Concrib had to overcome several site challenges when building a retention structure at the Toowoomba Grammar School.

The construction of a new aquatic sports centre (below the main playing fields) required a retaining structure on the east side of the building, about 10 metres below the main oval. Concrib not only had to deal with old fill material but also navigate restricted site access during the construction process.

There were additional concerns about the corrosive nature of the leachate degrading the soil nails prematurely as well as the poor angle of friction making it difficult to use a steep retention structure with a small construction footprint.

Concrib was invited by the builder, McNab Construction, to offer a design that would best address the on-site issues.

Concrib’s design consisted of a triple-cell, three-tiered crib wall 10 metres in height, with a face area of 810 square metres. The tiers on each level would provide an area for planting shrubs and creepers post-construction to enhance the aesthetics and amenity of the wall structure.

Since access constraints prevented the use of the necessary compaction equipment behind the wall, Concrib cut the old fill material back to a 45-degree angle, and filled this area with self-compacting, recycled concrete, providing an excellent friction angle.

Concrib also used a ‘telebelt’ materials handler to place the recycled concrete, wall infill, and soil, helping save significant construction time and increase construction efficiency. This helped reduce the projected 12-week construction time to 8 weeks from foundation pour to wall top out.

Concrib’s crib wall design saved time and money with estimated savings of 20 per cent from using the crib wall system over soil nailing.