Mine Void Treatment on Hunter Expressway Alliance – A Success Story

Dr Olaf Stahlhut

Nick The Hunter Expressway is a new government funded dual carriageway motorway built to relieve congestion between Newcastle and Thornton, Maitland and Rutherford. The expressway is continuous over 40 km between the F3 at Seahampton and Branxton. The easternmost 13 km between the F3 and Kurri Kurri is being built by the Hunter Expressway Alliance (HEA), comprising constructors Thiess and designers Parsons Brinckerhoff and Hyder Consulting partnering with NSW Roads and Maritime Services (RMS).

The Newcastle Coalfield has made a significant contribution to the economic prosperity of the Newcastle region, but some of the abandoned mine workings now present a major engineering challenge for infrastructure and buildings that are constructed over the workings. The proposed Minmi to Buchanan section of the Hunter Expressway passes over an area where coal has been previously mined for over a century and further mining is proposed in the future. Subsidence movements associated with the sudden collapse of standing pillars have the potential to impact on some of the key elements of the new motorway infrastructure, including major bridge structures and sections of pavement. The strategies adopted for managing the subsidence risk include both mine fill and infrastructure design components.

A solution was required to manage the risk of mine subsidence under the viaduct and bridge foundations. The mine fill treatment concept is relatively simple; and comprises the filling of abandoned mine voids below the protected structure out to a distance of half the seam depth in all directions.

Validation of the fill to confirm the design requirements have been met has nevertheless presented some significant challenges. This presentation outlines the subsidence challenges, the mine fill treatment design, and the development and implementation of the validation strategy for the Hunter Expressway Alliance. Furthermore specially designed infrastructure components to accommodate movements are part of the presentation.

There were several outcomes from the work done. It has been demonstrated video camera monitoring can play a significant role in mining and geotechnical applications, and have a positive impact on time and budget-related issues. The HEA minefill was successfully delivered as measured by the treatment validation. However success of the project can also be measured at other levels; a fully integrated sub-alliance, open and honest communication, an aligned and engaged workforce and a project delivering to budget and programme; a true “success story”.

Speaker biography

Olaf has over 18 years experience in Geotechnical Engineering, managing sub-consultants, project management and construction phase support (CPS) in Germany and Australia. He is currently employed with Parsons Brinckerhoff, Sydney, but will start a new position in Germany in April 2013. Olaf’s first employment in Australia was with Sinclair Knight Merz (SKM). Before joining SKM, Olaf was employed by a German consultant (IWB) in Hamburg within the Geotechnical and Management Group. Prior to IWB, Olaf worked as research associate at the Institute for Soil Mechanics and Foundation Engineering of the Technical University of Braunschweig, Germany.

Olaf’s current role is the geotechnical design team leader for the upgrade of the Pacific Highway between Woolgoolga and Glenugie. On Hunter Expressway Olaf was the lead geotechnical design manager and CPS manager for mine void treatment. As CPS manager Olaf was responsible for the interface with various construction teams, internal and peer reviewers and the assessment and validation of the successful execution of the mine void treatment.

Amongst other projects Olaf delivered the land reclamation in Hamburg Harbour for the Airbus Company and several independent verification (e.g. Gateway Upgrade Project in Brisbane), design and CPS projects.

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