2011 NSW Research Awards

Mohammad Pournaghiazar & Nayoma Tennakoon

Cone Penetration Tests in Unsaturated Soils

Mohammad Pournaghiazar, University of New South Wales

The Cone Penetration Test (CPT) is a widely used in situ test. CPT data are used to evaluate the engineering properties of soils based on a number of correlations proposed for saturated or dry soils. However, no such correlations currently exist for interpretation of CPT data in unsaturated soils. The objective of this research is to advance experimental and theoretical bases for interpretation of CPT data in unsaturated soils.

A calibration chamber has been developed to perform laboratory controlled cone penetration tests in unsaturated soils. The chamber allows the independent application of lateral and vertical pressures to an unsaturated soil specimen. Suction is controlled using the axis translation technique within the unsaturated specimen. The results of cone penetration tests conducted on saturated and unsaturated sand specimens are presented and significant contribution of suction to cone penetration resistance is highlighted. Also the problem of cavity expansion in soils of finite radial extent is investigated to evaluate the boundary effects and extend the results to field condition.

Geotechnical Study of Engineering Behaviour of Clay Fouled Ballast

Nayoma Tennakoon, University of Wollongong

Ballast is a uniformly graded assembly of coarse-aggregates placed underneath railway sleepers. The main purpose of ballast is to facilitate rapid drainage and excellent structural support for heavy loading applied by trains. During track operation, fine particles can migrate into the ballast voids (ballast fouling) causing significant decrease in bearing capacity that compromises the stability of track and the safe operation of trains. Currently there are no proper guidelines to schedule ballast maintenance due to the lack of knowledge of the impact ballast fouling on track behaviour.

In this study, a new fouling index has been introduced to capture the effect of different specific gravities of the fouling material. Comprehensive laboratory experiments have been carried out to assess the mechanical and hydro-mechanical properties of clay fouled ballast using large scale permeability apparatus and large scale tri-axial test apparatus. Both experimental results show that, decreasing trends with increasing the degree of fouling. Numerical analysis using finite element programme has been conducted to simulate a more realistic two-dimensional flow to quantify the drainage capacity of ballast with different degree of fouling incorporating the actual track dimensions. Also this study presents a quantitative classification chart for drainage capacity in relation to the degree of fouling and track geometry as a preliminary design tool for the practicing engineers.

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