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Exeter Street - Lyttelton - retaining wall repairs

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Traffic
Road closure on Exeter Street at Dublin Street
When
From Monday 18 April 2016 for about three months

In this notice

Where we are working

Map. Sourced from LINZ data, Crown Copyright reserved. Work area and road closure (red): Exeter Street (between Dublin Street and the eastern side of the northwestern bend); Lane closure (light blue): southeastern side of Dublin Street (adjacent northeast of the intersection with Exeter Street); Walkway (yellow): between Dublin Street and the northern side of the northwestern bend of Exeter Street; Detour route (bright green): Winchester Street (between Dublin Street and Canterbury Street) and Canterbury Street (between Winchester Street and Exeter Street) and Exeter Street (between Canterbury Street and work area); Priority give way: Dublin Street (a location between Winchester Street and Exeter Street, and a location north of Exeter Street).

Traffic impacts

  • There will be a road closure on Exeter Street.
  • The detour will be along Canterbury Street and Winchester Street.
  • There will be a priority give way on Dublin Street.

What we are doing

  • City Care, as part of the SCIRT team, is repairing the retaining wall on Exeter Street, at the intersection of Dublin Street.
  • We are building a cantilevered, soil nail* wall.
  • Our work will start on Monday 18 April 2016 and will take about three months to complete.

Our methods

What is a retaining wall?
A retaining wall is a structure used to hold sloping ground in place. Retaining walls are used where there is not enough space for a natural slope.
How do earthquakes affect retaining walls?
In an earthquake, the soil behind the wall moves horizontally back and forth. When the shaking stops, the wall stops moving at a different time from the soil behind it. Put simply, the soil and the wall act as separate elements. If the soil load gets too heavy for the wall, it may collapse.
*Soil nails
We call them soil nails, because we hammer them into the soil. We use steel reinforced bars and anchor them using plates.
  1. A drill rig drills a hole into the soil behind the wall.
  2. The soil nail is installed in the drilled hole and grouted.
  3. After the grout cures, the soil nail's strength is tested.

A cantilever wall relies on a section of the wall being buried in the ground (the footing). This footing means that a cantilever wall requires less area. Its size is limited by the strength of the cantilever section and the amount of ground it is buried in.

Shotcrete
Once we install our soil nails, we'll cover the slope with shotcrete. Shotcrete is a mixture of cement, stones, and water applied to the wall using a spray gun. When used for retaining walls, shotcrete is usually sprayed over a framework of reinforcing bars and steel mesh.
Once the shotcrete is set, we then pour the fence of the new retaining wall.

History

Much of Lyttelton's historic infrastructure, including red rock retaining walls, was built using convict labour between the 1860s and 1930s. The workers would have included convicts from the Lyttelton Gaol.

SCIRT is repairing more than 100 earthquake damaged, publicly-owned retaining walls in Lyttelton. These walls have an essential function; be it supporting and protecting private properties, roads and footpaths, or protecting electricity, water, telephone and wastewater services.

There were two major periods of retaining wall construction in Lyttelton. The first was between the late 19th century and the start of World War Ⅰ; these walls were built by the gaol hard labour gang. The second period occurred during the Depression of the 1930s, and these walls were built by relief workers. Retaining walls built during the Depression period typically feature stones of irregular size and shape, set in a 'crazy paving' style.

Red scoria (volcanic) rock was quarried, cut and fitted by hand along embankments and walls up to eight metres tall. Walls were backfilled with loose rubble, clay or rock. SCIRT has designed all of its repairs to red rock walls so they can be re-faced with red rock in future. In the meantime, all red rock taken from historic walls is being carefully stored at Windy Point and Naval Point.

SCIRT consults with an archaeologist from Underground Overground Archaeology before starting work on each retaining wall in Lyttelton. The archaeologist tells SCIRT if an archaeologist is needed on site while the work takes place. For post-1900 walls, the archaeologist is more interested in what's behind the wall than the wall itself.

General Information

  • We want to stay safe and we want you and your family to be safe too. Please stay alert, drive to the conditions, follow on-site signage.
  • Our standard hours are Monday to Friday 7am to 6pm. Sometimes we will work over the weekend to finish work.
  • The work will result in increased dust, noise and vibrations. We will try to keep any disruption to a minimum and we apologise for any inconvenience.
  • All work is subject to favourable weather and on-site construction conditions.
  • Your rubbish and recycling will not change. Please put your bins in the normal spot by 5pm the night before collection and our crew will move and return them if needed.
  • Please contact us on 0800 632 889 if you have any access needs e.g. nurse/doctor visits, Meals on Wheels or planned work on your property.

How could the work impact you?

  • Footpaths will be closed while repairs are done and some small detours may be necessary. Please follow our signage. The footpath between Exeter Street and Dublin Street will remain open.
  • Some on-street parking will be affected in the work area and in areas where a one way is in place. Cones will show where parking is not available.
  • Repairing roads and retaining walls can be noisy because of the heavy machinery needed. We apologise for the disruption and will work quickly to get this job done.

Start date: 
Mon, 18/04/2016
End date: 
Sun, 24/07/2016
Project numbers: 
11009