Gen Fyansford Quarry Transformation

Tonkin + Taylor played a key role in the transformation of the former Gen Fyansford basalt quarry into land ready for residential development – supporting one of the largest urban growth projects west of Geelong.

The old Gen Fyansford basalt quarry is being filled and redeveloped into a residential subdivision. The deepest part of the quarry is below the groundwater level. The waterbody has formed as previous basalt quarrying activities extended below the water table. Pumping to facilitate quarrying ceased and groundwater rebounded to form the waterbody. The base of the waterbody is expected to be primarily basalt with some sediment and uncontrolled fill, including large boulders. Preliminary pumping trials by the contractor identified that temporary dewatering to allow placement of fill is not possible. The ponds contained up to about 0.9m of sediment and some aquatic plants. Water levels varied between about 0.3m and 3.5m with Final fill levels were planned to be between 5.5m and 6.5m above the base of the ponds. T+T was engaged to assist with the completion of the earthworks and to achieve design levels to allow development of the subdivision to proceed in the section of the quarry which was below groundwater level, by developing a methodology and specification for the placement of fill within the waterbody on site and provide construction supervision and laboratory testing services. 

We began with an unusual first step – one of our geotechnical engineers took to the water, kayaking across the waterbody to assess the depth and conditions of the quarry base. This enabled our team to understand the site and begin planning with confidence.

The strategy for the filling of the waterbody was developed on the understanding that dewatering is not feasible and fill will be placed below the water table, and where possible, site-derived material will be used to reduce the amount of imported material.  The base of the waterbody was expected to be primarily basalt with some sediment and uncontrolled fill, including large boulders. The approach adopted was construct a highly permeable rock fill platform on which to base subsequent conventional clay filling. The design approach incorporated the following layering system:

• Rock fill
• Transition filter zone
• Clay fill

Due to the different particle sizes, conventional density testing was not appropriate for compaction compliance testing in some layers. For this reason, a combination of method specifications and performance specifications were proposed .

In conjunction with appropriate site supervision and testing to validate the placement and compaction of the fill, the installation and monitoring of settlement instrumentation was integral to demonstrating that the performance of the fill was acceptable.

• 225,000 tonnes of engineered rock placed and compacted

• Innovative filter layer design enabling safe transition from rock to clay

• Full-time on-site supervision by Tonkin + Taylor

• Strong collaboration with ICD Property, Sinclair Brook, Stantec, and Winslow Constructors

The Fyansford Quarry project exemplifies how smart, collaborative engineering can unlock the potential of challenging land. Our solution was driven by sustainability and tailored design—creating a stable foundation for future housing that will support healthier living environments and a vibrant new community.