Invention Journal of Research Technology in Engineering & Management (IJRTEM) ISSN: 2455-3689 www.Ijrtem. com Volume 3 Issue 5 ǁ July –August 2019 ǁ PP 32-39
Effect of Feldspar on the Properties of Swelling, Shrinkage and Bearing Capacity of Expansive Clay Soil 1, 1,2,3)
Gatot Rusbintardjo, 2,Lisa Fitriyana, 3,Abdul Rochim3)
Department of Civil Engineering, Faculty of Engineering, Sultan Agung Islamic University (UNISSULA), Semarang, Indonesia
ABSTRACT: Expansive soil is a kind of soil to have high potential for swelling and shrinkage where it has low bearing capacity. On the pavement that laid over the expamsive soil, the uneveness of upward movement caused swelling that it potentially damaged to the road. This study aimed at minimizing the potential of swellimg and shrinkage, while at the same time improving the bearing capacity of the subgrade expansive clay soil through stabilization using the Feldspar, a group rock-forming tectosilicate minerals that made up about 41% of the earth’s continental crust by weight. 5 to 30% of Feldspar with increment of 5% by weight of the soil were added. Atterberg Limit, Direct Shear, and California Bearing Ratio (CBR) test were conducted. Result in Atterberg Limit test showed that the adding of Feldspar to 30% in the expansive soil did not indicate reduction in thr swelling potential. Potential for swelling become zero only if was Feldspar content added to 55% by weight of the expansive soil. However, the results in Direct Shear and CBR tests indicated that the bearing capacity of the expansive soil improved as a result in the increasing of Feldspar content in the soil. With reference to the result in the study, it could be inferred that Fldspar was feasible and had the potential to be stabilizing materials for expansive clay soil.
KEYWORD: Soil stabilization, Expansive clay soil, Feldspar, Swelling/Shrinkage, Bearing Capacity I. INTRODUCTION Most types of soil in North-East of Java island are expansive clay soil which contains a lot of montmorillonite minerals [1], cause the roads built in that area are always damaged. Expansive soil is a term usually applied to any soil that has a potential for shrinking or swelling due to changes in its moisture content. It is recognized there are two main factors that provides the potential of the soil to swell and/or shrink: the properties of the soil and the environmental conditions of the area. The main soil parameters included within the first factor are the clay mineralogy, the soil water chemistry, the soil suction, the structure of the soil (fabric) and its dry density. Within the environmental conditions of the area, the initial moisture condition, the moisture variations and the stress conditions are the factors believed to control the soil movement [2]. The mechanism of the development of longitudinal cracks at the pavement in arid environments has been described by [3] . Mechanism of longitudinal crack development on pavement over expansive clays during dry season, illustrated in Fig. 1, while tensile stresses induced by flexion of the pavement during settlements caused by the dry season leads to the development of longitudinal cracks are shown in Fig. 2.
Fig. 1. Mechanism of longitudinal crack development on pavement over expansive clays during dry season. (Modified from [3]). During the dry season there is a drop off in moisture content of the soil in the shoulders of the pavement structure. The consequence of this reduction in moisture is a settlement in the shoulders that does not take place in the centre of the pavement where the moisture of the soil remains stable thorough the year. The appearance of cracks in the shoulder of the pavement accelerates the evaporation of the interstitial water of the soil reaching also greater depths [2]. The great volumetric expansion and contraction potential of these soils can be explained empirically through a direct correlation to plasticity index [4] or from a theoretical approach [5].
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Effect of Feldspar on the Properties of Swelling‌
Fig. 2. Longitudinal cracks near the edge of pavement [3] Over that expansive clay soil, the pavement of Semarang to Purwodadi which located in North-East of Java island, is constructed. As the result the pavement always damaged, since heave and cracks causing swelling and shrinkage occur. In addition, damage of the pavement is also caused by the low bearing capacity of the sungrade soil where their CBR value is below 2%. Similar levels of damage have also been reported in other countries [612]. Because expansive soil damage engineering structures, estensive studies on using additive to improve these soils have been performed [13,14]. To overcome the damage to the pavement above the expansive clay, control of the swelling shrinkage must be performed. Controlling the shrink-swell behavior through the following alternatives firstly by replacing existing expansive soil with non-expansive soil, secondly, by maintaining a constant moisture content, and thirdly by improving the expansive soils by stabilization. In this study method 3, stabilization with feldspar was carried out. Based on the above reasons, this study aimed to overcome the damage of pavement of Semarang-Purwodadi by controling subgrade swelling and shrinkage through chemical stabilization using feldspar, as well as by improving bearing capacity of soil.
II.
RESEARCH METHODOLOGY
This research was conducted in the Soil Mechanic Laboratory, Faculty of Engineering, Universitas Islam Sultan Agung (UNISSULA) of Semarang, Indonesia. Soil to be stabilized was expansive clay soil obtained from the location Km. SMG 23+00 the road of Semarang-Purwodadi (23.00 kilometers East city of Semarang), which is 64 km length of provincial road located in North-East Central Java Province of Indonesia.Firstly some tests are carried out to determine the properties of the original soil. Preparing felsdpar by crushing coarse of fledspar (Fig. 3) and sieving using sieve # 100, so that it is obtained uniform particle with diameter 0.15 mm of fine feldspar. 5, 10, 15, 20, 25, 30% of the fine feldspar by weight of soil were then added to expansive soil and evenly mixed, resulted in six Feldspar-Soil Mixtures. To each Feldspar-Soil Mixtures and original soil, Atterberg Limit [15], direct shear, and California Bearing Ratio (CBR) [16] tests are conducted. Prior to those tests, activilty to find the optimum moisture content and dry density of each feldspar-soil mixtures. Original expansive soil data are given in Table 1.
Fig. 3. Coarse of Feldspar (Source: [17])
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Effect of Feldspar on the Properties of Swelling‌ Table 1. Properties of original expansive clay soil
III.
RESULTS
Water content : Water content of original expansive clay soil and fledspar-clay soil mixtures are shown in Table 2. It appeares that the water content decreases with increasing of feldspar content in the soil. Table 2. Water content optimum in original soil and fledspar-soil mixtures
Dry density : Dry density of orginal soil and Feldspar-Soil mixtures are given in Table 3 The results show dry desnity slightly increases with increasing of feldspar content in the soil. Table 3. Dry density of original soil and feldspar-soil mixtures
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Effect of Feldspar on the Properties of Swelling‌ Atterberg Limit and Direct Shear tests : Atterberg limit test results are shown in Table 4. and in Regression Model in Fig. 5. It can be seen that the PI value decreases with increasing of Feldspar content in the soil. These results correspond to the directional hypotheses that the lower PI value, the lesser potential of the soil to become expansive. This means that by adding more Feldspar to the soil, it will become less expansive. Decreasing of PI value was caused by reducing of pores in the soil and was filled with Feldspar. Meanwhile, the results of direct shear test of Feldspar stabilized soil are given in Table 5 and presented in the regression model in Fig. 6 for cohesion value and Fig. 7 for angle of internal friction φ. The results of the tests are in accordance with the prevailing rules namely the higher the angle of internal friction, the lower the value of cohesion. Table 4. Atterberg Limit test results
Table 5. Direct shear test results
California Bearing Ratio (CBR) test : The results of CBR test for Feldspar which stabilize expansive soil are shown in Table 6 and presented in the regression model in Fig. 8. The result shows that by adding more Fedlspar content to the expansive soil will result in a higher the CBR value. Regression model gives coefficient of determination, R-square = 0.9930 and coefficient of correlation, R = 0.9610, and shows that between Feldspar content and CBR there is a strong correlation, where the contribution of Feldspar to CBR value is above 90%. It is seen that the CBR value of the Feldspar soil is in accordance with the hypothesis.
Fig. 5. Regression model of Atterberg Limit test results
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Effect of Feldspar on the Properties of Swelling‌
Fig. 6. Regression model of cohesion (c)
Fig. 7. Regression model of Angle of Internal Friction (φ)
Table 6. California Bearing Ratio (CBR) test results
IV.
DISCUSSION
As explained in the introduction, that pavement constructed on expansive clay soil will always be damaged due to a change in water content caused by swelling and shrinkage as well as low CBR value or bearing capacity of soil.
Fig. 8. Regression model of CBR test results
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Effect of Feldspar on the Properties of Swelling… Water content test results : Water content test results show that the water content of soil decrease if the fledspar content is increased. Pavement laid over expansive clay soil, increasing the water content will be followed by an heave of the pavement due to swelling. As the water content decreases with the increasing of the feldspar content, the swelling as well as the upward movement of the pavement will also decrease. Swelling potential : To characterize swelling potential of a soil, Holtz and Gibbs used Plasticity Index (PI) and Liquid Limits (LL), while Chen, used only LL [18]. Holtz and Gibbs as well as Chen divided swelling potential into four groups, low, medium, high, and very high. Table 7 and Table 8 show the correlations with common soil tests to determine swelling potential conducted by Holtz and Gibbs, and Chen respectively [18]. Table 7. Correlations between PI – LL and swelling potential by Holtz and Gibbs [18]
Table 8. Correlations between LL and swelling potential by Chen[18]
Based on common tests by Holtz and Gibbs [18], as well as Atterberg Limit values from Table 4., the swelling potential values of feldspar-soil mixtures are categorized as high and very high, and shrinkage limit values ranges between 7 to 12. Meanwhile based on common tests conducted by Chen and also Atterberg Limit values, 10 to 30% of feldspar-soil mixtures are categorized as high swelling potential, - and 5% ledspar-soil mixtures as well as original soil are catgorized as very high swelling potential. Swelling pressures are 250 to 1000 kPa for 10 to 30% of feldspar-soil mixtures, and > 1000 for 5% feldspar-soil mixtures and original soil. Probable expansion for 10 to 30% of feldspar-soil mixtures based on Chen is 3 to 10, and for 5% fedspar-soil mixtures is more than 10. By using the line equation in regresion model of Atterberg limit test results and feldspar content 55%, LL, PL, and PI can be found as follows: Liquid Limit (LL): .........................................................................................................(1) where: y = liquid limit value, and x = fledspar content = 55%
Plastic Limit (PL): .........................................................................................................(2) where: y = Plastic limit value, and x = fledspar content = 55% Therfore Plasticity Index (PI) value = LL – PL = 30.80 – 23.72 = 7.08
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Effect of Feldspar on the Properties of Swelling… With LL = 30.80 and PI = 7.08, and based on common tests from Holtz and Gibbs as well as Chen, swelling potential is categorized as low, and probable expansion is <1, shrinkage limit < 15 and swelling pressure = 50 kPa. Moreover from the plot of LL and PI values in the Casagrande’s chart, the soil is classified as low plasticity silt (ML). The addition of feldspar to clay soil cam changes soil classification into silt soil. Bearing Capacity : CBR test results show that CBR values increase with increasing feldspar.content in the soil. This also means that the bearing capacity of the soil increases with increasing feldspar content in the soil. Other evidence that bearing capacity of soil increases with increasing of feldspar content is from the result of direct shear test. Table 5 shows, by the increasing of feldspar content, cohesion of soil becomes smaller, whereas the angle of internal friction φ becomes larger. The greater the angle of internal friction φ, the greater the bearing capacity of the soil can also be explained by using Terzaghi’s equation21 as follows: Assuming the pavement as strip footing and Terzaghi’s equation for strip footing is: ..........................................................................................................(3) where: Qu c γ D B Nc; Nq. and Nr
= bearing capacity of soil, = cohesion of soil, = unit weight of soil, = depth of foundation (tickness of pavement) = width of foundation (per meter width of pavement) = Terzaghi’s bearing capacity factors depend on the angle of internal friction of the soil φ.
Table 5 and Fig. 7 show that angles of internal friction φ increase with increasing of feldspar content. While in Fig. 9 chart of Terzaghi’s bearing capacity factors [19] show that the greater the angle of internal friction φ the greater the value of Nc, Nq, and Nr. Therefore, it can be proved that the bearing capacity of the feldspar-soil mixtures increases.
Fig. 9. Terzaghi’s Bearing Capacity factors [19]
V.
CONCLUSION
From overall test results and discussion then conclusions can be drawn as follows: Analyzed using regression models, almost all test results, except the results of Plastic limit, have a coefisien of determination R-square and
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Effect of Feldspar on the Properties of Swelling… coefficient of correlation R above 90%. This means the feldspar has a strong influence on the properties of expansive clay. 1. Swelling potential is very low and even zero if it is added 55% of feldspar to the clay soil. This means that the upward movement of the soil does not occur anymore, and the pavement is no longer damaged. 2. The value of bearing capacity increases with increasing feldspar content. This means that the greater the feldspar content the stronger the subgrade, and the more resistant the pavement to the traffic load.
ACKNOWLEDGEMENTS My special thanks are addressed first to the Institute for Research and Community Service Universitas Islam Sultan Agung (UNISSULA) to financially support this research. Secondly my gratitude is extended to Mrs. Lisa Fitryani and her staff in Soil Mechanic l;aboratory Faculty of Engineering UNISSULA, with their help of this research can be carried out..
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