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Geotechnical News • June 2013
41
THESIS ABSTRACTS
was demonstrated to be a useful tool for the examination of
the porous architecture, and the performance of PRB reac-
tive materials in a novel yet quantifiable manner.
A comprehensive field study involved the monitoring
of groundwater via piezometers and observation wells,
installed up-gradient, within and down-gradient of the PRB,
to observe changes in the level of the phreatic surface along
with water quality parameters (e.g. pH, electrical conductiv-
ity (EC), oxidation reduction potential (ORP), temperature
and concentration of anion and cations). Groundwater pH
inside the PRB was maintained near neutral throughout the
monitoring period. The concentration of Al
3+
and total Fe
were maintained below the Australian and New Zealand
Environment and Conservation Council (ANZECC) (2000)
criteria, in a similar manner to what was observed in the
column experiments. Steady piezometric head observed
within the PRB throughout the monitoring period confirmed
that chemical and physical clogging did not occur within the
PRB to an extent that would affect the permeability of the
reactive material.
One-dimensional, simple reactive transport modelling was
carried out based on data from a laboratory column experi-
ment, mineralogical analysis of the recycled concrete and
the PRB. Numerical modelling using MIN3P provides
insights into the neutralisation mechanisms and geochemical
evolution of groundwater along a flow path inside the PRB.
The ability to make comparisons between the geochemically
complex transport scenarios within the column experi-
ments and pilot-scale PRB confirm that it can be used as an
analysis tool for investigating the performance of PRBs in
ASS terrain.
Overall, this study contributes a better understanding of
the acid neutralisation processes occurring inside the PRB
for the remediation of contaminated groundwater from
ASS terrain and offers novel field, laboratory and model-
ling techniques to investigate and quantify these processes.
The findings from the first pilot-scale PRB using recycled
concrete as the reactive material confirms that it is a suitable
environmentally friendly and cost-effective alternative to
other conventionally utilised techniques (e.g. watertable
manipulation, lime neutralisation) for the spot treatment of
acidic groundwater in ASS terrain.
Sponsoring Professor and University: Prof. Buddhima
Indraratna, Professor of Civil Engineering, Faculty of Engineer-
ing, University of Wollongong, Wollongong, NSW 2522, Australia.
T: +61 2 4221 3046; F: +61 2 4221 3238, E:
Geotechnical Study of Engineering
Behaviour of Fouled Ballast
Nayoma Chulani Tennakoon
Nayoma Chulani Tennakoon, Email:
,
Mobile: +61430900406
When the ballast voids are wholly or partially filled with the
intrusion of fine materials, particle breakage and pumping
of soft subgrade soil, the track can be considered as being
“fouled”. In order to ensure acceptable track performance
and longevity, it is pertinent to maintain rapid drainage
conditions within the ballasted bed. However, fouling
reduces the drainage capacity of the ballast, excess pore
water pressure can be generated under the passage of fast
moving trains (cyclic load), which further compromises
track resiliency while contributing to increased maintenance
costs. In addition, fouling causes differential settlement of
the track and also decreases its load bearing capacity due to
the reduction in internal friction of the granular assembly.
A series of large scale hydraulic conductivity tests with
specimen size of 500 mm x 500 mm high, were conducted
with different proportions of fouling to study the relation-
ship between the extent of fouling and hydraulic conduc-
tivity. Since the hydraulic conductivity obtained from
laboratory experiments were one-dimensional given that
two-dimensional flow conditions may prevail in reality, a
numerical analysis was conducted using SeepW (2007a)
to quantify the drainage capacity of ballast under different
degrees of fouling. Subsequently, a quantitative classifica-
tion for drainage in relation to the degree of fouling, which
is very useful tool for practical engineers, is presented in
this thesis.
In order to establish the relationship between the extent of
fouling and the associated strength-deformation properties,
a series of large scale (300 mm diameter by 600 mm height)
monotonic and cyclic triaxial tests were carried out for dif-
ferent levels of fouling for confining pressures in the range
of 10-60 kPa. Based on the laboratory findings, a novel
empirical relationship between the peak deviator stress and
VCI
has been proposed to assist the practitioner in their
preliminary track condition assessment.
A constitutive model for clay fouled ballast is formulated
using bounding surface framework under monotonic loading
and drained condition. The model is validated with the large
scale triaxial experiments carried out in this research.
Sponsoring Professor and University: Prof. Buddhima
Indraratna, Professor of Civil Engineering, Faculty of Engineer-
ing, University of Wollongong, Wollongong, NSW 2522, Australia.
T: +61 2 4221 3046; F: +61 2 4221 3238, E: