Geotechnical News • June 2012
61
Geotechnical News • March
THESIS ABSTRACTS
oped and validated against extensive case histories as well
as experimental studies and numerical analyses performed
by others.
Sponsoring Professor: Prof. George M. Filz, Virginia Tech, Civil
and Environmental Engineering, 120-C Patton Hall, Blacksburg,
VA 24061, T: 540-231-7151, E:
Column-supported Embankments: Full-scale
Tests and Design Recommendations
Joel Sloan
Joel Sloan, 525 Windsor Drive, Christiansburg, VA 24073,
T: 540-267-5452, E:
When an embankment is to be constructed over ground
that is too soft or compressible to adequately support the
embankment, columns of strong material can be placed in
the soft ground to provide the necessary support by transfer-
ring the embankment load to a firm stratum. This technol-
ogy is known as column-supported embankments (CSEs).
There are two principal reasons to use CSEs: 1) accelerated
construction compared to more conventional construction
methods such as prefabricated vertical drains or staged
construction, and 2) protection of adjacent facilities from
distress, such as settlement of existing pavements when
a roadway is being widened. One of the most significant
obstacles limiting the use of CSEs is the lack of a standard
design procedure which has been properly validated. Twelve
design/analysis procedures are described in this dissertation,
and ratings are assigned based on information available in
the literature.
A test facility was constructed and the facility, instru-
mentation, materials, equipment, and test procedures are
described. A total of 5 CSE tests were conducted with 2
ft diameter columns in a square array. The first test had a
column center-to-center spacing of 10 ft and the remaining
four tests had center-to-center spacings of 6 ft. The Adapted
Terzaghi Method of determining the vertical stress on the
geosynthetic reinforcement and the Parabolic Method of
determining the tension in the geosynthetic reinforcement
provide the best agreement with the test results. The tests
also illustrate the importance of soft soil support in CSE
performance and behavior.
A generalized formulation of the Adapted Terzaghi Method
for any column/unit cell geometry and two layers of
embankment fill is presented, and two new formulations
of the Parabolic Method for triangular arrangements is
described. A recommended design procedure is presented
which includes use of the GeogridBridge Excel workbook
described by Filz and Smith (2006, 2007).
Sponsoring Professor: Prof. George M. Filz, Virginia Tech, Civil
and Environmental Engineering, 120-C Patton Hall, Blacksburg,
VA 24061, T: 540-231-7151, E:
Pipe-soil Interaction Aspects in Buried
Extensible Pipes
Lalinda Weerasekara
Lalinda Weerasekara, EBA Engineering, Oceanic Plaza, 9th. floor,
1066 West Hastings Street, Vancouver, BC V6E 3X2, T: (home)
604-771-8659, Office: 604-685-0017, E:
The performance of buried pipelines in areas subjected to
permanent ground displacements is an important engineer-
ing consideration in the gas distribution industry, since the
failure of such systems poses a risk to public and property
safety. Although, the ground movements and its variations
over time can be detected and mapped with reasonable
confidence, these data are of little use due to a lack of reli-
able models to correlate such displacements to the condition
of the buried pipe. The objective of this thesis is to develop
methods to estimate the pipe performance based on the
measured ground displacement.
An analytical method was developed to estimate the pipe
performance when the pipe is subjected to tensile load-
ing caused by the relative ground movements occurring
along the pipe axis. As a part of the derivation, a modified
interface friction model was developed considering the
increase in friction due to constrained dilation of the soil,
and the impact of mean effective stress on soil dilation. This
interface friction model was combined with a nonlinear pipe
stress–strain model to derive an analytical solution to repre-
sent the performance of the pipe. Using the proposed model,
axial force, strain, and mobilized frictional length along the
pipe can be obtained for a measured ground displacement
can be obtained. Large-scale field pipe pullout tests were
performed to verify the results of the proposed analytical
model, in which good agreements were observed for tests
conducted at different soil/burial conditions, displacement
rates and pipe properties. Considering the similarities in the
axial pullout mechanism, the analytical model was extended
to explain the pullout response of geotextiles buried in
reinforced soil structures. In this derivation, a new inter-
face friction model was developed for planar members by
considering the changes in normal stress due to constrained
soil dilation.
Another analytical model was derived for the case of a pipe
that is subjected to combined loading from axial tension and
bending when the initial soil loading is acting perpendicular
to the pipe axis. With the direct account of the axial tensile
force development, more realistic pipe performance behav-
iors were obtained as compared to the results obtained from
traditional numerical formulations.
Supervisor: Dr. Dharma Wijewickreme, Professor, Univer-
sity of British Columbia, 6250 Applied Science Lane, Van-
couver, B.C., Canada V6T 1Z4, T: (Office) 604-822-5112,
E:
