Stone column is often employed for strengthening of an embankment seated on deep soft clay. But in very soft clay having undrained shear strength less than or equal to 15？kPa, stone column may not derive adequate load carrying capacity and undergo large lateral deformation due to inadequate lateral confinement. In such circumstances, reinforcement to individual stone column by geosynthetics enhances load carrying capacity and reduces lateral deformation. This paper addresses parametric study on behaviour of embankment resting on Geosynthetic Reinforced Stone Column (GRSC) considering parameters such as stone column spacing to diameter ratio, deformation modulus of stone column material, geosynthetic stiffness, thickness of soft clay, and height of embankment by 3D numerical analysis. Finally, equation for Settlement Improvement Factor (SIF), defined as ratio between settlement of embankment without treatment and with geosynthetic reinforced stone column, is proposed that correlates with the major influence parameters such as stone column spacing to diameter ratio, deformation modulus of soft clay, and geosynthetic stiffness. 1. Introduction Embankment seated on deep soft clay may undergo large settlement both vertically and horizontally. Various ground improvement techniques adopted to mitigate the settlements are stone column [1, 2], preconsolidation using prefabricated vertical drains [3, 4], vacuum preconsolidation [5, 6], deep mixed column [7, 8], and so forth. Provision of stone column in the embankment foundation has advantage of reinforcing effect, reduction in settlement, and acceleration of consolidation settlement. However, in soft clay having undrained cohesion less than or equal to 15？kPa, there will be excessive lateral deformation of stone column. Also, soft clay may penetrate into the stone column [9]. To overcome these problems, individual stone column may be reinforced peripherally by using a suitable geosynthetic. Numerous researchers have acknowledged this concept [10–18]. Most of the previous studies have focused on the effect of geosynthetic reinforcement on load carrying capacity of isolated stone column only. Very few authors have studied behaviour of GRSC under long-term loading condition, that is, embankment loading [19–21]. Current study examines the performance of embankment supported on GRSC. Effect of GRSC spacing to diameter ratio, deformation of stone column material, geosynthetic stiffness, thickness of soft clay, and height of embankment on embankment settlement is studied. Based on the present study, equation for SIF is
References
[1]
D. Greenwood, “Mechanical improvement of soils below ground surface,” in Proceedings of Ground Engineering, pp. 11–22, The Institution of Civil Engineers, London, UK, 1970.
[2]
J. M. O. Hughes, N. J. Withers, and D. A. Greenwood, “Field trial of the reinforcing effect of a stone column in soil,” Geotechnique, vol. 25, no. 1, pp. 31–44, 1975.
[3]
A. T. Yeung, “Design curves for prefabricated vertical drains,” Journal of Geotechnical and Geoenvironmental Engineering, vol. 123, no. 8, pp. 755–759, 1997.
[4]
S. L. Shen, J. C. Chai, Z. S. Hong, and F. X. Cai, “Analysis of field performance of embankments on soft clay deposit with and without PVD-improvement,” Geotextiles and Geomembranes, vol. 23, no. 6, pp. 463–485, 2005.
[5]
J. Chu, S. W. Yan, and H. Yang, “Soil improvement by the vacuum preloading method for an oil storage station,” Geotechnique, vol. 50, no. 6, pp. 625–632, 2000.
[6]
B. Indraratna, C. Bamunawita, and H. Khabbaz, “Numerical modeling of vacuum preloading and field applications,” Canadian Geotechnical Journal, vol. 41, no. 6, pp. 1098–1110, 2004.
[7]
H. Krenn and M. Karstunen, “Numerical modelling of deep mixed columns below embankments constructed on soft soils,” in Proceedings of the 2nd International Workshop on Geotechnics of Soft Soils, pp. 159–164, Glasgow, Scotland, September 2008.
[8]
J. Huang and J. Han, “3D coupled mechanical and hydraulic modeling of a geosynthetic-reinforced deep mixed column-supported embankment,” Geotextiles and Geomembranes, vol. 27, no. 4, pp. 272–280, 2009.
[9]
D. Alexiew, D. Brokemper, and S. Lothspeich, “Geotextile Encased Columns (GEC): load capacity, geotextile selection and pre-design graphs,” in Proceedings of the Geo-Frontiers, pp. 497–510, ASCE Geotechnical Special Publication, Austin, Tex, USA, January 2005.
[10]
S. Murugesan and K. Rajagopal, “Geosynthetic-encased stone columns: numerical evaluation,” Geotextiles and Geomembranes, vol. 24, no. 6, pp. 349–358, 2006.
[11]
M. Raithel and H. G. Kempfert, “Calculation models for dam foundations with geotextile-coated sand columns,” in Proceedings of the International Conference on Geotechnical and Geological Engineering (GeoEngg '00), p. 347, Melbourne, Australia, 2000.
[12]
H. G. Kempfert, W. M？bius, P. Wallis, M. Raithel, M. Geduhn, and R. G. McClinton, “Reclaiming land with geotextile-encased columns,” Geotechnical Fabrics Report, vol. 20, no. 6, pp. 34–39, 2002.
[13]
M. Raithel, H. G. Kempfert, and A. Kirchner, “Geotextile Encased Columns (GEC) for foundation of a dike on very soft soils,” in Proceeding of 7th International Conference on Geosynthetics, pp. 1025–1028, Balkema, The Netherlands, 2002.
[14]
D. Brokemper, J. Sobolewski, D. Alexiew, and C. Brok, “Design and construction of geotextile encased columns supporting geogrid reinforced landscape embankments: Bastions Vijfwal Houten in the Netherlands,” in Proceeding of the 8th International Conference on Geosynthetics, pp. 1681–1684, Amsterdam, The Netherlands, 2006.
[15]
D. Lee, A. Song, S. Kim, and C. Yoo, “Short and long term load carrying capacity of geogrid-encased stone column-a numerical investigation,” Journal of Korean Geotechnical Society, vol. 23, no. 8, pp. 5–16, 2007.
[16]
C. Yoo, A. Song, S. Kim, and D. Lee, “Finite element modeling of geogrid-encased stone column in soft ground,” Journal of Korean Geotechnical Society, vol. 23, no. 10, pp. 133–150, 2007.
[17]
J. Gniel and A. Bouazza, “Improvement of soft soils using geogrid encased stone columns,” Geotextiles and Geomembranes, vol. 27, no. 3, pp. 167–175, 2009.
[18]
C. S. Wu and Y. S. Hong, “Laboratory tests on geosynthetic-encapsulated sand columns,” Geotextiles and Geomembranes, vol. 27, no. 2, pp. 107–120, 2009.
[19]
C. Yoo and S. B. Kim, “Numerical modeling of geosynthetic-encased stone column-reinforced ground,” Geosynthetics International, vol. 16, no. 3, pp. 116–126, 2009.
[20]
S. R. Lo, R. Zhang, and J. Mak, “Geosynthetic-encased stone columns in soft clay: a numerical study,” Geotextiles and Geomembranes, vol. 28, no. 3, pp. 292–302, 2010.
[21]
C. Yoo, “Performance of geosynthetic-encased stone columns in embankment construction: numerical investigation,” Journal of Geotechnical and Geoenvironmental Engineering, vol. 136, no. 8, pp. 1148–1160, 2010.
[22]
R. B. Brinkgreve and P. A. Vermeer, PLAXIS 3D-Finite Element Code for Soil and Rocks Analysis, Balkema, Rotterdam, The Netherlands, 2012.
[23]
M. Raithel, A. Kirchner, C. Schade, and E. Leusink, “Foundation of constructions on very soft soils with geotextile encased columns—state of the art,” in Proceedings of the Geo-Frontiers, pp. 1867–1877, Austin, Tex, USA, January 2005.
[24]
H. G. Kempfert, “Embankment foundation on geotextile-coated sand columns in soft ground,” in Proceedings of the 1st Euopean Geosynthetics Conference in Maastrich, Geosynthetics. Applications, Design and Construction, pp. 245–250, A. A. Balkema, Rotterdam, The Netherlands, 1996.
