Retaining Structures

Placemakers, Silverdale

PlacemakersWall 400
Redevelopment of a 0.9525ha brownfield site (previously a truck depot) as a Placemakers store, offices, and car park. Work included an environmental assessment, geotechnical investigation, and civil design. Bulk earthworks were required to create flat platform areas. Deep counterfort drains were installed to maintain groundwater levels, and polyrock was used as a lightweight fill alternative to ensure adequate slope stability. Retaining consisted of timber pole and steel Universal Column cantilever walls up to 6m high and 240m long. Stormwater mitigation measures were incorporated into the design to attenuate the runoff generated from the development and provide sufficient treatment prior to discharging into the downstream environment.

Luxury Car Showroom, Wairau Park

Car Showroom 400
A four level luxury car showroom is under construction in Wairau Road on Auckland’s North Shore on a steep site overlain with non-engineered sidling fill supporting the northern motorway. The showroom will be retained by walls up to 5.1m high that will be integrated into the building structure and will enable vehicle access. Due to the site’s close proximity to the motorway, the design incorporated top down construction involving soldier pile walls, with shotcrete infill and capping beam, and 600mm diameter piles spaced at 1.5m crs. Site excavation involved the removal of approximately 18,500m3 of material. To date, environmental, geotechnical, and civil engineering inputs have included finite element wall loading analyses in support of resource and building consents, and construction tendering documentation for the walls and site preparation.

Summerset Retirement Village, Ellerslie

Ellerslie foundations 400
The Summerset retirement village development has been designed to include a mixture of lightweight and heavy structures. Until the 1960s this historically mixed-use site was quarried for basalt rock, after which it was landscaped and a heritage park created in the 1980s. Following closure of the park the land was used by St Johns until purchased by Summerset. Geotechnical aspects of the construction include basement excavations though variable quality fill and basalt rock; and design and construction observation of shallow footings and large diameter pile foundations within the rock or upon compacted SPR fill. An assessment of groundwater and stormwater disposal has also been undertaken. The geotechnical role has subsequently expanded to include due-diligence investigations; detailed investigations; design input and review; and verification and approval of ground conditions and foundations. Unique aspects of the site construction include creating ponds on fractured basalt; piling in areas of highly fractured rock; finding solutions for exceptional retention problems; and accommodating historic fill.

Upper Harbour Highway

UpperHarbour 400
Final design and supervision of Miragrid reinforced slopes for three culverts up to 15m high.  The wrapped face walls enable a green facing in environmentally sensitive areas.  The project consisted of three mechanically stabilised earth walls (MSE) up to 100m long and, in places, 7m high.

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Beach Road, Castor Bay

41 Beach Rd 400
A new house incorporating basement levels to 5m and a pool extending out over the top of a palisade wall was proposed for a 1,897m2 site on an approximately 25m high section of cliff-top. A geotechnical investigation and assessment of site stability and founding conditions was undertaken with design input provided for the palisade wall, and basement retention. Additional design was provided for soil nails to reinforce the cliff-top to prevent or slow natural regression, and provide a more intact base from which vegetation grows and is enhanced, thereby reducing short and longer-term exposure of the palisade wall. The basement excavation was undertaken in close proximity to neighbouring structures and careful design, construction and monitoring was undertaken to prevent damage to these buildings.

North East Industrial Subdivision

NE Industrial 400
Investigation, design, and supervision of geotechnical aspects of large scale earthworks (300,000m3) to form a large detention basin in Palmerston North as part of a commercial development adjacent to the airport. Design of 500m length of 3m high gabion walls optimising development potential. Design of a detention dam to store up to 100,000 CM in extreme flooding events, which involved extensive erosion protection and included reno mattresses for an overflow spillway.

Hillcrest Avenue Culvert Retention Design

Hillcrest Ave 400
Design and supervision during construction of temporary 3.7m deep retention measures for culvert duplication works. The programme required that a busy feeder road be kept open during construction with work limited to one half at a time. Work involved liaison with site contractor to determine preferred construction methods and materials. Two different retaining wall types were designed to support adjacent walls of a 3.7m deep cutting. The wall supporting the road traffic used vertical propped cantilevered timber pole driven into pre-drilled holes.  This wall had two layers of tie backs. The upper layer installed in trenches extending to deadmen across the road. The lower layer was drilled at an inclination and grouted into the sandstone underlying the low strength alluvium soils above. The wall at right angles resisted smaller loads and was excavated at a 60-degree angle with shotcrete face protection.

Residential Retaining Walls

Residential Retaining Walls
Investigation, reporting, civil design, and construction monitoring for the repair of multiple residential retaining walls damaged by the Canterbury earthquake sequence.  Design work was carried out in accordance with MBIE retaining wall design methods developed specifically for the Canterbury region.  Design solutions ranged from replacement timber pole walls, masonry walls, and reinforced concrete walls with stone facades.

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