Behaviour of granular base materials as unsaturated geomaterials.

Program Code: 

A/Prof Robert Lo (

Dr Rajah Gnanendran (

Description of Work: 


Motorways have to be designed to very high performance level to ensure safety at high car speed. One component that controls the performance of a motorway pavement system is the behaviour of road foundation constructed with granular base (GB) subject to cyclic loading. A granular base (GB) material is a heavily compacted well-graded silty sandy gravel. It may be unbound (ie no cementing agent added) or stabilised (ie with cementing agent added to give an unconfined compressive strength of ~2MPa). Traditional pavement design is based on empirical rules, and the associated prescriptive requirements may place severe environmental pressure because of the need of extensive quarrying and haulage over long distances. Furthermore, some of the empirical rules on fines content, role of cement additives are inconsistent.

As part of an effort to develop analysis-based design for pavement foundations, a new research area, referred to as “Pavement Geotechnics”, has been initiated recently.

A significant component of pavement geotechnics is on material behaviour and modelling. As the pavement foundation material is in an unsaturated state its behaviour of is also governed by the fundamentals of unsaturated soil mechanics. We are the only research group in Australia, and one of the few internationally, that have a track record in this area of research.

Description of Study:

We intend to take in one PhD (maybe two if we have outstanding applicants) to conduct PhD research in this pioneering area. The research work involves:

  • Conducting cyclic triaxial testing on GB materials (unbound or stabilized) with using unsaturated soil mechanics testing technology.
  • Synthesizing the test results to establish the stress state parameters (including matric suction) for characterizing the influence of fines. This in return will ensure under top model the role of fines using initial stress state parameters.
  • Characterizing the cumulative effects of load repetitions framed in term of stress state parameters.