Development of Design Charts for Pavement Thickness Design of Unsealed Mine Access Roads Subject to High Volume Heavy Vehicle Traffic

Alex Petty

Austroads Guide to Pavement Technology Part 6 Unsealed Pavements (AGPT6) provides recommended design processes and a thickness design chart based on empirical methods. The Australian Road Research Board (ARRB) Unsealed Roads Best Practice Guide also provides guidance on pavement thickness design and provides a similar design chart. However, the empirical design charts are only applicable to design Equivalent Standard Axles (DESA) of less than 5 × 10⁵. 

Often unsealed roads in Western Australia are designed based on a single pavement layer constructed from locally available gravel material. This presentation aims to provide some design charts and an associated design spreadsheet for pavement thickness design along with some practical guidance to enable concept or budget level designs to be completed for heavily trafficked unsealed pavements. The design methodology incorporates an assessment of the DESA and uses mechanistic design processes, dependent on whether the proposed pavement is a combined basecourse and wearing course or has a separate wearing course, to provide a recommended pavement profile including accounting for gravel loss. The methodology, assumptions and calculation methods are outlined, and the design charts and spreadsheet output examples are presented.

Alex Petty Geotechnical Director, PTG Consulting

Alex is a geotechnical and pavement engineer with over 20 years’ experience on major road and bridge construction projects in the transport and infrastructure sectors, as well as the resources, buildings, and marine sectors.

He has extensive experience in geotechnical applications, including geological mapping, geomorphological and terrain assessments, geotechnical investigations (including groundwater), materials assessments, identification of geohazards and risks, risk analysis, remediation solutions, soil and rock slope stability assessments, foundation and retention system design, pavement engineering (including cost effective and innovative new design and rehabilitation and overlay design) and pavement investigations using both pavement dipping and insitu testing (FWD) and tailings, earthworks and pavement construction.

Alex has worked on a number of projects for Main Roads Western Australia (MRWA) and local authorities, providing geotechnical services, from investigations to design and pavement engineering. He also has significant experience completing these services for the mining sector for sealed and unsealed access roads and haul roads.

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