As evaporation prevails, soils lose water and shrink upon desiccation, which lead to formation of desiccation cracks. The cracking of desiccated clay soils is problematic to many civil structures hence an adequate understanding of the desiccation cracking process is of great significance. To build this understanding, knowledge of how crack forms, their position, orientation and connectivity in space are necessary. This paper aims to investigate shrinkage problem deeply. A series of shrinkage test were conducted. The container dimensions were 50mm X50mm X 50mm. the soil was selected as kaolin clay. Different initial moisture content of 45% and 40% considered. The results proved that water content decreased as desiccation rate increased. The engineering graph of change in water content versus time and shrinkage strain versus change in water content was plotted for each test. The desiccation curves shows similar behaviour for different initial moisture content as finally reached the balance with local climate

Chegenizadeh, Amin

Nikraz, Hamid

English

espace@Curtin

1 INTRODUCTION  Compacted clay is commonly used in embank-ment dam cores, low permeable barriers in waste landfills, canal sections, foundations and roadways. Areas that are susceptible to damage from expansive soils are those that have large surface deposits of clay and climates characterised by alternating peri-ods of rainfall and drought. Expansive soil is a term used by geotechnical engineers for soils that expand or contract depending on the amount of water that is present. In a research on reactive clayey soil, Nah-lawi (2004) found out that the economical aspect of  this problem can be significant in Australia. This view was reviewed by Dudal and Eswaran (1988). Soil shrinkage is problematic around the world and poses risks of damage to light buildings, road pave-ments and clay liners used for waste containment in landfills. Soil shrinkage and shrinkage cracks are caused by a decreasing in soil moisture content through either evaporation from the soil surface in dry climates, lowering of the groundwater table, or desiccation of soil by trees during humid climates. In a study on shrinking and swelling of soils, Holtz and Kovacks (1981) found that as water content de-creases, capillary stress in the void spaces enhances due to the increased surface tension. This increased surface tension tends to pull adjacent soil particles closer together resulting in an overall soil volume decrease. The key factors effecting the shrinkage po-tential of a soil can be evaluated in three different groups, the soil characteristics that influence the ba-sic nature of the internal force field, the environ-mental factors that influence the changes that may occur in the internal force system, and the state of stress (Kudikarra, 2005,Nelson and Miller, 1992). In conventional application of reinforcement in soil, the inclusion of tire, bars, grids etc are usually in a preferred orientation. The advances of these mate-rials have usually been considered by an increase in their applications. The randomly discrete fibers are easily added and mixed randomly with soil part, the same way as cement, lime or other additives. Some researches have been done on cement additive (Con-soli et.al. 2009; Cai et.al 2006; Lorenzo and Berga-do, 2004) and can be used as a pattern of additive usage in soil. Fibre reinforced composite shows more ductility and small losses of peak strength i.e. in compared to unreinforced material. Therefore, fi-ber-reinforced soil composite is a practical solution in civil engineering projects. The main application of composite soil can be in embankment, subgrade, subbase, and slope stability problems. However, the data concerning the effects of fiber inclusion on the characteristics of compacted native or virgin soils are limited, (Maher and Ho, 1993). This shortage is more considerable in pavement engineering and landfill systems in terms of crack control. Limited Investigation on Shrinkage behaviour of kaolin clay  Amin Chegenizadeh  PhD candidate, Department of Civil Engineering, Curtin University of Technology, Perth, Australia; Tel: +61-413165961; Fax: +61 8 9266 2681;Email: amin.chegenizadeh@postgrad.curtin.edu.au Prof. Hamid Nikraz  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      ABSTRACT: As evaporation prevails, soils lose water and shrink upon desiccation, which lead to formation of desiccation cracks. The cracking of desiccated clay soils is problematic to many civil structures hence an adequate understanding of the desiccation cracking process is of great significance. To build this understand-ing, knowledge of how crack forms, their position, orientation and connectivity in space are necessary. This paper aims to investigate shrinkage problem deeply. A series of shrinkage test were conducted. The container dimensions were 50mm X50mm X 50mm. the soil was selected as kaolin clay. Different initial moisture con-tent of 45% and 40% considered. The results proved that water content decreased as desiccation rate in-creased. The engineering graph of change in water content versus time and shrinkage strain versus change in water content was plotted for each test. The desiccation curves shows similar behaviour for different initial moisture content as finally reached the balance with local climate. KEYWORDS: Desiccation; clayey soil; cracking attempts have been made to control clay cracking by fibre reinforcement (Allan and Kukacka, 1995; Al Wahab and El-Kedrah, 1995; Ziegler et al., 1998). Miller and Rifai (2004) studied the effects of fibre reinforcement on the development of desiccation cracking in compacted clay samples. Therefore, the significance this study is to evaluate the effect of fi-bre inclusion on shrinkage behavior of clayey soil. The application of controlling crack cause signifi-cant improvement in land fill systems and pavement engineering as cracking which lead these systems to be failed in the real civil projects.    2 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.  2.1 Soil Type The soil type in this study was kaolin clay. The properties of clay are presented in table 1. This type of kaolin clay is widely used in industrial project and research activities in Western Australia.  Table 1. Clay properties No.  Size (cm)  1 Soil type Clay 2 Liquid Limit 49 3 Plastic Limit 23 4 Pl. Index 26    2.2 Fiber Type  The plastic fiber has been used for this investiga-tion. Figure1 shows the used fiber. The used fiber has good potential to absorb energy and good adhe-sion with soil particle.              Figure. 1   Plastic fiber 3 TEST PROGRAM Test program in this study includes a series of shrin-kage test were conducted to investigate the effect of fibre inclusion on shrinkage phenomenon.  3.1  Main Equipments        Metal container for shrinkage test  Balance    Figure 2 shows the metal container which was used to run the crack test.            Figure 2.   Metal Container used for shrinkage test   4 SAMPLE PREPARATION FOR SHRINKAGE TEST Isotropic shrinkage tests were conducted on clay samples. This rather contemporary method involved compacting soil into small moulds to produce blocks of soil compacted to a specific density (Nahlawi et. al. ,2006). Compacting soil at specific moisture con-tent to a specific density may be ideal when trying to model landfill conditions. The aim of this test is to determine the shrinkage strain of compacted clay as time elapses with different starting moisture content and sizes, and generate desiccation curves. Accord-ingly, this will determine what size sample(s) will be good for carrying out further testing. Specimens were compacted at 40% moisture content and 40% moisture content. Ideally we would want to compare slurry clay to compacted clay for this test however, since the dry density is unknown for moisture con-tent beyond 45%, a comparison of clay at 45% and 40% was carried out. Moreover to an unknown dry density, slurry state clay would not hold its shape once the moulds are removed. Shrinkage tests were undertaken in a constant temperature room in the civil engineering laboratories. 50 mm x 50mm x 50 mm size blocks clay, were left to dry under similar environmental conditions. Their weight and shrink-age were recorded over time. The following section will explain in detail the experimental procedures. 5 TEST METHODOLOGY AND PROCEDURE 5.1 General steps .  Once the soil had been compacted into the moulds, ‘cling wrap’ was used to wrap the sample to prevent moisture loss. Water was then sprayed, and soil was put in sealable plastic bags to cure overnight. Approximately a day later the soil specimens were isolated from the moulds. Firstly the lid of each mould was carefully removed, and excess soil was cut with a wire. Once the entire soil was exposed, metal tacks were positioned in the centre of each face of the block using glue as a reference point for measuring shrinkage in two dimensions with a calli-per. The soil blocks were then put on a metal rack in a constant temperature room where the soil was to undergo drying at a constant temperature of 24°C and relative humidity of 40%. The degree of shrink-age and weight of each sample were recorded each day until the samples reached equilibrium with the local climate or cracked. Same procedure was ap-plied with putting fibre inside the clayey soil and ef-fect of fibre also investigated on shrinkage behav-iour.  The fibre length was selected as 10 mm and fibre content varied during the tests. (i.e. 1% , 2% and 3%)  5.2 Shrinkage analysis  Desiccation curves were plotted by weighing the soil specimens over time to determine the water loss.(Kudikara ,2005) The change in water content in each sample was determined by applying Equa-tion 1, where wi  is the initial water content and wt  is the water content at the specific desiccation time.  W = Wi- Wt                                             (1)  Shrinkage strain also recorded as ratio of changing in length to initial length.  6 RESULTS AND DISCUSSIONS   Desiccation curves were plotted for each soil sample to identify the desiccation rate. The graph plotted for 40% and 45% moisture content.                   Figure. 3   Changing in moisture content in shrinkage test   The degree of shrinkage was calculated in all 3 di-rections with a calliper on each specimen and an av-erage shrinkage strain was recorded. The graph of the drying process and strain evolution of soil sam-ples were derived as indicated in Figure 4. The shrinkage strain versus change in moisture content, Δw was plotted in figure 4.    Figure. 4   Changing in moisture content in shrinkage test  6.1 Effect of fibre inclusion  A series of shrinkage tests was conducted to find out the effect of fibre inclusion on linear shrinkage be-havioure. Figure 5 shows the effect of fibre content which changed from 1% to 3%. The results proved that with increasing in fibre content linear shrinkage was reduced.                   Figure. 5   Effect of fibre content in shrinkage test 7 CONCLUSION A series of shrinkage test on a block sample of clayey soil was conducted and following results ob-tained:  Kaolin clay experiences shrinkage in all direc-tions, and shrinkage of the clay layer was fol-lowed by cracking due to desiccation.   Using fibre caused huge decrease in crack in-tensity factor   Increasing in fiber content directly decreased the linear shrinkage.   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, Vol. 15, No. 2, pp. 171-177. [3] Al Refeai, T.O. (1991) .Behaviour of granular soils reinforced with dis-crete randomly oriented inclusions, Journal of Geotextiles and Geomem-branes, 10, pp. 319–333.  [4] Cai, Y., Shi, B., Charles, W.W. Ng. & Tang, C. , (2006),,Effect of poly-propylene 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 cementa-tion range, Geotextiles and Geomembranes 27, pp. 196–203.  [6] Dvorak, G.K. and Bahei-El-Din, Y.A., (1982) ,Plasticity analysis of fibr-ous composites, Journal of Applied Mechanics 49, , pp. 327–335. [7] Freitag, D.R. , (1986) ,Soil randomly reinforced with fibers, Journal of Geotechnical Engineering ASCE 112 (8), ,pp. 823–826. [8] 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. [9]  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. [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] 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. [12] Maher, M. H., Ho, Y. C., (1994), ,Mechanical-properties of kaolinite fi-ber soil composite,. J. of Geotech. Engrg, ASCE, Vol. 120, No. 8, pp. 1381-1393. [13] Nataraj, M. S., Mcmanis, K. L., (1997),  Strength and deformation prop-erties of soils reinforced with fibrillated fibers., Geosynthetics Int., Vol. 4, No. 1, pp. 65-79. [14] Sivakumar Babu, G.L., Vasudevan, A.K. and Haldar, S. (2008) Numeri-cal simulation of fiber-reinforced sand behaviour, Geotexiles and Geo-membranes 26, pp. 181–188. [15] Waldron, L. J., ,(1977),Shear resistance of root-permeated homogeneous and stratified soil., Soil Society. Of American Journal41.  (5), pp. 843–849. [16] Yetimoglu, T. and Salbas, O.,A (2003)  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 Foun-dations, 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. [20] H. Nahlawi and J.K. Kodikara, (2006) , Laboratory experiments on desic-cation cracking of thin soil layers Geotechnical and Geological Engineer-ing 24: 1641–1664  

Investigation on shrinkage behaviour of kaolin clay

As evaporation prevails, soils lose water and shrink upon desiccation, which lead to formation of desiccation cracks. The cracking of desiccated clay soils is problematic to many civil structures hence an adequate understanding of the desiccation cracking process is of great significance. To build this understanding, knowledge of how crack forms, their position, orientation and connectivity in space are necessary. This paper aims to investigate shrinkage problem deeply. A series of shrinkage test were conducted. The container dimensions were 50mm × 50mm × 50mm. the soil was selected as kaolin clay. Different initial moisture content of 45% and 40% considered. The results proved that water content decreased as desiccation rate increased. The engineering graph of change in water content versus time and shrinkage strain versus change in water content was plotted for each test. The desiccation curves shows similar behaviour for different initial moisture content as finally reached the balance with local climate

Nikraz, H.

https://espace.curtin.edu.au/bitstream/20.500.11937/14316/2/183379_57226_67796.pdf

Investigation on shrinkage behaviour of kaolin clay

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