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Geotechnical News • June 2014
41
THESIS ABSTRACTS
and RAS on the performance of asphalt mixes, and the mois-
ture-induced damage mechanism. Important design input
parameters, developed in this study, may be used for the local
calibration of M-EPDG for new asphalt mixes.
Academic Advisor and Chair of the Ph.D. Committee:
Dr. Mush-
arraf Zaman, David Ross Boyd Professor and Aaron Alexander
Professor of Civil Engineering, Alumni Chair Professor of
Petroleum and Geological Engineering, College of Engineering,
The University of Oklahoma, 202 W. Boyd St., Room: CEC 450C,
Norman, OK 73019, Phone: (405) 325-2626, email: zaman@ou.edu.
Simulation of Failure Mechanisms Around
Underground Coal Mine Openings Using
Discrete Element Modelling
Fuqiang Gao
Fuqiang Gao, 500 - 4260 Still Creek Drive, Burnaby, BC Canada
V5C 6C6, Tel: +1 (604) 296 7228, email: gaofq0215@gmail.com
Roof failure has always been a major concern in under-
ground coal mine roadways. Understanding the failure
mechanism of roadway roofs is important for improving the
safety of underground coal mines and reducing economic
loss. In this research, a numerical modelling methodology
named UDEC Trigon in 2D and 3DEC Trigon in 3D and
based on a discrete element framework is developed to
model rock mass behaviour, with a particular focus on the
damage process including generation and propagation of
fractures, and heavy dilation in the post-peak failure stage.
Simulation of compression and Brazilian tests indicates that
the methodology can capture different failure mechanisms
under varying loading conditions. The UDEC Trigon is
then used to investigate shear failure mechanism in road-
way roofs. The results suggest that shear cracking plays a
dominant role in the roof shear failure. Rock bolts can aid in
ensuring the retention of more rock bridges which is critical
to the roof stability. Cutter roof failure, which is a three-
dimensional roadway rock failure mechanism, is studied
using both PFC3D and 3DEC Trigon. The 3D models
explicitly capture the cutter roof failure process and found
that incorporating bedding planes and cross joints results
in a more distinct cutter failure. Roadway squeezing failure
mechanism is studied using the UDEC Trigon approach.
The results show that the UDEC Trigon approach is able to
reproduce the large dilation due to fracturing of rock mass
surrounding a roadway under two distinct situations: high
mining-induced stress and strength degradation of moisture
sensitive rocks. In addition, the UDEC Trigon approach is
used to simulate the progressive caving process of a long-
wall panel of coal. It is found that compressive shear failure,
rather than tensile failure, is the dominant failure mecha-
nism in the strata above the goaf. A further demonstration of
the potential of UDEC Trigon in capturing roadway failure
is presented as a case study of a roadway driven adjacent
to unstable goaf in the Wuyang Coal Mine. The case study
reveals that the combination of Synthetic Rock Mass (SRM)
and UDEC Trigon is able to evaluate failure mechanisms in
underground coal mines.
The insights gained from this research provide an improved
understanding of typical failure mechanisms in underground
coal mine roadways, guiding the design of panel layout and
roadway support. The 3DEC Trigon method provides an
alternative for simulating rock damage under real 3D condi-
tions.
Sponsoring Professor: Prof. Douglas Stead, Department of
Earth Sciences, Simon Fraser University, 8888 University Drive,
Burnaby, BC, Canada V5A 1S6, Tel: (778)-782-6670
fax: (778)-782-4198 email: dstead@sfu.ca
Soil Restraints on Steel Buried Pipelines
Crossing Active Seismic Faults
O. Manuel Monroy-Concha
O. Manuel Monroy-Concha -, 500-4260 Still Creek Drive, Burnaby
B.C., Canada V5C 6C6 / Office: (604)-296-7231,
Fax: (604)-298-5253, email: mmonroy@golder.com
The quantification and prediction of soil restraint on buried
pipelines are essential for the design of pipeline systems
crossing seismic faults, and in turn to reduce the risk of
pipeline damage due to geotechnical earthquake hazards.
Full-scale soil-pipe interaction tests were undertaken to
better simulate the mobilization of soil restraints under
controlled conditions and to provide insight on a number of
currently unresolved technical issues that so far have been
investigated only based on small-scale tests. In particular, an
existing full-scale testing chamber was significantly modi-
fied to simulate pipeline breakout from its soil embedment
on one side of a strike-slip fault and on the footwall side of
a reverse fault in an effort to characterize lateral, combined
axial and lateral, and vertical oblique soil restraints. The
experimental system was also used to assess the effective-
ness of reducing soil loads on pipelines using geotextiles.
The following was noted: (1) approaches based on limit
equilibrium reasonably well predict maximum values of lat-
eral soil restraint for shallow pipelines backfilled with sand,
with mixture of crushed gravel and sand, and with crushed
limestone; (2) the lateral soil restraint on pipes in geotex-
tile-lined trenches increased with increasing relative pipe
displacement and could even be higher than the restraint
without the geotextile lining. A procedure was developed
to capture this behaviour; (3) experimental and numerical
results for geotextile-lined trenches suggest that the shear
resistance is not controlled solely by the geotextile interface;
as such, there is no clear benefit in using geotextile-based
mitigation measures for reducing soil loads; (4) the results
from tests on combined axial and lateral soil restraints
provided limited clarification on whether or not these soil
restraints should be considered independent for fault cross-
ing designs. This was due to the difficulty in selecting an
axial soil restraint value to anchor existing soil restraint
interaction relationships. No axial soil restraint tests were