AN INQUISITIVE METHOD OF IMPROVING CALIFORNIA BEARING RATIO (CBR) VALUE OF MARGINAL SOIL SUBGRADE OF FLEXIBLE PAVEMENT CONSTRUCTION

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 6, June 2017, pp , Article ID: IJCIET_08_06_091 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed AN INQUISITIVE METHOD OF IMPROVING CALIFORNIA BEARING RATIO (CBR) VALUE OF MARGINAL SOIL SUBGRADE OF FLEXIBLE PAVEMENT CONSTRUCTION Pandu Kurre Research Scholar, Civil Engineering Department, University College of Engineering, Osmania University, Hyderabad, India M. Kumar Professor, Civil Engineering Department, University College of Engineering, Osmania University, Hyderabad, India G. V. Praveen Professor, Civil Engineering Department, S. R Engineering College, Warangal, India M. Heeralal Associate Professor, Civil Engineering Department, National Institute of Technology, Warangal, India ABSTRACT Various factors such as wheel loads, traffic intensity and class of traffic have been involved in the interplay of soil layers within the flexible pavement system. In addition to these factors, climate, type of terrain and subgrade condition influences the pavement performance. The construction of flexible pavements requires suitable improvement techniques for subgrade which deform and degrade subsequently under dynamic loads and hence, the long term performance of flexible pavement system is considerably affected mainly by the soil properties, strength and stability of the underlying soil layers. In general, in-situ subgrades may not provide the adequate support that required for attaining satisfactory performance under traffic loading based on materials used for the construction and environmental conditions. It is evident that, good quality materials are required for flexible pavement construction and in many work sites, marginal soils have been used for construction of underlying soil layers. The underlying subgrade is a layer is supposed to have good quality soil prepared to receive the stresses from the layers above. It is required that, at no time soil subgrade is overstressed. Further, it is supposed to be compacted to the desirable density at or near the optimum moisture content editor@iaeme.com

2 An Inquisitive Method of Improving California Bearing Ratio (CBR) Value of Marginal Soil Subgrade of Flexible Pavement Construction In the present study, an attempt is made to modify the locally available marginal soils using cement/lime and also to study the feasibility of using marginal soil mixed with fly ash for construction of subgrade layer of flexible pavement. The present study also includes the study of performance of flexible pavement system constructed with geotextile embedded in plain/modified marginal soil subgrade. Further, an attempt is made to develop a typical California Bearing Ratio (CBR) design charts of based on most affecting parameters such as quantity of cement or lime required to get desired CBR value of marginal soils used for laying of subgrade in flexible pavement using the comprehensive data obtained from the present study. Key words: Flexible Pavement; Subgrade; Marginal soil; California Bearing Ratio (CBR); Cement modification; Geotextile reinforcement. Cite this Article: Pandu Kurre, M. Kumar, G. V. Praveen and M. Heeralal, An Inquisitive Method of Improving California Bearing Ratio (CBR) Value of Marginal Soil Subgrade of Flexible Pavement Construction. International Journal of Civil Engineering and Technology, 8(6), 2017, pp INTRODUCTION California Bearing ratio (CBR) test is the penetration test meant for evaluation of subgrade strength for pavement construction. This test is the most widely used method especially for the design of flexible pavements. CBR= (Test load/standard load) 100 Table 1 Standard loads adopted for different penetrations for the standard material with CBR value of 100% Penetration of plunger (mm) Stadard Load (kg) In the present work, locally available marginal soil was modified using cement/lime to overcome the ill-effects of its plasticity. A detailed laboratory California Bearing Ratio (CBR) testing was carried out using geotextile reinforcement on marginal soil samples without and with cement/lime modification without/with admixing fly ash to understand the strength mechanisms through CBR tests. These results were compared with those obtained from conventional soil (gravel) samples. Further, in the present investigation, the above objectives were set to study the viability of usage of marginal soil in place of prescribed conventional soil (gravel) and thus, to overcome associated problems in laying subgrade layer of flexible pavement. 2. MATERIALS USED The present investigation is undertaken to understand the mechanical strength behavior of reinforced marginal soil without and with cement modification admixed without/with fly ash for which the following materials were used editor@iaeme.com

3 Pandu Kurre, M. Kumar, G. V. Praveen and M. Heeralal Gravel: Gravel is a coarse grained soil with particle size under 2.36 mm with little or no fines contributing to cohesion of materials used in the present investigation. Gravel is the product of decomposition and weathering of the pavement rock. Marginal Soils: The following 3 types of marginal soils (Table 2) posses plasticity index (PI) greater than the specified limits (>10) and are likely to give CBR values in the range of 3 6%. This is due to the presence of higher amount of plastic fines, which causes reduction of CBR value. Table 2 Types of Marginal Soils used for CBR tests S.No. Type of Marginal Soil % of Plastic Fines Range of Liquid Limit 1 Marginal Soil Marginal Soil Marginal Soil Marginal Soil Cement: The marginal soil cement mixes with different cement contents were tested for their Atterberg limits and UCS values as given in Table 3. Table 3 The properties of plain and cement modified marginal soil Property Atterberg Limits (Immediately after adding the cement) Liquid Limit, w l (%) Plastic Limit, w p (%) Atterberg Limits (At 3 days curing period) Liquid Limit, w l (%) Table 4 The properties of plain and lime modified marginal soil Property Atterberg Limits (Immediately after adding the lime) Liquid Limit, w l (%) Plastic Limit, w p (%) Atterberg Limits (At 3 days curing period) Liquid Limit, w l (%) Lime content in Marginal Soil 0% 2% 4% 6% 8% 10% Cement content in Marginal Soil 0% 2% 3% 4% 5% 10% NP --- NP NP NP NP NP Plastic Limit, w p (%) Unconfined Compressive Strength (kpa) (At 3 days curing period) NP --- NP NP NP NP NP Plastic Limit, w p (%) Unconfined Compressive Strength (kpa) (At 3 days curing period) editor@iaeme.com

4 An Inquisitive Method of Improving California Bearing Ratio (CBR) Value of Marginal Soil Subgrade of Flexible Pavement Construction Marginal Soil Lime: Similar to the marginal soil cement mixes, tests were conducted by varying 2, 4, 6, 8 and 10 percent of lime by weight of soil mass. The properties of marginal soil lime mix have been mentioned in the table 3. From the table 3, it can be observed that the soil has become non-plastic (NP) at 2% cement content and for the subsequent CBR studies with 3, 6, 9 and 12% cement/lime contents by dry weight of soil were used. Cement: Ordinary Portland cement of 53 grade is used to modify the marginal soil. Geotextile: Fibertex G 100, a non woven geotextile was used as reinforcing materials and its properties are given in Table 5. The properties were determined as per the standard procedures. Table 5 Properties of Geotextile Property Weight Thickness at 2 kpa Wide width tensile strength In-plane permeability Apparent opening size, O 95% Fibertex G 100 (non-woven) 100 g/m mm 4.0 kn/m 0.13 m/sec 110 micron 3. TESTING PROCEDURE In the present investigation, CBR tests were performed with three marginal soils, individually admixed with different proportions of cement and/or lime or fly ash as per IS: 2720 Part without soaking and after 4 days of soaking. For this, the calculated weight of marginal soil mass with and without admixture (cement/lime/fly ash) is with compacted by thoroughly mixed with optimum moisture content to obtain desired maximum dry density. In the present study, these tests have been performed on remoulded soil samples with static compaction. Figure 1 Schematic diagram of California Bearing Ratio test set up editor@iaeme.com

5 Pandu Kurre, M. Kumar, G. V. Praveen and M. Heeralal 4. CBR TESTS The results of CBR testing data have been presented in the following table Marginal Soil Cement or Lime Mixes Type of Soil Sample Table 6 CBR values of Marginal soils Soaked CBR values of Marginal Soil (without and with cement or lime) Soaked CBR in % % of cement content % of lime content Marginal Soil Marginal Soil Marginal Soil Soaked CBR values of Marginal Soil (without and with cement or lime) with geotextile reinforcement Marginal Soil Marginal Soil Marginal Soil Soaked CBR values of Plain and 10% Fly ash mixed Marginal Soil without/with geotextile reinforcement Marginal Soil Marginal Soil Marginal Soil Soaked CBR values of Plain and 10% Fly ash mixed Marginal Soil without/with geotextile reinforcement Marginal Soil Marginal Soil Marginal Soil It is observed from the above table that, CBR values of marginal Soils are increased in case of marginal soil cement mixes. This could be due to modification of plasticity characteristics of plastic fines present in these marginal soils. Due to this reason, the added cement content could bind the soil particles and only fraction of cement content is being utilized for modifying plastic nature of soils. Further, in case of marginal soil lime mixes, CBR values of marginal soils have been significantly improved up to addition of 6% lime content. The improved CBR could be attributed to decreased plasticity and flocculation of finer particles within the soil mass. From the table 6, it is further observed that, the improvement of CBR values are not much significant beyond the addition of 6% lime as no cementitious reactions could be developed as the pozzolonic reactions are being long term reactions Marginal Soil Cement or Lime Mixes Without/With Geotextile The CBR values of cement/lime modified marginal soils without/with embedment of geotextile (Fibertex G 100) are presented in table 6. The geotextile was introduced in the middle height of the soil specimen. In the preliminary testing of modification of marginal soil with cement or lime, it is observed that, 3% cement or 5% lime content could be sufficient to convert marginal soil in to non plastic nature. From the above table (Table 6), in case of geotextile embedded and modified marginal soils, it could be clearly observed that, at 3% cement content or 6% lime content, CBR values are much significant. This is attributed to the fact that, geotextile could enhance the strength editor@iaeme.com

6 An Inquisitive Method of Improving California Bearing Ratio (CBR) Value of Marginal Soil Subgrade of Flexible Pavement Construction of the subgrade soil due to the attainment of flexible nature of marginal soil from nullified plasticity of finer particles. In this case, geotextile could provide the almost complete strength by development of bonding due to frictional forces in soil geotextile interface. Further, it can be observed from the results that, CBR values are more significant at 3% cement content and 6% lime content. The modified marginal soil has become stiffer at 6% cement content and the soil particles could not derive the reinforcing action from the geotextile. The same phenomenon is observed in case of specimens modified with the lime content above 6% Marginal Soil Cement or Lime Mixes Reinforced without/with Geotextile without/with mixing 10% Fly ash The table 6 shows the CBR values obtained by plain and cement modified marginal soil without/with mixing of 10% fly ash and without/with the provision of geotextile reinforcement. From the above table, it can be observed that, at 6% cement content, the CBR value is more significant due to nullified plasticity of marginal soil, filling up of voids of marginal soils by fly ash and induction of binding property by adequate amount of cement content. On the other hand, the table 6 shows the CBR values obtained by plain and lime modified marginal soil without/with mixing of 10% fly ash and without/with the provision of geotextile reinforcement. From this table, the CBR values of lime modified and 10% fly ash mixed marginal soil embedded with geotextile fabric reinforcement (Fibertex G 100) are higher at 9% lime content at which pozzolonic action took place without altering the flexible nature of modified marginal soil particles. It can be inferred from above results that, the addition of cement or lime in the range of 3 to 6% significantly modifies the plasticity of marginal soils and making it into non plastic soils. Further, a multifold increase in the CBR values of marginal soil (plastic soils) is observed upon addition of little quantity of cement/lime modification despite of embedding geotextile and mixing with 10% fly ash. 5. DEVELOPMENT OF DESIGN CHART Using the data obtained from extensive research study of present work, it is tried to develop typical CBR design charts to obtain the approximate cement content, lime content for the given marginal soil (with plasticity) without/with mixing of fly ash. To use this chart, the liquid limit and percent fines of given marginal soil are to be obtained from laboratory testing. Based on the values the quantity of cement or lime to be added to marginal soil will be estimated. To get desired CBR value for the given marginal soil, quantities of cement or lime or fly ash to be added can be approximately known by drawing a horizontal line to the band in which the given soil properties are lying and then drawing a vertical line to the abscissa editor@iaeme.com

7 Pandu Kurre, M. Kumar, G. V. Praveen and M. Heeralal Figure 2 CBR Design Charts for various combinations of 3 types of marginal soil modified with cement/lime The proposed CBR design chart could be used as a preliminary guide to select the possible cement content to get desired CBR value for marginal soil over a predetermined range of plasticity and percent fines. 6. CONCLUSIONS From the variation of soaked CBR of the soil stabilized with cement marginal soil fly ash, it is clearly noticed that the soil shows great increase in the CBR with 3% cement and 10% fly ash combined when compared to 5% lime and fly ash. This improvement in CBR may be attributed to change of soil structure from dispersed to flocculate. Hence, the proposed marginal soil modified with cement or lime, mixed with fly ash and reinforced with geotextile can be a potential alternative to conventional soil subgrade. It does not involve the construction and maintenance problems that could help in faster construction of flexible pavements with considerable economy. This study summits up that the locally available marginal soil mixed with fly ash and reinforced with geotextile can be advantageously utilized as subgrade material by adopting cement or lime modification. By adopting this stabilization technique, the load carrying capacity of flexible pavement has also been significantly improved. REFERENCES [1] Antiohos., S and Tsimas, S. (2004). Activation of Fly Ash Cementitious Systems in the Presence of Quicklime: Part I. Compressive Strength and Pozzolanic Reaction Rate. Cement and Concrete Research, 34, pp editor@iaeme.com

8 An Inquisitive Method of Improving California Bearing Ratio (CBR) Value of Marginal Soil Subgrade of Flexible Pavement Construction [2] EuroSoilStab. (2002). Development of Design and Construction Methods to Stabilize Soft Organic Soils: Design Guide for soft soil stabilization. CT , European Commission, Industrial and Materials Technologies Programme (Rite-EuRam III) Bryssel. [3] Goel, R. Mechanically Stabilized Earth Walls and Reinforced Soil Slopes: Indian Scenario- A Comprehensive Review. Journal of the Indian Roads Congress, 2006, Vol. 67, No.1, [4] I.S: 2720 (Part XVI)-1965: Indian standard for laboratory determination of CBR, Bureau of Indian Standards Publications, New Delhi. [5] Jones, D., Rahim, A., Saadeh, S., and Harvey, J.T. (2010). Guidelines for the Stabilization of Subgrade Soils in California FHWA No: CA122201A (2010). [6] Kandhal, P. S., and Mallick, R. B. (2001). Effect of Gradation on Rutting Potential of Dense Graded Asphalt Mixtures. TRR 1767, TRB, USA, pp [7] Koerner, R.M. Emerging and Future Developments of Selected Geosynthetic Applications. Journal of Geotechnical And Geoenvironmental Engineering, 2000, Vol.126, No.4, [8] Mandal, J.N., and Divshikar, D.G. A Guide to Geotextiles Testing New Age International (Pvt. Ltd.) Publishers, New Delhi, ISBN: X [9] G Pradeep Reddy, G Tarun Krishna, K Hemantha Raja and S Shahabas, Design of Polyester (Recron-3S) Fiber Reinforced Flexible Pavement. International Journal of Civil Engineering and Technology, 8(4), 2017, pp [10] Waweru S.G, Onchiri R.O and Masibayi E.N., Factors Causing Structural Failure of the Flexible Pavement along Timboroa to Malaba Road in Kenya. International Journal of Civil Engineering and Technology, 7(4), 2016, pp editor@iaeme.com