Deformation behaviour of granular column reinforced by geosynthetic encasement

Science & Technology Development Journal – Engineering and Technology, 4(2):948-954
Open Access Full Text Article Research article
Faculty of Geology and Petroleum
Engineering, Ho Chi Minh City
University of Technology, Vietnam
Correspondence
Le Quan, Faculty of Geology and
Petroleum Engineering, Ho Chi Minh
City University of Technology, Vietnam
Email: quanlepvep@gmail.com
History
 Received: 8-10-2020
 Accepted: 19-5-2021
 Published: 25-5-2021
DOI : 10.32508/stdjet.v4i2.777
Copyright
© VNU-HCM Press. This is an open-
access article distributed under the
terms of the Creative Commons
Attribution 4.0 International license.
Deformation behaviour of granular column reinforced by
geosynthetic encasement
Le Quan*, Vo Dai Nhat, Pham Tien Bach, Nguyen Viet Ky
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QR code and download this article
ABSTRACT
In Vietnam, the overpopulation and strong economic development require the synchronous de-
velopment of infrastructure such as roads, urban areas, industrial parks, export processing zones,
etc. With such requirements, the development of land fund for infrastructure construction is an
indispensable need. Meanwhile, the appropriate land fund is very limited. Therefore, the land fund
must be developed for areas with little value for agriculture, such as swamps, estuaries, and coastal
areas, etc. These areas often have weak geological conditions; hence, to meet the requirements
of infrastructure construction on the soft ground, it is necessary to carry out soil improvement to
ensure load bearing capacity, total settlement, and consolidation settlement but still ensuring eco-
nomic effectiveness. Beside several conventionalmethodswidely used for soft soil improvement in
order to increase bearing capacity and accelerate consolidation settlement of the ground, geosyn-
thetic reinforced granular column is one of the new methods that has been applied to improving
soft ground in designing practice in the recent years due to the many advantages of this method
compared with other methods. In this paper, based on the unit cell model, the authors research on
deformationbehavior of granular column reinforcedbygeosynthetic encasement through the ana-
lytical analysis by varying external loadings corresponding to column diameter, stiffness of geosyn-
thetic encasement. The settlements of a single geosynthetic encased granular column and load
bearing capacity of the composite foundation are calculated on geological conditions of Ash Pond
Area of Song Hau 1 Thermal Power Plant located in Hau Giang Province. The relationship between
settlement and load bearing capacity with external loadings for different column diameters and
geosynthetic stiffnesses are shown schematically. Other considerations related to factor of safety
are also presented. The future researches are also proposed.
Key words: Geosynthetic encased granular column, soft soil, settlement, vertical stress
INTRODUCTION
There are many methods that have being used to im-
prove soft soil such as granular column, vertical drain,
vacuum preloading, limestone column, soil cement
column, concrete column, etc. Recently, scientists
have proposed a method for soft soil improvement by
geosynthetic encased granular column. This is an ex-
tension of the stone columnmethod. Thismethod has
advantages over granular column due to geosynthetic
granular column derives its loading capacity through
two factors including i) passive pressure from the sur-
rounding soft soil owing to bulging of granular col-
umn ii) additional lateral confinement by considering
the hoop tensile force in the geosynthetic encasement.
Furthermore, geosynthetic prevents clogging of the
granular aggregate by surrounding soft soil, preserves
the drainage and frictional properties of the granular
soils as described by Raithel et al. 20021, Alexiew et
al. 2005 2, Brokemper et al. 2006 3, Kempfert and Ge-
breselassie 20064, Tandel Y.K et al. 2014 5, Domenico
Gioffrè et al. 2016 6.
In this study, the authors use a simple analytical
method developed to estimate the settlement and
bearing capacity of an individual geosynthetic en-
cased granular column and its composite foundation
due to the possible bulging failure mechanism pro-
posed by Murugesan and Rajagopal 20107. The au-
thors investigated the importance of column diame-
ter, tensile stiffness of geosynthetic to the settlement
and bearing capacity. The settlement and bearing ca-
pacity are calculated based on geological conditions
of Ash Pond Area of SongHau 1Thermal Power Plant
located in Hau Giang province.
METHODOLOGY
In this paper, the authors apply the unit cell model in-
troduced by Raithel and Kempfert 2000 8. The model
is used to calculate settlement and bearing capacity of
geosynthetic encased granular column by using ana-
lytical solution. The problem is tested in a real project
in Viet Nam. The results then are shown and dis-
cussed.
Cite this article : Quan L, Nhat V D, Bach P T, Ky N V. Deformation behaviour of granular column rein-
forced by geosynthetic encasement. Sci. Tech. Dev. J. – Engineering and Technology; 4(2):948-954.
948
Science & Technology Development Journal – Engineering and Technology, 4(2):948-954
ANALYTICAL SOLUTION
Settlement
The proposed analytical method by Raithel and
Kempfert 20008, for the settlement of a geosynthetic
encased granular column reinforced foundation is
based on a unit cell model as present in Figure 1. This
model considers the contribution of geosynthetic en-
casement by providing additional confinement to the
column9.
Figure1: Unit cellmodel for a geosynthetic encased
column 9
The radial stresses in soil and column are given by:
4sr;c =4scKa;c+sz0;cKa;c (1)
4sr;s =4ssKa;s+sz0;sKa;s (2)
The radial stress on the geosynthetic encasement is
given by:
4sr;g = J4rcr2g (3)
The radial stress difference between the column and
the soil which represents the parti ... Song Hau 1 Thermal Power Plant is located in
the Song Hau Power Complex situated in Hau Giang
Province. The layout plan of the complex is an approx-
imately occupied area of the total 115.2 hectares. The
facilities can be divided into several blocks in accor-
dance with the location of the plant facilities, includ-
ing the main power plant island, Coal storage yard
and balance of Plant, switchyard area, and ash pond
area and various buildings, etc. This study presents
the ground improvement analysis of soft soil ground
under the dyke of the ash pond. The required ser-
vice loading is 20 kN/m2 and 5 m height for Dyke
after completion of soft soil improvement. The max-
imum allowable total settlement is 2.3 m. The allow-
able factor of safety for bearing capacity of the com-
posite foundation is greater than 2 10,11.
Geological Conditions
A series of calculation was carried out based on ma-
terial parameters of column presented in Table 1 and
soil parameters presented in Table 210,11 for Ash Pond
Area.
Results and discussion
Effect of diameter of column
It can be seen in Figure 2 the stress – settlement re-
sponse of 0.6 m diameter. The settlement is found to
be increasing corresponding to an increase of verti-
cal stress. The settlement at stress of 100 kN/m2 is
found lower than 2 to 5 times correspondingly to ver-
tical stress at 200, 300, 400 kN/m2.
Figure 2: Stress – Settlement response of 0.6 m di-
ameter
Figure 3 shows the relationship between the verti-
cal stresses - factor of safety against bearing failure
of the composite foundation of 0.6 m diameter. The
factor of safety decreases with increasing the vertical
stress, respectively. The factor of safety reduces cor-
respondingly to an increase of the settlement of the
column and vice versa. It is found that the factor of
safety at 100 kN/m2 higher than 2, 3, 4 times of fac-
tor of safety corresponding to stresses at 200, 300, 400
kN/m2. It can be seen in Figure 3 that vertical stress
is found lower than 230 kN/m2 leading to factor of
safety higher than 2 times and meeting requirements
of the project.
Figure 3: Stress – Safety factor response
Figure 4 shows the settlement - stress responses of 0.6
m, 0.8m, 1.0m diameter columns and tensile stiffness
of J = 500 kN/m. The settlements have also shown
similar trends of increasing with an increase of ver-
tical stress. The settlement of column reduces with
an increase of the diameters at the same vertical stress
and tensile stiffness of geosynthetic.
As indicated in Figure 4, the settlement of 0.6mdiam-
eter column is found higher than settlement of 0.8 m
diameter column from 2 down to 1.6 times and higher
than settlement of 1.0 m diameter column from 6.6
down to 3 times. The settlement of 0.8 m diameter
column is higher than settlement of 1.0 m diameter
column from 3.2 down to 1.9 times.
Figure 5 shows the comparative relationship between
the vertical stress – factor of safety against bearing fail-
ure of the composite foundation with 0.6m, 0.8m, 1.0
m of diameter column. The curves also show similar
trends of decreasing with an increase of vertical stress.
The factor of safety increaseswith an increase of diam-
eter at the same vertical stress and tensile stiffness of
geosynthetic. The factor of safety in case of 0.8 m di-
ameter is found higher than factor of safety in case of
0.6 m diameter about 1.3 times. The factor of safety in
case of 1.0 m diameter is found higher than factor of
safety of 0.6 m about 1.7 times. The factor of safety in
case of 1.0 m diameter is found higher than it of 0.8 m
diameter about 1.2 times. It is shown that the column
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Science & Technology Development Journal – Engineering and Technology, 4(2):948-954
Table 1: Material of column and its parameters
Material Type gsat (kN/m3) E (kN/m2) j (o) v
Coarse sand 19.1 40,000 400 0.3
Table 2: Soil layers and its parameters of the ground site
Soil Type Filling Soil Very soft Clay Stiff Clay Very stiff Clay
Depth (m) 1.5 14.5 17.0 42.0
g (kN/m3) 15.1 15.2 17.4 19
E (kN/m2) - 420 - -
c (kN/m2) - 9.7 18.4 20.1
j (0) - 30 59’ 100 25’ 170 40’
v 0.35 0.35 0.35 0.35
Figure 4: Settlement – Stress response for different
diameters
with higher diameter will increase the bearing capac-
ity of composite foundation. As can be seen in Fig-
ure 5, vertical stress is found lower than 200 kN/m2
leading to factor of safety higher than 2 times for all
curves and meeting requirements of the project.
Figure5: Stress – Safety factor response fordifferent
diameters
Effect of tensile stiffness of geosynthetic
Figure 6 shows vertical stress – settlement responses
of the column for different values of tensile stiffness
of 1 m column diameter. As can be seen, stress on
column increases with an increase of tensile stiffness
of geosynthetic. The hoop stress in geosynthetic in-
creases, it leads to increasing in confining pressures in
the column as described byMurugesan and Rajagopal
200612. Hence, the column with higher tensile stiff-
ness will induce larger confining pressures, leading to
a stiffer and stronger response of the column5.
As indicated in Figure 6, the settlement of column
at 500 kN/m tensile stiffness is higher than that at
1000 kN/m tensile stiffness from 1.16 to 1.2 times and
higher at 1500 kN/m tensile stiffness from 1.35 to 1.4
times. The settlement of column at 1000 kN/m ten-
sile stiffness is higher than that at 1500 kN/m tensile
stiffness from 1.16 to 1.4 times. The variation of set-
tlement slightly increases with an increase of vertical
tress.
Figure 6: Settlement – Stress response for different
tensile stiffness
951
Science & Technology Development Journal – Engineering and Technology, 4(2):948-954
Figure 7 shows the relationship between the vertical
stresses - factor of safety against bearing failure of the
composite foundation for different tensile stiffness.
The factor of safety also shows the similar trend with
an increase of tensile stiffness of the column and vice
versa. It is shown that the geosynthetic with higher
stiffness has a higher bearing capacity of composite
foundation. The factor of safety in case of 500 kN/m
tensile stiffness is found lower than that of 1000 kN/m
and 1500 kN/m tensile stiffness about 1.8 times and
2.6 times, respectively, corresponding to stresses at
100, 200, 300, 400 kN/m2. The factor of safety of
1000 kN/m tensile stiffness is found lower than that
of 1500 kN/m tensile stiffness about 1.45 times corre-
sponding to stresses of 100, 200, 300, 400 kN/m2. It
is shown that the column with higher tensile stiffness
of geosynthetic will increase the bearing capacity of
composite foundation.
Figure7: Stress – Safety factor response fordifferent
tensile stiffness
CONCLUSIONS
From the analytical results, some main conclusions
can be taken:
• The settlement increases from 2 to 5 times while
factor of safety decreases from 2 to 4 times cor-
respondingly with an increase of vertical stress
varying from 200 to 400 kN/m2 in case of 0.6 m
diammeter.
• In case of diameter varying from 0.6m up to
1.2m, the settlement of column decreases con-
tinuously from maximum of 6.6 times down to
1.6 times, respectively; factor of safety increases
from 1.3 to 1.7 times correspondingly with in-
creasing diameter of column.
• The variation of settlement slightly decreases
from 1.4 to 1.16 times while factor of safety in-
creases from 1.8 to 2.6 times for different values
of tensile stiffness from 500 to 1500 kN/m.
• Through this investigation, the importance role
of diameter and tensile stiffness of granular col-
umn reinforcement by geosynthetic are shown.
FUTUREWORK
• Study on deformation behavior of GEC by ana-
lytical method and numerical method.
• Study on deformation behavior of GEC by con-
sidering the impact of interface area between
geosynthetic and soil, geosynthetic and column.
• Study on deformation behavior of GEC by con-
sidering the effect of geosynthetic reinforcement
length.
• Study on the effect of internal friction angle and
cohesive of column materials to its bearing ca-
pacity.
CONFLICT OF INTEREST
The authors pledge that there are no conflicts of inter-
est in the publication of the paper.
AUTHOR CONTRIBUTION
Le Quan presents the idea of study and discuss with
Dr. Vo Dai Nhat. Besides, Le Quan carries out data
collecting, computes result and writes a draft or the
paper. Dr. Vo Dai Nhat checks the results, review
the paper, corrects all. Pham Tien Bach supports and
reviews the calculation data, input data, output data.
Assoc. Prof. Dr. Nguyen Viet Ky gives some advice
during researching process.
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Tạp chí Phát triển Khoa học và Công nghệ – Kĩ thuật và Công nghệ, 4(2):948-954
Open Access Full Text Article Bài nghiên cứu
Khoa Kỹ thuật Địa chất và Dầu khí,
Trường Đại học Bách khoa, ĐHQG –
HCM, Việt Nam
Liên hệ
Lê Quân, Khoa Kỹ thuật Địa chất và Dầu khí,
Trường Đại học Bách khoa, ĐHQG – HCM,
Việt Nam
Email: quanlepvep@gmail.com
Lịch sử
 Ngày nhận: 8-10-2020
 Ngày chấp nhận: 19-5-2021 
 Ngày đăng: 25-5-2021
DOI : 10.32508/stdjet.v4i2.777 
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Ứng xử biến dạng của cọc hạt rời bọc vải địa kỹ thuật
Lê Quân*, Võ Đại Nhật, Phạm Tiến Bách, Nguyễn Việt Kỳ
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TÓM TẮT
Tại Việt nam, sự bùng nổ dân số và phát triển mạnh mẽ của nền kinh tế đòi hỏi phải có sự phát
triển đồng bộ cơ sở hạ tầng như hệ thống đường bộ, đô thị, khu công nghiệp v.v. Với nhu cầu đó,
việc phát triển quỹ đất phục vụ cho phát triển cơ sở hạ tầng là tất yếu. Trong khi đó, quỹ đất còn
lại rất hạn chế. Bởi vậy, phải phát triển quỹ đất ra các khu vực như đầm lầy, cửa sông, ven biển v.v.
Đây là các khu vực ít có giá trị về nông nghiệp, nuôi trồng thủy hải sản. Các khu vực này thường
có điều kiện địa chất yếu; do đó, để đảm bảo an toàn cho việc xây dựng cơ sở hạ tầng thì cần thiết
phải tiến hành các biện pháp cải tạo nền đất yếu nhằm đảm bảo sức chịu tải, độ lún tổng, độ lún
cố kết nhưng vẫn phải đảm bảo hiệu quả kinh tế.
Bên cạnh các phương pháp thông thường đã được sử dụng rộng rãi để cải tạo đất yếu nhằm tăng
khả năng chịu tải và rút ngắn tốc độ lún cố kết của nền đất, cọc hạt rời bọc vải địa kỹ thuật là một
trong những phương phápmới được áp dụng trong thực hành thiết kế cải tạo đất yếu trong những
năm gần đây nhờ các ưu điểm vượt trội của nó so với các phương pháp khác. Trong bài báo này,
nhóm tác giả dựa trên mô hình lăng trụ để nghiên cứu ứng xử biến dạng của cọc hạt rời bọc vải
địa kỹ thuật thông qua tính toán giải tích bằng cách thay đổi tải trọng thẳng đứng của ngoại lực
tương ứng với từng đường kính cọc và độ cứng của vải bọc địa kỹ thuật. Độ lún của cọc đơn và
sức chịu tải của tổ hợp cọc và đất được tính toán dựa trên điều kiện địa chất của khu vực bể chứa
xỉ than Nhàmáy nhiệt điện Sông Hậu 1 tại tỉnh Hậu Giang. Quan hệ giữa biến dạng lún và sức chịu
tải với tác động của ngoại lực đối với các giá trị đường kính khác nhau, độ cứng của vải địa kỹ thuật
khác nhau được trình bày dưới dạng đồ thị. Các vấn đề liên quan đến hệ số an toàn cũng được
trình bày trong bài báo. Các nghiên cứu tiếp theo trong tương lai được đề xuất.
Từ khoá: cọc bọc vải địa kỹ thuật, đất yếu, độ lún, ứng xuất thẳng đứng
Trích dẫn bài báo này: Quân L, Nhật V D, Bách P T, Kỳ N V. Ứng xử biến dạng của cọc hạt rời bọc vải 
địa kỹ thuật. Sci. Tech. Dev. J. - Eng. Tech.; 4(2):948-954.
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