Experimental and Numerical Studies on Load-Carrying Capacity of Single Floating Aggregate Piers Reinforced with Vertical Steel Bars

Document Type : Research Article


1 Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran

2 College of Civil Engineering, Tafresh University, Tafresh , Iran

3 School of Civil Engineering, University College of Engineering, University of Tehran, Tehran, Iran


The load-carrying capacity of the aggregate piers increases by circumferential confinement created by the surrounding soil. In soft clay soils, the amount of confinement is usually not sufficient to develop a load-carrying capacity. Because of that, it is practical to use geosynthetic reinforced aggregate piers in this type of soils. This paper intends to evaluate the use of vertical steel bars as an alternative for geosynthetics. In this study, some small-scale laboratory tests were performed on floating aggregate piers with diameters of 80 and 100 mm and a length of 400 and 500 mm, respectively reinforced with vertical steel bars. Moreover, two-dimensional numerical modeling using the Plaxis software was conducted. The results show that using bars with more stiffness leads to more increase in load-carrying capacity. Reinforcing the full length of the aggregate piers, compared to half-length, will further improve the load-carrying capacity of the aggregate piers. In the early stages, by applying the load, the stone aggregates tend to compress, so load-carrying capacity increases and by continuing this process, the tendency to the occurrence of lateral bulging is seen and due to the low resistance of kaolin clay to the bulging, the increase of load-carrying capacity is negligible. Also, numerical modeling results show that the floating aggregate pier penetrated into soft clay soil in the full-length case, and the failure state changed from bulging to slip.


Main Subjects

1.Hughes JMO, Withers NJ (1974) Reinforcing of soft cohesive soils with stone columns. Ground Engineering 49–42:(3)7.
2.Madhav MR, Miura N (1994) Soil improvement. Panel report on stone columns. Proceedings of the 13th International Conference on Soil Mechanics and Foundation Engineering, New Delhi, India, 164-5:163.
3.Van Impe WF (1989) Soil improvement techniques and their evolution, Balkema, Rotterdam, the Netherlands.
4.Raithel M, Kempfert HG (2000) Calculation model for dam foundations with geotextile coated sand columns. International Conference on Geotechnical and Geological Engineering, Melbourne, Australia.
5.Alexiew D, Brokemper D, Lothspeich S (2005) Geotextile encased columns (GEC): load capacity, geotextile selection and pre-design graphs. Geo-frontiers Conference, Austin, Texas 510-497.
6.Ayadat T, Hanna AM (2005) Encapsulated stone columns as a soil improvement technique for collapsible soil. Ground Improvement 147–137 :(4)9. https://doi. org/10.1680/grim.2005.9.4.137
7.Gniel J, Bouazza A (2009) Improvement of soft soils using geogrid encased stone columns. Geotextiles and Geomembranes 175–167:(3)27. https://doi.org/10.1016/j. geotexmem.2008.11.001
8.Gniel J, Bouazza A (2010) Construction of geogrid encased stone columns: a new proposal based on laboratory testing. Geotextiles and Geomembranes 118–28,108. https://doi. org/10.1016/j.geotexmem.2009.12.012
9.Wu C.S., Hong, Y.S., 2009. Laboratory tests on geosynthetic encapsulated sand columns. Geotextiles and Geomembranes 120–107 ,(2) 27. https://doi.org/10.1016/j. geotexmem.2008.09.003
10.Murugesan S, Rajagopal K (2010) Studies on the behavior of single and group of geosynthetic encased stone columns. Journal of Geotechnical and Geoenvironmental Engineering 139-129:(1)136.https://doi.org/10.1061/)ASCE(GT.5606.0000187-1943
11. Lo SR, Zhang R, Mak J (2010) Geosynthetic-encased stone columns in soft clay: a numerical study. Geotextiles and Geomembranes 302-292:)3( 28. https://doi.org/10.1016/j. geotexmem.2009.09.015
12. Almeida, M. S. S., Hosseinpour, I., Riccio, M. & Alexiew, D. (2015). Behaviour of geotextile-encased granular columns supporting test embankment on soft deposit. Geotechnical and Geoenvironmental Engineering, 141, No. 04014116 ,3. https://doi.org/10.1061/)ASCE( GT.5606.0001256-1943
13. Hong YS, Wu CS, Yu YS (2016) Model tests on geotextileencased granular columns under -1g and undrained conditions. Geotextiles and Geomembranes 27-13:(1)44. https://doi.org/10.1016/j.geotexmem.2015.06.006
14. Miranda M, Costa AD (2016) Laboratory analysis of encased stone columns. Geotextiles and Geomembranes 277-269:)3(44. https://doi.org/10.1016/j. geotexmem.2015.12.001
15. Hasan M, Samadhiya NK (2016) Experimental and numerical analysis of geosynthetic-reinforced floating granular piles in soft clays. International Journal of Geosynthetics and Ground Engineering 3–1:(22)2. https://doi.org/10.1007/s6-0062-016-40891
16. Muzammil SP, Varghese RM, Joseph J (2018) Numerical simulation of the response of geosynthetic encased stone columns under oil storage tank. International Journal of Geosynthetics and Ground Engineering 12–1:(4)4. https://doi.org/10.1007/s6-0122-017-40891
17. Lajevardi SH, Enami S, Hamidi M, Shamsi HR (2018) Experimental study of single and groups of stone columns encased by geotextile. Journal of Science and Technology. https://doi.org/10.22060/CEEJ.2018.12789.5269
18. Lajevardi, SH, Shamsi HR, Hamidi M, Enami S (2018) Numerical and experimental studies on single stone columns. Soil Mechanics and Foundation Engineering 5(55(:345-340. https://doi.org/10.1007/s-9546-018-112049
19. Madhav MR, Alamghir M, Miura N (1994) Improving granular column capacity by geogrid reinforcement. Proceedings of the 5th International Conference on Geotextiles, Geomembranes and Related Products, Singapore 356–351.
20. Malarvizhi SN, Ilamparuthi K (2007) Comparative study on the behavior of encased stone column and conventional stone column. Soils and Foundations 885-873:(5)47. https://doi.org/10.3208/sandf.47.873
21. Samadhiya NK, Maheshwari P, Zsaki A, Basu P, Kundu A (2009) Strengthening of clay by geogrid reinforced granular pile. International Journal of Geotechnical Engineering, 386–377 ,3. https://doi.org/10.3328/IJGE.386-2009.03.03.377
22. Dash SK, Bora MC (2013) Influence of geosynthetic encasement on the performance of stone columns floating in soft clay. Canadian Geotechnical Journal 765–50:754. https://doi.org/10.1139/cgj0437-2012-
23. Gu M, Zhao M, Zhang L, Han J (2016) Effects of geogrid encasement on lateral and vertical deformations of stone columns in model tests. Geosynthetics International 112-100:(2)23. https://doi.org/10.1680/jgein.15.00035
24. Debnath P, Dey AK (2017) Bearing capacity of geogrid reinforced sand over encased stone columns in soft clay. Geotextiles and Geomembranes 664-653:(6)45. https:// doi.org/10.1016/j.geotexmem.2017.08.006
24. Shivashankar R, Babu MRD, Nayak, S, Manjunath, R (2010) Stone columns with vertical circumferential nails: laboratory model study. Geotechnical and Geological Engineering 706–695:(5)28. https://doi.org/10.1007/ s1-9329-010-10706
25 Rezaei MM, Lajevardi SH, Saba HR, Ghalandarzadeh A, Zeighami E (2019) Laboratory study on single stone columns reinforced with steel bars and discs. International Journal of Geosynthetics and Ground Engineering :(2)5 14-1. https://doi.org/10.1007/s1-0154-019-40891
26. Shivashankar R, Babu MRD, Nayak S (2011) Performance of stone columns with circumferential nails”, Proceedings of the Institution of Civil Engineers-Ground Improvement 106-97:(2)164. https://doi.org/10.1680/ grim.2011.164.2.97
27. Murugesan S, Rajagopal K (2007) Model tests on geosynthetic-encased stone columns”, Geosynthetics International 354–346:(6)14. https://doi.org/10.1680/ gein.2007.14.6.346
28. Yoo C, Lee D (2012) Performance of geogrid-encased stone columns in soft ground: full-scale load tests. Geosynthetics International 490–480:)6(19. https://doi. org/10.1680/gein.12.00033
29. Ghazavi M, Afshar JN (2013) Bearing capacity of geosynthetic encased stone columns”, Geotextiles and Geomembranes 36-38:26. https://doi.org/10.1016/j. geotexmem.2013.04.003
30. Hasan, M., Samadhiya, N.K., 2017. Performance of geosynthetic-reinforced granular piles in soft clays: model tests and numerical analysis. Comput. Geotech. –178 ,87  187. https://doi.org/10.1016/j.compgeo.2017.02.016
31. Castro, J., 2014. Numerical modelling of stone columns beneath a rigid footing. Comput. Geotech. 77 ,60e87. https://doi.org/10.1016/j.compgeo.2014.03.016
32. Yoo, C., Kim, S.B., 2009. Numerical modelling of geosynthetic-encased stone column-reinforced ground. Geosynthetics International 116 ,(3) 16e126. https://doi. org/10.1680/gein.2009.16.3.116
33. Lo, S.R., Zhang, R., Mak, J., 2010. Geosynthetic-encased stone columns in soft clay: a numerical study. Geotextiles and Geomembranes 292 ,(3) 28e302. https://doi. org/10.1016/j.geotexmem.2009.09.015
34. Wehr J, (2006) The undrained cohesion of the soil as criterion for the column installation with a depth vibrator. Proceedings of the International Symposium on Vibratory Pile Driving and Deep Soil Vibratory Compaction, TRANSVIB, Paris, 162-157.
35. Wood DM, Hu W, Nash, DFT (2000) Group effects in stone column foundations: Model tests. Geotechnique 698–689:(6)50.https://doi.org/10.1680/geot.2000.50.6.689
36. Barksdale RD, Bachus RC )1983( Design and construction of stone columns. Report No. FHWA/RD026/83-, Office of Engineering and Highway Operations Research and Development, Federal Highway Administration, Washington, DC.
37. Iai S (1989) Similitude for shaking table tests on soilstructure fluid models in 1g gravitational field. Soils and Foundations 118-105 :(1)29. https://doi.org/10.3208/ sandf1972.29.105
38. Danilov AI (1964) Diagram for dividing soils into ordinary, slumping and swelling. Translated from Osnovaniyan, Fundamental i Mekhanik O Gruntov, 5.
39. Dakshanamurthy V, Raman V (1973) A simple method of identifying an expansive soil. Soils and Foundations, 104-97 :(1)13. https://doi.org/10.3208/sandf1972.13.97
40. Hamidi M, Lajevardi SH (2018) Experimental study on the load-carrying capacity of single stone columns. International Journal of Geosynthetics and Ground Engineering -1:(26)4 10. https://doi.org/10.1007/s-0142-018-40891x
41. Vermeer PA, Brinkgreve RBJ (1998) Plaxis finite element code for soil and rock analyses. Balkema, Rotterdam.
42. Yu Y, Damians IP, Bathurst RJ (2015) Influence of choice of FLAC and PLAXIS interface models on reinforced soilestructure interactions. Computers and Geotechnics, 174-164 ,65. https://doi.org/10.1016/j. compgeo.2014.12.009
43. Castro J (2017) Groups of encased stone columns: influence of column length and ar-rangement. Geotextiles and Geomembranes 45, 80–68.https://doi.org/10.1016/j.geotexmem.2016.12.001