Composite soils have been widely used in civil engineering applications, especially in slopes, embankment dam and landfills. This paper aims to investigate effect of fiber inclusion on CBR values of composite soil (i.e. sand composite). A series of laboratory CBR tests carried out to evaluate fiber effect on CBR values behavior of composite sand. Clayey sand was selected as soil part of the composite and natural fiber was used as reinforcement. The fiber parameters differed from one test to another, as fiber length were changed from 20 mm to 50 mm and fiber content were varied from 1% and 3%. For each test, CBR values were calculated and compared. The results proved that inclusion of fiber affected CBR values of sand composite so that increasing in fiber content and length caused increasing in CBR

Chegenizadeh, Amin

Nikraz, Hamid

English

Composite soils have been widely used in civil engineering applications, especially in slopes, embankment dam and landfills. This paper aims to investigate effect of fiber inclusion on shear stress of composite soil (i.e. sand composite). A series of laboratory direct shear tests carried out to evaluate fiber effect on strength behavior of composite sand. Clayey sand was selected as soil part of the composite and natural fiber was used as reinforcement. The fiber parameters differed from one test to another, as fiber length were changed from 10 mm to 35 mm and fiber content were varied from 0.6% and 3%. Normal stress kept constant at 100 kpa. For each test, stress_ displacement graph derived and the results were compared. The results proved that inclusion of fiber affected strength behaviour of sand composite so that increasing in fiber content and length caused increasing in shear stress

espace@Curtin

   Abstract—Composite soils have been widely used in civil engineering applications, especially in slopes, embankment dam and landfills. This paper aims to investigate effect of fiber inclusion on shear stress of composite soil (i.e. sand composite). A series of laboratory direct shear tests carried out to evaluate fiber effect on strength behavior of composite sand. Clayey sand was selected as soil part of the composite and natural fiber was used as reinforcement. The fiber parameters differed from one test to another, as fiber length were changed from 10 mm to 35 mm and fiber content were varied from 0.6% and 3%.Normal stress kept constant at 100 kpa. For each test, stress_ displacement graph derived and the results were compared. The results proved that inclusion of fiber affected strength behaviour of sand composite so that increasing in fiber content and length caused increasing in shear stress.   Keywords—Direct shear, Reinforced, Fiber, Sand  I. INTRODUCTION The direct shear test is one of the oldest strength tests for soils. In this study, a direct shear device will be used to determine the shear strength of a fiber reinforced soil. Applications of soil strengthening or stabilization range from the mitigation of complex slope hazards to enhancing the subgrade stability. Together with the many applications for improving soil, there are several widely varied methods. The mixing of randomly oriented fibers to a soil sample may be considered same as other admixtures used to stabilize soil. Material used to make fibers for reinforcement may be obtained from paper, metal, nylon, polyester and other materials having widely varied physical properties. There have been numerous past papers published on the topic of fiber strengthening of soils. Examples include Lee et al., 1973, Hoare,1979, Andersland and Khattac,1979, Freitag,1986, Gray and Ohashi, 1983, Gray and Rafeai, 1986, Maher and Gray 1990, Maher and Ho, 1994, Michalowski and Zhao 2002, Ranjan et al. 1996, Kaniraj and Havanagi 2001, Consoli et al. 2009. All of the papers listed above have generally shown that; strength of the soil was improved by fiber reinforcement. The investigation on clayey sand is very limited. The purpose of this survey is to evaluate clayey sand behaviour induced by fiber inclusion.  1F. A. Author is with the Curtin University of Technology, Perth, Australia Tel: +61-413165961;Email: amin.chegenizadeh@postgrad.curtin.edu.au 2S. B. Author, Head of the Department of Civil Engineering, Curtin University of Technology, Perth, Australia; Tel: +61 8 9266 7573; Fax: +61 8 9266 2681; Email: H.Nikraz@curtin.edu.au    II. MATERIAL   Composite soils consist of two parts. The first part is soil part which can be dealt as normal soil. The second part is reinforcement part which can be made up of any material which helps soil to have better performance.   A. Soil Type  The soil type in this study was Western Australian sand. The properties of clay are presented in table 1. The sand distribution curve is presented in Fig 1. The soil part was reconstituted in lab by using sand with 20% of kaolin clay.    Table1. Clay properties                         Fig. 1   Sand Particle Distribution Shear Test on Reinforced Clayey Sand Amin Chegenizadeh1, Prof. Hamid Nikraz 2 No. Type  1 Soil type Clay 2 Liquid Limit 49 3 Plastic Limit 23 4 Pl. Index 26   B. Fiber Type The natural fiber has been used for this investigation. Figure2 shows the used fiber. The used fiber has good potential to absorb energy and good adhesion with soil particle.                   Fig. 2   Natural fiber  III. TEST PROGRAM  A series of direct shear tests have been conducted on reinforced sand composite.  A. Direct Shear Test  The test is carried out on either undisturbed samples or remoulded samples. To facilitate the remoulding purpose, a soil sample may be compacted at optimum moisture content in a compaction mould. Then specimen for the direct shear test could be obtained using the correct cutter provided. Alternatively, sand sample can be placed in a dry state at a required density, in the assembled shear box. A normal load is applied to the specimen and the specimen is sheared across the pre-determined horizontal plane between the two halves of the shear box. Measurements of shear load, shear displacement and normal displacement are recorded. From the results, the shear strength parameters can be determined. B. Main Equipments • Direct Shear Test Machine •  Specimen preparation equipment • fiber •  Balance  Figure 3 shows automated direct shear which was used to run shear test. The device is fully automated so the results easily transferred without any user interference.                    Fig. 3   Direct Shear Test Machine  IV. SAMPLE PREPARATION   The samples were prepared by mixing clay and three percentage of fiber (i.e. 0.6%, 0.8%, 1.5%, 3%) The soil was first dried under laboratory air-dried conditions then ground and passed through a 2 mm sieve. The dry powder was carefully wetted with a spray gun to the standard optimum moisture content. The moist soil was then put in sealed plastic bags in a humidity room for about two days before use. The moist residual soil was then compacted in a 300 mm x 300 mm shear box mould by machine compaction to the appropriate height and unit weight at the optimum moisture content.  V. TEST METHODOLOGY AND PROCEDURE   1.  The shear box was assembled and the specimen was put into the shear box. Special care was made that the alignment screws working well. 2. The shear box was placed into the shearing device.  3.  Normal load was applied to the specimen using the load transfer plate and the loading hanger.   4. Set the shearing device the advance at a rate of 0.50 mm/min.    7. The data acquisition system was run. 8. Once data acquisition has begun, the shearing device was started.  9. The Shear Stress-Displacement curve plot used for strength behavior investigation   VI. RESULTS AND DISCUSSIONS   The direct shear tests were performed in order to determine effect of fiber inclusion on shear strength of reinforced clayey sand. Figure 4 showed the stress-displacement curve obtained from the tests at 10mm fiber length and constant normal stress of 100 kpa.   Fig. 4   Results of direct shear test in different fiber content (at 10mm, Normal stress 100 kpa) Figure 4 proved increasing in fiber content will increase the strength. Figure 5 shows the effect of fiber length on strength of composite clayey sand at constant fiber content of 0.6% and normal stress of 100 kpa.    Fig. 5   Results of direct shear test in different fiber length (at 0.6% fiber content, Normal stress 100 kpa)  VII. CONCLUSION   Increasing in fiber percentage increased shear strength in clayey sand samples  During the test, it was observed that ductility behaviour of reinforced sand increased because of fiber inclusion.  The results proved that with increasing in fiber length, the shear stress of composite clayey sand was increased.  Short and randomly Fiber inclusion showed to be reliable in industry projects as it helps to minimize the cost of projects.  ACKNOWLEDGEMENTS  The technical support from the Curtin University Laboratory is gratefully acknowledged.   REFERENCES   [1] Akbulut, S., Arasan, S. and Kalkan, E. (2007)” Modification of clayey soils using scrap tire rubber and synthetic fibers”, Journal of Applied Clay Science 38, 23-32.  [2] Al Refeai, T.O. (1991) “Behaviour of granular soils reinforced with discrete randomly oriented inclusions”, Journal of Geotextiles and Geomembranes, 10, pp. 319–333.  [3] Cai, Y., Shi, B., Charles, W.W. Ng. & Tang, C. (2006) “Effect of polypropylene fiber and lime admixture on engineering properties of clayey soil”, Engineering Geology 87, 230– 240. [4] Consoli, N.C., Vendruscolo, M.A., Fonini, A. and Dalla Rosa, F. (2009) “Fiber reinforcement effects on sand considering a wide cementation range”, Geotextiles and Geomembranes 27, pp. 196–203.  [5] Freitag, D.R. (1986) “Soil randomly reinforced with fibers”, Journal of Geotechnical Engineering ASCE 112 (8), pp. 823–826. [6] Gray, D. and Al-Rafeai, T. O. (1986). “Behavior of fabric versus fiber reinforced sand”. Journal of Geo-technical Engineering, vol. 112, no. 8, pp. 804-820. [7]  Gray, D. H. and Ohashi, H. (1983). “Mechanics of fiber reinforcement in sand”. Journal of Geotechnical and Geo-environmental Engineering, ASCE, vol. 109, no. 3, pp. 335-353. [8] Lorenzo, G. A. and Bergado, D. T. (2004). “Fundamental parameters of cement-admixed clay – New approach”. Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130, No. 10, pp. 1-9. [9] Michalowski, R. L., Cermak, J. (2002), “Strength anisotropy of fiber-reinforced sand”. Computers and Geotechnics, Vol. 29, No. 4, pp. 279-299. [10] Kaniraj, S. R. and Havanagi, V. G.( 2001). “Behavior of cement-stabilization fiber-reinforced fly ash-soil mixtures. Journal of Geo-technical and Geo-environmental Engineering, vol. 127, no. 7,pp. 574-584. [11] Maher, M. H., Ho, Y. C. (1994), “Mechanical-properties of kaolinite fiber soil composite”. J. of Geotech. Engrg, ASCE, Vol. 120, No. 8, pp. 1381-1393.   [12] Nataraj, M. S., Mcmanis, K. L. (1997),” Strength and deformation properties of soils reinforced with fibrillated fibers.”, Geosynthetics Int., Vol. 4, No. 1, pp. 65-79. [13] Sivakumar Babu, G.L., Vasudevan, A.K. and Haldar, S. (2008) Numerical simulation of fiber-reinforced sand behaviour, Geotexiles and Geomembranes 26, pp. 181–188. [14] Yetimoglu, T. and Salbas, O. (2003) “A study on shear strength of sands reinforced with randomly distributed discrete fibers”, Geotextiles and Geomembranes 21 (2), pp. 103–110.  [15] Ziegler, S., Leshchinsky, D., Ling, H. I., and Perry, E. B. (1998)” Effect of short polymeric fibers on crack development in clays. Soils and Foundations”, J of Applied clay science,Vol. 38, No. 1, pp. 247-253. [16] Zornberg, J. G., Cabral, A. R. and Viratjandr, C. (2004) “Behavior of tire shred-sand mixtures”, Canadian Geotechnical Journal 41 (2), pp. 227–241. [17] Zornberg, J. G. (2002) “discrete framework for limit equilibrium analysis of fiber-reinforcement”, Geotechnique Journal 52 (8), pp. 227–241.     

Shear test on reinforced clayey sand

Composite soils have been widely used in civil engineering applications, especially in slopes, embankment dam and landfills. This paper aims to investigate effect of fiber inclusion on shear stress of composite soil (i.e. sand composite). A series of laboratory direct shear tests carried out to evaluate fiber effect on strength behavior of composite sand. One of the most respective model of behavior prediction clayey sand (Michalowski model) was verified. Natural fiber was used as reinforcement in this verification. The fiber parameters differed from one test to another, as fiber length were changed from 10 mm to 35 mm and fiber content were varied from 0.6% and 3%. Normal stress kept constant at 100 kPa. For each test, stress_ displacement graph derived and the results were compared. The results proved that inclusion of fiber affected strength behavior of sand composite so that increasing in fiber content and length caused increasing in shear stress and Michalowski model showed good agreement with the lab results

Numerical shear test on reinforced clayey sand

   Abstract—Composite soils have been widely used in civil engineering applications, especially in slopes, embankment dam and landfills. This paper aims to investigate effect of fiber inclusion on CBR values of composite soil (i.e. sand composite). A series of laboratory CBR tests carried out to evaluate fiber effect on CBR values behavior of composite sand. Clayey sand was selected as soil part of the composite and natural fiber was used as reinforcement. The fiber parameters differed from one test to another, as fiber length were changed from 20 mm to 50 mm and fiber content were varied from 1% and 3%. For each test, CBR values were calculated and compared. The results proved that inclusion of fiber affected CBR values of sand composite so that increasing in fiber content and length caused increasing in CBR.   Keywords—CBR, Reinforced, Fiber, Sand  I. INTRODUCTION CBR test is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mm/min. to that required for the corresponding penetration of a standard material. The California Bearing Ratio Test (CBR Test) is a penetration test developed by California State Highway Department (U.S.A.) for evaluating the bearing capacity of subgrade soil for design of flexible pavement. Tests are carried out on natural or compacted soils in water soaked or un-soaked conditions and the results so obtained are compared with the curves of standard test to have an idea of the soil strength of the subgrade soil. Applications of soil strengthening or stabilization range from the mitigation of complex slope hazards to enhancing the subgrade stability. Together with the many applications for improving soil, there are several widely varied methods. The mixing of randomly oriented fibers to a soil sample may be considered same as other admixtures used to stabilize soil. Material used to make fibers for reinforcement may be obtained from paper, metal, nylon, polyester and other materials having widely varied physical properties. There have been numerous past papers published on the topic of fiber strengthening of soils. Examples include Lee et al., 1973, Hoare,1979, Andersland and Khattac,1979, Freitag,1986, Gray and Ohashi, 1983, Gray and Rafeai, 1986, Maher and Gray 1990, Maher and Ho, 1994, Michalowski and Zhao 2002, Ranjan et al. 1996, Kaniraj and Havanagi 2001, Consoli et al. 2009.  1F. A. Author is with the Curtin University of Technology, Perth, Australia Tel: +61-413165961;Email: amin.chegenizadeh@postgrad.curtin.edu.au 2S. B. Author, Head of the Department of Civil Engineering, Curtin University of Technology, Perth, Australia; Tel: +61 8 9266 7573; Fax: +61 8 9266 2681; Email: H.Nikraz@curtin.edu.au     All of the papers listed above have generally shown that; strength of the soil was improved by fiber reinforcement. The investigation on clayey sand is very limited. The purpose of this survey is to evaluate of CBR values of clayey sand induced by fiber inclusion. The CBR tests were conducted as per ASTM D1883 on the selected soils with and without reinforcement to investigate the influence of length and fiber content on CBR values. Moreover, the obtained CBR values were taken as indication of improvement in the soil strength due to fiber reinforcement. For different length and fiber contents, the dry weight required to fill the CBR mould was calculated based upon maximum dry densities of the soil and the volume of the mould. The water corresponding to Optimum Moisture Content (OMC) was put and mixed thoroughly. The water was added prior to fiber to prevent floating problems.   II. MATERIAL   Composite soils consist of two parts. The first part is soil part which can be dealt as normal soil. The second part is reinforcement part which can be made up of any material which helps soil to have better performance.   A. Soil Type  The soil type in this study was Western Australian sand. The properties of clay are presented in table 1. The sand distribution curve is presented in Fig 1. The soil part was reconstituted in lab by using sand with 20% of kaolin clay.   Table1. Clay properties             CBR Test on Reinforced Clayey Sand Amin Chegenizadeh1, Prof. Hamid Nikraz 2 No. Type  1 Soil type Clay 2 Liquid Limit 49 3 Plastic Limit 23 4 Pl. Index 26                    Fig. 1   Sand Particle Distribution B. Fiber Type The natural fiber has been used for this investigation. Figure2 shows the used fiber. The used fiber has good potential to absorb energy and good adhesion with soil particle.                   Fig. 2   Natural fiber III. TEST PROGRAM  A series of CBR tests have been conducted on reinforced sand composite.     A. CBR Test  The California Bearing Ratio (CBR) test was developed by the California Division of Highways as a method of classifying and evaluating soil- subgrade and base course materials for flexible pavements. CBR is a measure of resistance of a material to penetration of standard plunger under controlled density and moisture conditions. CBR test may be conducted in remoulded or undisturbed sample. Test consists of causing a cylindrical plunger of 50mm diameter to penetrate a pavement component material at 1.25mm/minute. The loads for 2.5mm and 5mm are recorded. This load is expressed as a percentage of standard load value at a respective deformation level to obtain CBR value. B. Main Equipments  Mould  Steel Cutting collar  Spacer Disc  Surcharge weight  Dial gauges  IS Sieves  Penetration Plunger  Loading Machine  Miscellaneous Apparatus  Figure 3 shows the mechanism of CBR test machine.                     Fig. 3   Mechanism of CBR Test Machine( Gray,1983)      IV. TEST METHODOLOGY AND PROCEDURE         The sample was sieved through 20mm IS sieve.  5kg of the sample of soil specimen was taken. Water was added to the soil in the quantity such that optimum moisture content or field moisture content was reached. Then soil and water were mixed thoroughly. Spacer disc was placed over the baseplate at the bottom of mould and a coarse filter paper was placed over the spacer disc. The prepared soil water mix was divided into five. The mould was cleaned and oil was applied. Then was filled one fifth of the mould with the prepared soil. That layer was compacted by giving 56 evenly distributed blows using a hammer of weight 4.89kg. The top layer of the compacted soil was scratched. Again second layer was filled and process was repeated. After 3rd layer, collar was also attached to the mould and process was continued. After fifth layer collar was removed and excess soil was struck off.  The base plate was removed and the mould was inverted. Then it was clamped to baseplate. Then the normal load was applied and CBR values recorded. The fibre content and length were varied during the tests. Fibre contents were selected as 1%, 2% and 3%. On other hand, fibre lengths were varied from 20mm up to 50mm.       V. RESULTS AND DISCUSSIONS   The CBR tests were performed in order to determine effect of fiber inclusion on CBR values of reinforced clayey sand. Figure 4 showed the CBR values obtained from the tests at different fiber length and content. The maximum CBR value obtained for an length of 50mm and 3 percent fiber content   Fig. 4   Results of CBR test in different fiber content and lengths  VI. CONCLUSION Two important parameters have been well investigated in this paper. The first parameter is fiber content and the second one is aspect ratio. The effect of these two parameters studied on CBR values. Following results were derived:  Increasing in fiber percentage increased CBR values in clayey sand samples  The results proved that with increasing in fiber length, the CBR values of composite clayey sand were increased.  Short and randomly Fiber inclusion showed to be reliable in industry projects as it helps to minimize the cost of projects.  ACKNOWLEDGEMENTS  The technical support from the Curtin University Laboratory is gratefully acknowledged.   REFERENCES   [1] Akbulut, S., Arasan, S. and Kalkan, E. (2007)” Modification of clayey soils using scrap tire rubber and synthetic fibers”, Journal of Applied Clay Science 38, 23-32.  [2] Allan, M. L., Kukacka, L. E. (1995) “Permeability of microcracked fibre-reinforced containment barriers.” Waste Management 15 (2), pp. 171-177.  [3] Al Refeai, T.O. (1991) “Behaviour of granular soils reinforced with discrete randomly oriented inclusions”, Journal of Geotextiles and Geomembranes, 10, pp. 319–333.  [4] Cai, Y., Shi, B., Charles, W.W. Ng. & Tang, C. (2006) “Effect of polypropylene fiber and lime admixture on engineering properties of clayey soil”, Engineering Geology 87, 230– 240. [5] Consoli, N.C., Vendruscolo, M.A., Fonini, A. and Dalla Rosa, F. (2009) “Fiber reinforcement effects on sand considering a wide cementation range”, Geotextiles and Geomembranes 27, pp. 196–203.  [6] Freitag, D.R. (1986) “Soil randomly reinforced with fibers”, Journal of Geotechnical Engineering ASCE 112 (8), pp. 823–826. [7] Gray, D. and Al-Rafeai, T. O. (1986). “Behavior of fabric versus fiber reinforced sand”. Journal of Geo-technical Engineering, vol. 112, no. 8, pp. 804-820. [8]  Gray, D. H. and Ohashi, H. (1983). “Mechanics of fiber reinforcement in sand”. Journal of Geotechnical and Geo-environmental Engineering, ASCE, vol. 109, no. 3, pp. 335-353. [9] Kaniraj, S. R., Havanagi, V. G. (2001). “Behaviour of cement-stabilized fibre reinforced fly ash-soil Mixtures”, Journal of Geotech. and Geoenvironmental. Engineering 127 (7), pp. 574-584.  [10] Lorenzo, G. A. and Bergado, D. T. (2004). “Fundamental parameters of cement-admixed clay – New approach”. Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130, No. 10, pp. 1-9. [11] Michalowski, R. L., Cermak, J. (2002), “Strength anisotropy of fiber-reinforced sand”. Computers and Geotechnics, Vol. 29, No. 4, pp. 279-299. [12] Kaniraj, S. R. and Havanagi, V. G.( 2001). “Behavior of cement-stabilization fiber-reinforced fly ash-soil mixtures. Journal of Geo-technical and Geo-environmental Engineering, vol. 127, no. 7,pp. 574-584. [13] Maher, M. H., Ho, Y. C. (1994), “Mechanical-properties of kaolinite fiber soil composite”. J. of Geotech. Engrg, ASCE, Vol. 120, No. 8, pp. 1381-1393. [14] Nataraj, M. S., Mcmanis, K. L. (1997),” Strength and deformation properties of soils reinforced with fibrillated fibers.”, Geosynthetics Int., Vol. 4, No. 1, pp. 65-79. [15] Sivakumar Babu, G.L., Vasudevan, A.K. and Haldar, S. (2008) Numerical simulation of fiber-reinforced sand behaviour, Geotexiles and Geomembranes 26, pp. 181–188.   [16] Yetimoglu, T. and Salbas, O. (2003) “A study on shear strength of sands reinforced with randomly distributed discrete fibers”, Geotextiles and Geomembranes 21 (2), pp. 103–110.  [17] Ziegler, S., Leshchinsky, D., Ling, H. I., and Perry, E. B. (1998)” Effect of short polymeric fibers on crack development in clays. Soils and Foundations”, J of Applied clay science,Vol. 38, No. 1, pp. 247-253. [18] Zornberg, J. G., Cabral, A. R. and Viratjandr, C. (2004) “Behavior of tire shred-sand mixtures”, Canadian Geotechnical Journal 41 (2), pp. 227–241. [19] Zornberg, J. G. (2002) “discrete framework for limit equilibrium analysis of fiber-reinforcement”, Geotechnique Journal 52 (8), pp. 227–241.     