Combined Encased Stone Column and Vacuum Consolidation Technique for Soft Clay Improvement
Soft clay improvement using stone column is one of the popular ground improvement techniques adopted for soft clay deposits. The load carrying capacity can be further improved by encasing it with geosynthetic material around the column which offers effective lateral confinement, prevents column contamination with improved drainage and strength characteristics. The load carrying capacity can be further increased by improving the undrained shear strength of surrounding soil. Use of vacuum consolidation is a well-developed hydraulic modification technique which involves application of vacuum through prefabricated vertical drains in a sealed membrane system. The improvement in effective stress during vacuum application resulted in improved undrained shear strength of surrounding soil. In this research work, combined geosynthetic encased stone column and vacuum treatment method is examined for improving of extremely soft clay soils. Small scale unit cell tests were performed to evaluate the efficiency of encased stone column subjected vacuum loading under different pressure levels. The results were then compared with that of ordinary surcharge preloading conditions. It was observed that both time, rate of consolidation and undrained shear strength of soil increases significantly with vacuum application. With this reduction in time required for consolidation and improvement in undrained shear strength, the construction activity can be accelerated which makes the project economically beneficial.
KeywordsEncased stone columns Vacuum consolidation Ground improvement Soft soils
This investigation was performed as part of a sponsored research project supported by the Department of Science and Technology of Government of India under sanction number SR/S3/MERC/065/2007, dated 19-03-2009.
The author sincerely acknowledges his guides Prof. K. Rajagopal and Prof. R. G. Robinson, Civil Engineering Department, Indian Institute of Technology Madras for their mentorship and continuous support during his research period at IIT Madras.
The author would like to thank Director, CSIR-Central Building Research Institute, Roorkee for giving permission to publish this research work.
- 1.Barron, R.A.: Consolidation of fine-grained soils by drain wells. Trans. Am. Soci. Civ. Eng. 113(2346), 718–724 (1948)Google Scholar
- 2.Brokemper, D., Sobolewski, J., Alexiew, D., Brok, C.: Design and construction of geotextile encased columns supporting geogrid reinforced landscape embankments: Bastions Vijfwal Houten in the Netherlands. In: Proceedings of the 8th International Conference on Geosynthetics, Yokohama, Japan, pp. 889–892 (2006)Google Scholar
- 5.Cognon, J.M., Juran, I., Thevanayagam, S.: Vacuum consolidation technology – principles and field experience. In: Yeung, A.T., Félio, G.Y. (eds.) Vertical and Horizontal Deformations of Foundations and Embankments, vol. 40, no. 2, pp. 1237–1248. Geotechnical Special Publications, ASCE (1994)Google Scholar
- 7.Greenwood, D.A.: Mechanical improvement of soils below ground surface. In: Ground Engineering, Proceedings of the Conference by the Institution of Civil Engineers, London (1970)Google Scholar
- 9.Kjellman, W.: Consolidation of clay soil by means of atmospheric pressure. In: Proceedings of Conference on Soil Stabilization, pp. 258–263. MIT, Cambridge (1952)Google Scholar
- 11.Mitchell, J.K., Huber, T.R.: Stone column foundations for a waste water treatment plant – a case history. Geotech. Eng. 14, 165–186 (1983)Google Scholar
- 14.Raithel, M., Kirchner, A., Schade, C., Leusink, E.: Foundation of constructions on very soft soils with geotextile encased columns - state of the art. Geotechnical Special Publication, No. 130-142, pp. 1867–1877 (2005)Google Scholar
- 15.Short, R.D, Prashar, Y., Metcalf, B.: Repairing railway spur roadbed failure using geotextile encased columns. In: Transportation Research Board. 84th Annual Meeting Compendium of Papers, Washington, D.C (2005)Google Scholar
- 17.Van Impe, W., Silence, P.: Improving of the bearing capacity of weak hydraulic fills by means of geotextiles. In: Proceedings of the 3rd International Conference on Geotextiles, Vienna, Austria, pp. 1411–1416 (1986)Google Scholar