Stabilization of Soil using Polypropylene Fiber

Abstract

The main objective of this case study is to explore the use of waste raw materials in different types of soil found in our surroundings and to evaluate the effects of waste raw material polypropylene fiber. There are several types of soil found in our surroundings such as hard soil, clayey soil, sandy soil, loose soil and so on. There is greater strength in the hard soil but in the loose soil there need to increase the strength of the unsaturated soil. This case study is done on the loose soil to increase in the shear strength of the unsaturated soil by carrying types of lab experiments tests soil sample. And the process through out the soil stabilization helps to acquire the required properties in the soil needed in the construction work. Structures that are constructed on the expansive soil may have occurred several damages due to its hill swell-shrinkage behavior. So, these types of soil need to be stabilized in order to increase the shear strength of the soil, durability of the soil as well to prevent from the erosion. Various case studies have been carried out for these types of soil to increase the soil properties. In this case study raw fiber known as polypropylene fiber have been used to increase the soil properties and interlocking of the soil and has become the one of the major practices used in construction work.

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This project purposes to conduct the case study to check the improvements in properties of sandy soil by adding raw material polypropylene fiber. Several lab tests have been carried out using varying percentage of reinforcement (0.05%,0.10%,0.15%,0.20% and 0.25%). The soil parameters such as specific gravity, plastic limit, liquid limit, compaction test and direct shear test have been studied. The results are obtained, and implications are strained towards the usability and effectiveness of the fiber reinforcement in the replacement of the deep foundation.

Introduction

The structures which are constructed on land transfer their load to the foundation. So, it is very essential to construct the strong and stable foundation to support the structure. To make the foundation strong, the soil plays a critical role. There are different types of soil and vary with the properties of the soil. And if the soil is not capable to carry the load of the entire structure, we must alter the properties of the soil, so that it can bear the load and transfer on it. As we can find different types of soil in our areas and all the soil have their own properties.

In the ancient time after adding water to the soil and when necessary the soil was compacted by elephants’ foot by walking on the surface of soil. It was also seen that soils are usually compacted by tampers of shapes like of an elephant or a cow. In the initial phase of any construction work it is very much essential to check the strength of the soil weather it can bear the overall load of the structure or not. In the ancient time peoples from Chinese, romans and Incas, they used to apply various techniques to improve the soil strength. And some of the methods adopted by them is still effective and we can find some of the existence of the building and roads made by them.

In Nepal, soil stabilization was normally started in early 1970s but due to the use of absolute methods and the absence of proper technique, soil stabilization lost kindness. But in the modern time due to the increase in demand of infrastructure, raw materials and fuel, soil stabilization is playing a vital role in construction of large structures. Several researches were adopted by several researchers and due to the available of materials and equipment, it has become a popular and the best thing about it is cost effective method for soil improvement.

In any construction of buildings and other civil engineering structures on loose or soft soil, there is a high risk because these types of soil are susceptible to differential settlements and its due to its poor shear strength and high compressibility. Improvement of certain desired properties like bearing capacity, shear strength and permeability characteristics of soil can be undertaken by a variety of ground improvement techniques such as the use of prefabricated vertical drains (e.g. Abuel-Naga et al., 2006; Chu et al., 2006) or soil stabilization.

In this research paper, we will investigate the use of waste materials like polypropylene fiber and to evaluate the effects of this fiber on shear strength of unsaturated soil by doing the tests like direct share test and unconfined compression test

Inn this case study, soil stabilization is done by using randomly distributed raw material polypropylene fiber. As it is a small particle have different properties and is insoluble in water as well as it is acid and alkali resistance, therefore it has a capacity to increase the strength the capacity of soil. There is a variation of increase in the strength due to the gradually increase of certain percentage of polypropylene fibers in the soil. The improvement in the shear strength parameters has been stressed upon and comparative studies have been carried out using different percentage of polypropylene fibers.

Figure 1. Image of PP (Polypropylene) fiber and its properties

With the increase in the polypropylene fiber, there will be gradually improvement in the strength of the soil, and it helps in increasing the bearing the capacity of the soil. Moreover, it is termed as most economical method in terms of cost and as well as the energy by increasing the bearing capacity of their soil relatively than going for deep foundation. And in some cases, soil stabilization is also used to prevent from soil erosion as well as from the formation of dust. And these are importantly useful in mostly dry and arid weather.

Literature Review

Many case studies have been done for the analysis of stabilization of different types of soil with loose foundation by using the waste materials such as polypropylene fiber.

(Chaosheng Tang, Bin Shi, Wei Gao, Fengjun Chen, Yi Cai, 2006) stated that about 500 years ago, the concept of soil stabilization was dated and treated earth roads were used in ancient Mesopotamia and Egypt, and that the Greek and Roman used soil-lime mixtures.

Jesna Varghese, Remya.U. R et al, 2016) indicated that strengthened soil with fiber has following properties, the link between optimum wetness content and most dry density of soil considerably littered with the addition of plastic fiber. throughout the study, MDD will increase with decreasing OMC. From unconfined compressive check, it absolutely was determined that the unconfined compressive strength worth of untreated soil was found to be 15.1 KN/m² and therefore the strength worth accrued with increase additionally of plastic fiber up to 0.05% then decreases. there’s a rise of strength of concerning 454.37%, which will result to extend in surface shear strength at 0.05 %. For higher quantity of plastic fiber, it shows reverse trend. The strength is accrued in low proportion of PPF addition, it ensures additional economical in construction. So finally, it absolutely was ended that the plastic fiber will doubtless stabilize the clayey soil. Whereas (Mona Malekzadeh and HuriyeBilsel ,2012), according that optimum water content isn’t influenced by plastic fiber inclusion, whereas most dry density has been reduced. She attributed to the reduction of average unit weight of solids within the soil-fiber mixture. finding out the influence of plastic fiber on swell characteristics, the she concludes that one-dimensional swell decreases significantly with Chronicles fiber addition.

(Ranjan et al,1996) have studied on various types of soils like sand, medium sand, fine sand, silty sand and silt reinforced with polypropylene monofilament coir and bhabar the result of triaxial test showed greater ductility, no loss of post peak strength and increase in stiffness. Due to tensile strength in fibers confining pressure is greater than critical confining pressure.

(Charan,1996) studied on different types of soil such as silt, sand to coarse sand reinforced with polypropylene fiber and triaxial and CBR test were conducted in the laboratory and the test results shows the confining pressure is less that critical confining pressure. Also, the CBR value is improved by 2 times at the fiber of increase in 1.5%.

(Santoni et al, 2001) studied on six types of non-plastic cohesion less soils reinforced with monofilament polypropylene fiber the unconfined compressive strength of reinforced soil on the moisture content 2.6% and saturation 14% and they found optimum fiber content is 0.8% and fiber content is less than 0.6% caused strain softening more than 0.85% causes strain hardening.

(Chandra et la,2008) have studied on three types of soil reinforced with polypropylene fiber of 0.3mm diameter the static triaxial test of unreinforced and reinforced soil shows that uniaxial compressive strength is 3.824, 4.836 and 9.712 Mpa respectively

(Malekzadeh and Bilsel in, 2012) studied the effect of polypropylene fiber on mechanical behavior of expansive soils. It was concluded that mitigation of expansive soils using polypropylene fiber might be an effective method in enhancing the physical and mechanical properties of sub-soils on which roads and light buildings are constructed.

(Ayyappan et al. in, 2010) studied the influence of polypropylene fibers on engineering behavior of soil−fly Ash mixtures for road construction. The purpose of this investigation was to identify and quantify the influence of fiber variables (content and length) on performance of fiber reinforced soil- fly ash specimens. It was observed that inclusion of randomly distributed fibers significantly improved the unconfined compressive strength of soil fly ash mixtures, increase in fiber length reduced the contribution to peak compressive strength while increased the contribution to strain energy absorption capacity in all soil fly ash mixtures, optimum dosage rate of fibers was identified as 1.00 % by dry weight of soil- fly ash, for all soil fly ash mixtures and maximum performance was achieved with fiber length of 12 mm as reinforcement of soil fly ash specimens

(Maheshwari, k.v. desai, a.k. solanki, c.h.) investigated the influence of randomly distributed fibers on highly compressible clayey soil, series of laboratory model footing tests were conducted. The dosages of polyester fibers having 12 mm in size were taken as 0.25%, 0.50% and 1.00%. the results of load settlement curve of different sizes of square footing on unreinforced soil and soil reinforced with various amount and depths of fiber reinforced soil were recorded. The bearing capacity is also calculated in term of bearing capacity ratio. The results indicate that reinforcement of highly compressible clayey soil with randomly distributed fibers caused an increase in the ultimate bearing capacity and decrease in settlement at the ultimate load

polypropylene fibers are used in soil mass to resist tensile failure, cracking, shrinkage, biological decay, acid and alkali attack (Maher and Gray, 1990; Kumar and Singh, 2008) observed that an admix of polypropylene fiber into soil have significantly improved its engineering properties (e.g. tensile / compressive / shear strengths, fracture toughness, durability) applied in retrofitting and repairing the covering of structures, carpentries stabilizing, landfill, slope protection, road subgrade etc.

(Puppala and Musenda, 2000; Yetimoglu and Salbas, 2003; Yi et al., 2006; Consoli et al., 2009) at the same time soils reinforced with discrete polypropylene fiber have shown considerable decrease in the stiffness of the soil (hence reduced crack) and enhanced the self-seaming ability of soils

Moreover, soil reinforced with polypropylene fiber exhibits greater toughness and ductility, increases formability and bending strength and lessen loss of post peak strength, as compared to soil alone (Gray and Ohashi, 1983; Attom and Tamimi, 2010; Freilich et al., 2010; Malekzadeh and Bilsel, 2012).

Methodology

From the several journal papers, Case study has been done for this research project, but there must be comparison of the results adopted from different journals. Different lab test has been applied and results has been given in the papers. Some of the experiment conducted for these projects are mentioned below. The experimental work consists of the following steps:

• Specific gravity of soil
• Determination of soil index properties
  • Liquid limit
  • Plastic limit
• Determination of the maximum dry density (MDD)
• Optimum Moisture Content of the soil by Proctor compaction test
• Direct Shear test

As 5 to 6 different lab methods must be done in this project to get a good result on strength of soil but in most of the journal papers only 2 to 3 methods have been carried out such as specific gravity and compression test. But for the good results of this case study it must have been conducted at least compaction test and shear test. Because these are the best experimental test for the soil about the increase of strength and bearing capacity of the soil. And most of the experiments of previous scholars did not cover the necessary aspects and have difficulty in comparison.

Similarly, I have difficulties on applying some percentage of polypropylene fibers in soil. In most of the articles I have been trough they have used 0.1% to 0.9% of polypropylene fibers and mixed with the soil. And the results of different articles are different. So, it has become a bit difficult in doing a case study on this research project.

Results

• Specific Gravity

Table 1. Specific Gravity

• Index properties

Liquid Limit

Table 2. Liquid Limit

Fig 2. Liquid Limit

Plastic limit

Table 3. Plastic Limit

Plasticity Index

Ip = WL – WP = 28.90 – 22.58 = 6.32

• Particle Size Distribution

Mass of the soil taken for analysis=1000 gm

Table 4. Particle Size Distribution

Fig 3. Particle size distribution

D₆₀₌1.1

D₃₀₌0.8

D₁₀=0.43

Co-efficient of uniformity, C_u=D₆₀/D₁₀₌1.1/0.43=2.56

Co-efficient of curvature, C_c=D₃₀²/(D₁₀*D₆₀)=0.8²/(0.43*1.1)=1.35

• Standard Proctor Test

         Internal diameter of mould (d) cm = 10 

         Height of mould (h) cm = 13

         Volume of mould (V) = (π/4) d²h cc =1000

Tabular Column

Table 5. Standard Proctor Test

Fig 4. Standard Proctor test curve

From the figure on the left side, it is evident that,

Optimum Moisture Content (OMC) = 12.6%

Maximum Dry Density (MDD) = 1.91 g/cc

• Direct Shear Test

i) Unreinforced soil

Table 6. Direct shear test with unconfined soil

Fig 5. Direct shear test with unconfined soil

Computing from graph,

Cohesion (C) = 0.325 kg/cm²

Angle of internal friction (φ) = 30.96

ii) Reinforcement = 0.05%

Table 7. Direct shear test with 0.05% reinforcement

Fig 6. Direct shear test with 0.05% reinforcement

Computing from graph,

Cohesion (C) = 0.35kg/cm²

Angle of internal friction (φ) = 41.987^◦

iii)Reinforcement=0.10%

Table 8. Direct shear test with 0.10% reinforcement

Fig 7. Direct shear test with 0.10% reinforcement

Computing from graph,

Cohesion (C) = 0.37 kg/cm2

Angle of internal friction (φ) = 42.6^◦

iv) Reinforcement=0.15%

Table 9. Direct shear test with 0.15% reinforcement

Fig 8. Direct shear test with 0.15% reinforcement

Computing from graph,

Cohesion (C) = 0.3747 kg/cm²

Angle of internal friction (φ) = 41.61◦

v)Reinforcement=0.20%

Table 10. Direct shear test with 0.20% reinforcement

Fig 9. Direct shear test with 0.20% reinforcement

Computing from graph,

Cohesion (C) = 0.3800 kg/cm²

Angle of internal friction (φ) = 42.62◦

vi)Reinforcement=0.25%

Table 11. Direct shear test with 0.25% reinforcement

Fig 10. Direct shear test with 0.25% reinforcement

Computing from graph,

Cohesion (C) = 0.3887 kg/cm2

Angle of internal friction (φ) = 42.63◦

Comparison of shear parameters (cohesion and reinforcement) between soil

Fig 11. Comparison of different % of Reinforcement

Discussions and Performance

From the above result, we can find the different values for various methods that was studied during the project. After adding few percentages of polypropylene fiber in the loose soil and mixed thoroughly. Keeping it in normal atmosphere, after some time it shows the change in behavior of soil properties and starts to increase the compressive strength of the soil. Raw material polypropylene fiber used in this research project has high resistance and doesn’t affect during the acidity. Loose soil has low strength than the hard soil. In this case study we have increased the certain percentage of polypropylene and increase the shear strength of the soil. So, we can see that using the polypropylene fiber there is increase in strength of the loose soil and it will help us to make the foundation of any civil structures stronger.

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During the shear test conducted for this project from one of the researchers found that Cohesion value increases from 0.325 kg/cm² to 0.3887 kg/cm² and the graph provided shows that there is a gradual decline in the slope. Clearly, we can see that angle of friction increases from 47.72 to 48.483 degrees. So, the increment in shear strength of the soil due to reinforcement is marginal.

It is necessary to recognize the shear strength of the loose soil thus by increasing the percentage of polypropylene fibers. By addition of fiber in the soil, it compacts the soil and make the soil moist and more compacted. So, it is more important to check the stability factors of the soil and determination of the shear strength of the soil and increase the effectiveness of the soil in the structures. There are mainly two factors that influences the application of soil sample.

• Soil Performance

Soil performance is most important aspect of stabilization of soil sample. Without good soil performance, foundation of any civil structures cannot have the standard value and cannot be determined as a good aspect of the buildings or any structures. Above case studies shows that in increment of polypropylene fiber that are used to increase the bearing capacity of soil are very much better that use of other raw materials. And the performance of the soil by using fiber gives the better strength of the soil.

• Economy

Soil stabilization process is one of the most economical factors that is used in modern era. It can be done in within certain time and it is also a cost approach method. In most of the design in construction of structures, it is cost effective process and most economic. This process of soil stabilization saves a lot of time and money.

Conclusions

The shear strength of soil with the reinforcements were determined by direct shear test ion the laboratory. From the graph it was found that the increase in the value of cohesion for fiber reinforcement of 0.05%, 0.15%, and 0.255 are 34.7%, 6.09% and 7.07% respectively. Figure illustrates that the increase in the internal angle of friction (Ø) was found to be 0.8%, 0.31% and 0. 47% respectively The results from direct shear test indicated that the values of cohesion of soil sample without  fiber reinforcement was 0.325kg/cm² and with reinforcement of 0.05%, 0.1%,0.15%, 0.2% and 0.25% were 0.35kg/cm², 0.37kg/cm², 0.3747kg/cm², 0.38kg/cm² and 0.3887kg/cm² respectively. The results from direct shear test indicated that the values of angle of friction soil sample without fiber reinforcement was 30.96 and with reinforcement of 0.05%, 0.1%,0.15% 0.2% and 0.25% were 41.987^o, 42.6^o, 42.61^o, 42.62^o, 42.63^o, respectively. All the results mentioned above gives the desired strength that need for stabilization of soil in loose soil.  Therefore, the use of polypropylene fiber as reinforcement for soil is recommended for the use of for case studies.

Due to the increment of the polypropylene fiber in different types of soil, it plays a important role in increasing the shear strength of the soil. Overall its can be said that fiber reinforced soil using polypropylene fiber can be considered for the improvement in the deep foundation and the soil properties specially in the engineering projects on loose soils or weak soils and it can be used as a substitute to deep foundation by reducing the cost as well as energy.

References

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