Investigation of the behavior of cellular confinement unit (Geocell) under static loading

Authors
A. Haddad
M. Parsa
S. Nasrollahi
Abstract
Geological and site investigations in the world indicates that there are too many fields with soft soil. The existence of such soils in construction sites of buildings may create numerous problems for the foundations, for example the circumstances of roads, foundations and etc. Symmetrical and unsymmetrical settlement of foundations in soft soil areas may destroy even best constructions.

Three dimensional geosynthetics could significantly improve the performance of soil and reduce the costs compared with conventional methods. In this article the behavior of this system has been investigated under vertical load in granular soil for the gap between the applications and the design theories of reinforced base with geocell. Although the geocll system behavior and the effects of adjacent cells on central cell is one of the cases that has not been studied sufficiently.

In this article, the results of the plate loading tests on geocell reinforced sand bases have been studied, and the behavior of three dimensional cellular unit and the effects of adjacent cells have been considered as well. The effective parameters include the diameter and the number of cells. The test sample was a wooden box with 90 cm length and width and 60 cm height filled with poorly graded granular sand. In this study, geocells have been created by sewing the non-woven geotextile in a symmetrical pattern and dimension, and cells diameter were 12, 15, 17.5 and 22.5 cm. The strain gages were attached in order to eliminate measurement errors. The loading processes were carried out by a steel loading plate with 15 cm diameter.

In this investigation besides the considering the geocell behavior, the optional design parameter of this system has been considered with the purpose of decreasing the settlement. Also, the non-woven geotextiles has been sewed in a symmetrical arranged pattern and the behavior of one-cell and multi-cell geocell has been compared. In order to evaluate the failure mechanism of geocell, the novel method of strain gage installation in nonwoven geotextile has been used.

The results include the bearing capacity, the soil surface and cells deformations under a vertical loading. The results indicate that the cells which have a diameter equal to the loading plate have better performance than the others. Also it has been clarified that the existence of adjacent cells with the diameter of 0.8 times the diameter of loading plate, are more suitable for eliminating the settlement. It is also observed that the cells which are smaller than the loading plate, encountered more deformation than the bigger ones.

Also it has been proved that one-cell geocell with the diameter equal to the diameter of loading plate, improve the bearing capacity and base stiffness more than one- cell and nine-cell with diameter equal to 0.8 and 1.7 times of the loading plate diameter. It can be concluded that if the loading position was fixed, one-cell geocell wih diameter equal to foundation diameter is recommended. For moving loads (car load on road), geocell with diameter less than diameter of loading plate should be used.

Keywords

Subjects

[1] Boushehrian, J.H. and Hataf, N. Experimental and numerical investigation of the bearing capacity of model circular and ring footings on reinforced sand", Journal of Geotextiles and Geomembranes, 21(4), pp. 241-256 (2003).
[2] Tafreshi, S.N. et.al. (2010a). "Comparison of bearing capacity of a strip footing on sand with geocell and with planar forms of geotextile reinforcement", Geotextiles and Geomembranes, 28(1), 72–84. doi:10.1016/j.geotexmem.2009.09.003.
 [3] Bathurst, R.J., Nernheim, A.,Walters, D.L., Allen, T.M., Burgess, P., Saunders, D.D. (2009) "Influence of reinforcement stiffness and compaction on the performance of four geosynthetic-reinforced soil walls", Geosynthetics International 16 (1), 43e49.
[4] Dash, S. K., Sireesh, S., & Sitharam, T. G. (2003). Model studies on circular footing supported on geocell reinforced sand underlain by soft clay. Geotextiles and Geomembranes, 21(4), 197-219.
[5] Yang, X.M. (2010). "Numerical Analyses of Geocell-Reinforced Granular Soils under Static and Repeated Loads", Ph.D. dissertation, CEAE Department, the University of Kansas.
 [6] Sawwaf, M.E., Nazer, A., 2005. Behaviour of circular footings resting on confined granular soil. Journal of Geotechnical and Geoenvironmental Engineering 131 (3), 359–366.
[7] Pokharel, S. K. et .al. (2010). "Investigation of factors influencing behavior of single geocell-reinforced bases under static loading", Geotextiles and Geomembranes, 28(6), 570–578.
 [8] Rajagopal, K., Krishnaswamy, N.R., Latha, G.M., 1999. Behaviour of sand confined with single and multiple geocells. Geotextiles and Geomembranes 17 (3),171e184.Ll
[9] Dash, S.K., Rajagopal, K., Krishnaswamy, N.R., 2004. Performance of different geosynthetic reinforcement materials in sand foundations. Geosynthetics International 11 (1), 35e42.
[10] Haddad, A., Bahrehdar, M. (2016). "Numerical and Analytical Evaluation of Bearing Capacity of Half Oval Soil- Bag System under Vertical Loading", Journal of Sharif Civil Engineering 31 (2), 67e75. (In Persian)
 [11] Zhou, H., Wen, X., 2008. Model studies on geogrid e or geocell-reinforced sand cushion on soft soil. Geotextiles and Geomembranes 26 (3), 231e238
[12] Madhavi L. G., & Rajagopal, K. (2007). "Parametric finite element analyses of geocell-supported embankments", Canadian Geotechnical Journal, 44(8), 917–927. doi:10.1139/T07-039.
 [13] Emersleben, A., Meyer, N., 2009. Interaction between hoop stresses and passive earth resistance in single and multiple geocell structures. In: GIGSA GeoAfrica 2009 Conference, Cape Town, September 2e5.
 [14] Madhavi Latha, G., Amit Somwanshi, S. (2009). "Bearing capacity of square footings on geosynthetic reinforced sand", Geotextiles and Geomembranes 27 (4), 281e294
Modares Civil Engineering journal
Volume 17, Issue 5
November and December 2017
Pages 25-36