Basic HTML Version
46
Geotechnical News • June 2013
www.geotechnicalnews.com
THESIS ABSTRACTS
Modelling MSW Leachate Characteristics
and Clogging
Yan Yu
Yan Yu, 1 Traymoor Ave., Kingston, ON K7L 4K9, Canada,
T: +1-613-583-3898, E:
A numerical model (BioClog) is developed to examine
changes in key municipal solid waste (MSW) leachate
characteristics and the porosity of porous media (clog-
ging) as the leachate passes through the drainage layer of
a leachate collection system (LCS). The model considers
multiple-species reactive leachate transport through porous
media. It simulates biofilm growth and loss, deposition of
suspended particles, and precipitation of minerals on the
surface of porous media. It is used to examine the long-
term performance of both the granular porous media and
nonwoven geotextiles in LCSs. Modelling of laboratory
mesocosm cells filled with gravel usually used in landfills
and permeated by landfill leachate shows encouraging
agreement between the observed and measured effluent
chemical oxygen demand (COD) and calcium concentra-
tions as well as the gravel porosity within the saturated
drainage layers. Studies of early generation LCSs involving
finger (French) drain systems show that the finger drains are
not effective at controlling leachate mounding within the
landfill and the calculated leachate mound thicknesses agree
well with observed field data. A numerical examination of
the recent generation of LCSs, comprised of the granular
drainage blanket and perforated drainage pipes, shows that
an increase in grain size increases the service life and that
increasing the spacing between collection pipes (i.e., the
drainage path) decreases the service life of LCSs. Filter-sep-
arator layers between the waste and granular drainage layers
are shown to increase the service life of LCSs. The model-
ling results indicate that the calculated clog mass within
the saturated drainage layer is dominated by the inorganic
material and the calculated service life of LCSs is dependent
on the leachate strength examined. Finally, a new practical
model for estimating the service life of LCSs is developed
and calibrated against the data from the BioClog model. The
simplified model could be used by the practicing engineers
for estimating the service life and optimizing the design of
LCSs in MSW landfills.
Advisor: Dr. R. Kerry Rowe, Professor and Canada Research
Chair in Geotechnical and Geoenvironmental Engineering,
GeoEngineering Centre at Queen’s-RMC, Department of Civil
Engineering, Queen’s University, Kingston, ON K7L 3N6, Canada,
F: +1-613-533-2128, E:
The Analysis of a Deep Excavation in a
Gassy Soil
Ahmed Badr Mabrouk
Ahmed Badr Mabrouk, 102, 2535 - 3rd Avenue S.E., Calgary,
Alberta, Canada T2A 7W5, C:+1 (403) 540 8944,
T: +1 (403) 299 5600, D: +1 (403) 387 8589,
F: +1 (403) 299 5606, E:
The study presents a numerical analysis of series of unan-
ticipated events that took place upon the excavation of a
landfill in a deep deposit of clayey soil (till) southwestern
Ontario, Canada. During the excavation of a landfill cell to
be used for waste disposal, unexpected lateral slope move-
ments were observed followed by gas and water venting in
several locations . The clayey till is known to be underlain
by permeable, natural gas bearing, rock and gas has been
diffusing through the clayey deposit over about the last
13,000-15,000 years.
Preliminary 2D and 3D elasto-plastic effective stress analy-
ses using conventional soil revealed the need for model
modification to account for other governing factors (gassy
soil and hydrofracturing) to be able to explain the mecha-
nism that might have lead to the evolution of gas vents and
upward water flow through the thick shale aquitard.
Clayey deposit encountered silty sand lenses at different
elevations. The thesis studies the potential of gas exsolution
(either prior or during the excavation) within the sand lenses
due to upward migration of methane and chloride from the
bedrock aquifer through the clay till.
FE model is modified to account for hydrofacturing and
gassy soil behavior (for sand lenses). 2D and 3D forensic
modeling studies are presented examining the potential
causes for the unanticipated movements and the gas and
water venting observed during the excavation. The model
studies the role of presence of gassy sand lenses and of
the presence of discontinuous weak sandy clayey silt layer
between the bedrock and the low permeability till on the
hydrofracturing path and gas venting.
Finally, a parametric study is conducted to examine the
effect of different parameters on the soil behavior when
excavated. Recommendations regarding further excavations
within the same soil deposit are presented.
Sponsor: R. Kerry Rowe, Department of Civil Engineering,
Queen’s University, Ellis Hall, 58 University Avenue, Kingston, ON
K7L 3N6 Canada, T: +1 (613) 533-3113, F: +1 (613) 533-2128,
E: kerry@civil.queensu.ca.