EFFECT OF CEMENT CONTENT ON UNCONFINED COMPRESSIVE STRENGTH OF JAMSHORO SOIL

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1 International Symposium on Sustainable Geosynthetics and Green Technology for Climate Change (SGCC) 2 to 21 June 212 Bangkok, Thailand EFFECT OF CEMENT CONTENT ON UNCONFINED COMPRESSIVE STRENGTH OF JAMSHORO SOIL Aneel Kumar 1* and Ghous Bux Khaskheli 2 1 Professor, Department of Civil Engineering, Mehran University of Engineering and Technology, Jamshoro, Pakistan; Tel: ; Fax: ; aneel4u@hotmail.com 2 Professor, Department of Civil Engineering, Mehran University of Engineering and Technology, Jamshoro, Pakistan; Tel: ; Fax: ; gbk_6@hotmail.com ABSTRACT Superhighway is a major highway which connects Karachi with north of Pakistan. The road is experiencing severe rutting problems near the Jamshoro city. In the near future the construction of Motorway between Jamshoro and Karachi is forecasted. Thus it may be beneficial to improve the engineering properties of the Jamshoro soil. This paper describes the effect of cement content on unconfined compressive strength of Jamshoro soil. The specimens were prepared with cement content of different proportions that is %, 5%, 1%, 15% and 2% of air dry soil weight. The soil cement was mixed at liquid limit of soil that is high water content mixing. The curing times of the specimens were 7 and 14 days. The paper also explains the basic geotechnical properties of Jamshoro soil which is still not very well reported. The results show that the Jamshoro soil is highly compressible and not suitable for highway subgrade material. The mixing of cement in the soil can significantly increase its unconfined compressive strength. Higher the cement content higher the unconfined compressive strength but the optimum effects were achieved at cement content of 15%. Curing time also increased the unconfined compressive strength of the soil. At 2% of cement content the soil achieved a sufficient stiffness and failure behavior is changed from gradual to sudden. Keywords: Jamshoro soil, unconfined compressive strength, cement, high water content INTRODUCTION Pakistan has four provinces which are Khyber Pakhtunkhwa, Punjab, Balochistan and Sindh. Sindh is the second most populated and third largest among the provinces of Pakistan. Sindh is surrounded by the Arabian Sea in south, River Indus and Balochistan in west, Punjab in north and India in east. Karachi is the capital of Sindh and most populated city of the country. Karachi is also considered as a major financial hub and major seaport of Pakistan. Karachi is located in south of Sindh along the coastline of Arabian Sea. Superhighway is a major highway which connects Karachi with north of Pakistan. This is the densely trafficked highway in Pakistan. This road is experiencing severe rutting problems near the Jamshoro city which is approximately 15 km in north-east of Karachi. In the near future the construction of Motorway between Jamshoro and Karachi is planned by the concerned authorities (NHA, 29). If the Motorway is constructed by directly using the local soil of Jamshoro, there may be chances of its failure and if it is constructed by using the borrowed soil its cost may be substantially increased. Thus it may be beneficial to improve the engineering properties of the Jamshoro soil by altering its one or more geotechnical properties by applying soil stabilization techniques with help of certain chemical additives. The various chemicals such as cement, lime, gypsum, fly ash etc are being used worldwide to alter the basic geotechnical properties of the various soils (Amu et al. 25; Chae et al. 23; Diamond and Kinter, 1965; Ji-ru and Xing, 22; Lorenzo and Bergado, 26; Yilmaz and Civelekoglu, 29). However the influence of these chemicals on the geotechnical properties of the Jamshoro soil is not well investigated. This research is thus aimed to examine the effect of cement content on unconfined compressive strength of Jamshoro soil. The paper also explains the basic geotechnical properties of Jamshoro soil which is still not very well reported. GEOTECHNICAL PROPERTIES OF JAMSHORO SOIL The sample of Jamshoro soil is collected from the vicinity of MUET (Mehran University of Engineering and Technology) Jamshoro. The color of Jamshoro soil is dark yellow brown. The soil contained a very small percentage of visible lime particles. The natural water content of the soil (w N ) was determined by following ASTM D

2 International Symposium on Sustainable Geosynthetics and Green Technology for Climate Change (SGCC211) 7 to 8 December 211 Bangkok, Thailand (ASTM 1998) and it comes out as 3%. The specific gravity of the Jamshoro soil solids (G) was determined by following ASTM D (ASTM 22 a) and it comes out as Following the ASTM D (ASTM 1999) the field dry density (γ df ) of the Jamshoro soil was determined as 13.1 kn/m 3. Water content % w L =6% w L = 52% Fall cone method Casagrande cup method Particle Size Distribution 45 Figure 1 shows the particle size distribution curve of the Jamshoro soil. Particle size distribution was performed by following ASTM D (ASTM 22 b). Percent finer Particle size (mm) Fig. 1 Particle size distribution of Jamshoro soil It is found that more than 75 % of the soil is silt and clay size and about 23 % of the soil is sand size. Soil Consistency Limits Figure 2 shows the flow lines of Jamshoro soil obtained from Casagrande cup method and fall cone method. In case of Casagrande cup method, flow line is a relationship between water content and terminal blows by utilizing standard Casagrande cup. The liquid limit (w L ) is the water content (w) on flow line corresponding to 25 blows. In case of fall cone method the flow line is a relationship between water content and penetration by utilizing standard fall cone apparatus. The w L is water content corresponding to 2 mm penetration. The w L by Casagrande cup method was determined by following ASTM D (ASTM 2) and the w L by Fall cone method was determined by following the procedure of BS 1377 (Das, 25). It is seen that the w L of Jamshoro soil comes out 52 % by Casagrande cup method and 6 % by fall cone method (Fig. 2). The w L of Jamshoro soil is considered as 52% for rest of the calculations and interpretations. The plastic limit (w P ) of the soil was determined by following ASTM D (ASTM 2). It is found that the plastic limit of Jamshoro soil is 26%. The plasticity index (I P ), which is the difference between the w L and w P, of Jamshoro soil remains 26% (w L =52%) Number of Blows/ Penetration (mm) Fig. 2 Liquid limits test of Jamshoro soil The shrinkage limit (w S ) of the soil was determined by following ASTM D (ASTM 24) and it comes out as 14%. Shrinkage ratio (SR) of the Jamshoro soil is calculated by utilizing Eq. 1 which comes out as SR = ws G (1) SR of the soil is equal to the bulk specific gravity of soil (G b ) in its dry state (Garg, 21). Following Eq. 2, the volumetric shrinkage (VS) is calculated at w L and w P. ( ) VS SR wa ws = (2) w a is equal to w L for VS at liquid limit and w a is equal to w P for VS at plastic limit. The VS at liquid limit is calculated as 74% and 23% at plastic limit. Volume of soil/ V d V L =1.74V d V P =1.23V d V d w S =14% w P =26% w L =52% water contnet (%) Fig. 3 Soil consistency diagram of Jamshoro soil Figure 3 shows the soil consistency diagram of the Jamshoro soil where volume of soil is normalized with the V d which is volume of soil at shrinkage limit or volume of dry soil. V P is the volume of soil at plastic limit and V L is the volume 17

3 International Symposium on Sustainable Geosynthetics and Green Technology for Climate Change (SGCC) 2 to 21 June 212 Bangkok, Thailand of soil at liquid limit. The V L and V P are calculated by utilizing Eq. 3. Va Vd VS = x1 (3) Vd V a is equal to V L for VS at liquid limit and V a is equal to V P for VS at plastic limit. Classification of Jamshoro Soil Figure 4 shows the plasticity chart of Jamshoro soil. According to unified soil classification system (USCS) the Jamshoro soil comes under the category of CH which shows the Jamshoro soil is inorganic clay of high plasticity (Das, 25). According to AASHTO classification the Jamshoro soil is categorized as A-7-6 which shows the Jamshoro soil is a clayey soil (Das, 25). Plasticity index CL-ML Jamshoro soil CL ML U-Line I P =.9 (w L - 8) A-Line I P =.73 (w L -2) Liquid limit CH MH Fig. 4 Plasticity chart of Jamshoro soil To evaluate the suitability of the soil as a highway subgrade material the group index (GI) is also one of the parameters. The group index is calculated by Eq. 4. The terms A and B in Eq. 4 are calculated by Eqs. 5 and 6, respectively. F 2 represents the percentage of particles passing through No. 2 sieve. GI = A + B (4) [ ] A = ( F2 35 ).2 +.5( wl 4 (5) ( )( ) B =.1 F2 15 IP 1 (6) A represents the partial GI based on w L and B represents the partial GI based on I P. Summing A and B the value of GI is calculated as 2. Generally lower the value of group index better is the quality of soil as a highway subgrade material. GI of zero represents a good highway subgrade material and 2 or higher shows very poor highway subgrade material (Arora, 29). Generally GI is written in parentheses after the AASHTO group designation. Thus the Jamshoro soil comes under the category of A-7-6 (2) according to AASHTO classification and it is classified as a poor highway subgrade material (Das, 25). Dry Density (γ d ) and Water Content Relationship of Jamshoro Soil The compaction curve that is the relationship between dry density (γ d ) and water content relationship is obtained by performing modified effort. The test was performed by following the ASTM D (ASTM 22 c). Figure 5 shows the dry density and water content relationship of the Jamshoro soil. Dry density (kn/m 3 ) γ d(max) =17.9 (kn/m 3 ) OMC=15.7% Water content (%) Fig. 5 Compaction cure of Jamshoro soil It is seen that the maximum dry density (γ d(max) ) remained 17.9 kn/m 3 at optimum moisture content (OMC) of 15.7 %. EFFECT OF CEMENT CONTENT ON UNCONFINED COMPRESSIVE STRENGTH OF JAMSHORO SOIL To investigate the effect of cement on geotechnical properties of soil, the mixing of cement in soil is generally made at water content lower than the liquid limit of soil i.e. low water content mixing or water content equal to or higher than the liquid limit of soil that is high water content mixing (Lorenzo and Bergado, 26). In this research the effect of cement content on unconfined compressive strength of Jamshoro soil (q u ) is investigated by considering both the low and high water content mixing. However this paper describes the effect of cement content on unconfined compressive strength of Jamshoro soil considering high water content mixing. The water content of the soil cement mix is kept equal to the liquid limit of the soil i.e. 52%. Sample Preparation and Testing The air dry soil sample was mixed with the cement content of different proportions that is %, 5%, 1%, 15% and 2% of air dry soil weight. Then 171

4 International Symposium on Sustainable Geosynthetics and Green Technology for Climate Change (SGCC211) 7 to 8 December 211 Bangkok, Thailand the soil cement was mixed with water to obtain the soil cement pastes. The water content of the soil cement pastes was raised to the amount of liquid limit of soil. The care was taken to obtain the uniform mixing conditions in all the specimens. Then the soil cement pastes were filled into the stainless steel molds of 4 mm diameter and 8 mm length. The molds can be detached into two equal portions. The filling of molds was performed in three layers and each layer was slightly compacted to remove the air voids. The molds filled with soil cement paste were then kept on vibration table to remove air voids. The density (γ) of specimens was kept constant. The molds filled with specimen were than waxed and kept in desiccators to prevent loss of moisture. The wax of the molds was removed after 7 or 14 days (curing time). The molds were then detached and samples were moved to the strain controlled unconfined compression machine. The axial load was applied at the rate of 2mm/min. A strain gauge and load cell were used to measure the deformation and axial load respectively. The unconfined compressive strength of the specimens was then obtained by utilizing Eq. 7. qu P = (7) A where P is the applied load in kpa measured from load cell and A is the corresponding cross sectional area for the applied load, measured in mm 2. The A is calculated by using Eq. 8. A A 1 ε 1 = (8) where A is the initial cross sectional area of the specimen in mm 2 and ε 1 is the axial strain for applied load in %. ε 1 is calculated by using Eq. 9. ε = (9) 1 L L where L is initial height of the specimen and L is the change in length is specimen under applied load. The L was measured from strain gauge. Unconfined Compressive Strength of Jamshoro Soil at High Water Content Mixing and Various Cement Contents To observe the effect of cement content on unconfined compressive strength of Jamshoro soil it become essential to get the q u of Jamshoro soil at liquid limit, i.e. high water content mixing, without having any cement content i.e the base value. Figure 6 shows the relationship between axial stain and unconfined compressive strength for specimen having % cement content. It is observed that the unconfined compressive strength comes out in the range of.57 kpa to.61 kpa. The specimen cured for 14 days gave a slightly higher q u than that cured for 7 days Fig. 6 Stress-strain curves of Jamshoro soil at water content equals to liquid limit Figures 7, 8, 9 and 1 show the unconfined compressive strength and axial strain relationship for specimen having 5%, 1%, 15% and 2% cement content respectively. For 5% cement content the q u of the soil remained 131 kpa for 7 days of curing and 286 kpa for 14 days of curing. In case of 1% cement content, the obtained value of q u is 38 kpa and 766 kpa for 7 and 14 days of curing respectively. For 15% cement content and 7 days curing the q u remained 86 kpa which increased to 1385 kpa for 14 days of curing. As for as 2% of cement content is concerned, the qu remained 1 kpa for and 17 kpa for 14 days curing. Thus it can be said the mixing of cement in Jamshoro soil significantly increased its unconfined compressive strength. Fig Stress-strain curves of Jamshoro soil mixed with 5% of cement content and water content equals to liquid limit 172

5 International Symposium on Sustainable Geosynthetics and Green Technology for Climate Change (SGCC) 2 to 21 June 212 Bangkok, Thailand Fig. 8 Fig Stress-strain curves of Jamshoro soil mixed with 1% of cement content and water content equals to liquid limit Stress-strain curves of Jamshoro soil mixed with 15% of cement content and water content equals to liquid limit Fig. 1 Stress-strain curves of Jamshoro soil mixed with 2% of cement content and water content equals to liquid limit It is also observed that in all the cases the q u for time remained higher that of 7 days. Thus higher will be the curing time, higher will be the effect of cement content on q u of Jamshoro soil. Figures 11 and 12 show the q u of the soil at 7 days of curing and 14 days of curing respectively. It can be observed that not only the q u of the soil is increased with increase in cement content but the behavior of failure is also changed with cement content. At 2% of cement content the soil achieved a sufficient stiffness and failure behavior is changed from gradual to sudden. Unconfined compressive strength (q u ) (kpa) % cement content 5% cement content 1% cement content 15% cement content 2% cement content Fig. 11 Stress-strain curves of Jamshoro soil mixed with different % of cement content and cured for 7 days Unconfined compressive strength (q u ) (kpa) % cement content 5% cement content 4 1% cement content 15% cement content 2 2% cement content Fig. 12 Stress-strain curves of Jamshoro soil mixed with different % of cement content and cured for 7 days Figure 13 shows the trend of increase in unconfined compressive strength of Jamshoro soil with cement content for 7 days and 14 days of curing time. The q u is increasing with increase in the cement content but the slope of the curves is getting flatter after 15% of cement content. The 173

6 International Symposium on Sustainable Geosynthetics and Green Technology for Climate Change (SGCC211) 7 to 8 December 211 Bangkok, Thailand higher amount of cement content means the higher cost. Thus it can be said that the optimum percentage of cement content, as far as unconfined compressive strength of Jamshoro soil is concerned, may be 15%. Unconfined compressive strength (q u ) (kpa) Cement content (%) Fig. 13 Unconfined compressive strength versus cement content CONCLUSIONS In this paper the geotechnical properties of Jamshoro soil are discussed. In addition to that the effected of cement content on unconfined compressive strength of Jamshoro soil is investigated by considering high water content mixing. It is found that more than 75 % of the soil is silt and clay size and about 23 % of the soil is sand size. According to unified soil classification system the Jamshoro soil comes under the category of CH. This means the Jamshoro soil is inorganic clay of high plasticity. The Jamshoro soil comes under the category of A-7-6 (2) according to AASHTO classification. This indicates the soil shall not be used as a highway subgrade material. The mixing of cement in Jamshoro soil at high water content mixing significantly increased the unconfined compressive strength of soil. Thus higher the cement content, higher the unconfined compressive strength. However the optimum effect was achieved at cement content of 15%. The increase of curing time also caused the increase in unconfined compressive strength of soil at high water content mixing. The behavior of failure of Jamshoro soil is also changed with cement content. At 2% of cement content the soil achieved a sufficient stiffness and failure behavior is changed from gradual to sudden. REFERENCES (ASTM) (1998). Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass, ASTM D , Philadelphia. (ASTM) (1999). Standard Test Methods for Density of Soil and Rock in Place by the Sand Replacement Method in a Test Pit, ASTM D , Philadelphia. (ASTM) (2). Standard Test Methods for Liquid Limit, Plastic limits and Plasticity Index of Soils, ASTM D 4318-, Philadelphia. (ASTM) (22 a). Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer, ASTM D 854-2, Philadelphia. (ASTM) (22 b). Standard Test Methods for Particle Size Analysis of Soils, ASTM D (Re-approved 22), Philadelphia. (ASTM) (22 c). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort, ASTM D (Reapproved 22), Philadelphia. (ASTM) (24). Standard Test Methods for Shrinkage Factors of Soil by the Mercury Method, ASTM D 427-4, Philadelphia. Amu. O.O., Fajobi, A. B., and Afekhui S. O. (25). Stabilization Potential of Cement and Fly Ash Mixture on Expansive Clay Soils. Journal of Applied Sciences, Vol 5, pp Arora, K, R. (29). Soil Mechanics and Foundation Engineering, Standard Publishers India Chae K. I., Kwon M. N., Lee S.H. and Nam, H. S., (23). Permeability of Soil Bentonite Mixtures. J. Korea Soc. Agric. Eng., Vol. 45, pp Das, B. M (25), Fundamentals of Geotechnical Engineering, Thomson Publisher Canada Diamond, S. and Kinter, E. B. (1965). Mechanism of Lime Stabilization-An Interpretative Review. Highway Research Rec. Vol. 92, pp Garg, S.K. (21). Soil Mechanics and Foundation, Khanna Publishers India Ji-ru, Z. and Xing, C., (22). Stabilization of Expansive Soil by Lime and Fly Ash. Journal of Wuhan University of Technology Materials Science, Vol. 17, pp Lorenzo, G. A. and Bergado, D. T. (26). Fundamental Characteristics of Cement- Admixed Clay in Deep Mixing. Journal of Materials in Civil Engineering, Vol. 18, pp

7 International Symposium on Sustainable Geosynthetics and Green Technology for Climate Change (SGCC) 2 to 21 June 212 Bangkok, Thailand National Highway Authority (NHA) (29). Design Review and Construction Supervision of Karachi-Hyderabad M-9, PQ/EOI Document, National Highway Authority (NHA) Pakistan Yilmaz, I. and Civelekoglu, B. (29). Gypsum: An Additive for Stabilization of Swelling Clay Soils. Applied Clay Science, Vol. 44, pp

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TABLE OF CONTENTS DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK

TABLE OF CONTENTS DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS LIST OF SYMBOLS LIST OF APPENDICES