SHEAR STRENGTH IMPROVEMENT OF SANDY SOIL USING COCONUT FIBRE

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 3, May June 2016, pp , Article ID: IJCIET_07_03_029 Available online at Journal Impact Factor (2016): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication SHEAR STRENGTH IMPROVEMENT OF SANDY SOIL USING COCONUT FIBRE Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar, Bikramjit Deb U.G. Student, Department of Civil Engineering, Assam Engineering College, Guwahati, Assam, India ABSTRACT Coconut fibre or more popularly known as coir fibre is obtained from the outer shell of coconut. It is a suitable example of a waste material that can be utilised as a reinforcing material for soil. The fact that it is easily available makes it all the more suitable for this purpose. The main aim of this research work is to investigate the variation in shear strength parameters of sandy soils by the use of brown coconut fibre as reinforcing material, at a fixed length of 15 mm, using the direct shear test. It also involves the determination of optimum fibre content required for the corresponding maximum value of shear strength paramenter. The results showed that almost 21.5% enhancement in shear strength parameter can be obtained on use of coconut fibre as reinforcement material. Keywords: Sandy Soil, Shear Strength Parameter, Internal Friction, Coconut Fibre, Direct Shear. Cite this Article: Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb, Shear Strength Improvement of Sandy Soil Using Coconut Fibre. International Journal of Civil Engineering and Technology, 7(3), 2016, pp INTRODUCTION Soil reinforcement is a wide field of research in the current times. This is because there are several cases where the soil at shallow depth is not of good quality, and deep foundations may be expensive. There are several cases where the soil is not of good quality even at greater depth; and replacement of the soil may not be feasible. Thirdly, there are situations of underground constructions such as tunnels, or underground air base and bunkers for defence purposes; in such situations the soil has to be able to take the overlaying pressure of unsupported walls. In all of these, and several other situations alike, it is necessary to reinforce the soil with suitable materials, so as to enable it to have higher efficiency of purpose. The main concept of reinforcement is the development of friction between the soil and the reinforcement leading to the transfer of the built up loads of the soil to the reinforcement editor@iaeme.com

2 Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb As is naturally observed, soil reinforcement is done to a certain extent by the roots of plants and trees which hold the soil together and prevent soil erosion. This is one of the main reasons why a lot of emphasis is now being focussed on afforestation and reduction of deforestation in many parts of the world. Along with plants, we also have several natural and man made materials that can be utilised for the purpose of reinforcing the soil. Artificial materials include the likes of geotextiles and geonets. A few examples of natural materials are hair fibres, sisal fibres and coconut fibres. These materials can be used for reinforcing the soil. Jute bags, for example, are very commonly used to reinforce the river embankments and prevent erosion and reduce damage during floods. The use of coconut fibres can prove to be a highly efficient means of soil reinforcement. Coconut fibres are of two types-brown fibres and white fibres. Brown fibres are obtained from mature coconuts while the white fibres are obtained from immature coconuts. This paper focuses on the use of brown fibres because these are thick, coarse, strong, durable and have high abrasion resistance. Also, the use of coconut fibres can be particularly advantageous to India because of the widespread cultivation of coconut in the country. As of 2013 records, India s production of coconut stands at 11.9 million tonnes, which is the second in the world, behind only Indonesia and Phillipines. Of the total cultivation of coconut, the four states of South India account for almost 90% of the production, headed by Coimbatore and Tirupur regions of Tamil Nadu. The states of Goa, Maharashtra, Odisha, West Bengal, Tripura and Assam are the producers of the remaining 10%. Thus, we observe that India has a rich cultivation of coconut, and if the fibres obtained from such high degree of cultivation can be put to use for reinforcing of soil, it shall prove to be a highly economic measure of strengthening of soil and with high degree of efficiency. Following tables illustrate the general properties of coconut fibres: Table 1 Chemical Composition of Coconut Fibre Component Percentage Lignin Cellulose Hemi-cellulose 0.25 Pection and related compound 3.00 Ash 2.22 Table 2 General Physical Properties of Coconut Fibres Property Specifications Length 6-8 inches Density 1.4 g/cc Tenacity 10.0 Breaking elongation 30% Diameter.1mm-.5mm Modulus of Rigidity dyne/cm² Swelling in water 30% editor@iaeme.com

3 Shear Strength Improvement of Sandy Soil Using Coconut Fibre 2. MANUFACTURING OF COCONUT FIBRES The process of manufacturing of coconut fibres involves three major steps-husking, retting and extraction of fibres. Husking involves the separation of the husk from the harvested fruits. To obtain good quality coir, the fruits are harvested when still green. Figure 1 Husking of Coconut Fibres It is then followed by retting, which is essentially a curing process. The husks are kept in an environment that encourages microbial action, which leads to decomposition of the pulp of the husk that allows it to be separated into coir fibres and coir pith. For fresh water retting, ripe husks are buried in pits along riverbanks, immersed in water filled concrete tanks or suspended by nets in a river, for a soaking period of about six months. For salt water retting, green husks are soaked in salinated fresh water, for a period of eight to ten months. Figure 2 Retting of Coconut Fibres Retting is followed by the extraction of fibres. The husks are taken out of water and washed. The outer skin is peeled off, placed on wooden blocks and beaten for separating the fibres from the pith. After this separation, fibres are cleaned and dried, with occasional beating and tossing to remove any impurities remaining in contact with the fibres. Figure 3 Extraction of Coconut Fibres editor@iaeme.com

4 Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb 3. THE MATERIALS 3.1. SOIL SAMPLE The sample used for this research work is sand. Sieve analysis, as per the provisions of IS provided that the sample belongs to Zone III, having a Fineness Modulus of COCONUT FIBRES For the purpose of this work, the coconut fibres used were taken in finite lengths of 15 mm. The fibres were extracted from the outer shell of the coconut, soaked in water and then dried under the sun. As the required quantity of fibres was less, hence shorter time period of soaking and drying was utilised, as compared to that of large scale manufacturing process. Following are the properties of the coconut fibres that have been used for this research work: Property Length Density Diameter Major proteins present Modulus of Rigidity Table 3 Properties of Coconut Fibres used Specifications 15 mm 1.4g/cc 0.1mm-1.5mm Lignin, Cellulose dyne/cm² 4. METHODOLOGY Direct shear tests were performed on the soil sample. The initial results shown by the specimen without any reinforcing materials, at normal stresses of 0.5, 1.0 and 1.5 kg/cm² was first obtained. Next, direct shear test was performed using coconut fibre as reinforcement at 1.0%, 2.0% and 3.0% by weight of soil. The fibres were randomly mixed with the soil specimen. Once all the required direct shear tests had been performed, the stress-strain curves were plot for every individual situation and at every value of normal stress, from which the maximum shear stress was determined in each case. This was followed by graphs of maximum shear stress and normal stress to determine the value of angle of internal friction in each case. The variation of angle of internal friction with fibre content was studied and the optimum fibre content required was evaluated. 5. RESULTS OBTAINED The stress-strain relationship was obtained in each case, of soil without reinforcement and with reinforcement at various percentages, from which the values of maximum shear stress were obtained. Then, from the relationship of maximum shear stress and normal stress, the angle of internal friction was determined in each case. A final relationship between the angle of internal friction and fibre content was deduced, from which the maximum value of angle of internal friction and the corresponding optimum fibre content was obtained editor@iaeme.com

5 Shear Strength Improvement of Sandy Soil Using Coconut Fibre 5.1. Unreinforced sand Figure 4 Stress-strain relationship for unreinforced sand Figure 4 shows the stress-strain relationship for unreinforced soil. The maximum value of shear stress are 0.32 kg/cm², 0.63 kg/cm² and 0.95 kg/cm² at normal stresses of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively. Figure 5 Relation between Maximum shear stress and Normal Stress for unreinforced soil Figure 5 shows the relationship between the maximum shear stress and normal stress for unreinforced soil. The angle of internal friction obtained when sand is not reinforced is 32.21ᵒ Reinforced sand Sand reinforced at 1% by weight Figure 6 Stress-strain relationship for sand reinforced at 1% by weight Figure 6 shows the stress-strain relationship when sand is reinforced at 1% by weight. The maximum value of shear stress are 0.30 kg/cm², 0.72 kg/cm² and 1.12 kg/cm² at normal stresses of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively editor@iaeme.com

6 Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb Figure 7 Relation between Maximum shear stress and Normal Stress for sand reinforced at 1% by weight. Figure 7 shows the relationship between maximum shear stress and normal stress for sand reinforced at 1% by weight. The angle of internal friction for sand reinforced at 1% by weight is 36.05ᵒ Sand reinforced at 2% by weight Figure 8 Stress-strain relationship for sand reinforced at 2% by weight Figure 8 shows the stress-strain relationship for sand reinforced at 2% by weight. The maximum value of shear stress are 0.39 kg/cm², 0.75 kg/cm² and 1.25 kg/cm² at normal stresses of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively. Figure 9 Relation between Maximum shear stress and Normal stress for sand reinforced at 2% by weight. Figure 9 shows the relationship between the maximum shear stress and normal stress when sand is reinforced at 2% by weight. The angle of internal friction for sand reinforced at 1% by weight is 39.14ᵒ editor@iaeme.com

7 Shear Strength Improvement of Sandy Soil Using Coconut Fibre Sand reinforced at 3% by weight Figure 10 Stress-strain relationship for sand reinforced at 3% by weight. Figure 10 shows the stress-strain relationship for sand reinforced at 3% by weight, The maximum value of shear stress are 0.37 kg/cm², 0.75 kg/cm² and 1.18 kg/cm² at normal stresses of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively. Figure 11 Relation between Maximum shear stress and Normal stress for sand reinforced at 3% by weight. Figure 11 shows the relationship between the maximum shear stress and normal stress when sand is reinforced at 3% by weight. The angle of internal friction for sand reinforced at 1% by weight is 37.66ᵒ Optimum Fibre Content Figure 12 Variation of angle of internal friction with percentage of fibre content

8 Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb From the relationship between the angle of internal friction and percentage by weight of reinforcemnt utilised, it has been observed that the maximum value of internal friction is obtained as 39.20ᵒ. This maximum value is obtained corresponding to an optimum reinforcement content of 2.1% by weight. 6. INTERPRETATION OF RESULTS It has been observed that the application of coconut fibres on sand results in an increase in the shear strength parameter, that is the angle of internal friction. The main cause of this increase is reasoned out to the fact that in absence of reinforcement, soil shows brittle failure. However, when coconut fibres are utilised, ductility is provided to the soil. As has been stated, the main concept behind this is the development of friction between the soil and the reinforcement. Moreover, we observe that on application of fibres, the soil gradually shifts to the condition of general shear failure, which ensures that the analysis of the soil capacity is feasible through analytical calculations. It has been observed that on application of hair fibres, an increase in the shear strength parameter of soil is obtained. The shear strength parameter has been observed to rise upto a certain limit of percentage of reinforcement utilised, and then it undergoes a reduction with further increase of fibre content. The optimum value of coconut fibre content, for obtaining maximum value of angle of internal friction is at 2,1%, at which the angle of internal friction is 39.20ᵒ. Hence, it is observed that at the instant of optimum fibre content or maximum angle of internal friction, the soil undergoes general shear failure, while in the absence of coconut fibres, the soil is observed to undergo failure which is the transition between general shear failure and local shear failure. This thus, simplifies the process of theoretical analysis of bearing capacity of the sand, as governed by IS CONCLUSION The effect of reinforcement of sandy soil by the use of coconut fibres has been analysed in this paper. The results show an increase in the value of angle of internal friction, on utilisation of reinforcement. The maximum increase in the parameter is 21.70%, corresponding to an optimum fibre content of 2.1%. Beyond the optimum content, a reduction in the angle of internal friction is obtained. Thus, it can be concluded that coconut fibre can be utilised for enhancing the shear strength parameter of sandy soils, and its easy availability due to widespread cultivation of coconut in the country can prove to be an efficient and economic measure of reinforcement of sand. Further research can be conducted on efficient methods of random placing of the fibres in the soil for yielding better results. Research can also be conducted on further enhancement of the cultivation of coconut, and the manufacture of coconut fibre. REFERENCES [1] Manjunath K.R, Venugopal G and Rudresh A.N, 2013, Effect of Random Inclusion of Sisal Fibre on Strength Behavior of Black Cotton Soil, International Journal of Engineering Research & Technology 2(7) July [2] Wajid Ali Butt, Karan Gupta, Hamidullah Naik, Showkat Maqbool Bhat, 2014 Soil Sub grade Improvement Using Human Hair Fiber, International Journal of Scientific & Engineering Research, 5(12), ISSN , December [3] Rohin Kaushik, An Innovative Technique of Improving the C.B.R Value of Soil Using Hair fibre Global Journal of Engineering Science and Researches, ISSN , June editor@iaeme.com

9 Shear Strength Improvement of Sandy Soil Using Coconut Fibre [4] D.P. Ray, L.K. Nayak, L. Ammayappan, V B Shambhu, D Nag, 2013, Energy Conservation Drives for Efficient Extraction and Utilization of Banana Fibre International Journal of Emerging Technology and Advanced Engineering, 3(8), ISSN , ISO 9001:2008 Certified Journal. [5] Bestun J. Nareeman and Mohammed Y. Fattah, 2012, Effect of Soil Reinforcement on Shear Strength and Settlement of Cohesive- Frictional Soil, Int. J. of Geomate, OMATE, 3(1) (Sl No 5), pp , ISSN: , September [6] Deepjyoti Das, Raja Sarkar, Bikramjit Deb, Dhrubajyoti Kaundinya, 2016, Shear Strength Enhancement of Sandy Soil Using Hair Fibre, International Journal of Innnovative Research in Science, Engineering and Technology, 5(5) ISSN , May [7] An Overview of Coconut or Coir Fibre. [8] Coconut Fibre. [9] IS Grading of fine aggregates [10] M. Said and T. M. Elrakib, Enhancement of Shear Strength and Ductility For Reinforced Concrete Wide Beams Due To Web Reinforcement. International Journal of Civil Engineering and Technology, 4(5), 2013, pp [11] Nagendra Prasad.K, Sivaramulu Naidu.D, Harsha Vardhan Reddy. M and Chandra.B, Framework For Assessment of Shear Strength Parameters of Residual Tropical Soils. International Journal of Civil Engineering and Technology, 4(2), 2013, pp [12] IS 2720-(Part XIII) Direct Shear Test editor@iaeme.com