Geotechnical News • June 2012
59
Geotechnical News • March
THESIS ABSTRACTS
2350 Hayward Street, Ann Arbor, MI 48109-2125, T: 734 764-0057,
E:
A Laboratory Investigation and Modeling of
Dynamic Modulus of Asphalt Mixes for
Pavement Applications
Dharamveer Singh
Dharamveer Singh, School of Civil Engineering and Environmen-
tal Science, The University of Oklahoma, 202 West Boyd Street,
Room 210, Norman, OK, 73019, T: 405-325-2626,
E:
Traditionally, stiffness of hot mix asphalt (HMA) has been
used as a measure of the pavement’s ability to carry vehicu-
lar traffic loads without undergoing excessive deformation.
Early deterioration of pavements due to rutting, fatigue
cracking, and other type of distresses may be attributed to
inadequate stiffness. The mechanistic empirical pavement
design guide (MEPDG) emphasizes the use of dynamic
modulus of asphalt mixes at all three levels of flexible pave-
ment design. HMA mixes and aggregates that are commonly
used in Oklahoma for the construction of flexible pavements
were characterized in this study.
A database of dynamic modulus and master curves was
developed for the mixes used in this study, which is
expected to be useful in the implementation of the MEPDG
for the design and analysis of flexible pavements. In addi-
tion, the effect of plant production and sample preparation
methods on different aggregate shape parameters was evalu-
ated. The results indicate that texture and form of coarse
aggregates can change significantly during plant production
and compaction in a gyratory compactor. No significant
differences were observed for fine aggregates. The present
study also compared the shape properties of three different
types and sizes of coarse aggregates. The larger size aggre-
gates were found to be rougher and more cubical compared
to the smaller size aggregates, indicating that aggregate
particles become smoother and elongated with a reduction
in size.
Three different input levels of the MEPDG for modified
and unmodified mixes were compared in this study. It was
found that the accuracy of Level 2 and Level 3 depend on
the mix type. The current study also evaluated the strengths
and weaknesses of four empirical models (i.e., Witczak
1999, Witczak 2006, Hirsch, and Al-Khateeb) that are com-
monly used in estimating dynamic modulus. Analyses of the
results show that the performance of a model varies with
air voids and temperature. Statistical and neural network
(NN) models were developed to estimate dynamic modulus
including angularity, texture, form, and sphericity of aggre-
gates as variables. Inclusion of shape parameters is found to
enhance the predictive capability of a model significantly. It
was found that the long-term oven (LTO) aging resulted in
approximately a 42% to 60% increase in dynamic modulus,
depending upon the amount of reclaimed asphalt pavement
(RAP) in the mix and air voids. Overall, enhanced charac-
terization of aggregates and asphalt mixes is found to be
extremely important for pavement design applications.
Sponsoring Professor and University: Professor Musharraf Za-
man, David Ross Boyd Professor and Aaron Alexander Professor
of Civil Engineering, Professor of Petroleum and Geological En-
gineering, Associate Dean for Research and Graduate Program,
College of Engineering, The University of Oklahoma, 202 West
Boyd Street, Room 107, Norman, OK, 73019, T: 405-325-2626,
E:
Stability of Levees and Floodwalls
Supported by Deep-Mixed Shear Walls: Five
Case Studies in the New Orleans Area
Tiffany E. Adams
Tiffany E. Adams, URS Corporation, 8181 E Tufts Ave, Denver, CO
80237, T: 303-740-3947. E:
Increasing interest, from the U.S. Army Corps of Engineers
(USACE) and other agencies, in using deep-mixing methods
(DMM) to improve the stability of levees constructed on
soft ground is driven by the need to reduce levee footprints
and environmental impacts and to allow for more rapid con-
struction. Suitable methods for analysis and design of levees
supported on deep-mixing methods (DMM) shear walls
are needed to ensure that the DMM technology is properly
applied.
DMM shear walls oriented perpendicular to the levee align-
ment are an effective arrangement for supporting unbal-
anced lateral loads. Shear walls constructed by overlapping
individual DMM columns installed with single-axis or
multiple axis equipment include vertical joints caused by the
reduced width of the wall at the overlap between adjacent
columns. These joints can be made weaker by misalignment
during construction, which reduces the efficiency of the
overlap. Depending on the prevalence and strength of these
joints, complex failure mechanisms, such as racking due to
slipping along vertical joints between adjacent installations
in the shear walls, can occur. Ordinary limit equilibrium
analyses only account for a composite shearing failure
mode; whereas, numerical stress-strain analyses can account
for other failure modes.
Five case studies provided by the USACE were analyzed
to evaluate the behavior of levee and floodwall systems
founded on soft ground stabilized with DMM shear walls.
These projects identified and illustrated potential failure
mechanisms of these types of systems. Two-dimensional
numerical stability and settlement analyses were performed
for the case studies using the FLAC computer program.
Key findings and conclusions for the individual case studies
were assessed and integrated into general conclusions about
design of deep-mixing support for levees and floodwalls.
Sponsoring Professor: Prof. George M. Filz, Virginia Tech, Civil
and Environmental Engineering, 120-C Patton Hall, Blacksburg,
VA 24061, T: 540-231-7151, E:
