please note: This drawing is for illustration purposes only. Sourced from LINZ data, Crown Copyright reserved.

    How we will replace the culverts

    • Each end of the existing culverts will be blocked off with sand bag walls.
    • The water inside the culvert area will be pumped out (dewatering).
    • The existing culvert will be removed and the new pipe trench excavated to the required depth.
    • The new PE pipes will be installed and the trench will be backfilled.
    • Dewatering and the sand bag walls will be removed once construction is complete.
  2. Construction of new culvert bridge in middle of the causeway (six months work).

    The new culvert bridge

    Drawing of new culvert bridge. Section on road centreline, showing: Steel props to be fixed to existing culvert; Existing culvert roof removed; New concrete cap on top of existing walls; and Existing culvert walls and wingwalls to remain in place. Please note: This drawing is for illustration purposes only.

    How we will build the new culvert bridge

    • The site will be established and the existing services will be located and marked and isolated where required. The existing Telecom and Orion services will be protected throughout the construction process.
    • Temporary props between the existing culvert walls will be installed.
    • The road and footpath will be excavated down to the top of the existing culvert and trenches will be dug around the sides of the culvert.
    • Sheet pile walls will be installed at either end of the culvert and water will be pumped out of the construction area (dewatering).
    • The roof of the existing culvert will be cut off and removed with a crane.
    • The height of culvert walls will then be reduced.
    • The existing culvert walls and invert will be strengthened and new rip rap boulders will be installed.
    • The piles for the bridge ends and bridge beams will be installed.
    • The approach to the bridge will be realigned and re-levelled, before the road is sealed.
  3. Seawall reconstruction

    Revetment of the seawall by two crews working from west to east (six months work). Revetments are sloping structures placed on banks, to absorb the energy of incoming water.

    Drawing of the seawall and causeway (section view). Showing: Estuary of the Heathcote and Avon Rivers/Ihutai (to the left); Geotextile (Fabric) layer; Under layer; Cover layer; Compacted aggregate (which is underneath: Allowance for future coastal pathway; Cycle lane; Traffic lane; Traffic lane; and Cycle lane); Footpath; and McCormacks Bay (to the right). Please note: This drawing is for illustration purposes only.

    How we will build the new seawall

    The seawall will be completed progressively in sections:

    • A large 20 tonne excavator will form the new toe of seawall at low tide.
    • A geotextile (fabric) layer will be placed along the current floor and gravel will be placed between the new toe and the existing seawall using a small excavator.
    • Top layer rocks will be placed and the final rock wall profile will be formed to shape.
    • Additional pavement/walkway aggregate will be placed and compacted between the new seawall and the existing pavement.
  4. Road reconstruction and resurfacing

    Following the completion of sections of the seawall, kerb and pavement formation works will be undertaken to form the new profile.

  5. Following this, pavement stabilisation will occur in some areas followed by road surfacing improvements (this is likely to occur after Main Road is reopened to traffic).

Environmental protection

The Main Road causeway works are being undertaken in a coastal estuarine environment that provides important amenity, recreation and ecological values to the region.

To help to protect this sensitive location, works are being performed under a site specific resource consent with Environmental Canterbury.

A number of safeguards have been included in the methodology to limit potential disturbance to the coastal estuary environments including:

  • Limiting vehicle and plant movements in the tidal areas to low tide times where practicable
  • Dewatering through sediment tanks to contain potential sediment discharge
  • Maintaining tidal flows to McCormacks Bay throughout the contract period
  • Minimising the volume of excavations required during the course of the works.

Aquatic research consultants have also been involved in this project to examine the local population of cockles. Recommendations from this research have been incorporated into these works to ensure that the current population of cockles will not be significantly compromised. This research highlighted the importance of using different sized boulders in the seawall in order to provide variable habitats for local species. This has been incorporated into the seawall design and will enable species recovery in the long term.

Need more information?

Phone: 0800 277 34 34 (8.30am–5.00pm Monday–Friday)
Email: [email protected]
Website: Visit www.strongerchristchurch.govt.nz
Follow us on Twitter: twitter.com/scirt_info

Start date: 
Mon, 29/04/2013
End date: 
Thu, 31/10/2013
Project numbers: 
10634
11027
10908