Relationship between the percentage of clay with liquid limit, plastic limit and plastic index in four different soils texture class

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1 Technical Journal of Engineering and Applied Sciences Available online at TJEAS Journal / ISSN TJEAS Relationship between the percentage of clay with liquid limit, plastic limit and plastic index in four different soils texture class Salahedin Moradi 1* and Eisa Ebrahimi 2 1- Department of Agriculture, Payame Noor University, PO. BOX Tehran, I. R. IRAN 2- Former M.Sc. student, Department of Soil Science, Buali sina University, College of Agriculture, Hamedan, I. R. Iran Corresponding author ms@pnu.ac.ir ABSTRACT: The Atterberg limits and the Proctor compaction test parameters are related to agronomy with regard to compaction hazard for soils and tillage. This study was conducted to characterize the percentage of clay with consistency limits (liquid limit, LL; plastic limit, PL and plastic index, PI) of in four different soils texture class (clay, silty clay, silty clay loam and clay loam). The result revealed soil plasticity has direct correlation with percentage of clay. The consistency limits, and plasticity index (PI = LL - PL) were measured for the soil taken from the 0-20 cm layer. The LL varied from 38 to 63 in clay soil texture, 27 to 55 in silty clay, 21 to 44 in silty clay loam and 15 to 35 in clay loam texture. The PL varied from 13 to 34 in clay soil texture, 12 to 33 in silty clay, 10 to 27 in silty clay loam and 10 to 26 in clay loam texture. The lowest PI was recorded in clay loam texture. The results of this study showed that soil clay content significantly change Atterberg limits and plastic index. Soil clay content in all experimental soils significantly (p < 0.01) increased liquid limit (LL) plastic limit (PL), and plastic index (PI) values. The highest LL, PL and PI values were obtained in clay-textured soil. There was a significant relationship between the soil clay content and the Atterberg limits and plastic index. The positive relationship between soil clay content and PL, LL and PI was found to be significantly linear whereas the relationship with the soil sand content was significantly negative. Regression analysis for Atterberg limits in four soil texture class showed that the percentage of clay were important character on liquid limit, plastic limit and plasticity index. Keywords: liquid limit, plastic limit, plastic index, soil texture, clay INTRODUCTION Soil liquid limit and plastic limit are very important physical parameters for soil science which are also called Atterberg limits (Li et, al., 2012; Venkata et, al., 2011). To improvement of soil characteristics for maintaining its allowable load sustainability, deformation and stability understanding of soils nature in creation of model by mixing soil technique is first requirement at design of soil foundation. The composition of any soil is an important factor which influences many soil properties, such as shear strength, liquid limit (LL), plastic limit (PL) etc. The Atterberg limits and the Proctor compaction test parameters are related to agronomy with regard to compaction hazard for soils and tillage. Soil liquid limit and plastic limit are very important physical parameters for soil science, which are also called Atterberg limits (Ying and Qi, 2009). The liquid limit of a soil is the moisture content, expressed as a percentage of the mass of the oven dried soil, at the boundary between the liquid and plastic states. The moisture content at this boundary is arbitrari1y defined as the liquid limit and is the moisture content at a consistency as determined by means of the standard liquid limit apparatus (Namdar and Pelko, 2010). It is too important in civil engineering awareness of soil science for seismic mitigation of structure placed on soil foundation consists of soft soil. The liquid limit is defined as the minimum moisture content at which a soil will flow upon application of a very small shearing force. When a soil becomes a viscous fluid, the soil will begin to flow under its own weight and very small amount of energy input, as shown in picture on the right. The liquid limit is primarily used by civil and geotechnical engineers as a physical property of a soil. The liquid limit allows engineers to classify soils into their applications. For instance one soil may have applications in sub-bases of roads, where another soil may be better suited for foundations of buildings. Plastic Limit (PL or WP) the water content, in percent, of a soil at the boundary between the plastic and semisolid states. The plastic limit is defined as the water content (θm) when homogenized soil samples start to

2 crack when rolled to a diameter < 4 mm (Warrick, 2002). Plasticity Index (PI) the range of water content over which a soil behaves plastically. The difference between the water content (θm) at the liquid and plastic limits is the plasticity value, often used as an index of soil workability. Sensitivity to plastic deformation increases with increasing plasticity value; the smaller the value, the sooner the soil can be trafficked without further soil deformation. The higher the plasticity value, the smaller the angle of internal friction for sandy soils. Many attempts have been made to correlate the plasticity value to soil strength (Hartge and Horn, 1992; Kretschmer, 1997). In principle, this test only gives information on minimum strength values. Below a certain threshold water content, approximating the plastic limit, even relatively large energy inputs had little effect on clay dispersion. As the water content increased above the plastic limit, the soil became increasingly sensitive to mechanical disruption. MATERIALS AND METHODS This laboratory study was aimed to assess effects of soil texture on soil consistency limits and soil compactability parameters. Atterberg limit tests were conducted following the Australian standard test methods for Atterberg limits (AS, 1995). To define the liquid limits of the sediments, the results of the percussion-cup test and the fall cone test are compared for raw sediments and treated sediments. For the determination of the plastic limit, the results of the rolling test method are compared to the prediction of the fall cone test. Finally, the relationship between the water contents and the penetration depths between the liquid limit and the plastic limit is explored. The plastic limits measured by the rolling test method. The relationships between the water content and the penetration depth of the cone, between the liquid limits and the plastic limits, are investigated. On the basis of the liquid limit and the plastic limit, the plasticity index (PI) can be defined as the numerical difference between them: PI = LL - PL The plasticity index is expressed in percent of the dry weight of the soil sample. It shows the size of the range of the moisture contents at which the soil remains plastic. RESULTS AND DISCUSSION This paper examines the effects of treatments inducing the four different soils texture class with the different percentage of clay on the Atterberg limits of soil. The results of regression analysis for liquid limit in different soil texture class (Table 1 and Figure 1, 2, 3 and 4) indicated that clay percentage in clay soil texture class can justify 91.3 percent of the liquid limit variation. So this traits the most important component of liquid limit. Clay percentage in silty clay, silty clay loam and clay loam soil texture class made 76, 60 and 57 percent of the liquid limit variation, respectively. Regression Coefficient Table 1. Regression Analysis of liquid limit in different soil texture class. Significant Coefficient of determination T Test Level component Intercept Clay Silty clay Silty clay loam Clay loam Coefficient of cumulative determination The liquid limit increases with clay and organic matter contents, ionic strength, cation valency and proportion of 2:1 clay minerals in the soil (Warrick, 2002). Although CEC values play an important role in the swelling behaviour of clayey soils, there is no universally accepted simple quantitative swelling potential classification at present (Yilmaz, 2006). Soils having high CEC values can swell more than the soil having low CEC value. Figure 1. Regression Analysis of liquid limit in clay soil texture class 698

3 Figure 2. Regression Analysis of liquid limit in silty clay soil texture class. Figure 3. Regression Analysis of liquid limit in silty clay loam soil texture class. Figure 4. Regression Analysis of liquid limit in clay loam soil texture class. The results of regression analysis for plastic limit in different soil texture class (Table 2 and Figure 5, 6, 7 and 8) indicated that silty clay loam soil texture class can justify 33 percent of the plastic limit variation. Clay, silty clay and clay loam soil texture class made 23, 15 and 9 percent of the plastic limit variation, respectively. Both the liquid and plastic limits depend upon the amount and type of clay present in the soil: A soil with a high clay content usually has high LL and PL; Colloidal clays have higher LL and PL than non-colloidal clays. Table 2. Regression Analysis of plastic limit in different soil texture class. Regression Significant Coefficient of determination Coefficient of cumulative T Test Coefficient Level component determination Intercept Clay Silty clay Silty clay loam Clay loam Figure 5. Regression Analysis of plastic limit in clay soil texture class. 699

4 Figure 6. Regression Analysis of plastic limit in silty clay soil texture class. Figure 7. Regression Analysis of plastic limit in silty clay loam soil texture class. Figure 8. Regression Analysis of plastic limit in clay loam soil texture class. The results of regression analysis for plastic index in different soil texture class (Table 3 and Figure 9, 10, 11 and 12) indicated that clay percentage in clay soil texture class can justify 42 percent of the plastic index variation. So this traits the most important component of plastic index in in different soil texture class. Clay percentage in silty clay, clay loam and silty clay loam soil texture class made 31, 28 and 9.8 percent of the plastic index variation, respectively. In general, the plasticity index depends only on the amount of clay present. It indicates the fineness of the soil and its capacity to change shape without altering its volume. A high PI indicates an excess of clay or colloids in the soil. Its value is zero whenever the PL is greater or equal to the LL. Textural class from silty clay loam to silt and silty clay; The Atterberg Limits show that the soil is fairly plastic and suitable for embankment construction (good stability and low seepage losses). This later result was confirmed by the data reviewed by Prakash and Sridharan (2006) and Zentar et, al., Regression Coefficient Table 3. Regression Analysis of plastic index in different soil texture class. Significant Coefficient of determination T Test Level component Intercept Clay Silty clay Silty clay loam Clay loam Coefficient of cumulative determination 700

5 Figure 9. Regression Analysis of plastic index in clay soil texture class. Figure 10. Regression Analysis of plastic index in silty clay soil texture class. Figure 11. Regression Analysis of plastic index in clay loam soil texture class. Figure 12. Regression Analysis of plastic index in silty clay loam soil texture class. REFERENCES Australian Standards, Methods of testing soils for engineering purposes: soil classification tests. AS / Hartge, K. H. and R. Horn Bodenphysikailsches Praktikum, 3rd ed., Enke Verlag, Stuttgart, Germany. 701

6 Kretschmer, H Körnung und Konsistenz, in H. P. Blume, P. Felix-Henningsen, W. Fischer, H. G. Frede, R. Horn, and K. Stahr (eds.), Handbuch der Bodenkunde, Ecomed Verlag, Landsberg, Germany.Li, J. Xiaodong, Z. Meng, Z. Hao, L Soil Liquid Limit and Plastic Limit Treating System Based on Analytic Method. Procedia Earth and Planetary Science 5: Li, J. Zhang, X. Zou, M. and Li, H Soil Liquid Limit and Plastic Limit Treating System Based on Analytic Method. Procedia Earth and Planetary Science 5: Namdar. A. and Pelko, A. K Liquid and Plastic Limits Evaluation of Mixed Soil Matrices. E -Journal of Science & Technology (e-jst). 5(5):1-8. Prakash, K. and Sridharan, A A critical appraisal of the cone penetration method of determining soil plasticity. Canadian Geotechnical Journal 43(8,1): Venkata, C. Subramanian, G. and Dhinakaran, E Effect of Bio-Enzymatic Soil Stabilization on unconfined Compressive Strength and California Bearing Ratio. Journal of Engineering and Applied Sciences. 6(5): Warrick, A. W Soil physics companion. (ed.). CRC Press LLC. Boca Raton, London, New York Washington, D.C. P: 19. Yilmaz, I Indirect estimation of the swelling percent and a new classification of soils depending on liquid limit and cation exchange capacity. Engineering Geology 85: Ying, G. and Qi, W Experimental research on fall cone test to determine liquid limit and plastic limit of silts. Rock and Soil Mechanics. 30(9): Zentar, R. Abriak, N. E. and Dubois, V Effects of salts and organic matter on Atterberg limits of dredged marine sediments. Applied Clay Science 42: