Cone Penetration Tests in Unsaturated Soils

Adrian Russel

This seminar will present results of UNSW’s ten year study on the cone penetration test in unsaturated soils.

Firstly, laboratory-controlled cone penetration test results in two unsaturated soils will be presented, obtained using a suction-controlled calibration chamber. For unsaturated Sydney sand, the cone penetration resistances are found to increase significantly due to the presence of suction when compared to those for saturated or dry states, for a given relative density and net confining stress. Increases as much as 50% for a relative density of 0.33 and net confining stress of 50 kPa are recorded. For an unsaturated clayey silty sand (a decomposed granite), suction also increases the cone penetration resistances significantly.

Secondly, a theoretical analysis of the penetration problem in unsaturated soils using cavity expansion theory will be presented. The results will show that the two drainage conditions of constant suction and constant moisture content produce very similar cavity expansion pressures, which are akin to cone penetration resistances. This discovery greatly simplifies the interpretation of cone penetration test data.

Finally, it will be shown that when suction is included in the effective stress, the same semi-empirical expressions used for saturated soils are found to link penetration resistance to the relative density and effective confining stress. The expressions may also be used to back-calculate the suction changes in a soil profile when cone penetration resistances for two unsaturated states are known. It will also be shown that failure to account for suction influences may lead to significant and non-conservative overestimations of relative density or peak friction angle.

Speaker biography

Dr Adrian Russell has 16 years experience in academia and industry, in Australia and the UK. His research discoveries have been presented in more than 50 refereed papers and received seven awards and honours. His research interests include: applied unsaturated soil mechanics, mechanics of fibre reinforced soils, fundamental modelling of soils, and fundamental rock mechanics.

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