Geotechnical News June 2011
57
THESIS ABSTRACTS
The Small Strain Characterization of
Unbound Highway Base Course Materials
Torsten Mayrberger
Torsten Mayrberger, 8165 Kronos Dr., Anchorage, AK 99502,
email:
Tel: 907.887.9401
This dissertation, The Small Strain Characterization of Unbound
Highway Base Course Materials, investigated the influence of sev-
eral variables on the resilient modulus of unbound base course ag-
gregate materials. The following variables that affect the resilient
modulus were investigated: gradation, varying degrees of satura-
tion and undrained Conditions, parent material type, stress ratio and
stress history, resilient Poisson’s ratio and volume change, and the
effects of data acquisition methods on final results.
This research program utilized testing protocols AASHTO T 307
The Standard Method of Test for Resilient Modulus of Unbound
Granular Base/Sub-base Materials and Sub-grade Soils (AASHTO
2002) and NCHRP Project 1-28A Harmonized Test Methods for
Laboratory Determination of Resilient Modulus for Flexible Pave-
ment Design - Task II: Unbound Materials (NCHRP 2004). Unique
test protocols and methods were also developed for this disserta-
tion’s testing regimes. This includes large scale saturated – und-
rained cyclic triaxial tests. These types of tests are uncommon due
to their complexity. It is believed the undrained-saturated large scale
specimen test program at Michigan Tech was the most ambitious
test program to date.
While it is quite difficult to monitor the volumetric behavior of
soil specimens while they are being subjected to resilient modulus
determinations, it is essential to determine Poisson’s ratio for the
materials being tested in order to understand the effects of the test
variables used in the standard protocol. This required the develop-
ment and manufacture of unique instrumentation that would attach
to the compacted specimen while inside the triaxial chamber, and
measure both lateral and axial cyclic, small strain deformations dur-
ing testing.
This unique instrumentation allowed for original work regarding
the stress history, strain hardening, lateral and volumetric deforma-
tions, and Poisson’s ratio of engineered unbound aggregates. These
topics are discussed relative to gravel/base course performance and
traditional assumptions regarding small strain behavior of coarse
aggregate materials. Finally a qualitative model describing the small
strain behavior of unbound coarse aggregates is presented.
Sponsor: Ralph J. Hodek, Ph.D., P.E., Michigan Technological Uni-
versity
Postcyclic Behavior of Low-plasticity Silt
Shuying Wang
Shuying Wang, Dept. of Civil, Architectural, and Environmen-
tal Engineering, Missouri University of Science & Technology,
117 Butler Carlton Hall, 1401 N Pine Street, Rolla, MO 65401, Tel:
573-202-9945, email:
Liquefaction of low-plasticity silt has been reported during
earthquakes in the recent past. Excess pore pressure builds up due
to the dynamic loading and then dissipates. The postcyclic behavior
of low-plasticity silt was investigated in this research for materi-
als obtained from the Mississippi River Valley. The experimental
program involved specimen preparation using a slurry consolida-
tion approach. A special technique was developed for specimen
movement, which reduced the testing program time by half. Both
static and cyclic triaxial tests were conducted to confirm the ability
to prepare replica specimens. In order to characterize the monotonic
behavior, triaxial tests were conducted to determine the effective
friction angle, critical state line, and normalized behavior. Then
replica specimens were subjected to cyclic loading to develop the
liquefaction curve. After full liquefaction, excess pore pressure was
allowed to dissipate to achieve various reconsolidation levels. The
effect of full liquefaction on the permeability and compressibility
was studied. The variation in postcyclic shear strength and stiffness
with reconsolidation level and the effect of apparent consolidation
on shear behavior were also discussed. The critical state lines for
the pre- and postliquefaction conditions were compared and found
to be not parallel. After limited liquefaction, two unique conditions
were tested, at no reconsolidation and at full reconsolidation. The
shear strength and stiffness of the material changed significantly
when the limited liquefaction reached an excess pore pressure ratio
of about 0.70. The experimental program culminated with the study
of the effect of plasticity on the pre- and postcyclic shear behavior.
Silt-bentonite mixtures resulted in modified plasticity of the mate-
rial and the transformation from a dilative to a plastic behavior were
captured at relatively low plasticity (PI > 6).
Sponsor: Ronaldo Luna, PhD, PE, Dept. of Civil, Architectural,
and Environmental Engineering, Missouri University of Science &
Technology
Hydraulic Properties of Asphalt Concrete
Ronald Eric Pease
Ronald Eric Pease, 8229 Colfax Ave NE, Albuquerque, NM 87109,
Tel: 505 828-1734, cell: 505 850-9076,
email:
This research has applied standard unsaturated flow models and
laboratory methods common to soil analysis, to characterize the
hydraulic properties of asphalt concrete. Wetting and drying water
characteristic curves were measured for six asphalt concrete cores.
From the water characteristic curves, it is proposed that asphalt
concrete may require bi-modal sigmoid curves to represent drying.
It is also proposed that asphalt concrete is a hydrophobic material
during wetting and a hydrophilic material during drying. The wet-
ting curves developed for the asphalt concrete were fit with power
functions, while the drying curves follow a sigmoid curve as ex-
pected for a wettable material. Unsaturated hydraulic conductivity
for wetting and drying was predicted according to Mualem’s (1976)
solution. The unsaturated hydraulic conductivity of three asphalt
cores was measured using an original method in the laboratory. The
results of the measured unsaturated hydraulic conductivities were
used to support the predicted values.
The unsaturated hydraulic conductivity of the asphalt concrete
during wetting was described with simple power functions; very
similar to ones proposed for soils, but with a different range of ex-
ponents.
The predicted values of unsaturated hydraulic conductivity dur-
ing wetting, for some of the cores, fit very well with an equation
derived by Parker (1989) to describe the unsaturated hydraulic con-
ductivity of immiscible fluids. Nieber (2000) proposed that Park-
er’s equation could be used to describe the unsaturated hydraulic
conductivity of water on hydrophobic materials. This research has
shown that the asphalt concrete follows Parker’s equation during
wetting, which supports the predictions of unsaturated hydraulic
conductivity and that asphalt concrete behaves as a hydrophobic
material during wetting.
Sponsor:
Professor and Chair, Civil En-
gineering Department, University of New Mexico
