Behavior of Partially Saturated Cohesive Soil under Strip Footing
Main Article Content
Abstract
In this paper, a shallow foundation (strip footing), 1 m in width is assumed to be constructed on fully saturated and partially saturated Iraqi soils, and analyzed by finite element method. A procedure is proposed to define the H – modulus function from the soil water characteristic curve which is measured by the filter paper method. Fitting methods are applied through the program (SoilVision). Then, the soil water characteristic curve is converted to relation correlating the void ratio and matric suction. The slope of the latter relation can be used to define the H – modulus function. The finite element programs SIGMA/W and SEEP/W are then used in the analysis. Eight nodded isoparametric quadrilateral elements are used for modeling both the soil skeleton and pore water pressure. A parametric study was carried out and different parameters were changed to study their effects on the behavior of partially saturated soil. These parameters include the degree of saturation of the soil (S) and depth of water table. The study reveals that when the soil becomes partially saturated by dropping water table at different depths with different degrees of saturation, the bearing capacity of shallow foundation increases about (4 – 7) times higher than the bearing capacity of the same soil under saturated conditions. This result is attributed to matric suction value (i.e negative pore water pressure). The behavior of soil in partially saturated condition is like
that of fully saturated condition but with smaller values of displacement. It is found that the settlement is reduced when the water table drops to a depth of 2 m (i.e. twice the foundation width) by about (92 %).
Article Details
Section
How to Cite
References
Agarwal, K. B. and Rana, M. K., (1987), “Effect of Ground Water on Settlement of Footings in Sand,” Proceedings, Ninth European Conference on Soil Mechanics and Foundation Engineering, E. T. Hanrahann, T. L. L. Orr, and T. F. Widdis, Eds., Vol. 2, A. A.Balkema, Dublin, pp. 751–754.
ASTM-D-5298-03, "Standard Test Method for Measurement of Soil Potential (Suction) Using Filter Paper", Annual Book of ASTM Standards, Vol. 04.08, Soil and Rock, pp. 1 –6
Brooks, R.H., and Corey, A.T., (1964), "Hydraulic Properties of Porous Media", Colorado State University, Hydrology paper No.3, March.
Costa, Y.D., Cintra, J.C. and Zornberg, J.C., (2003), "Influnce of Matric Suction on the Results of Plate Load Tests Performed on a Lateritic Soild Deposit", Geotechnical Testing Journal, Vol. 26, No. 2, pp. 219-226.
Fredlund , D.G., and Rahardjo, H. (1993), "Soil Mechanics for Unsaturated Soils" John Wiley & Sone Inc. New York, United States of America.
Fredlund, D.G., Xing, A., (1994), "Equation for the Soil Water Characteristic Curve", Canadian Geotechnical Journal Vol. 31, No. 3, pp. 521 – 532.
Fredlund, D. G., (2006), "Unsaturated Soil Mechanics in Engineering Practice", Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 132, No. 3, pp. 286 – 321.
Krahn, J., (2004), "Stress and Deformation Modeling With SIGMA/W", GEO-SLOPE International, Ltd.
Lu, N., and Likos, W. J., (2004), “Unsaturated Soil Mechanics”, John Wiley & Sons, New York.
Mohamed, F. M. O. and Vanapalli, S. K., (2006), "Laboratory Investigations for the Measurement of the Bearing Capacity of an Unsaturated Coarse-Grained Soil", Proceedings of the 59th Canadian Geotechnical Conference, Vancouver 1-4 October, pp. 219-226.
Rahardjo, H. and Fredlund, D. G., (1992), “Mechanics of Soil with Matric Suction,” Proceedings, International Conference in Geotechnical Engineering—Geotropika 92, Universiti Teknologi Malaysia, Johor Bahru, Malaysia.
Vanapalli, S. K., Fredlund, D. G., Pufahl, D.E., and Clifton, A.W., (1996), " Model for the Prediction of Shear Strength with Respect to Soil Suction" , Canadian Geotechnical Journal, Vol. 33, No. 3, pp. 379-392.
Vanapalli, S. K. and Mohamed, F. M. O., (2007), "Bearing Capacity of Model Footings in Unsaturated Soils", in Experimental Unsaturated Soil Mechanics, Springer Proceedings in Physics, Springer -Verlag Berlin Geidelberg, Vol. 112, pp. 483-493.
Wong, T.T., Ferdlund, D.G., and Krahn, J., (1998), "A Numerical Study of Coupled Consolidation in Unsaturated Soils", Canadian Geotechnical Journal, Vol. 35, pp. 926 – 937