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Volume 1, Number 1, March 2009
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Effects of fines content on void ratio, compressibility, and static liquefaction of silty sand
Poul V. Lade, Jerry A. Yamamuro and Carl D. Liggio, Jr.
Abstract;
Full Text (2184K)
Abstract
Many aspects of the behavior of sands are affected by the content of non-plastic fine
particles and these various aspects should be included in a constitutive model for the soil behavior. The
fines content affects maximum and minimum void ratios, compressibility, shear strength, and static
liquefaction under undrained conditions. Twenty-eight undrained triaxial compression tests were performed
on mixtures of sand and fine particles with fines contents of 0, 10, 20, 30, 50, 75, and 100% to study the
effects of fines on void ratio, compressibility, and the occurrence of static liquefaction. The experiments
were performed at low consolidation pressures at which liquefaction may occur in near-surface, natural
deposits. The presence of fines creates a particle structure in the soil that is highly compressible,
enhancing the potential for liquefaction, and the fines also alter the basic stress-strain and volume change
behavior, which should be modeled to predict the occurrence of static liquefaction in the field. The void
ratio at which liquefaction occurs for each sand/fines mixture was determined, and the variation of
compressibility with void ratio was determined for each mixture. This allowed a relation to be determined
between fines content, void ratio, compressibility, and the occurrence of static liquefaction. Such relations
may vary from sand to sand, but the present results are believed to indicate the trend in such relations.
Key Words
compressibility; fines; instability; silty sand; static liquefaction; triaxial tests.
Address
Poul V. Lade; Department of Civil Engineering, The Catholic University of America, Washington, D.C. 20064, U.S.A.
Jerry A. Yamamuro; School of Civil and Construction Engineering, Oregon State University, Corvallis, Oregon 97331, U.S.A.
Carl D. Liggio, Jr.; Pharos Enterprise Intelligence, LLC, 150 East 56th Street, Suite PHB, New York, NY 10022, U.S.A.
Abstract
There has been growing agreement that geotechnical reliability-based design (RBD) is
necessary for establishing more advanced and integrated design system. In this study, resistance factors for
LRFD pile design using CPT results were investigated for axially loaded driven piles. In order to address
variability in design methodology, different CPT-based methods and load-settlement criteria, popular in
practice, were selected and used for evaluation of resistance factors. A total of 32 data sets from 13 test
sites were collected from the literature. In order to maintain the statistical consistency of the data sets, the
characteristic pile load capacity was introduced in reliability analysis and evaluation of resistance factors.
It was found that values of resistance factors considerably differ for different design methods, loadsettlement
criteria, and load capacity components. For the total resistance, resistance factors for LCPC
method were higher than others, while those for Aoki-Velloso
Key Words
LRFD; resistance factor; reliability index; pile load capacity; driven pile; cone penetration
test.
Address
Junhwan Lee; School of Civil and Environmental Engineering, Yonsei University, 134 Shinchon-dong,
Seodaemun-gu, Seoul 120-749, Korea
Minki Kim; Project Engineer, Kumho Engineering and Construction, Sinmunno 1-ga, Jongno-gu, Seoul 100-061, Korea
Seung-Hwan Lee; Department of Mathematics, Illinois Wesleyan University, Bloomington, Il, USA
Abstract
A significantly thick zone of steep slopes is commonly encountered above groundwater table
and the soils within this zone are unsaturated with negative pore-water pressures (i.e., matric suction).
Matric suction contributes significantly to the shear strength of soil and to the factor of safety of
unsaturated slopes. However, infiltration during rainfall increases the pore-water pressure in soil resulting
in a decrease in the matric suction and the shear strength of the soil. As a result, rainfall infiltration may
eventually trigger a slope failure. Therefore, understanding of shear strength characteristics of saturated
and unsaturated soils under shearing-infiltration (SI) conditions have direct implications in assessment of
slope stability under rainfall conditions. This paper presents results from a series of consolidated drained
(CD) and shearing-infiltration (SI) tests. Results show that the failure envelope obtained from the
shearing-infiltration tests is independent of the infiltration rate. Failure envelopes obtained from CD and
SI tests appear to be similar. For practical purposes the shear strength parameters from the CD tests can
be used in stability analyses of slopes under rainfall conditions. The SI tests might be performed to obtain
more conservative shear strength parameters and to study the pore-water pressure changes during infiltration.
Key Words
shear strength; triaxial test; consolidated drained test; shearing-infiltration tests; pore-water
pressure.
Address
H. Rahardjo, I. Meilani and E. C. Leong; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore
R. B. Rezaur; Department of Civil Engineering, Universiti Teknologi Petronas, 31750 Tronoh, Perak, Malaysia
Abstract
In recent years, several computer-aided pattern recognition and data mining techniques have
been developed for modeling of soil behavior. The main idea behind a pattern recognition system is that it
learns adaptively from experience and is able to provide predictions for new cases. Artificial neural networks
are the most widely used pattern recognition methods that have been utilized to model soil behavior.
Recently, the authors have pioneered the application of genetic programming (GP) and evolutionary
polynomial regression (EPR) techniques for modeling of soils and a number of other geotechnical
applications. The paper reviews applications of pattern recognition and data mining systems in geotechnical
engineering with particular reference to constitutive modeling of soils. It covers applications of artificial
neural network, genetic programming and evolutionary programming approaches for soil modeling. It is
suggested that these systems could be developed as efficient tools for modeling of soils and analysis of
geotechnical engineering problems, especially for cases where the behavior is too complex and conventional
models are unable to effectively describe various aspects of the behavior. It is also recognized that these
techniques are complementary to conventional soil models rather than a substitute to them.
Key Words
artificial intelligence; data mining; neural network; genetic programming; evolutionary computation;
soil modeling; geotechnical engineering.
Address
A. A. Javadi
Abstract
Artificial neural networks (ANNs) are a new type of information processing system based on
modeling the neural system of human brain. The prediction of swell pressures from easily determined soil
properties, namely, initial dry density, initial water content, and plasticity index, have been investigated by
using artificial neural networks. The results of the constant volume swell tests in oedometers, performed
on statically compacted specimens of Bentonite-Kaolinite clay mixtures with varying soil properties, were
trained in an ANNs program and the results were compared with the experimental values. It is observed
that the experimental results coincided with ANNs results.
Key Words
Artificial neural networks; Bentonite; clays; Kaolinite; swell pressure
Address
Yusuf Erzin; Department of Civil Engineering, Celal Bayar University, 45140 Manisa, Turkey
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Searching for critical failure surface in slope stability
analysis by using hybrid genetic algorithm
Shouju Li, Zichang Shangguan, Hongxia Duan, Yingxi Liu and Maotian Luan
Abstract;
Full Text (1318K)
Abstract
The radius and coordinate of sliding circle are taken as searching variables in slope stability
analysis. Genetic algorithm is applied for searching for critical factor of safety. In order to search for critical
factor of safety in slope stability analysis efficiently and in a robust manner, some improvements for simple
genetic algorithm are proposed. Taking the advantages of efficiency of neighbor-search of the simulated
annealing and the robustness of genetic algorithm, a hybrid optimization method is presented. The numerical
computation shows that the procedure can determine the minimal factor of safety and be applied to slopes
with any geometry, layering, pore pressure and external load distribution. The comparisons demonstrate that
the genetic algorithm provides a same solution when compared with elasto-plastic finite element program.
Key Words
hybrid genetic algorithm; slope stability; critical factor of safety; hybrid optimization.
Address
Shouju Li; State Key Lab. of Struct. Anal. of Ind. Equip, Dalian University of Technology, Dalian 116023, P R China
Zichang Shangguan; School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian 116023, P R China
Institute of Civil Engineering, Dalian Fishery University, Dalian 116023, P R China
Hongxia Duan; State Key Lab. of Struct. Anal. of Ind. Equip, Dalian University of Technology, Dalian 116023, P R China
College of Architecture & Civil Engineering, Dalian Nationalities University, Dalian 116605, P R China
Yingxi Liu; State Key Lab. of Struct. Anal. of Ind. Equip, Dalian University of Technology, Dalian 116023, P R China
Maotian Luan; School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian 116023, P R China
Abstract
The interactions between a granular pile and raft placed on top are investigated using the
continuum approach. The compatibility of vertical and radial displacements along the pile - soil interface
and of the vertical displacements along the raft - top of ground interfaces are satisfied. Results show that
consideration of radial displacement compatibility does not influence the settlement response of or sharing
of the applied load between the granular pile and the raft. The percentage load carried by the granular
pile (GP) increases with the increase of its stiffness and decreases with the increase of the relative size of
raft. The normal stresses at the raft - soil interface decrease with the increase of stiffness of GP and/or
relative length of GP. The influences of GP stiffness and relative length of GP are found to be more for
relatively large size of raft. The percentage of load transferred to the base of GP increases with the
increase of relative size of raft.
Key Words
granular piles; stone columns; raft; continuum approach; settlement; contact pressures; load
sharing.
Address
Madhira R. Madhav; Geoenvironmental Engineering Centre, J.N. Technical University, Hyderabad 500072, India
J. K. Sharma; College of Engineering, Kota, India
V. Sivakumar; School of Civil Engineering, Queen
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Editors-in-Chief
Analytical, computational, and experimental multiscale and interaction mechanics
