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Geotechnical News June 2011
THESIS ABSTRACTS
The implications of using uniaxial test parameters in analytical and
numerical models where multi-axial stress is present is discussed.
Sponsor: Joseph Wartman, Ph.D., University of Washington
Deformational Behavior of Fouled Railway
Ballast
Ali Ebrahimi
Ali Ebrahimi, Research Associate, Civil and Environmental
Engineering, University of Wisconsin-Madison, Madison, WI
53706, email:
One of the major concerns facing the freight rail industry in the
United States (US) is increased substructure maintenance due to
heavier freight load and higher speed trains. The main objective of
this dissertation is to characterize deformational behavior of railway
ballast and predict the required maintenance of railway track due to
deformation of rail substructure. A testing protocol was developed
to quantify the deformation of ballast at a laboratory-scale which
closely simulates field conditions. Accumulation of plastic deforma-
tion of railway ballast under traffic loading was discussed. Effect of
type of fouling, fouling content, moisture, and state of stress on plas-
tic deformation of ballast was discussed. Mechanisms, such as con-
taminated contact points of ballast particles and change in strength
properties of fouling materials, that affect the plastic deformation
of ballast were described. A geophysical (i.e., an electromagnetic
surveying) technique to inspect the fouling content and moisture in
railway ballast was presented. A deformation model for railway bal-
last was developed to predict maintenance cycles for railway track
due to deformation of rail substructure.
Sponsors: Tuncer B. Edil, and James M. Tinjum, University of Wis-
consin- Madison
Compression Behavior of Solid Waste
Christopher A. Bareither
Christopher A. Bareither, Research Associate, Geological
Engineering, University of Wisconsin-Madison, 1217 Engi-
neering Hall, 1415 Engineering Drive, Madison, WI 53706,
Tel: 708-297-4844, email:
A field-scale experiment (Deer Track Bioreactor Experiment
- DTBE) and series of laboratory experiments were conducted to
evaluate the physical, chemical, and biological response of solid
waste with leachate addition. Laboratory experiments designed
to replicate field-scale conditions were conducted in 64, 100, and
305-mm diameter compression cells. Physical and biochemical
mechanisms contributing to waste compression were evaluated to
distinguish immediate compression, mechanical creep, and bio-
compression phases. Waste from the DTBE was used in all labora-
tory experiments; three fresh wastes and three decomposed wastes
were tested. The immediate compression ratio (Cc’) for the DTBE
was 0.23; and Cc’ ranged between 0.22 and 0.28 for all wastes in
305-mm cells. A waste compressibility index (WCI) is proposed for
estimating the Cc’, and is based on dry weight water content, dry
unit weight, and the percent contribution of organic waste. The rate
of mechanical creep (CaM’) was dependent on waste composition,
with larger CaM’ corresponding to higher WCI and higher ratios of
cellulose + hemicellulose to lignin ([C+H]/L). Leachate addition to
solid waste was shown to increase waste compression via moisture-
induced softening and enhancing anaerobic decomposition. During
leachate dosing in the DTBE, the rate of compression varied ranged
from a CaM’ of 0.048 to a biocompression ratio (CaB’) of 0.35. This
variation was due to waste temperature fluctuations that were be-
lieved to have suppressed (at temperatures < 42 °C) and stimulated
(at temperatures > 42 °C) biological activity. Laboratory-derived
settlement parameters were shown to be relevant to field-scale com-
pression behavior when contributions of physical and biochemical
compression were equivalent. Application of a first-order decay
rate settlement model revealed a scale effect on the elapsed time
for onset of biocompression and first-order decay rate. An increase
in experiment scale corresponded to an increase in time for onset of
biocompression and a decrease in decay-rate.
Advisers: Craig H. Benson, PhD, PE, DGE, and Tuncer Edil, PhD,
PE, DGE, University of Wisconsin-Madison
Application of Constriction Size Based
Filtration Criteria for Railway Subballast
Under Cyclic Conditions
Laricar Dominic O. Trani
Laricar Dominic O. Trani, BSc (Civil), MEng, PhD, MIEAust,
Geotechnical Engineer, Coffey Geotechnics, 8/12 Mars Road,
Lane Cove West, NSW 2066 Australia, Tel: (+61) (2) 9911 1000,
Fax: (+61) (2) 9911 1001, Mobile: (+61) 406 384 657,
email:
In rail track environments, the loading system is cyclic unlike the
steady seepage force that usually occurs in embankment dams. The
mechanisms of filtration, interface behavior, and time dependent
changes of the drainage and filtration properties occurring within
the filter medium require further research to improve the design
guidelines. A novel cyclic process simulation filtration apparatus
was designed and commissioned at the University of Wollongong,
and a standard test procedure was established. The test apparatus
was designed to simulate heavy haul train operations. The key pa-
rameters that influence the change in porosity and pore water pres-
sure within the subballast layer under cyclic conditions in rail track
environments were identified.
Laboratory results suggest that the present subballast selection
criteria adopted by the railway industry do not address the filtra-
tion mechanism of subballasts under cyclic conditions. Subballasts
containing approximately 20% fine sand and 30% fine gravel are
too porous to effectively capture the fines within its voids. Labora-
tory findings further show that uniformly graded subballasts with
particle range of 0.15 to 0.425 mm not more than 30% had an en-
hanced filtering capacity. Due to the lack of mechanical resistance
against axial deformation, the application of cyclic stress to uni-
formly graded subballasts reduces porosity and enables the filter to
trap migrating fines more effectively. Moreover, this intrusion of
fines changes the particle size distribution of the subballast which
reduces its porosity and further inhibits drainage.
A multi-layer mathematical approach was used to predict the
time dependent permeability of this filter, with (a) a reduction in po-
rosity as a function of compression under cyclic loading, and (b) the
amount of fines trapped within the filter voids, being the two main
aspects of this proposed model. Laboratory test results conducted
on a novel cyclic loading permeameter were used to validate the
proposed model. The set of equations that forms an integral part of
the proposed model is then presented as compact visual guidelines
anticipated to provide a more practical tool for railway practitioners.
Sponsor: Buddhima Indraratna, PhD, FIEAust, FASCE, FGS, FIES,
DIC, CEng, CPEng., Professor of Civil Engineering, Head, School
of Civil, Mining and Environmental Engineering; Director, Centre
for Geomechanics & Railway Engineering; Faculty of Engineering,
University of Wollongong
