Fiber-Reinforced Soil

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 1 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 2 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. 3 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 4 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 5 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). 6 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. 7 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. 8  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). 9 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). 10 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). 11 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. 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