2493
Experimental investigation on bearing capacity of geosynthetic encapsulated stone
columns
Étude expérimentale sur la capacité portante des colonnes de pierre géosynthétiques encapsulées
Hataf N., Nabipour N.
Department of Civil and Environmental Engineering, Shiraz University, Shiraz, Iran
aBstract: civil engineers have developed different soil improvement techniques in recent decades to improve the bearing
capacity of soft soils loaded by foundations and reduce soil settlement. a method for increasing the bearing capacity of foundation
soil is the use of stone columns. however, one of the major weaknesses in use of stone columns in loose soils is lack of confinement.
Using geosynthetic reinforcement to compensate low confinement pressure in these soils, is a solution to this problem. this paper
presents the results of an experimental study on the improvement of the bearing capacity of stone columns reinforced by
geosynthetics. in this study the influences of three variables have been investigated, including: surrounding soil types (i.e. clay and
sand), stone column aggregate size and length of reinforcement. having mentioned these variables, the results showed that
encapsulating stone column with geosynthetic is more effective in cohesive soil compared to granular soil. the results of the
experiments revealed that the coarser the aggregate the better behavior is expected for the stone column. the results also showed that,
reinforcing half height of stone columns is the optimal encapsulating length.
rÉsUmÉ: ces dernières décennies, les ingénieurs civils ont développé différentes techniques pour l'amélioration de la capacité
portante du sol mou ainsi que celles des fondations. Une des techniques couramment utilisée permettant l'augmentation de la capacité
portante des sols et des fondations est l'utilisation des colonnes de pierre. cependant, l'une des grandes faiblesses de l'utilisation de
colonnes de pierre dans les sols mous est le manque de confinement. l'utilisation de renforts géosynthétiques permet de compenser
pour la faible pression de confinement. cet article présente les résultats d'une étude expérimentale sur l'amélioration de la capacité
portante des colonnes de pierre renforcées par des méthodes géosynthétiques. dans cette étude, l'influence de trois variables ont été
étudiées, notamment: le type de sol environnant (i.e. argile et sable) ainsi que la longueur de l'armature de renforcement. les résultats
démontrent que l'emploi de la colonne en pierre avec encapsulation géosynthétique est plus efficace dans un sol consistant comparé
aux sols granulaires. de plus, les résultats de ces expériences ont révélé que plus la rugosité de l'agrégat augmente, plus le
comportement des colonnes de pierres est amélioré. finalement, les résultats indiquent que la longueur d'encapsulation optimale est
atteinte en renforçant la hauteur médiane des colonnes de pierre.
KeYWords: stone column, bearing capacity, geosynthetic, reinforcement.
1 introdUction.
in recent years with increasing in population density in specific
locations,the value of land has increased signifacntly. this has
made the use of areas with soft soils inevitable.
due to the lack of bearing resistance in these soils, different
methods of soil improvement techniques, including stone
columns as a method of strengthening the loose soil are used.
stone columns behavior has been studied experimentally,
theoretically and numerically by many researchers (
Bergado and
teerawattanasuk2008, Guetif et al. 2007, castro and sagaseta2011)
however, one of the major weaknesses in use of
stonecolumns in loose soils is lack of confinement. this lead
researchers and practioners to use geosentitics to increase
confinement of column, compansating the scarcity of studding
around reinforced stone columns (
malarvizhi and ilamparuthi2007,
Gniel and Bouazza2009, Gniel and Bouazza2010
)
.
in this study the
parameters affecting the behavior of reinforced stone columns
have been investigated. these parameters are reinforced length,
column material and surrounding soil type.
2 laBoratorY settinGs
since the focus of this research was on the laboratory results,
the phyical model, is described, firstly.
2.1 Test apparatus
a cylindrical tank (height=1.0 m and dia.=1.0m) filled with soil
was used as the soilenvironment. stone column run in the
middle of the tank.the static loading system consists of a
loading arm and weights were used(razavi and hataf, 2003) to
determine the bearing capacity of a circular foundations resting
on stone column, figure 1.
2.2 Soil tested
to test and evaluate the behavior of reinforced stone columns in
loose soil, two soil types were used, a clay soil as cohesive soil
and a sandy soil as granular soil.
physical properties of the soils are listed in table 1.
2.3 Specimens preparation
to prepare the soil and column, first two 10 cm soil layers has
been poured in the tank and compacted using 20 strokes caused
by dropping a 50 n weight attached to a wooden handle from a
distance of 40 cm as the substrate layer.the next layerswere
compacted with 10 strokes from 10cm distance to provide loose
soil.
toprepare the stone column an open ended hollow
cylindrical pipe with a diameter of a little more than the
diameter of the stone column was used.after that the cylinder
was placed at its position and the surrounding was filled slowly
with soil.
