As the availability of prime land across Perth decreases, the need to develop marginal land is becoming more relevant and pragmatic approaches to ground improvement are needed to keep the design sustainable.

The site occupies an area of about 28ha and comprises an existing clay quarry, schist resource and inert waste landfill site. The proposed development plan intends to extend the existing clay quarry and upon completion will be infilled, capped, and levelled in order to prepare for a subdivision development.


  • Completion of nine geotechnical boreholes using wire line diamond coring techniques to depths of up to 24m.
  • On-site geotechnical logging of boreholes.
  • Mapping of subsurface profile using exposed quarry faces.
  • Assessment of site classification in accordance with AS2870-2011.
  • Recommendations to improve site classifications from ‘Class H1’ and ‘Class H2’ to a ‘Class A’.  
  • Recommendations to improve the ‘P Class’ sub-surface conditions over the portion of the site underlain by inert waste, such that footings complying with the requirements of a ‘Class A’ site will perform adequately on this portion of the site.
  • Assessment of the suitability of excavated material for reuse as structural fill.
  • Provision of material specifications, placement recommendation and compaction recommendations for site won material and imported granular fill material.

Key Challenges and Solutions

Material Sampling and Evaluation:

A key element for developments is the availability of suitable construction materials.

We collected samples and transported them to Perth, where laboratory testing was completed using our NATA registered laboratory contractor

The results were used to assess the materials and assist in providing subdivision development recommendations and recommendations for material reuse on-site as structural fill.

Site Classification:

The targeted site classification set by the developer was a ‘Class A’ in accordance with AS2870-2011.

Following geotechnical investigation the area of inert waste at site was considered a ‘Class P’. GGC provided recommendations for engineered fill thickness, such that footing complying with the requirements of a ‘Class A’ site will perform adequately on the portion of the site underlain by inert waste.

Other areas the site, following clay quarry excavation, were considered Class H1’ and ‘Class H2’. We provided recommendations for remedial earthworks to improve the site classification to ‘Class A’