28 April 2009
General Manager's Report No. GM19/09
Folder No: PROJ/10483/2009
There is a significant sandstone retaining wall on
The wall was constructed approximately 80 – 90 years ago and is now in poor condition.
The reconstruction of 70m of this retaining wall has been listed in the draft 2009-10 Capital Works Program. This report requests that funds be borrowed from reserves to allow the work to commence in the 2008-09 financial year and then repaid with the proposed 2009-10 funds for this project.
Recently, a collapsed drainage pipe has resulted in damage to the
retaining wall and the land behind the wall outside of
The properties on the southern side of
Wall Description and Condition
The sandstone wall is approximately 124m in length. It varies in height from 0.8m to 2.4m. The tallest part of the wall is 50m in length and includes 2 sets of stairs for access between the road and the properties.
The wall consists of sandstone blocks with mortar joints. The mortar has deteriorated over time and cracks have formed along the mortar joints. Along its tallest section, the wall has horizontal displacement, at the top away from the road, of over 100mm.
The movement and settlement of the stairs has resulted in a slope across the step.
The wall is a segmental wall that has the potential for sliding. The wall has commenced overturning as is indicated by the horizontal displacement at the top.
The wall was structurally assessed by consultants in December 2003. At the time, they noted the same damage and concluded that remedial measures would need to be undertaken at some time.
In the meantime, we have monitored the wall for any changes. Up until recently, the extent of movement (deflection) had stabilised. However, with the recent rain, there are now signs that the movement has increased.
Should the wall fail and collapse, it would cause damage to private
property and could cause injury to a pedestrian. If the wall did collapse, it
would block the footpath, closing access to the properties in this section of
The lower footpath provides access to private property. This prohibits the closing of the lower footpath.
To assess the stability of the sandstone retaining wall, we have engaged Structural Engineers. The Structural Engineers will first assess if short-term measures are needed to stabilise the wall and then produce a design for the reconstruction to the wall. Once the design is completed, it is proposed to engage contractors and commence work immediately.
Modern retaining structures that retain ground over 2m in height are generally reinforced concrete structures.
The sandstone texture and look provides an aesthetic that is a prominent feature of this area.
On this basis, it is proposed to construct a retaining structure that will have a similar look to the existing sandstone wall. It is Council’s intention to retain the existing sandstone wall if structurally possible.
Relationship to City Plan
The relationship with the City Plan is as follows:
Outcome 6: A Liveable City.
Direction 6a: Our public assets are planned, managed and funded to meet the community expectations and defined levels of service.
Financial impact statement
There is funding in the 2009/2010 budget to repair this wall.
This report requests that funds be borrowed from infrastructure reserves to allow the work to commence in the 2008-09 financial year. The borrowings will be repaid from the project funds proposed for this project in 2009-10.
The condition of the wall is poor. We have engaged Structural Engineers to assess the stability of the wall and recommend measures to temporarily stabilise the retaining wall.
The reconstruction of 70m of this sandstone retaining wall was proposed in the draft 2009-10 Capital Works Budget. However, it is proposed that the work commence immediately to avoid any potential collapse due to recent deterioration of the wall due to heavy rainfall.
a) funds be borrowed from the infrastructure reserve fund to allow commencement of planning and work on the Alison Road Retaining Wall.
b) the borrowings be repaid from funds allocated in the 2009-10 Capital Works Budget.