18
1735-0522
668
Soil Mechanics Classic
Effect of principal stress rotation in cement-treated sands using triaxial and simple shear tests
Eghbali
A. H.
^{
b
}
Fakharian
K.
^{
c
}
^{
b
}Amirkabir University of Technology
^{
c
}Amirkabir University of Technology
1
1
2014
12
1
1
14
29
01
2012
02
10
2013
Portland cement can be mixed with sand to improve its mechanical characteristics. Many studies are reported in literature on this topic, but the effect of principal stress rotation has not been investigated yet. Considering the inherent anisotropy of most sands, it is not clear whether the added cement shall contribute to equal increase in strength and stiffness at vertical and horizontal directions or not. Furthermore, it is not well understood how the cement as an additive in non-compacted (loose) sand compared to compacted (dense) sand without cement, contribute to improving the material behavior in undrained condition such as limiting the deformations and the liquefaction potential. In this research, undrained triaxial and simple shear tests under different stress paths are carried out on different mixtures of Portland cement (by adding 1.5, 3 and 5 percent) with clean sand to investigate the effect of principal stress rotations. The triaxial test results revealed that the cement mixture reduces the anisotropy, while it improves the mixture mechanical properties compared to compacted sand without cement. The results of the simple shear tests validated the triaxial test results and further clarified the effect of the parameter or rotation of principal stresses on the behavior of cemented sand mixtures.
672
Geotechnique
A simple analytical method for calculation of bearing capacity of stone-column
Nazari Afshar
J.
^{
d
}
Ghazavi
M.
^{
e
}
^{
d
}Shahr-e-Qods Branch. Islamic Azad University
^{
e
}Khajejh Nassir University of Technology
1
1
2014
12
1
15
25
06
02
2012
02
10
2013
The Stone-column is a useful method for increasing the bearing capacity and reducing settlement of foundation soil. The prediction of accurate ultimate bearing capacity of stone columns is very important in soil improvement techniques. Bulging failure mechanism usually controls the failure mechanism. In this paper, an imaginary retaining wall is used such that it stretches vertically from the stone column edge. A simple analytical method is introduced for estimation of the ultimate bearing capacity of the stone column using Coulomb lateral earth pressure theory. Presented method needs conventional Mohr-coloumb shear strength parameters of the stone column material and the native soil for estimation the ultimate bearing capacity of stone column. The validity of the developed method has been verified using finite element method and test data. Parametric studies have been carried out and effects of contributing parameters such as stone column diameter, column spacing, and the internal friction angle of the stone column material on the ultimate bearing capacity have been investigated.
669
Seismic Geotechnique
Seismic behavior of topographic features with material damping using BEM in time domain
Afzalirad
M.
^{
f
}
Kamalian
M.
^{
g
}
Jafari
M. K.
^{
h
}
Sohrabi-bidar
A.
^{
i
}
^{
f
}Science and Research Branch, Islamic Azad University
^{
g
}International Institute of Earthquake Engineering and Seismology (IIEES)
^{
h
}International Institute of Earthquake Engineering and Seismology (IIEES)
^{
i
}University of Tehran
1
1
2014
12
1
26
44
30
01
2012
02
10
2013
In this paper, an advanced formulation of time-domain, two-dimensional Boundary Element Method (BEM) with material damping is presented. Full space two-dimensional visco-elastodynamic time-convoluted kernels are proposed in order to incorporate proportional damping. This approach is applied to carry out site response analysis of viscoelastic topographic structures subjected to SV and P incident waves. Seismic responses of horizontally layered site, semi-circular canyons, slope topography and ridge sections subjected to these incident waves are analyzed in order to demonstrate the accuracy of the kernels and the applicability of the presented viscoelastic boundary element algorithm. The results show an excellent agreement with recent published results obtained in frequency domain. Also, the effects of different material damping ratios on site response are investigated.
744
Geotechnique
Efficiency of methods for determining pile axial capacity-applied to 70 cases histories in Persian Gulf northern shore
Eslami
A.
^{
j
}
Tajvidi
I.
^{
k
}
Karimpour-Fard
M.
^{
l
}
^{
j
}Amir Kabir University of Technology
^{
k
}Islamic Azad University, Central Tehran Branch
^{
l
}he university of Guilan
1
1
2014
12
1
45
54
13
07
2012
02
10
2013
Three common approaches to determine the axial pile capacity based on static analysis and in-situ tests are presented,
compared and evaluated. The Unified Pile Design (UPD), American Petroleum Institute (API) and a SPT based methods were
chosen to be validated. The API is a common method to estimate the axial bearing capacity of piles in marine environments,
where as the others are currently used by geotechnical engineers. Seventy pile load test records performed in the northern
bank of Persian Gulf with SPT profile have been compiled for methods evaluation. In all cases, pile capacities were measured
using full scale static compression and/or pull out loading tests. As the loading tests in some cases were in the format of proof
test without reaching the plunging or ultimate bearing capacity, for interpretation the results, offset limit load criteria was
employed. Three statistical and probability based approaches in the form of a systematic ranking, called Rank Index, RI, were
utilized to evaluate the performance of predictive methods. Wasted Capacity Index (WCI) concept was also applied to validate
the efficiency of current methods. The evaluations revealed that among these three predictive methods, the UPD is more
accurate and cost effective than the others.
931
Geotechnique
Evolutionary-based approaches for settlement prediction of shallow foundations on cohesionless soils
Shahnazari
H.
^{
m
}
Shahin
M. A.
^{
n
}
Tutunchian
M. A.
^{
o
}
^{
m
}Iran University of Science and Technology
^{
n
}Curtin University
^{
o
}Iran University of Science and Technology
1
1
2014
12
1
55
64
05
06
2013
02
10
2013
Due to the heterogeneous nature of granular soils and the involvement of many effective parameters in the geotechnical
behavior of soil-foundation systems, the accurate prediction of shallow foundation settlements on cohesionless soils is a
complex engineering problem. In this study, three new evolutionary-based techniques, including evolutionary polynomial
regression (EPR), classical genetic programming (GP), and gene expression programming (GEP), are utilized to obtain more
accurate predictive settlement models. The models are developed using a large databank of standard penetration test (SPT)-based case histories. The values obtained from the new models are compared with those of the most precise models that have
been previously proposed by researchers. The results show that the new EPR and GP-based models are able to predict the
foundation settlement on cohesionless soils under the described conditions with R2
values higher than 87%. The artificial
neural networks (ANNs) and genetic programming (GP)-based models obtained from the literature, have R2
values of about
85% and 83%, respectively which are higher than 80% for the GEP-based model. A subsequent comprehensive parametric
study is further carried out to evaluate the sensitivity of the foundation settlement to the effective input parameters. The
comparison results prove that the new EPR and GP-based models are the most accurate models. In this study, the feasibility of
the EPR, GP and GEP approaches in finding solutions for highly nonlinear problems such as settlement of shallow
foundations on granular soils is also clearly illustrated. The developed models are quite simple and straightforward and can
be used reliably for routine design practice.
748
Geotechnique
A simplified approach to estimate the resultant force for the equilibrium of unstable slopes
Vieira
C.
^{
p
}
^{
p
}University of Porto
1
1
2014
12
1
65
71
20
07
2012
02
10
2013
This paper presents a simplified approach to estimate the resultant force, which should be provided by a retention system,
for the equilibrium of unstable slopes. The results were obtained with a developed algorithm, based on limit equilibrium
analyses, that assumes a two-part wedge failure mechanism. Design charts to obtain equivalent earth pressure coefficients are
presented. Based on the results achieved with the developed computer code, an approximate equation to estimate the
equivalent earth pressure coefficients is proposed. Given the slope angle, the backslope, the design friction angle, the height of
the slope and the unit weight of the backfill, one can determine the resultant force for slope equilibrium. This simplified
approach intends to provide an extension of the Coulomb earth pressure theory to the stability analyses of steep slopes and to
broaden the available design charts for steep reinforced slopes with non-horizontal backslopes
714
Geotechnique
Investigation on the effect of carpet fiber inclusion on hydraulic conductivity of clean sand using laboratory and random finite element analyses
Esfandiari sowmehsaraei
M. B.
^{
}
Jamshidi Chenari
R.
^{
}
^{
}The university of Guilan
^{
}The university of Guilan
1
1
2014
12
1
72
79
20
05
2012
02
10
2013
Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.
717
Geotechnique
A numerical approach for one dimensional thermal consolidation of clays
Lotfi
E.
^{
}
Delfan
S.
^{
}
Hamidi
A.
^{
}
Shahir
H.
^{
}
Fardi
Gh.
^{
}
^{
}Kharazmi University
^{
}Kharazmi University
^{
}Kharazmi University
^{
}Kharazmi University
^{
}Kharazmi University
1
1
2014
12
1
80
87
26
05
2012
02
10
2013
In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion
coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent
volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with
time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature,
hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective
of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this
regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed
using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis.
Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of
other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements
compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one
indicated that preconsolidation pressure has an important effect on results of analysis.