TECHNICAL
NEW BASEGRADE STABILISATION TECHNOLOGY RESOLVES THIN PAVEMENT ISSUES IN REDLAND CITY
Scott Young BE (Hons), MPavtTech, RPEng (Civil), RPEQ
Sealed flexible pavements typically consist of a wearing surface, a base layer and a subbase layer to protect the subgrade from damage caused by traffic loads over time. Local government urban roads in Australia often only have a base layer sitting directly on the subgrade. When the thickness of the existing granular base layer is deemed too thin to satisfy rehabilitation design requirements, the base and subgrade layers can be insitu stabilised simultaneously with an appropriate binding agent. This is termed ‘Basegrade Stabilisation’ (Young, 2020). Experimental research completed in 2020 developed a mix design procedure for basegrade stabilisation to allow practitioners to confidently evaluate an existing pavement structure and select a trial mix design for laboratory testing.
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This paper explores the background of basegrade stabilisation, the subsequent development of a new mix design procedure and how it can apply to a local council asset management plan. A case study from Redland City also demonstrates the effectiveness of basegrade stabilisation. INTRODUCTION The typical pavement structure often designed in new flexible pavements consists of multiple pavement layers that absorb the traffic induced loads to protect the subgrade from permanent deformation. This typical pavement structure is illustrated in Figure 1. Wearing Surface Base Subbase
Typical Pavement Structure
Subgrade
Figure 1. Typical Flexible Pavement Structure (Young, 2020).
Local government roads however are not always this fortunate, and thin granular layers (or just a single layer) commonly exist between a bituminous wearing course and the subgrade. When these common pavement structures are identified for rehabilitation, the absence of a subbase layer results in the base layer having inadequate thickness to recycle using insitu stabilisation based on the requirements to satisfy structural design requirements (e.g. a 20year design life).
ENGINEERING FOR PUBLIC WORKS | JUNE 2021
Wearing Surface Base
Common Pavement Structure
Subgrade
Figure 2. Common Flexible Pavement Structure in Lightly Trafficked Roads (Young, 2020).
This challenge however can be overcome by adopting the process of basegrade stabilisation in lieu of other more expensive renewal treatments, such as complete removal of all pavement materials and replacement with imported quarried materials. BASEGRADE STABILISATION DEFINED Basegrade stabilisation (Young, 2020) is the process of insitu stabilising existing granular pavement materials that are mixed with subgrade materials with a suitable binder to improve the engineering properties of the combined layers. Basegrade stabilisation occurs when the existing pavement gravels comprising a base course (and/ or subbase course) are not thick enough and a deliberate decision is made to incorporate subgrade materials into the granular materials to satisfy the required depth of stabilisation (refer Figure 3). Wearing Surface Base Subgrade Subgrade
Required Depth of Stabilisation
Figure 3. The ‘Basegrade Stabilisation’ Concept (Young, 2020).
Basegrade stabilisation as a process is not a new concept and has been used widely in Australia,
