Macarthur Gardens Development, Campbelltown NSW Macarthur Gardens Development, Campbelltown NSW Macarthur Gardens Development, Campbelltown NSW Macarthur Gardens Development, Campbelltown NSW

Macarthur Gardens Development, Campbelltown NSW

Project featuring the Keystone Compac & Geogrid System.

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General Information

The proposed Macarthur Gardens Retirement Village development, located off Gilchrist Drive in Campbelltown, consisted of approximately 235 single storey dwellings, as well as a double storey community centre and several open spaces with a number of internal roads. The significantly sloping site required the construction of multiple reinforced concrete masonry cantilevered retaining walls and segmental concrete masonry reinforced soil walls, including the construction of a Reinforced Earth™ wall reaching a maximum height of 9.2m. TRN Group was contracted by Stockland Property Services to complete all the civil earthworks for the project. As part of these works, Retaining Solutions was subcontracted to design, supply and construct the 245m long, 9.2m high Keystone & Polyester geogrid Reinforced Earth™ wall.

Jeffery & Katauskas Pty Ltd, TRN Group engaged geotechnical engineers, carried out the geotechnical investigation. Boreholes disclosed topsoil covering residual clays that graded into shale and sandstone bedrock at shallow depths over large portions of the site. The proposed Reinforced Earth™ wall footings were located within the (CL-CH) medium to high plasticity, very stiff to high strength clays (Su strengths varying from 100kPa to 200kPa). External stability requirements for Reinforced Earth™ walls (sliding & bearing capacity checks) require assessment of both short and long term stability on varying foundation conditions; hence such review required L/H ratios in excess of 120% of wall heights to satisfy the sliding instability and bearing capacity requirements of AS4678. Traditionally L/H ratio would typically be 70% of the height for such walls. Wall heights varied from 1m up to 9.2m with geogrid lengths varying from 4.2m to 11.2m respectively. Due to the size (height and length) of the wall and associated large quantities (35,000m2) of geogrid required (strengths varied from 60kN/m up to 120kN/m) that a range of polyester geosynthetics be sourced from the local market suppliers i.e. Miragrid XT, Stratagrid and Acegrid geogrid products were installed within the wall profile. Poor foundation conditions also dictated the requirement for 0.6mx0.6m reinforced concrete strip footings with construction joints every 10m centres along wall.

Macarthur Gardens Development, Campbelltown NSW

 

A significant feature of this project involved the use of an innovative fall from height protection system to prevent workers falling from height during both block placement and hand compaction operations. Due to the difficult ground conditions in front of the wall, a traditional scaffolding system would have proven impractical and economically unviable. An alternate system was devised using circular hollow galvanised steel sections, expanding joint pins and swivel couplers. Vertical steel sections were fastened into the reinforced soil block at the rear of the facing units using star pickets and high tensile straps. Two horizontal steel sections were then connected to the vertical sections using swivel couplers to provide a handrail above the wall. The system allowed workers to easily slide the horizontal sections up as the wall was being erected allowing for 100 % fall protection over the entire wall construction duration.

Another key design feature of this wall was the incorporation of a colorbond fence to be located directly behind the facing column at the top of the wall. Fence posts were to be located @ 2350mm centres, with services from adjacent dwellings to a maximum depth of 600mm below top of wall profile. No-fines concrete was used at the top of the structure with the installation of PVC sleeves @ 2350mm centres to cater for proposed colorbond fence posts to be installed after wall construction was completed. Due to adjacent services the first layer of geogrid soil reinforcement was installed at a maximum depth of 4 courses (800mm) below the top of the wall level.

Retaining Solutions scope of works involved supply & installation of Keystone blocks; caps; geogrid soil reinforcement; reinforced concrete footings; spreading & compaction of imported crushed sandstone select backfill; geotextile encapsulated gravel chimney drains, No- fines concrete and fence post sleeves at rear of keystone facing column. Construction of the works was carried out over a period of challenging inclement weather conditions, but with a great working relationship with TRN Group completed the wall to both client and owner satisfaction as per advised construction programme. Another quality project completed by Retaining Solutions experienced construction personnel.


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Project Specs

  • Application - Fill Embankment Stabilisation
  • Product - Keystone Compac & Geogrid System
  • Finish - Plain Grey Smooth
  • Area - 1655m2
  • Max. Height - 9.2m
  • Length - 245m
  • Loadings - 20kPa
  • Design life - 100 years
  • Owner - Stockland Property Services
  • Client - TRN Group
  • Construction - 12 weeks

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