Physical FCV modeling of a stone column in sandy ground with a soft lens
ٔNiyousha Bazazzadegan
1
(
Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
)
Navid Ganjian
2
(
epartment,faculty,Islamic Azad University, Science and Research Branch, Tehran,Iran
)
Javad Nazariafshar
3
(
Department of Civil Engineering, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran
)
کلید واژه: Stone column, Frustum confined vessel (FCV), Soft lens, Bearing capacity, Stress concentration ratio, Geotextile,
چکیده مقاله :
The use of stone columns is an effective method to modify the behavior of problematic ground. When the ground contains a soft lens, the combined use of a stone column with a surrounding reinforcement improves the efficiency of this method for layered ground. The current study examined the efficiency and behavior of unreinforced and geotextile-reinforced stone columns embedded in sandy ground containing a soft lens. Physical modeling of ground with soft lenses of different thicknesses and placement levels was done in a Frustum confined vessel (FCV) under real stress conditions. The results of FCV testing on the bearing capacity, failure mode and stress concentration ratio revealed that a decrease in the soft lens thickness considerably increased the bearing capacity of the unreinforced and geotextile-encased columns. The absence of a soft lens increased the bearing capacity of the columns up to three-fold. While the unreinforced stone column underwent bulging failure in the soft lens range, geotextile encasement prevented bulging failure. As the lens depth increased, the bearing capacity of unreinforced and reinforced stone columns increased by about 40% and 10%, respectively. The occurrence of bulging in the soft lens range decreased the stress concentration ratio of the unreinforced stone column by 50% compared to the reinforced one.
چکیده انگلیسی :
The use of stone columns is an effective method to modify the behavior of problematic ground. When the ground contains a soft lens, the combined use of a stone column with a surrounding reinforcement improves the efficiency of this method for layered ground. The current study examined the efficiency and behavior of unreinforced and geotextile-reinforced stone columns embedded in sandy ground containing a soft lens. Physical modeling of ground with soft lenses of different thicknesses and placement levels was done in a Frustum confined vessel (FCV) under real stress conditions. The results of FCV testing on the bearing capacity, failure mode and stress concentration ratio revealed that a decrease in the soft lens thickness considerably increased the bearing capacity of the unreinforced and geotextile-encased columns. The absence of a soft lens increased the bearing capacity of the columns up to three-fold. While the unreinforced stone column underwent bulging failure in the soft lens range, geotextile encasement prevented bulging failure. As the lens depth increased, the bearing capacity of unreinforced and reinforced stone columns increased by about 40% and 10%, respectively. The occurrence of bulging in the soft lens range decreased the stress concentration ratio of the unreinforced stone column by 50% compared to the reinforced one.
[1] V. Schaefer et al., "Ground modification methods-reference manual-Volume II," US Department of Transportation Federal Highway Administration: Washington, DC, USA, 2017.
[2] D. Greenwood, "Mechanical improvement of soils below ground surface," in Inst Civil Engineers Proc, London/UK/, 1970.
[3] J. Hugher and N. Withers, "Reinforcing of soft cohesive soils with stone columns," Ground engineering, vol. 7, no. 3, 1974.
[4] J. McKenna, W. Eyre, and D. Wolstenholme, "Performance of an embankment supported by stone columns in soft ground," Geotechnique, vol. 25, no. 1, pp. 51-59, 1975.
[5] A. Demir, T. Sarici, M. Laman, B. Bagriacik, and B. Ok, "An experimental study on behaviour of geosynthetic reinforced stone columns," in 2nd International Balkans Conference on Challenges of Civil Engineering, 2013.
[6] Y. Tandel, C. Solanki, and A. Desai, "Laboratory experimental analysis on encapsulated stone column," Archives of Civil Engineering, pp. 359-379-359-379, 2013.
[7] U. R. Lone, M. H. Dar, and M. Y. Ahanger, "Effect of L/B Ratio of Stone Column on Bearing Capacity and Relative Settlement of Sandy Soil (An Experimental Study)," International Journal of Civil Engineering and Technology, vol. 6, no. 1, 2015.
[8] M. Ghazavi and J. N. Afshar, "Bearing capacity of geosynthetic encased stone columns," Geotextiles and Geomembranes, vol. 38, pp. 26-36, 2013.
[9] N. Mehrannia, F. Kalantary, and N. Ganjian, "Experimental study on soil improvement with stone columns and granular blankets," Journal of Central South University, vol. 25, no. 4, pp. 866-878, 2018.
[10] J. N. Afshar and M. Ghazavi, "Experimental studies on bearing capacity of geosynthetic reinforced stone columns," Arabian Journal for Science and Engineering, vol. 39, no. 3, pp. 1559-1571, 2014.
[11] P. Das and S. K. Pal, "A study of the behavior of stone column in local soft and loose layered soil," EJGE, vol. 18, pp. 1777-17786, 2013.
[12] S. K. Dash and M. C. Bora, "Influence of geosynthetic encasement on the performance of stone columns floating in soft clay," Canadian Geotechnical Journal, vol. 50, no. 7, pp. 754-765, 2013.
[13] S. S. G. Prasad, C. Vasavi, and K. P. Sai, "BEHAVIOUR OF STO LAYERED SOILS USIN REINFORCE," International Journal of Civil Engineering, vol. 8, no. 8, 2017.
[14] S. Sandhya Rani, Suresh Praveen Kumar, P.,, "A Study on Behaviour of stone column in layered soil," Journal of Research in Materials and Metallurgical Engineering,, vol. 1, no. 3, pp. pp.11-28, 2016.
[15] K. Ali, J. Shahu, and K. Sharma, "Model tests on single and groups of stone columns with different geosynthetic reinforcement arrangement," Geosynthetics International, vol. 21, no. 2, pp. 103-118, 2014.
[16] P. Mohanty and M. Samanta, "Experimental and numerical studies on response of the stone column in layered soil," International Journal of Geosynthetics and Ground Engineering, vol. 1, no. 3, pp. 1-14, 2015.
[17] N. Nayak, "Recent advances in ground improvements by stone column," in Proceedings of Indian Geotechnical Conference, Madras, IGC-83, 1983.
[18] M. Y. Fattah, K. T. Shlash, and M. J. M. Al-Waily, "Stress concentration ratio of model stone columns in soft clays," Geotechnical Testing Journal, vol. 34, no. 1, p. 1, 2011.
[19] Y. Hu, G. Zhang, J.-M. Zhang, and C. Lee, "Centrifuge modeling of geotextile-reinforced cohesive slopes," Geotextiles and geomembranes, vol. 28, no. 1, pp. 12-22, 2010.
[20] L. Wang, G. Zhang, and J.-M. Zhang, "Centrifuge model tests of geotextile-reinforced soil embankments during an earthquake," Geotextiles and Geomembranes, vol. 29, no. 3, pp. 222-232, 2011.
[21] R. Mitchell, "Centrifuge modelling as a consulting tool," Canadian Geotechnical Journal, vol. 28, no. 1, pp. 162-167, 1991.
[22] A. Jassim, N. Gangian, and A. Eslami, "Design and fabrication of frustum confining vessel apparatus for model pile testing in saturated soils," Innovative Infrastructure Solutions, 7:280, 2022.
[23] E. Selig and K. McKee, "Static and dynamic behavior of small footings," Journal of the Soil Mechanics and Foundations Division, vol. 87, no. 6, pp. 29-45, 1961.
[24] A. Verghese Chummar, "Bearing capacity theory from experimental results," Journal of the Soil Mechanics and Foundations Division, vol. 98, no. 12, pp. 1311-1324, 1972.
[25] S. R. Mohapatra, K. Rajagopal, and J. Sharma, "Direct shear tests on geosynthetic-encased granular columns," Geotextiles and Geomembranes, vol. 44, no. 3, pp. 396-405, 2016.
