Civil and Environmental Engineering Department

King Fahd University of Petroleum and Minerals

Fibers-Reinforced Soil Soil and Site Improvement (CE 553) Term Project Course

Rama Rizana (201309050)

Instructor: Prof. Omar S. Baghabra Al-Amoudi

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Topic: Modifications by Inclusions and Confinement

Fiber-Reinforced Soil

Rama Rizana

INTRODUCTION

Most buildings and other civil engineering construction projects are started as raw

land. The first step to be performed is site investigation in order to know the situation of

the site. It is difficult to find location that has perfect soil properties. Possible alternative

solutions to solve this reality are:

Avoid that site. Relocate the planned construction project to another site.

Replace unsuitable soils. After obtaining the soil properties, it can be determined

the soils are unsuitable, then remove with the better soils.

Try to modify the existing soil. This is called as ground modification.

Hausmann (1990) distinguished the ground improvement or modification or

stabilization into four groups, they are:

Mechanical modification. External mechanical forces are used to increase soil

density, including soil compaction by using many methods, such as static compaction,

dynamic compaction, or deep compaction by heavy tamping.

Hydraulic modification. Pore-water is forced out of the ground through drains or

wells. Lowering the groundwater level by pumping from trenches or boreholes can be

applied for coarse-grained or cohesionless soil, and for fine-grained or cohesive soil,

application of the long-term of external pressure (preloading) or electrical loads

(electrokinetic stabilization) is needed. Another technique can be applied such as

hydraulic modification is by using geosynthetics.

Physical and chemical modification. One example of this method is soil stabilization

by physically mixing/blending additives with top layers at depth. Additives can be natural

soils, industrial by-products or waste materials, and other chemical materials that can

react with the ground. Other applications are ground modification by grouting and

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thermal modifications which are already discussed before.

Modification by inclusions and confinement. This group is considered as

strengthening soil by materials, such as meshes, bars, strips, fibers, and fabrics

correspond to the tensile strength. Confining site with concrete, steel, or fabric elements

can also form stable-earth retaining structures. Conventional pile foundations are not

considered in this group, although sometimes they are called as “compressive

reinforcement”. This is because the principal purpose of pile foundation is not

strengthening the soil, but to send the load to a stronger or greater depth stratum.

Soil reinforcement, as one of ground improvement methods, is a process of using

synthetic or natural additive materials to improve the soil characteristics or properties.

There are some reinforcement techniques to handle problematic soils. Hence, the ground

reinforcement techniques can be divided into some categories with different points of

view. Figure 1 shows different scheme of ground improvement, especially site or ground

reinforcement (Hejazi et al., 2012).

Figure 1. Several methods of soil reinforcement (Hejazi et al., 2012)

Figure 2 presents a summary of ground or site improvement methods based on soil

grain size.

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Figure 2. Ground modification methods based on soil grain size (Day, 2012)

GROUND MODIFICATION BY INCLUSIONS AND CONFINEMENT (SOIL

REINFORCEMENT)

Reinforced soil is originally defined as a soil which is strengthened by a material able

to resist tensile stresses and which interacts with the soil through friction and/or adhesion.

Subsequently, the meaning of soil reinforcement was broadened, and this term is now

also used for other mechanical and structural methods of soil improvement, such as

compressive reinforcement by confinement and encapsulation (Hausmann, 1990).

The main purpose of soil reinforcement is to increase the stability or soil strength

(Bayormy et al., 2007; Liu et al., 2014; Abdi and Zandieh, 2014; Lajevardi et al., 2014),

improve bearing capacity and reduce settlements and lateral deformation. The wider

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definition of soil reinforcement also includes erosion control methods and stress transfer

via anchors and piles. This term becomes complicated since many materials used to

improve engineering properties of soil, for example geotextiles that can be used for

multiple purposes (e.g., strengthen structural behavior, control groundwater flow and

separate different soil layers during construction). Another material is even from the root

and natural geotextiles from Bamboo, that it can also increase strength of the soil

structures (Datye and Gore, 1994; Muntohar, 2012; Cazzuffi et al., 2014).

Soil reinforcement is not a new concept. The ancient ziggurats (Figure 3) found in

Iraq, which are more than 3000 years old is one of early examples of soil reinforcement

application. Reed-reinforced earth levees were constructed along the Tiber River by the

Romans. The modern uses of soil reinforcement appeared in the 1960s with the

development of Reinforced Earth retaining walls and geotextile stabilization of haul roads

and access roads (Bonaparte et al., 1987).

Figure 3. Ziggurats in Iraq (http://www.ancient.eu/Mesopotamia/)

FIBER-REINFORCED SOIL

Another solution to reinforce soil is by using fiber. It has been a solution to stabilize

thin soil and localized repair of failed slopes. Unlikely geosynthetics, another

reinforcement method using fibers is applied by distributing the fibers randomly. Fibers

which can be used either natural fibers or synthetic fibers. Hejazi et al. (2012) made a

simple study by reviewing more than 100 researches of soil reinforcement by using

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natural (Table 6) and synthetic fibers (Table 7).

To prepare sample or specimens of fiber-reinforced soils to be tested in the laboratory,

it can be mixed either manually or mechanically by using mixing machine. Whatever the

mixing method used, many researches implicitly assume that the fibers will be randomly

distributed in the soil mass. That orientation distribution would give the soil strength

isotropy.

Effects of fiber-reinforced soil are relatively similar to geosynthetics-reinforced soil

for both coarse-grained and fine-grained soils, such as increasing bearing capacity and

soil strength (Gray and Ohashi, 1983; Gray and Al-Refeai, 1986; Puppala and Musenda,

2000; Prabakar and Sridhar, 2002; Yetimoglu and Salbas, 2003; Babu et al., 2008,

Chauhan et al., 2008; Choudhary, 2010; Tang et al., 2010; Al-Adili et al, 2011;

Maheshwari et al., 2011; Lirer et al., 2012; Anagnostopoulos et al, 2013; Singh and

Gabra, 2013; Muntohar et al., 2013).

There are some common natural fibers discussed by Hejazi et al. (2012):

Coconut (coir) fiber

It is from matured coconut, or coconut husk, normally 50-350 mm long and

contains mainly cellulose, pectin, tannin, lignin and other water soluble substances.

Due to high lignin content, it will be degraded slowly than other natural fibers.

Because of that, the coconut fiber can be long-lasting, around 4-10 years of service

life. Typically, it has much tensile strength when wet. This fiber is produced mostly in

South Asian countries, like Indonesia, Philippines and India. Reinforcing soil by coir

fibers can increase tensile strength (Chauhan et al., 2008; Anggraini et al., 2015) and

reduce the settlement (Babu and Vasudevan, 2008).

Palm fibers

This fiber, which has low elasticity modulus and tensile strength, is extracted from

decomposed palm trees. Soil reinforced with palm fibers has greater unconfined

compressive strength (UCS) (as shown in Figure 26), CBR and shear strength

parameters (Marandi et al., 2008).

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Figure 4. Relationship between maximum strength and inclusion of palm fibers (Marandi

et al., 2008)

Jute

Jute is one of natural fibers grown in India, China, Pakistan, Bangladesh and

Thailand. Singh and Bagra (2013) conducted study about effect of jute fiber inclusion

on CBR improvements. The contents of Jute fiber were determined by dry weight of

soil, which are 0.25% to 1% (interval of 0.25%). Other variation used is dimension of

the fiber (the length and diameter). The lengths were 30 mm up to 90 mm with the

interval of 30 mm, while two diameters were considered: 1 mm and 2 mm. Tests

results (Figure 27) indicate that the CBR value of soil was increased as the inclusion

of jute fiber (0%-1%). Maximum increase is 200% at 1% jute fiber inclusion with the

diameter of 2 mm and 90 mm length.

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Figure 5. CBR value and jute fiber content relationship (extracted from Singh and Bagra,

2013)

Some synthetic (man-made) fibers are also discussed by Hejazi et al. (2012):

Polypropylene (PP) fibers

Polypropylene fiber is the most common synthetic fiber used as a reinforcement

material for the soil improvement and concrete (Song et al., 2005). This fiber has

properties of hydrophobic, non-corrosive resistance over chemicals, alkalis and

chlorides (Hejazi et al., 2012). Reinforcing soil with polypropylene fiber can increase

UCS and shear strength (Cai et al., 2006; Tang et al., 2007; Ghazavi and Roustaie,

2010; Zaimoglu, 2010; Lirer et al., 2012; Anagnostopoulos et al., 2013).

Polyester

One of polymer category contains the ester functional group in their main chain.

Although many types of this polymer, it is commonly referred to as polyethylene

terephthalate (PET). Maheshwari et al. (2011) studied clayey soil reinforced with

randomly distributed polyester fiber. Amount of polyester fibers (diameter of 12 mm)

mixed with clayey soil (highly compressible) varies from 0 to 1%. The result of this

study show that significant increase in bearing capacity with the inclusion of

polyester fibers up to 0.50%, then it will be decreased with further inclusion of fibers.

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Glass fibers

Glass fibers inclusion in silty sand increases the triaxial peak strength, because

fiber inclusion is more effective for uncemented soil. The friction angle of glass fiber

reinforced sandy soil is also increased from 35° to 46° (Consoli et al., 1998).

Significant improvement in soil strength parameters of glass fiber reinforced-soil

into various soil media happened. This is shown clearly by the increasing in cohesion

values and internal friction angles. The lightweight, ready availability and

non-biodegradable characteristics of this fiber is advantage proof that this fiber can be

used for long term soil improvement (Ahmad et al., 2012; Mujah et al., 2013).

Table 6. Summary of previous researches on natural-fibers to reinforce soil (adopted from

Hejazi et al., 2012)

D: diameter, SG: specific gravity, UTS: ultimate tensile strength, other fiber properties

can be found in Jones (1999).

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Table 7. Summary of previous researches on synthetic-fibers to reinforce soil (adopted

from Hejazi et al. (2012)

D: diameter, SG: specific gravity, UTS: ultimate tensile strength, other fiber properties

can be found in Jones (1999).

Advantages and Disadvantages of Soil Reinforcement Using Fiber

Advantages

1. Cheap, locally and widely available, ecofriendly (Li, C, 2005; Babu and Vasudevan,

2008; Singh and Bagra, 2013)

2. It can enhance the soil strength (Gray and Ohashi, 1983; Gray and Al-Refeai, 1986;

Hejazi et al., 2012), reduce the swelling and shrinkage properties (Hejazi et al.,

2012).

3. It is not significantly affected by weather conditions, compared to cement, lime and

other chemical stabilization techniques (Li, C, 2005).

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4. Reinforcing soil with fiber can inhibit the tensile crack propagation and change the

failure mechanism after initial formation (Marandi, et al., 2008; Hejazi et al., 2012)

5. The lightweight, ready availability characteristics of glass fiber is a proof that glass

fiber can be used for long term soil improvement (Ahmad et al., 2012; Mujah et al.,

2013).

Disadvantages

1. Despite the fact that many researches have been conducted to determine the effects of

using fibers to improve the soil, there are still no scientific procedures or standard,

especially for field projects (Hejazi et al., 2012).

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REFERENCES

http://www.ancient.eu/Mesopotamia/, accessed on November 29th, 2014.

Ahmad, F., Mujah, D., Hazarika, H., and Safari, A. (2012), “Assessing the Potential

Reuse of Recycled Glass Fibre in Problematic Soil Applications”, Journal of

Cleaner Production, Vol. 35, pp. 102-107.

Al-Adili, A., Azzam, R., Spagnoli, G., and Schrader, J. (2012), “Strength of Soil

Reinforced with Fiber Materials (Papyrus)”, Soil Mechanics and Foundation

Engineering, Vol. 48, No. 6, pp. 241-247.

Anagnostopoulos, C.A., Papaliangas, T.T., Konstantinidis, D., and Patronis, C. (2013),

“Shear Strength of Sands Reinforced with Polypropylene Fibers”, Geotechnical

and Geological Engineering, Vol. 31, No. 2, pp. 401-423.

Anggraini, V., Huat, B.B.K., Asadi, A., and Nahazanan, H. (2015), “Effect of Coir Fibers

on the Tensile and Flexural Strength of Soft Marine Clay”, Journal of Natural

Fibers, Vol. 12, No. 2, pp. 185-200.

Babu, G.L.S., and Vasudevan, A.K. (2008), “Strength and Stiffness of Coir

Fiber-Reinforced Tropical Soil”, Journal of Materials in Civil Engineering, Vol.

20, pp. 571-577.

Babu, G.L, Vasudevan, A.K., and Haldar, S. (2008), “Numerical Simulation of

Fiber-Reinforced Sand Behavior”, Geotextiles and Geomembranes, Vol. 26, pp.

181-188.

Cai, Y., Shi, B., Ng, C.W.W., and Tang, C. (2006), “Effect of Polypropylene Fibre and

Lime Admixture on Engineering Properties of Clayey Soil”, Engineering Geology,

Vol. 87, pp. 230-240.

Chauhan, M.S., Mittal, S., and Mohanty, B. (2008), “Performance Evaluation of Silty

Sand and Subgrade Reinforced with Fly Ash and Fibre”, Geotextiles and

Geomembranes, Vol. 26, pp. 429-435.

Choudary, A.K., Jha, J.N. and Gill, K.S. (2010), “Utilization of Plastic Wastes for

Improving the Sub-Grades in Flexible Pavements”, Paving Materials and

Pavement Analysis, pp. 320-326.

Consoli, N.C., Prietto, P.D.M., and Ulbrich, L.A. (1998), “Influence of Fiber and Cement

Addition on Behavior of Sandy Soil”, Journal of Geotechnical and

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Geoenvironmental Engineering, Vol. 124, pp. 1211-1214.

Date, K.R., and Gore, V.N. (1994), “Application of Natural Geotextiles and Related

Products”, Geotextiles and Geomembranes, Vol. 13, No. 6-7, pp. 371-388.

Day, R.W. (2012), Geotechnical Engineer’s Portable Handbook” - Second Edition,

Mc-Graw and Hill Publishing.

Ghazavi, M., and Roustaie, M. (2010), “The Influence of Freeze-Thaw Cycles on the

Unconfined Compressive Strength of Fiber-Reinforced Clay”, Cold Regions

Science and Technology, Vol. 61, No. 2-3, pp. 125-131.

Gray, D., and Ohashi, H. (1983), “Mechanics of Fiber Reinforcement in Sand”, Journal

of Geotechnical Engineering, Vol. 109, No. 3, pp. 335-353.

Gray, D. H., and Al-Refeai. (1986), “Behavior of Fabric- versus Fiber-Reinforced Sand”,

Journal of Geotechnical Engineering, Vol. 112, pp. 804-820.

Hausmann, M. (1990), Engineering Principles of Ground Modification, Mc-Graw and

Hill Publishing.

Hejazi, M.S., Sheikhzadeh, M., Abtahi, S.M., and Zadhoush, A. (2012), “A simple review

of soil reinforcement by using natural and synthetic fibers”, Journal of

Construction and Building Materials, Vol. 30, pp. 100-116.

Jones, R.M. (1999), Mechanics of Composite Materials, Taylor and Francis, United States

of America.

Li, C. (2005), Mechanical Response of Fiber-Reinforced Soil, Ph.D Dissertation, Faculty

of the Graduate School of the University of Texas at Austin.

Lirer, S., Flora, A., and Consoli, N.C. (2012), “Experimental Evidences of the Effect of

Fibres in Reinforcing a Sandy Gravel”, Geotechnical and Geological Engineering,

Vol. 30, pp. 75-83.

Maheshwari, K.V., Desai, A.K., and Solanki, C.H. (2011), “Performance of Fiber

Reinforced Clayey Soil”, The Electronic Journal of Geotechnical Engineering

(EJGE), Vol. 16, pp. 1067-1082.

Marandi, S.M., Bagheripour, M.H., Rahgozar, R., and Zare, H. (2008), “Strength and

Ductility of Randomly Distributed Palm Fibers Reinforced Silty-Sand Soils”,

American Journal of Applied Sciences, Vol. 5, No. 3, pp. 209-220.

Mujah, D., Ahmad, F., Hazarika, H., and Safari, A. (2013), “Evaluation of the Mechanical

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Properties of Recycled Glass Fibers-Derived Three Dimensional Geomaterial for

Ground Improvement”, Journal of Cleaner Production, Vol. 52, pp. 495-503.

Muntohar, A.S. (2012), “Effect of the Roots Densities on the Shear Strength of

Root-Reinforced Soil”, Proceeding of National Seminar VIII of Civil Engineering

Institut Teknologi Sepuluh November (ITS), Surabaya Indonesia.

Muntohar, A.S., Widianti, A., Hartono, E., and Diana, W. (2013). “Engineering Properties

of Silty Soil Stabilized with Lime and Rice Husk Ash and Reinforced with Waste

Plastic Fiber”, Journal of Materials in Civil Engineering, Vol. 25, pp: 1260-1270.

Prabakar, J., and Sridhar, R.S. (2002), “Effect of Random Inclusion of Sisal Fibre on

Strength Behaviour of Soil”, Construction and Building Materials, Vol. 16, pp.

123-131.

Puppala, A.J., and Musenda, C. (2000), “Effects of Fiber Reinforcement on Strength and

Volume Change in Expansive Soils”, Journal of the Transportation Research

Board, Vol. 1736, pp. 134-140.

Singh, H.P., and Bagra, M. (2013), “Improvement in CBR Value of Soil Reinforced with

Jute Fiber”, International Journal of Innovative Research in Science, Engineering

and Technology (IJIRSET), Vol. 2, Issue 8.

Song, P.S., Hwang, S., and Sheu, B.C. (2005), “Strength Properties of Nylon- and

Polypropylene-Fiber-Reinforced Concretes”, Cement and Concrete Research, Vol.

35, No. 8, pp. 1546-1550.

Tang, C., Shi, B., Gao, W., Chen, F., and Cai, Y. (2007), Strength and Mechanical

Behavior of Short Polypropylene Fiber Reinforced and Cement Stabilized Clayey

Soil”, Geotextiles and Geomembranes, Vol. 25, No. 3, pp. 194-202.

Tang, C.S., Shi, B., and Zhao, L.Z. (2010), “Interfacial Shear Strength of Fiber

Reinforced Soil”, Geotextiles and Geomembranes, Vol. 28, pp. 54-62.

Yetimoglu, T., and Salbas, O. (2003), “A Study on Shear Strength of Sands Reinforced

with Randomly Distributed Discrete Fibers”, Geotextiles and Geomembranes, Vol.

21, pp. 103-110.

Zaimoglu, A.S. (2010), “Freezing-Thawing Behavior of Fine-Grained Soils Reinforced

with Polypropylene Fibers”, Cold Regions Science and Technology, Vol. 60, No. 1,

pp. 63-65.