2016 CCF WA EARTH AWARDS

CATEGORY 2 WINNER

Ertech’s innovative use of a soil nail wall piling technique on the MAAC Carpark Expansion significantly

reduced the impact on a busy adjacent road and footpath, minimising the social and economic effect on the local community during construction.

Ertech was engaged to design and construct a permanent retaining wall to enable the extension of the existing car park by cutting into a sloped embankment.

Ertech concluded that the piled retaining structure originally proposed would involve a high social and economic effect on the local community during construction, as it would require the use of large, heavy piling equipment with the associated noise and vibration issues.

Working with the City of Joondalup

and its consultants, Ertech developed the alternative design involving a soil nail wall.

Soil nailing is a technique of reinforcing in-situ soils using fibre reinforced plastic (FRP) rods working in tension and held by soil friction forces. The lightweight bars offered a high tensile strength and can carry high loads that is well suited for applications without couplings in confined locations.

The stabilisation of slopes to provide a retained structure using this technique differs considerably from a ground anchoring approach in that it does not involve any stressing or tensioning. The process utilises arrays of fully bonded passive ties buried in the ground and installed at a relatively high density. The nailed soil volume may be likened to a reinforced gravity structure, retaining and stabilising the slope to the existing footpath side of the West Coast Drive.

An important aspect of soil nail wall design is the adequate pull-out resistance to the nail. As a risk management initiative, the Ertech team undertook a successful short test program of nail pull-outs on a number of sacrificial soil nails prior to commencing the works to prove the construction method and that the required grout-to-soil bond strength was achievable.

Another construction technique introduced by Ertech to successfully manage site constraints and enhance the topography of the site was to develop a practical solution for extending the car park seaward. The “compliant” design would have been extremely difficult to achieve within the dune system.

Working with Hera Engineering to improve constructability while maintaining the artistic vision, Ertech’s solution was to use 8m precast beams, greatly simplifying the construction process and ensuring the project had less environmental impact within the fragile coastal dune system.

Thirty 400mm diameter foundation piles, designed to support the loadings of the reinforced concrete cantilever deck, were drilled into bedrock at a depth of 10m to accommodate the design loadings for the 15 beams.

The site was in a very constrained area, with detailed planning and logistics required to ensure that materials were delivered and stored in an efficient manner so construction activities were not inhibited.

Now fully open, the carpark was finished under budget and on program. Its capacity has increased from 42 to 82 bays and accessibility to the beach has been improved.

ERTECH Marmion Angling & Aquatic Club Carpark ExpansionClient: City of Joondalup