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Geotextiles and Geomembranes 26 (2008) 279–289
Technical Note
Earth reinforcement using soilbags
Yongfu Xu
a,
, Jian Huang
b
, Yanjun Du
c
, De’an Sun
d
a
Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
b
Jiangsu Construction Headquarter of Highway Engineering, Jiangsu Province, Nanjing 210004, China
c
Geotechnical Engineering Institute, Southeast University, Nanjing 210096, China
d
Department of Civil Engineering, Shanghai University, Shanghai 200000, China
Received 9 April 2007; received in revised form 23 October 2007; accepted 25 October 2007
Available online 20 February 2008
Abstract
This paper describes the method of earth reinforcement using soilbags and illustrates its application for case studies involving a pond
and the expansive soil slope protection for a highway. The strength properties of soilbags were investigated using unconfined
compression tests and bearing capacity tests on real soilbags containing either medium grained sands or gravels. The test results show
that soilbags have high strength when subjected to an external load. This is primarily attributed to the mobilization of tensile forces in the
bags. It is concluded that earth reinforcement using soilbags could substantially improve the bearing capacity of soft ground as well as
minimizing deformation under working loads.
r2007 Elsevier Ltd. All rights reserved.
Keywords: Bearing capacity; Earth reinforcement; Retaining wall; Soilbag; Unconfined compressive strength
1. Introduction
Soilbags have long been used to reinforce dikes against
floods and are used to build temporary structures in case of
emergency (Kim et al., 2004). Soilbags, as new shore
protection structures, especially at sandy coasts, are
increasingly needed and widely used for flood emergency
protection in dams and dikes, and also as construction
elements for erosion control, bottom scour protection and
scour fill artificial reefs, groynes, seawalls, breakwaters and
dune reinforcement (Heibaum, 1999). Restalla et al. (2002)
outlined the historical development of the material types
used for geotextile containers and the diversity of applica-
tions in which these containers were used. Koerner and
Koerner (2006) described the field performance of three
geotextile tube case histories contrasted to the results from
12 hanging bag tests. Yasuhara and Recio-Molina (2007)
described recent developments of geotextile wrap-around
revetment structures resulting from small-scale model tests
and analyses. Large-scale model tests on the hydraulic
stability of geotextile containers in Germany were pre-
sented and the content of the German recommendations
dealing with geotextile containers, including example
applications were discussed by Saathoff et al. (2007).
Shin and Oh (2007) presented a stability analysis by the
two-dimensional limit equilibrium theory. In their studies,
the hydraulic model test results related to the geotextile
tube technology and case history of shore protection at
Young-Jin beach on the east coast of Korea were
presented. Recio and Oumeraci (2007) pointed out that
the deformations of the geotextile sand containers con-
siderably controlled the stability of a geotextile sand
container revetment.
So far, soilbags have seldom been used for constructing
permanent structures. The limited utilization of soilbags in
constructing permanent structures might be mainly due to
lack of mechanisms of the soil reinforcement by soilbags as
well as the deterioration of soilbags after a long termed
exposure to sunlight (Matsuoka and Liu, 2003). Matsuoka
and Liu (2003) summarized the advantages of soil
reinforcement by soilbags, as follows:
(1) The bearing capacity of a soft ground can be increased
by 5–10 times using soilbags.
ARTICLE IN PRESS
www.elsevier.com/locate/geotexmem
0266-1144/$ - see front matter r2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.geotexmem.2007.10.003
Corresponding author.
E-mail address: yongfuxu@hotmail.com (Y. Xu).
(2) Soilbags are easily constructed. Heavy construction
equipment is not needed, and mere manpower can be
enough.
(3) Soilbag is environment friendly due to no use of any
cement or chemical agents. The noise during the
construction is very low.
(4) The materials contained in soilbags can even be any
construction wastes such as recycled concrete, asphalt,
tire and tile. Therefore, the impact of the construction
wastes to environment can be mitigated.
(5) The soilbag itself has a high compressive strength,
which is nearly up to 3 MPa, nearly equals to 1/10
times that of the usual concrete.
(6) The traffic- or machine-induced vibration can be
reduced due to the absorption of vibration by soilbags.
(7) Frost heaving can be suppressed if granular coarse
materials are used.
Matsuoka (2003) indicated that the bearing capacity
of a foundation could be greatly improved if a part of the
foundation is wrapped up with flexible reinforcements.
Shao et al. (2005) and Xu et al. (2007) used soilbags to
fill up ponds in highway in Jiangsu Province, China.
Their field test results showed that solibags could
effectively reduce the settlement of subgrade and low
down the engineering costs. However, limited studies on
the unconfined compressive strength of real soilbags
subjected to external forces have been conducted. In this
paper, the strength properties of soilbags subjected to
external forces are presented. The bearing capacity of
the soilbag-reinforced foundation was investigated by
the static load tests. Two case studies using soilbags in
pond filling up and expansive soil slope protection are
presented.
2. Materials and test method
The fundamental mechanism of the reinforcement using
soilbags is that when a confining pressure is acted on the
contained soil, the tensile strength of woven bags will be
mobilized. The qualities of woven bags affect the reinforce-
ment effectiveness. Two important parameters, tensile
strength and maximum extension strain, were used to
describe the bag qualities. During the transport and
installation of soilbags in practice, tensile strength is
required. In this study, in order to determine the tensile
strength and maximum extension strain of woven bags, the
tensile tests of two woven bags, black woven bags and
yellow feedbags, were conducted on an extension–compres-
sion apparatus with electronic digital control device. The
black woven bags are specially brought for pond filling up,
while yellow feedbags are bought from local farmers. The
pulling speed was controlled as 5 mm/min in this study.
The tensile force–settlement relationship of two woven
bags is shown in Fig. 1. The tension test results are
tabulated in Table 1.
An unconfined compressive test is often used to
determine the behavior of a material when it is subjected
to a compressive load. For soilbags, loading was controlled
at a constant rate, about 200 kg/min in the unconfined
compressive testes. The typical size of soilbags was
10 mm 40 mm 40 mm. The soilbags used for unconfined
compressive strength tests were made of woven bags in
which medium graded sands and gravels were contained.
The soilbags were tamped and trimmed to a diamond
shape so that their initial length, width and height would be
easily measured before tests. The contained materials were
medium sands and gravels with internal friction angles of
401and 441, respectively. Unconfined compressive tests of
soilbags are shown in Fig. 2.
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Fig. 1. The tensile test result of woven bags.
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289280
Plate load tests were used to estimate the bearing
capacity of the soilbag foundation under field loading
conditions for a specific loading plate and depth of
embedment. The plate load tests were carried out on a
foundation reinforced by soilbags contained with sand, of
which the internal friction angle was 331. The test target is
to validate the reinforcement of soilbags through measur-
ing the bearing capacity (load) of real soilbag foundation,
which is different from the conventional ones such as
placing reinforcements (geotextiles, mattresses, strips, etc.)
horizontally installed in the grounds. In the load tests,
soilbags were kept at 10 cm in height, 40 cm in width and
length, respectively. The procedure of the bearing capacity
tests is shown in Fig. 3. The diameter of the load plate is
0.5 m. Fig. 3(a) is the load test for the undisturbed soil
foundation, and Fig. 3(b) is the load test for the soilbag-
reinforced foundation. The load was applied in stages and
at each stage the load was maintained constant until the
resulting settlement of foundation virtually ceases before
applying the next load increment. When the settlement rate
decreased to 0.5 mm/h, the next load increment was
applied. To measure the earth pressure between soilbags,
the earth pressure transducers were installed in two
different layers. The layout of the earth pressure transdu-
cers is shown in Fig. 4. The results of the plate load tests
are listed in Table 3.
3. Test results and discussion
3.1. Unconfined compressive strength of soilbags
From Fig. 2, it was observed at the failure, soilbags were
torn at the points such as contact points with the loading
plate, the tailoring points and the maximum distortion
points, where the external stress concentrated. The curves
of measured compressive force vs. settlement are shown in
Fig. 5. The curve of force–settlement relationship can be
divided into two stages. At the early stage, the extension
strain was less than the maximum extension strain of bags,
the force was low and the contained materials were loose.
The vertical settlement of soilbags increased rapidly with
increasing extension strain of woven bags. As a result, the
slope of the force–settlement curves is not high at the early
stage. At the later stage, the slope of force–settlement
curves is large. When the load was applied on the soilbag,
the load increased with the settlement. The load cannot
increase and decreased rapidly while the extension strain
was large enough to reach the maximum value, and the bag
was worn. At that point, the load was defined as the
ultimate load. Contained materials in the bags were
considerably compacted. The compressive force increased
rapidly with the increase in the settlement of soilbags. This
observation implies that during the late stage, even a large
force is applied on the soilbag-reinforced foundation, the
settlement could be small. In other words, soilbags can be
used to effectively reduce the foundation settlement. The
measured stress–strain relationship of soilbags is shown in
Fig. 6. The stress sis vertical stress acting on the horizontal
plane of soilbags, and equals to the vertical force divided
by the horizontal area (BL), here Band Lare the width
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Table 1
Test conditions and results of woven bags
Bag type Test type Width (mm) Length (mm) Tensile force
(N)
Maximum
extension
(mm)
Tensile
strength T
(kN/m)
Maximum extension strain l
(%)
Measurement Average
Black woven
bags
Radial 40 400 860 51 21.5 12.8 12.5
37 400 808 49 21.8 12.3
Latitudinal 40 450 1000 56 25.0 12.4 12.7
40 450 1070 58 26.7 12.8
Yellow
feedbags
Radial 40 450 832 40 20.8 8.9 9.5
40 450 838 46 21.0 10.2
Latitudinal 40 400 962 38 24.0 9.5 9.5
40 450 938 43 23.5 9.5
Fig. 2. Unconfined compressive tests for soilbags.
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289 281
and length of soilbags, respectively. The strain eis vertical
strain of soilbags.
The compression strength was defined as the value of the
ultimate load divided by the horizontal area of the soilbag.
The relationship between the unconfined compressive
strength of soilbags and the tensile strength of woven bags
is shown in Fig. 7. The unconfined compressive strength of
soilbags linearly increased with the increase in the tensile
strength T. The soilbags in which gravels were contained
have larger unconfined compressive strength than soilbags
in which medium graded sands were contained. This is
mainly because that the internal friction angle of the gravel
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Fig. 3. Plate load tests for undisturbed soil foundation and soilbag reinforced foundation: (a) undisturbed soil foundation and (b) soilbag reinforced
foundation.
Fig. 4. Earth pressure measurement between soilbags: (a) sketch map and
(b) installation of earth pressure transducer.
0
100
200
300
400
500
600
0 20406080
F (kN)
Feedbag contained sand, 12cm×47cm×55cm
Black bag contained sand, 14cm×52cm×57cm
Feedbag contained gravel, 13cm×25cm×30cm
Black bag contained gravel, 14cm×36cm×46cm
s (mm)
Fig. 5. Measured compressive force vs. settlement curves of soilbags.
0
500
1000
1500
2000
2500
0 1020304050
(kPa)
Feedbag contained sand,
12cm×47cm×55cm
Black bag contained sand,
14cm×52cm×57cm
Feedbag contained gravel,
13cm×25cm×30cm
Black bag contained gravel,
14cm×36cm×46cm
(%)
Fig. 6. The stress–strain curves of soilbags.
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289282
is larger than that of the sand. During the unconfined
compressive test, break of sand and gravel particles was
observed.
Fig. 8 is a schematic illustration of the stress distribution
when the soilbag is subjected to external principal stresses,
s
1f
and s
3f
. The tension force Tis induced in the bag when
it is exposed to the external forces. This tension induces
additional stresses that act on the soil particles inside
soilbags, as expressed by (Chen, 1999)
s01 ¼2T
B, (1a)
s03 ¼2T
H, (1b)
where Band Hare the width and height of soilbags,
respectively. Thus, the stresses acting on the soil particles
inside soilbags are the combined result of the externally
applied stresses and the additionally induced stresses by T
as shown in Fig. 8. At failure, the following equation
requires (Chen, 1999):
s1f þ2T
B¼Kps3f þ2T
H
, (2)
where K
p
¼(1+sinf)/(1sinf). It can be seen from Eq. (2)
that the confining effect induced by the tension force Tis
greater in s
3
direction than that in s
1
direction. This is
mainly attributed to the higher value of Bthan that of Hin
Eq. (1a,b). As a result, a large ratio B/H of soilbags would
enhance the reinforcement effectiveness. Comparing
Eq. (2) with the strength expression s1f ¼s3p Kpþ
2cffiffiffiffiffiffi
Kp
pfor a cohesive-friction material, the expression of
the apparent cohesion cof soilbags can be expressed by
(Chen, 1999)
c¼T
ffiffiffiffiffiffi
Kp
p
Kp
H1
B
, (3)
Eq. (3) shows that a frictional material can be considered
as a cohesive-frictional material merely by wrapping it up
with a bag.
In the unconfined compression tests (s
3
¼0), the
relationship between the unconfined compression stress s
f
and the apparent cohesive ccan be given by
sf¼2cffiffiffiffiffiffi
Kp
p, (4)
A comparison between the theoretical value calculated
from Eq. (3) and the experimental value of apparent
cohesive is shown in Fig. 9. It can be seen from Fig. 9 that
the difference between the theoretical values and the
experimental values is slight. The difference is mainly due
to the abnormal shape of soilbags and the difficulty in the
measurement of the soilbag size.
To obtain the stress–strain relationship of soilbags,
Matsuoka (2003) assumed that the ratio of principle stress
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0
100
200
300
400
0 100 200 300 40
0
Theoretical value of c (kPa)
This paper
Matsuoka and Liu (2003)
x=y
Ex
p
erimental value of c (kPa)
Fig. 9. Comparison between theoretical and experimental values of
apparent cohesion c.
0
1000
2000
3000
0 5 10 15 20 25
Tensile stren
g
th T (kN/m)
Compression strength (kPa)
Contained sand
Contained gravel
Fig. 7. Relationship between unconfined compressive strength and tensile
strength.
Fig. 8. Stresses acting on soilbags and on particles inside soilbags (Chen,
1999;Matsuoka, 2003).
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289 283
s
1m
/s
3m
was the function of principal strain e
1
under the
external load s
1
and s
3
, i.e.
s1m
s3m
¼fð1Þ, (5)
where s
1m
¼s
1
+2T/B,s
3m
¼s
3
+2T/H,f(e
1
)¼aexp(e
1
)+
K
p
,adepends on the original state of soilbags. If s
1m
/s
3m
¼1
and e
1
¼0, a¼1K
p
, the relationship of external stress s
1
and s
3
and principle strain e
1
can be written as
s1¼s3fð1Þþ2T
B
B
Hfð1Þ1
. (6)
The principal strain in the height direction of soilbags is
given by e
1
¼(H
0
-H)/H
0
. The tensile strength of woven
bags is written as T¼kl, where lis the maximum
extension strain of bags and kis the slope of the extension
curves (Fig. 10). Parameter kcan be determined by the
ratio of the tensile strength (T) to the maximum extension
strain (l) of bags. The value of kis listed in Table 2. The
volume of soilbags is assumed to be invariable and
constant, i.e. B
0
H
0
¼BH, where B
0
and H
0
are the original
length and height of soilbags, respectively. The stress–
strain relationship of soilbags can be written as (Matsuoka,
2003)
s1¼fð1Þ
B0
s3B02k1
m1þ1
ðmþ1Þð11Þ
ð11Þ
fð1Þm
11
(7)
where m¼B/H. In the unconfined compressive tests since
s
3
¼0, the stress–strain relationship of soilbags is then
given by
s1¼2k1fð1Þ
B0
m1þ1
ðmþ1Þð11Þ
ð11Þ
fð1Þm
11
. (8)
The parameters used for calculation are listed in Table 2.
The calculated stress–strain relationship of soilbags is
shown in Fig. 11. It can be seen from Fig. 11 that the
calculation matches well with the test results of the
stress–strain relationship of soilbags.
The main conclusions obtained from unconfined com-
pressive tests are listed as: (1) unconfined compressive
strength of soilbags is related to tensile strength of woven
bags and internal friction angle of contained materials. The
unconfined compressive strength of soilbags increases with
tensile strength of woven bags and internal friction angle of
contained materials. (2) The stress–strain relationship of
soilbags is different from that of soils. The theoretical
stress–strain relationship is validated by the unconfined
compressive tests. (3) Soilbags can effectively reduce
settlement due to the strong tensile strength of bags.
3.2. Bearing capacity of the soilbag foundation
A series of bearing capacity tests were carried out on the
real soilbag foundation. The slip surface of the soilbag
foundation is similar with that of the soil foundation
(Leshchinsky and Marcozzi, 1990;Matsuoka, 2003). It was
observed that the soilbags were very solid and deforms
similar to a footing foundation. The interparticle forces
inside the soilbags are considerably larger than those
outside (Yamamoto et al., 1995). This is because the
external force acting on the footing induces a tensile force
in the wrapping bags, and the tensile force thereafter acts
on the contained materials inside the soilbag.
The load–settlement curves of the plate load tests on real
soilbag foundation are shown in Fig. 12. The vertical
pressure, p, acts on the plate area. Soilbags are arranged as
shown in Fig. 4(a). The ultimate bearing capacity is
determined according to the failure in the ground. From
Fig. 12, it can be seen that the ultimate bearing capacity for
the cases without soilbag, with two layers of soilbag, and
with three layers of soilbag are 70, 17 and 240 kPa,
respectively. The bearing capacity of the soilbag-reinforced
ground is 2–3 times larger than that of the soil ground
without soilbag.
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Table 2
Parameters for the stress–strain curves of soilbags
Bag type Filling material T(kN/m) l(%) k(kN/m) F(1)K
p
a¼1K
p
B(cm) H(cm)
Yellow feedbags Medium grained sand 20.8 9.5 219 40 4.60 3.60 55 12
Black woven bags 21.5 12.5 172 57 14
Yellow feedbags Gravel 20.8 9.5 219 44 5.55 4.55 13 45
Black woven bags 21.5 12.5 172 14 46
Fig. 10. The meanings of k.
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289284
The relationship between the bearing capacity and the
height and width (length) of the soilbag foundation is
shown in Fig. 13.InFig. 13,B
SB
and H
SB
are the width
(length) and height of the soilbag foundation, respectively,
bis the width of the load plate. The relationship between
the bearing capacity and the size of the soilbag foundation
can be expressed by
puðSBÞ
puðSoilÞ
¼1þBSB
b
1þHSB
b
, (9)
where p
u(SB)
and p
u(Soil)
are the ultimate bearing capacity of
the soilbag foundation and undisturbed soil ground,
respectively. The soilbag foundation is constructed by
two layers at least according to Fig. 4(a).
The earth pressure distribution in soilbags is shown in
Fig. 14.InFig. 14,s
x
and s
z
are the horizontal and vertical
earth pressure between soilbags at the same plane. The
solid line in Fig. 14 denotes the active earth pressure
relationship, and the dashed line in Fig. 14 represents the
earth pressure distribution at rest. The active earth pressure
was calculated including apparent cohesion. It can be seen
from Fig. 14 that the horizontal earth pressure is less than
the active earth pressure and the earth pressure at rest, and
is nearly constant. This phenomenon implies that soilbags
were strongly confined by the tensile strength of bags, and
could not laterally expand. The measured results of the
earth pressure verify the reinforcement mechanism of
soilbags.
4. Practical applications of soilbags
4.1. Filling up of pond using soilbags
In the construction of highway in Jiangsu Province,
extremely weak pond foundations were encountered where
the ground was waterlogged and the construction machine
could not stand on it (see Fig. 15(a)). Initially the pond was
designed to be improved by filling up crushed stones.
However, this method is cost and usually results in large
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Feedbag contained sand,
12cm×47cm×55cm
0
500
1000
1500
0 1020304050
Experiments
Prediction
Black bag contained sand, 14cm×52cm×57cm
0
500
1000
1500
2000
01020304050
(kPa)
Experiments
Prediction
Feedbag contained gravel, 13cm×25cm×30cm
0
500
1000
1500
2000
2500
0 1020304050
(kPa)
Experiments
Prediction
Black bag contained gravel,14cm×36cm×46cm
0
500
1000
1500
2000
2500
01020304050
(kPa)
Experiments
Prediction
(kPa)
(%) (%)
(%)
(%)
Fig. 11. Comparisons between the calculated results and test results of the stress–strain curves of soilbags.
Table 3
Results of load tests
Foundation Ultimate bearing
capacity p
cr
(kPa)
Ultimate settlement s
cr
(mm)
Elastic modulus E
0
(MPa)
Undisturbed soil foundation 70 11 3.08
Soilbag foundation n¼2, B
SB
¼2m, H
SB
¼0.2m 160 14 5.00
Soilbag foundation n¼3, B
SB
¼2m, H
SB
¼0.3m 240 12 8.57
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289 285
settlement. Finally, a new reinforcement method, the
soilbag method was chosen to fill up the pond. In this
case, one layer soilbags were first placed into the mucky
ground, and the contained materials inside soilbags were
natural soils with optimum water content. After the
reinforcement by soilbags, the soft ground could even
withstand a heavy construction machine like vibro-roller
(Fig. 15(b)).
The design method of the pond filling-up by soilbags is
shown in Fig. 16.Fig. 16(a) is the design of soilbags filled
pond with a depth less than 3 m, Fig. 16(b) is the design of
soilbags filled pond with depth greater than 3 m, and
Fig. 16(c) is for the important structure foundation, such as
passage under road. The construction procedures are
described as follows: (1) excavate and remove the mucky
soil from the pond bottom, (2) compact the excavated
foundation with vibrators and then place a layer of
soilbags. The soilbags, having sizes of about 40 cm of
length, 40 cm of width, and 10 cm of height, were made of
natural soil with the optimum water content and poly-
ethylene woven bags. They were connected mutually using
high strength ropes and compacted thoroughly with vibro-
roller. The compaction degree of the soil contained in
woven bags was measured by the sand cone method, and
was greater than 93%, which met the design requirement.
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Load p (kPa)
-50
-40
-30
-20
-10
0
0 100 200 300 400
Settlement s (mm)
Undisturbed soil foundation
Soilbag foundation with n = 2
Soilbag foundation with n = 3
p = 70kPa
p = 160kPa
p = 240kPa
Fig. 12. Results of plate load tests.
0
5
10
15
20
25
0 5 10 15 20 25
pu (SB)/pu (Soil)
This paper
Matsuoka and Liu (2003)
(1+HSB/b) (1+BSB/b)
x = y
Fig. 13. Relationship between the bearing capacity and the size of the
soilbag foundation.
-700
-600
-500
-400
-300
-200
-100
0
-100 0 100 200 300
Tes No.1
Test No.2
Earth pressure at rest
Active earth pressure
k = 0.013
z (kPa)
x (kPa)
Fig. 14. Earth pressure distribution between soilbags.
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289286
(3) Place the second layer soilbags on the first layers and
compacted soilbags using vibro-roller. After the construc-
tion of the two layers of soilbags, the natural soil was filled
and rolled in a way similar to the tradition embankment
filling materials.
Since the confining stress sof the subgrade soil is very
small, its shear strength is therefore low. However, if soil is
reinforced by woven bags, the shear strength of the soil
would increase due to the tension force of the bags that is
mobilized when the wrapped soil dilated under the traffic
loading. This will lead to an increase in the bearing
capacity of the subgrade foundation and the reduction in
the settlement of subgrade soil. The effectiveness of this
reinforcement method has been verified through a series of
load tests on the soilbag foundation. The settlements of the
subgrade are plotted against the elapsed time is shown in
Fig. 17. The settlement reaches the ultimate value much
rapidly. The comparison of the ultimate settlement in the
pond filled by soilbags and by crushed stone is shown in
Fig. 18. It can be seen that the settlement reached more
than 275 mm for the case reinforced by crushed stone,
while reduced to less than 150 mm for the case reinforced
by soilbags.
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Fig. 15. Construction of the pond by filling up of soilbags: (a) initial condition of pond bottom and (b) compaction of soilbag reinforced foundation using
a vibro-roller.
Fig. 16. Design of the pond by filling up of soilbags: (a) Ho3m
(b) H43 m and (c) Important structure foundation.
Date
-160
-120
-80
-40
0
Settlement s (mm)
Left
Middle
Right
Jul MarFebJanDecNovOctSeptAug Ap
r
2005y 2006y
Fig. 17. Variation of measured settlement vs. time of the soilbag
subgrade.
0
50
100
150
200
250
300
8 9 10 11 12 1 2 3 4
Date
Settlement s (mm)
Filling-up by crushed stone
Filling-up by soilbags
2005y
Fig. 18. Comparison of subgrade settlement in the pond between the case
that filled by soilbags and the case that filled by crushed stone.
Y. Xu et al. / Geotextiles and Geomembranes 26 (2008) 279–289 287
4.2. Slope protection of expansive soil with soilbags
Fig. 19 shows a case of construction of retaining walls
using soilbags to protect the expansive soil slope. The
retaining walls were constructed on the expansive soil
foundation with a height of about 4 m, a total length of
about 71 m and an inclined angle of 301. Four soilbags
were connected in the lower part and the slope angle was
301(Fig. 20). One soilbag has a length of 40 cm, width of
40 cm, and height of 10 cm. The materials inside the
soilbags were natural soils with optimum water content.
The woven bags were made of polyethylene. Soilbags were
piled up and well compacted by vibrators layer by layer.
Since the polyethylene bag was sensitive to sunlight, a thin
layer of grass was cast on the outside surface of the wall, as
shown in Fig. 20. In this project, about 2000 soilbags were
used and the construction was very silent because of no use
of any heavy construction machines.
5. Conclusions
From the tests and analysis presented in this paper, the
merits of using soilbags as an earth reinforcement method
in practice were discussed. Following conclusions can be
drawn:
(1) Soilbags have high strength and little settlement when
subjected to external load. This is due to the mobiliza-
tion of tensile forces in the bags upon application of an
external load.
(2) An apparent cohesion, c, was induced in soilbags due to
the tensile strength of the bags, which significantly
increased the compressive strength. The apparent
cohesion, c, increased with the increase in the tensile
strength of the woven bags and the internal friction
angle of the contained materials.
(3) A soilbag-reinforced foundation has a high bearing
capacity. The lateral earth pressure between soilbags is
very low. The soilbags have high confining stress, which
constrained the lateral displacement and reduced the
settlement of the foundation.
Acknowledgements
The authors would like to acknowledge cooperation
in experimental work provided by Qubin Chen, Feng Sun,
Xin Huang, Bin Yang, YinYi Chen, Xin Jin, Lixin Tong,
Rui Li, Lei Zhang and Yuheng Bai. The Communication
Bureau of Jiangsu Province is acknowledged for its
fund support. Mingkang Lu, Xiaoan Gu and Yi Dong
of Changzhou Construction Headquarter of Highway
Engineering, and Boming Zhou of Jiangsu Construction
Headquarter of Highway Engineering are also acknowl-
edged for their help in the tests in situ. Shanghai
leading Academic Discipline Project (B208) was also
acknowledged.
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