Shallow Ground Improvement For A New Rail Depot / Maintenance Facility In Sydney

A new rail maintenance and stabling facility comprising rail sidings and associated maintenance buildings / facilities is to be constructed in a heavily urbanised area in Sydney, NSW. The site will be on a raised earthworks development platform for flood mitigation purposes.

Ground conditions include variable non-engineered surficial fill over up to 4m thickness of variable density alluvium (dune sands) overlying dense to very dense Botany Sands above deep alluvium to over 40m depth with a shallow groundwater level. Some site areas have been previously loaded by former development.

Identified geotechnical risk relates to potential unacceptable ground surface settlement of the development due to embankment loading of low density variable surface soils against the need to limit total and differential settlement of rail track-slab and building foundations within specified design and operational tolerances for a design life of 75 years.

A ground improvement solution was required to improve these surface soils to reduce the potential for both total and differential settlement under loading from the proposed earthworks and structures. The achievement of differential settlement criteria is critical to the long term performance of the track slab system, particularly at the interfaces with buildings.

This paper describes the site ground conditions, the ground improvement options considered and the selection of high energy impact compaction (HEIC) as the optimal solution for the proposed site development. HEIC trials including performance validation of the ground improvement are described. Site specific Specifications were then developed for HEIC construction phase works. The trials also included noise and vibration monitoring to define construction control limits and buffer zone distances from sensitive adjacent areas including residential properties and a heritage building.

Significant cost savings and construction programme benefits are realised utilising shallow ground improvement methods compared to the other ground improvement options considered.