Swelling , shrinkage and strength characteristics of expansive soil treated with rice husk ash
Influence of Rice Husk Ash On the Swelling and Strength Characteristics of Expansive Soil Anil Kumar Choudhary Department of Civil Engineering, National Institute of Technology Jamshedpur, Jamshedpur – 831014, E-mail:
[email protected]
J. N. Jha Muzaffarpur Institute of Technology (MIT), Muzaffarpur,Bihar, E-mail:
[email protected]
Arpit Jain Madhumita Mohanty Department of Civil Engineering, National Institute of Technology Jamshedpur, Jamshedpur – 831014 E-mail :
[email protected],
[email protected]
ABSTRACT: This paper presents the results of an experimental investigation to study the effect of rice husk ash (RHA) on swelling, shrinkage and strength characteristics of black cotton soil (BCS). India has a large production of rice as a major crop. The rice husk is generated as a by-product from milling operations. Non-volatile part of this husk is converted into ash and is known as rice husk ash. RHA and black cotton soil mixtures are thoroughly prepared by varying the content of RHA up to 20% by dry weight of soil. Differential Free Swell, Atterberg limit, shrinkage factor, light compaction tests, UU triaxial tests, soaked CBR were carried out after 3 days of curing. Test results reveal that addition of RHA not only reduces the swelling and shrinkage characteristics of black cotton soil but also increases its strength considerably. It is concluded that rice husk ash may serve as a cheaper alternative as compared to other additives for improving the performance of black cotton soil in various civil engineering projects. Keywords: Expansive soil; Black Cotton Soil; Rice Husk Ash; Strength characteristics
1. Introduction Soil is generally used as a support system for foundation of buildings, dams and pavements. It being a natural material plays a very crucial role in civil engineering projects. It is also used as a material for construction of retaining wall backfills, earth dam, unpaved roads etc. As soil is made by nature, its properties vary significantly with location, time and surrounding environment. Expansive soils are those category of soil whose unexpected behaviour cause damage to structures built over it, as its volume and strength properties changes with change in water content. Due to shrinkage and swelling characteristics of expansive soil, it causes ground movement causing distress and cracking of structure built over it. Expansive soils found in India are
commonly called as black cotton soil owing to their black colour and ability to grow cotton (Ranjan and Rao 2000). These soils create troubles in arid and semi arid regions of India like M.P, Jharkhand, Odisha, Gujarat etc where the rate of rainfall is less than the evaporation rate (chen 1975). Stabilization Techniques can be adopted on large scale when the treatment is of low cost and durable. Rice husk ash is one of the major wastes found abundantly. In India, the annual production of paddy is about 100 million tonnes. The burning of rice husk generates about 20% of its weight as ash; thereby generating more than 4 million tons of rice husk ash (Shrivastava,2014 ).Hence in the present investigation an attempt has been made to investigate the possible
Swelling , shrinkage and strength characteristics of expansive soil treated with rice husk ash
utilization of rice husk ash (RHA) in the improvement of geotechnical characteristics of black cotton soil. 2. Test Materials For the experimental investigation, the expansive soil was collected from a site nearby Sagar, M.P. The soil was taken from 0.5 m below the ground level to avoid the effects of vegetation. Rice Husk Ash (RHA) was procured from Vikha Enterprises, Rourkela, Odisha. The various physical properties of black cotton soil and RHA are presented in Table-1 and Table2 respectively. The grain-size distribution curves of black cotton soil and RHA are shown in Fig.1.
Fig.1Grain Size Distribution for BCS and RHA. Table-1 Physical properties of RHA PROPERTY VALUE Color Grey Specific Gravity 1.57 DFS (%) Nil Plasticity Index (%) Non Plastic Table-2 Physical properties of black cotton soil PROPERTY VALUE Specific Gravity 2.36 DFS (%) 55.00 Liquid Limit (%) 40.75 Plastic Limit (%) 11.30 Plasticity Index (%) 29.75 Classification (IS:1498-1970) CI OMC (%) 18.00 MDD (kN/m2) 17.94 CUU ( kN/m2) 41.16 ΦUU (degrees) 16.00
3. Sample Preparation and Testing The black cotton soil and RHA were at first oven dried in the laboratory at 105°C for 24hrs. Soil and RHA were then pulverized and passed through 4.75m sieve. Composite samples of soil-RHA were prepared by thorough mixing of RHA to the soil. The amount of RHA in the composite sample is taken as the percentage of dry weight of RHA in the total dry weight of composite sample. Details of composite mixtures used in the investigation are tabulated in Table-3. The various tests viz. Atterberg limits, shrinkage characteristics, light compaction, UU triaxial tests, soaked CBR tests were carried out with specimens prepared with each of these mixtures following the standard procedure as laid down in the respective Indian Standards codes of practice. Differential Free Swell test was also conducted following ASTM 4546. Table-3 Mix proportion of samples used for tests Mixture Designation Materials (%) BCS RHA BCS 100 0 95%BCS +5%RHA 95 5 90%BCS+10%RHA 90 10 85%BCS +15%RHA 85 15 80%BCS +20%RHA 80 20 4. Results and Discussions Variation of liquid limit, plastic limit and plasticity index with varying RHA content are presented through Fig.2 and it is observed that with an increase in RHA content, the liquid limit and plastic limit increase, whereas plasticity index decreases.
Fig. 2 Variation of Liquid Limit, Plastic Limit & Plasticity Index with RHA content
Indian Geotechnical Conference 2017 GeoNEst 14-16 December 2017, IIT Guwahati, India
The increase in water content is probably a consequence of additional water held within flocculated soil structure resulting from RHA soil interaction and soil class shifts to silt properties. Fig.3 presents the variation of DFS with increasing RHA content and it is observed that with increase in RHA content DFS value decreases and reaches to a minimum value of 12.08% at 20% RHA content, thus indicating the swelling potential from high to very low.
The low CBR of the clayey soil as compared to the RHA admixed soil sample is attributed to its inherent low strength which is due to the dominance of the clay fraction. This is due to the frictional resistance contributed by RHA in addition to the cohesion from the clayey soil.
Fig. 5 Variation of CBR with RHA content
Fig. 3 Variation of DFS with RHA content The remarkable decrease in DFS is attributed to non- cohesive and non-swelling characteristics of RHA. Fig. 4 presents the load –penetration curves for various mixes and it is observed that for any specific penetration; stabilized soil shows more resistance then its unstabilized counterpart and penetration resistance increases with increase in RHA content.
Unconsolidated undrained triaxial tests were carried out with specimens compacted to their maximum dry densities at their respective optimum moisture content and cured for three days for each of the mixes. Fig. 6 presents the variation of Peak deviatory stress at failure for various mixes at varying Cell pressures .It is observed that for a given mix peak deviatory stress increases with increase in cell pressure and also for a given cell pressure peak deviatory stress increases with increase in RHA content.
Fig. 6 Variation in Peak Deviatory stress with varying RHA at different cell pressures Fig. 4 Load Penetration curves for BCS – RHA mix Fig. 5 shows the variation of CBR with increasing RHA content and it is observed that CBR value increases with increasing RHA content. Increase in CBR value shall not only result in reduced pavement thickness but also result in considerable saving if black cotton soil stabilized with 20 % RHA is used a sub base/ base course.
Table-4 presents the variation of shear strength parameters viz. cuu and φuu with increasing RHA content in the mix. It is observed that initially cuu increases with increase in RHA content and reached a maximum at about 10% RHA content but addition of RHA beyond 10% however results in a decrease of cuu value while there is marginal decrease in φuu value with increasing in RHA content. The variation in shear strength parameters may be attributed to the change of gradation in the 3
Swelling, shrinkage and strength characteristics of expansive soil treated with rice husk ash
soil -RHA mix but the stress- strain characteristics of the mix changes significantly from that of raw soil. Table-4 Variation of Shear Strength Parameters with RHA content. RHA Content (%)
IRC: 37-2001,Guidelines for the design of Flexible Pavements. IS: 1498-1970, Classification and Identification of soils For General Engineering Purposes.IS: 2720 Part- 4 (1985), Grain Size Analysis.
Shear Strength Parameters (Unconsolidated Undrained) Cohesion ‘Angle of Internal ‘Cuu ‘ Friction φuu ‘ (kN/m2) (in degree) 0 41.16 16.00 5 58.80 10.22 10 64.68 11.21 15 62.72 10.28 20 50.78 9.50 5. Conclusions:
IS: 2720 Part- 5 (1985), Determination of Liquid and Plastic Limit.
From the present investigation, conclusions can be drawn:
Patel, P. and Mahiyar, H.K. (2014) Experimental study of black cotton soil stabilized with Rice Husk Ash, Fly Ash and Lime, International Journal Engineering, Research and Technology, 3(11), 660-665.
following
1. Addition of RHA to Black cotton soil changes its degree of expansiveness from high to low i.e DFS value decreased from 55 % for raw soil to12.08% for mix with RHA content of 20%. 2. Plasticity index of black cotton soil decreases with increasing RHA content in the mix making it less sensitive to moisture variation. 3. Addition of RHA to black cotton soil increases its penetration resistance and there is a considerable increase in the CBR value with increasing RHA content in the mix. 4. Addition of RHA results in an increase in cuu value upto 10% RHA content and thereafter decreases with further increase in RHA content while φuu decreases marginally with increasing RHA content in the mix. References Chen,F.H.(1975). Foundations on Expansive Soils. Elsevier Scientific Publishing Company.
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IS: 2720 Part-7 (1980), Water Content- Dry Unit Weight Relation Using Light Compaction. Manikandam ,A. T.and Moganraj,M.(2014) Consolidation and rebound characteristics of expansive soil by using lime and bagasse husk ash, International Journal of Research in Engineering and Technology, 3(4), 2321-7308.
Rao,,A.V.N.,,Penchalaiah,,B.,,Chitranjan, M.and Ramesh,P.(2014)Compressibility behaviour of black cotton soil admixed with rice husk ash 3(4), International Journal of Innovative Research in Science, 11473-11480. Sabat, A. K., and Pradhan, A. (2014).Fiber Reinforced- Fly Ash Stabilized Expansive Soil Mixes as Subgrade Material in Flexible Pavement,EJGE, 19, 5757–5770. Shrivastava D., Singal, A.K. and Yadav, R.K. (2014) Effect of rice husk ash on the engineering properties of black cotton soil,International Journal of Engineering Research and Science & Technology, 3(2), 292-296. Singhai,A.K. and Singh, S.S. (2014).Laboratory study on soil stabilisation using Rice Husk Ash International Journal of Research in Engineering and Technology, 3(11), 348-351.
