Deep Soil Mixing Ground Improvement To Minimise Differential Settlements For Rail Embankment Culvert Approaches For The Hexham New Loop Project, NSW

As part of key strategic upgrades programmed and in plan for the North Sydney Freight Corridor (NSFC), improvements to the rail network are close to completion at Hexham. The works at Hexham comprise construction of a new loop approximately 1.7 km in length parallel to the existing up main line to permit more efficient entry of southbound trains into the NSFC. The works are being delivered by an Alliance formed of Australian Rail Track Corporation, Transport Express Joint Venture and AECOM, working with specialist geotechnical contractor Keller Ground Engineering.

The site is located around 130m from the Hunter River in an area underlain by extensive very soft alluvial deposits. The low lying location also means groundwater is at or close to ground level and is subject to tidal influence.

To support the proposed new track and in view of the poor subsoil conditions, the ground improvement method comprising deep soil mixing (DSM) was adopted at the approach embankments and at the proposed culvert location below the rail embankment. The ground improvement is targeted at improving the strength and reducing the compressibility of the soft soils below the culvert to ensure stability of the railway and control differential settlements at the approaches to the culvert. The DSM treatment was considered the most practical, cost effective and suitable ground improvement method amongst the options considered.

This paper discusses the project, the ground conditions and the foundation options considered to meet the project performance criteria. It will present the design of the deep soil mixing technique as applied at this site, including tests results on sacrificial and working DSM columns during construction.