Earth reinforcement using soilbags

ARTICLE IN PRESS

Geotextiles and Geomembranes 26 (2008) 279–289 www.elsevier.com/locate/geotexmem

Technical Note

Earth reinforcement using soilbags Yongfu Xua,, Jian Huangb, Yanjun Duc, De’an Sund a

Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 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

b

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. r 2007 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 applications 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 preCorresponding author.

E-mail address: [email protected] (Y. Xu). 0266-1144/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.geotexmem.2007.10.003

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 considerably 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.

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(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 reinforcement 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–compression 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 401 and 441, respectively. Unconfined compressive tests of soilbags are shown in Fig. 2.

Fig. 1. The tensile test result of woven bags.

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Table 1 Test conditions and results of woven bags Bag type

Test type

Black woven bags

Radial Latitudinal

Yellow feedbags

Radial Latitudinal

Width (mm)

Length (mm)

Tensile force (N)

Maximum extension (mm)

Tensile strength T (kN/m)

Maximum extension strain l (%) Measurement

Average 12.5

40 37 40 40

400 400 450 450

860 808 1000 1070

51 49 56 58

21.5 21.8 25.0 26.7

12.8 12.3 12.4 12.8

40 40 40 40

450 450 400 450

832 838 962 938

40 46 38 43

20.8 21.0 24.0 23.5

8.9 10.2 9.5 9.5

12.7 9.5 9.5

applied. To measure the earth pressure between soilbags, the earth pressure transducers were installed in two different layers. The layout of the earth pressure transducers 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

Fig. 2. Unconfined compressive tests for soilbags.

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 measuring 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 soilbagreinforced 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

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 s is vertical stress acting on the horizontal plane of soilbags, and equals to the vertical force divided by the horizontal area (B  L), here B and L are the width

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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.

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

600

500

F (kN)

400

300

200

100

0 0

20

40 s (mm)

60

80

Fig. 5. Measured compressive force vs. settlement curves of soilbags.

2500 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

2000

Fig. 4. Earth pressure measurement between soilbags: (a) sketch map and (b) installation of earth pressure transducer.

 (kPa)

1500

and length of soilbags, respectively. The strain e is 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

1000

500

0 0

10

20

30

40

 (%) Fig. 6. The stress–strain curves of soilbags.

50

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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, s1f and s3f. The tension force T is 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 ¼

2T , B

(1a)

s03 ¼

2T , H

(1b)

where B and H are 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

3000 Contained sand

Compression strength (kPa)

Contained gravel

283

requires (Chen, 1999):   2T 2T ¼ K p s3f þ s1f þ , B H

(2)

where Kp ¼ (1+sinf)/(1sinf). It can be seen from Eq. (2) that the confining effect induced by the tension force T is greater in s3 direction than that in s1 direction. This is mainly attributed to the higher value of B than that of H in 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 ¼ s3p K p þ pffiffiffiffiffiffi 2c K p for a cohesive-friction material, the expression of the apparent cohesion c of soilbags can be expressed by (Chen, 1999)   T Kp 1  c ¼ pffiffiffiffiffiffi , (3) Kp H B 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 (s3 ¼ 0), the relationship between the unconfined compression stress sf and the apparent cohesive c can be given by pffiffiffiffiffiffi sf ¼ 2c K 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

2000

1000

400

0 5

10 15 Tensile strength T (kN/m)

20

25

Fig. 7. Relationship between unconfined compressive strength and tensile strength.

300 Theoretical value of c (kPa)

0

200

100 This paper Matsuoka and Liu (2003) x=y 0 0

Fig. 8. Stresses acting on soilbags and on particles inside soilbags (Chen, 1999; Matsuoka, 2003).

100 200 300 Experimental value of c (kPa)

400

Fig. 9. Comparison between theoretical and experimental values of apparent cohesion c.

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284

s1m/s3m was the function of principal strain e1 under the external load s1 and s3, i.e. s1m ¼ f ð1 Þ, (5) s3m where s1m ¼ s1+2T/B, s3m ¼ s3+2T/H, f(e1) ¼ a exp(e1)+ Kp, a depends on the original state of soilbags. If s1m/s3m ¼ 1 and e1 ¼ 0, a ¼ 1Kp, the relationship of external stress s1 and s3 and principle strain e1 can be written as   2T B f ð1 Þ  1 . s1 ¼ s3 f ð1 Þ þ (6) B H The principal strain in the height direction of soilbags is given by e1 ¼ (H0-H)/H0. The tensile strength of woven bags is written as T ¼ kl, where l is the maximum extension strain of bags and k is the slope of the extension curves (Fig. 10). Parameter k can be determined by the ratio of the tensile strength (T) to the maximum extension strain (l) of bags. The value of k is listed in Table 2. The volume of soilbags is assumed to be invariable and constant, i.e. B0H0 ¼ BH, where B0 and H0 are the original length and height of soilbags, respectively. The stress– strain relationship of soilbags can be written as (Matsuoka, 2003)    f ð1 Þ m  1 þ 1 ð1  1 Þ m  s1 ¼ s3 B0  2k1 B0 1  1 ðm þ 1Þð1  1 Þ f ð1 Þ

(7)

Fig. 10. The meanings of k.

where m ¼ B/H. In the unconfined compressive tests since s3 ¼ 0, the stress–strain relationship of soilbags is then given by   2k1 f ð1 Þ m  1 þ 1 ð1  1 Þ m  s1 ¼  . (8) B0 1  1 ðm þ 1Þð1  1 Þ f ð1 Þ 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 compressive 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.

Table 2 Parameters for the stress–strain curves of soilbags Bag type

Filling material

T (kN/m)

l (%)

k (kN/m)

F (1)

Kp

a ¼ 1Kp

B (cm)

H(cm)

Yellow feedbags Black woven bags Yellow feedbags Black woven bags

Medium grained sand

20.8 21.5 20.8 21.5

9.5 12.5 9.5 12.5

219 172 219 172

40

4.60

3.60

44

5.55

4.55

55 57 13 14

12 14 45 46

Gravel

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1500

285

2000 Black bag contained sand, 14cm×52cm×57cm

Feedbag contained sand, 12cm×47cm×55cm

Experiments Prediction

1500  (kPa)

 (kPa)

1000 1000

500 500

Experiments Prediction

0

0 0

10

20

30  (%)

40

50

0

2500

20 30  (%)

40

50

2500

Feedbag contained gravel, 13cm×25cm×30cm

Black bag contained gravel,14cm×36cm×46cm

Experiments

2000

10

2000

Prediction

Experiments

 (kPa)

 (kPa)

Prediction

1500 1000

1500 1000

500

500

0 0

10

20

30

40

0

50

0

10

20

 (%)

30  (%)

40

50

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 pcr (kPa)

Ultimate settlement scr (mm)

Elastic modulus E0 (MPa)

Undisturbed soil foundation Soilbag foundation n ¼ 2, BSB ¼ 2 m, HSB ¼ 0.2m Soilbag foundation n ¼ 3, BSB ¼ 2m, HSB ¼ 0.3m

70 160 240

11 14 12

3.08 5.00 8.57

The relationship between the bearing capacity and the height and width (length) of the soilbag foundation is shown in Fig. 13. In Fig. 13, BSB and HSB are the width (length) and height of the soilbag foundation, respectively, b is the width of the load plate. The relationship between the bearing capacity and the size of the soilbag foundation can be expressed by puðSBÞ ¼ puðSoilÞ

   BSB H SB 1þ 1þ , b b

(9)

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

where pu(SB) and pu(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. In Fig. 14, sx and sz 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

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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286

0

100

Load p (kPa) 200

x (kPa) 300

400

-100

0

0

p = 240kPa

-10 -100 Settlement s (mm)

100

200

300

0 Tes No.1 Test No.2 Earth pressure at rest Active earth pressure k = 0.013

-20 p = 70kPa

-200

-30 p = 160kPa -300 -40 z (kPa)

Undisturbed soil foundation Soilbag foundation with n = 2 Soilbag foundation with n = 3 -50

-400 Fig. 12. Results of plate load tests.

25 -500

This paper Matsuoka and Liu (2003) x=y

20

pu (SB)/pu (Soil)

-600 15

-700

10

Fig. 14. Earth pressure distribution between soilbags.

5

0 0

5

10 15 (1+HSB/b) (1+BSB/b)

20

25

Fig. 13. Relationship between the bearing capacity and the size of the soilbag foundation.

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 polyethylene woven bags. They were connected mutually using high strength ropes and compacted thoroughly with vibroroller. 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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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.

2005y Jul Aug

Sept

Date Nov Dec

Oct

2006y Jan Feb

Mar

Apr

0 Left Middle

Settlement s (mm)

-40

Right -80

-120

-160 Fig. 17. Variation of measured settlement vs. time of the soilbag subgrade. Fig. 16. Design of the pond by filling up of soilbags: (a) Ho3 m (b) H43 m and (c) Important structure foundation.

300

(3) Place the second layer soilbags on the first layers and compacted soilbags using vibro-roller. After the construction 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 s of 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

Settlement s (mm)

250

Filling-up by crushed stone Filling-up by soilbags

200 150 100 50 0 8 2005y

9

10

11

12 Date

1

2

3

4

Fig. 18. Comparison of subgrade settlement in the pond between the case that filled by soilbags and the case that filled by crushed stone.

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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288

Fig. 19. Retaining walls of soilbags to protect expansive soil slope.

(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. Fig. 20. Schematic design of a retaining wall using soilbags.

4.2. Slope protection of expansive soil with soilbags

Acknowledgements

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.

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 acknowledged for their help in the tests in situ. Shanghai leading Academic Discipline Project (B208) was also acknowledged.

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 mobilization of tensile forces in the bags upon application of an external load.

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