1 Introduction. 2 Site Description. Auckland Transport Private Bag Auckland 1142 New Zealand. 2 March Attention: Sunil Kariyawasam

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1 21 Pitt Street PO Box 6345, Auckland 1141, New Zealand T: // F: E: info@beca.com // Auckland Transport Private Bag Auckland 1142 New Zealand Attention: Sunil Kariyawasam Dear Sunil 9/21 Waller Street Retaining Wall - Initial Geotechnical Assessment 1 Introduction Auckland Transport (AT) have commissioned Beca Ltd (Beca) to inspect the retaining wall adjacent to the carpark 9/21 Waller Street, Onehunga, and provide an initial assessment of the stability of the wall and potential remediation solutions. This letter outlines the results of our initial assessment. This work is part of contract number PS. The retaining wall is approximately 50m long, with half being a basalt block and mortar wall, and half being a reinforced concrete wall. The basalt wall face has about 15m of bulging, with some cracks at the end of the wall indicating that this face has moved outward. The reinforced concrete wall appears to be a façade over a possible continuation of the basalt block wall, and the foundations of the wall are unknown. This wall is considered to be in a high-risk, failed state, and any further loading from a range of potential triggers could destabilise the wall further. Further movement will likely result in a catastrophic failure, which would be a safety risk to any people nearby. We recommend an initial survey of the wall and surrounding area, and a ground investigation incorporating at least two machine boreholes. We do not consider a Do Nothing solution to be appropriate. We recommend a remediation solution incorporating a mesh and shotcrete skin, tied to a dead man anchor at the top and anchored in the middle. An alternative solution would be to demolish the existing wall and replace it with a steel H-pile wall. 2 Site Description The wall below the carpark at 9/21 Waller Street separates the AT public carpark at this address from a currently cleared site below. The carpark has clearly been levelled, with fill likely underneath at least half of it to maintain the high level. The site below has recently been cleared for redevelopment, and previously was the site of a number of terraced houses or units (Figure 1 aerial image still shows houses below).

2 Page 2 Figure 1 Site Location 2.1 Geology According to Kermode (1992) and Edbrooke (2001), this site is underlain by basaltic lava, likely flowing from one of the cones to the north. Boreholes around the area also show basalt greater than 10m thick. No basalt was visible on site, due to the built up nature of the area, however aerial photographs from 1940 show what is likely to be the raised edge of a lava flow underlying what is now the carpark. 2.2 Wall Description The wall being assessed is a basalt block and mortar wall, the northern half of which has been covered by a reinforced concrete façade, and while basalt blocks can be seen extending behind the end of the concrete wall, it can only be assumed that these will continue further behind the wall. These two halves will be described separately. Figure 2 shows the basalt block wall in the centre, with part of the reinforced concrete wall on the right.

3 Page 3 Figure 2 Basalt block retaining wall in centre, reinforced concrete wall extends to the right. Photo taken from 64 Galway Street Basalt Block Wall The basalt block wall is 23m long and averages around 4m high. It is made of basalt blocks mortared together, with some additional concrete added in places later. It appears that there are voids and potentially uncontrolled fill immediately behind the wall surface. Some weep holes are observed approximately 2m above ground level, at ~1.3m spacing, along the central section of the wall. At either end of the wall, at approximately 2m centres, three 300mm diameter timber poles have been installed, likely in an attempt to stabilise the wall. The embedment depth of these poles is unconfirmed, and each is tied back at the top to a concrete block in the footpath above, using an approximately 20mm bolt. In front of the wall and the poles, a raised concrete path has been installed, ramping up to ~1m high in the centre, likely with uncontrolled fill below a <100mm concrete pavement. The concrete path/buttress has been poured around the poles and the current wall configuration. Vines have grown up much of the face, particularly near the timber poles, which have chicken mesh stretched between them Reinforced Concrete Wall The poured concrete wall is 22m long, and measures 4.5m high at its northern end, where it turns a corner and runs approximately 5m westward, forming a step in the carpark footprint. It has been poured in situ, and shows the imprint of wooden boxing used in its construction, including nails sticking out from the wall at three levels. The concrete is 300mm thick, and is reinforced with ~1 inch steel reinforcing bars at 350mm spacing. At the southern end of this section, where this wall abuts the basalt block wall, basalt blocks can be seen extending behind the concrete wall. North of this wall, a wooden retaining wall which ranges from 1.1m to 2m high supports the toe of what appears to be the natural slope above. This is capped by an approximately 1m high wooden fence.

4 Page 4 3 Wall Condition Assessment 3.1 Basalt Block Wall The southern end of the basalt block wall turns back ~1m towards the west, where it abuts the adjacent building. This end shows vertical cracking, with apertures up to 70mm wide, indicating that the face of the wall has moved outward here (Figure 3). Bulges in the face of the wall are present between 6m and 20m along the wall (measured northward from the south), and show up to 600mm of lateral movement (Figure 4). Voids are visible behind the surface blocks in the largest bulging area. Figure 3 Cracks visible along the southern end of the basalt block wall.

5 Page 5 Displaced pole Bulging wall Figure 4 Basalt block wall, showing the largest bulge in the centre, the timber poles (one displaced), and the buttress/footpath at the toe of the wall. The third timber pole from the north has been displaced from its original position, where it has been pushed outward 250mm by the slumping of the wall at its top, where the connection bolt has deformed the wood. The fence running along the top of the wall has rotated outwards, and a new fence has been placed to hold the tilted one in place. While there is no visible cracking in the footpath above, there is some deformation of the blocks at the immediate top of the wall, and the southern corner of the kerb appears to suggest that there has been some historic settlement in this area. The concrete buttress/path at the toe of the wall does not show any cracking, and the concrete appears to have been poured around the timber posts and the bulges in the wall. The wooden fence bounding the front of this buttress has rotated over time. The curve of the buttress/path around the bulge extends laterally by 350mm. This buttress/path is unlikely to have the mass to provide any significant stability benefits to the wall. This wall can be considered to be in a currently failed state. Any further loading, such as caused by adjacent construction activity or even heavy vehicles on top of the wall, and/or other triggers including seismic events could potentially destabilise the wall further. Further movement in the wall will likely result in a catastrophic failure, affecting the properties both above and below the wall and creating a significant safety risk to any people nearby. 3.2 Reinforced Concrete Wall The reinforced concrete northern portion of the gravity retaining wall does not show any visible deformation. No relevant cracks were observed either in the footpath at the toe of the wall, or in the pavement above the wall. Minor rust is visible on the reinforcing bars extending out from the south end of the concrete panel, and also seen passing through the formed space between panels ~8m from the northern end of this wall. Foundations of the wall are unknown. It is unclear if the concrete has sufficient support.

6 Page 6 4 Remedial Options Costs provided below are high-level estimates only. Further investigation would be required to refine these costs. 4.1 Do Nothing/Do Minimum Cost: $0 A Do Nothing option would involve leaving the wall in its current state, including toe buttress/path, as shown in Figure 5 below. We do not consider this option to be feasible for this wall, due to its failed and hazardous state. Considering the hazardous state of the wall, we do not consider there to be any low-cost remedial measure that would provide a meaningful level of stability, and therefore more robust options have been considered. Figure 5 Sketch of remedial Option 1 (do nothing) (not to scale)

7 Page Mesh and Shotcrete Cost: $300,000 - $400,000 A Mesh and Shotcrete option would involve pinning 2 layers of steel mesh and shotcrete (up to 300mm thick) to the existing surface of the basalt block wall (~23m long), with only one layer of mesh and 150mm of shotcrete over the reinforced concrete portion of the wall (~23m long). The top should be tied back (2 ties per 6m panel) to a dead man anchor located on the far side of the carpark. The middle of the shotcrete face should be anchored back into in situ ground behind the wall. The base of the steel mesh should extend into a 1m deep concrete footing, keyed 0.5m into basalt, tied together with 3x steel bars. Rock depth both below and behind wall should be confirmed with at minimum two geotechnical boreholes. Work should proceed in 6m sections (i.e. buttress removal, footing construction, shotcrete and mesh installation, and tying into the dead man anchor along a 6m length of the wall, then start the next section tied into the previous). It is likely that a re-seal of the carpark will be required once construction is complete. Figure 6 below shows a sketch of this option through the basalt block wall. Figure 6 Sketch of remedial Option 2 (not to scale)

8 Page Rebuild Cost: >$2.0 Million Rebuilding the wall would involve demolishing the existing failed block wall and replacing it (see Figure 7). A gravity wall of this height does not meet seismic standards, and as such a steel H-pile retaining wall tied into a dead man anchor, with a steel waler and reinforced concrete pre-cast panels, would be the most appropriate alternative. Removal of the existing wall would require material behind the wall to be removed to at least a 1:1 slope, and likely shallower. Excavated material is likely to be basaltic rubble, which may be appropriate for re-use. Testing will be required to confirm if the material is suitable or contaminated. An allowance for disposal of contaminated material is recommended. At minimum two geotechnical boreholes will be required to confirm pile depth and backfill material. Once the wall has been backfilled, the carpark pavement will need to be reinstated. Figure 7 Sketch of remedial Option 3 (not to scale)

9 Page 9 5 Summary and Recommendations In summary, the wall at 9/21 Waller Street is considered to be in a failed and hazardous state, and could be a risk to people both above and below the wall if it were to fail further with any appropriate triggers. Therefore, we consider remedial Option 2 to be the safest solution during construction, and to likely provide the best value for money. The costs provided are a high-level estimate only. Further investigation would be required to refine the costs further. We recommend that a full survey be undertaken of the wall and the ground above and below, including the carpark and road footpath above, and at least 5m out from the toe. A geotechnical investigation comprising at least two machine boreholes is recommended for all remediation options. Any works on this wall will likely require building consent. 6 Applicability Statement This report has been prepared by Beca on the specific instructions of our Client. It is solely for our Client s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk. Should you be in any doubt as to the applicability of this report and/or its recommendations for the proposed development as described herein, and/or encounter materials on site that differ from those described herein, it is essential that you discuss these issues with the authors before proceeding with any work based on this document.

10 Page 10 7 References Edbrooke, S. W. (compiler) 2001: Geology of the Auckland area. Institute of Geological and Nuclear Sciences 1:250,000 geological map 3. 1 sheet + 74p. Institute of Geological and Nuclear Sciences Ltd, Lower Hutt, New Zealand. Kermode, L. O. 1992: Geology of the Auckland urban area. Scale 1:50,000. Institute of Geological and Nuclear Sciences geological map 2. 1 sheet + 63p. Institute of Geological and Nuclear Sciences Ltd, Lower Hutt, New Zealand. Yours sincerely Alicia Newton Engineering Geologist on behalf of Beca Limited Phone Number: alicia.newton@beca.com Susan Tilsley Technical Director Engineering Geology on behalf of Beca Limited Phone Number: susan.tilsley@beca.com