Unified Method for Estimating the Ultimate Bearing Capacity of Shallow Foundations in Variably Saturated Soils under Steady Flow
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 142, Issue 4
Abstract
This study presents a unified method for estimating the ultimate bearing capacity of shallow foundations resting on variably saturated soils under a steady flow. The effective stress approach originally employed for predicting the bearing capacity of saturated soils is extended by incorporating a suction stress-based representation. A closed-form equation is used to define the suction stress characteristic curve, capturing changes in the effective stress because of varying soil saturation and matric suction. The proposed method uses the classic effective shear strength parameters and two fitting parameters to represent the soil water characteristic curve. The method can be used for different soil types, various degrees of saturation, and different surface flux boundary conditions. The results from the proposed formulation were compared, and good agreement was observed against three sets of experimental results from model footing and plate load tests. A parametric study was performed, and the ultimate bearing capacity profiles are presented for various surface flux boundary conditions and depths of the water table. It is shown that different flow conditions can significantly affect the ultimate bearing capacity of clay. However, different flow conditions have negligible effects on the ultimate bearing capacity of sand.
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References
Bishop, A. W. (1959). “The principle of effective stress.” Tek. Ukeblad, 106(39), 859–863.
Bowles, J. E. (1996). Foundation analysis and design, 5th Ed., McGraw-Hill, New York.
Costa, Y. D., Cintra, J. C., and Zornberg, J. C. (2003). “Influence of matric suction on the results of plate load tests performed on a lateritic soil deposit.” Geotech. Test. J., 2(2), 219–226.
Fredlund, D. G. (1996). “The scope of unsaturated soil mechanics: An overview.” Proc. 1st Int. Conf. on Unsaturated Soils, E. E. Alonso and P. Delage, eds., Vol. 3, Balkema, Rotterdam, Netherlands, 1155–1177.
Fredlund, D. G., and Morgenstern, N. R. (1977). “Stress state variables for unsaturated soils.” J. Geotech. Engrg. Div., 103(5), 447–466.
Fredlund, D. G. and Rahardjo, H. (1993). Soil mechanics for unsaturated soils, Wiley, New York, 517.
Gardner, W. R. (1958). “Some steady state solutions of the unsaturated moisture flow equation with application to evaporation from a water table.” Soil Sci., 85(4), 228–232.
Gavin, K. and Xue, J. (2010). “Design charts for the stability analysis of unsaturated soil slopes.” Geotech. Geolog. Eng., 28(1), 79–90.
Griffiths, D. V., and Lu, N. (2005). “Unsaturated slope stability analysis with steady infiltration or evaporation using elasto-plastic finite elements.” Int. J. Numer. Anal. Meth. Geomech., 29(3), 249–267.
Kumbhokjar, A. S. (1993). “Numerical evaluation of Terzaghi’s.” J. Geotech. Eng., 598–607.
Lu, N. (2008). “Is matric suction a stress variable?” J. Geotech. Geoenviron. Eng., 899–905.
Lu, N., Godt, J. W., and Wu, D. T. (2010). “A closed-form equation for effective stress in unsaturated soil.” Water Resour. Res., 46(5), W05515.
Lu, N., Kim, T.-H., Sture, S., and Likos, W. J. (2009). “Tensile strength of unsaturated sand.” J. Geotech. Geoenviron. Eng., 135(12), 1410–1419.
Lu, N., and Likos, W. J. (2004). Unsaturated soil mechanics, Wiley, New York.
Lu, N., and Likos, W. J. (2006). “Suction stress characteristic curve for unsaturated soil.” J. Geotech. Geoenviron. Eng., 131–142.
Mohamed, F. M. O. (2014). “Bearing capacity and settlement behaviour of footings subjects to static and seismic loading conditions in unsaturated sandy soils.” Ph.D. dissertation, Univ. of Ottawa, Ottawa.
Mohamed, F. M. O. and Vanapalli, S. K. (2006). “Laboratory investigations for the measurement of the bearing capacity of an unsaturated coarse-grained soil.” Proc., 59th Canadian Geotechnical Conf., Canadian Geotechnical Society, Vancouver, BC, Canada, 219–226.
Mualem, Y. (1976). “A new model for predicting hydraulic conductivity of unsaturated porous media.” Water Resour. Res., 12(3), 513–522.
Oh, W. T., and Vanapalli, S. K. (2011). “Modelling the applied vertical stress and settlement relationship of shallow foundations in saturated and unsaturated sands.” Can. Geotech. J., 48(3), 425–438.
Oh, W. T., and Vanapalli, S. K. (2013). “Interpretation of the bearing capacity of unsaturated fine-grained soil using the modified effective and the modified total stress approaches.” Int. J. Geomech., 769–778.
Oloo, S. Y., Fredlund, D. G., and Gan, J. K. M. (1997). “Bearing capacity of unpaved roads.” Can. Geotech. J., 34(3), 398–407.
Sheng, D. (2011). “Review of fundamental principles in modelling unsaturated soil behaviour.” Comput. Geotech., 38(6), 757–776.
Skempton, A. W. (1948). “The analysis for stability and its theoretical basis.” Proc., 2nd Int. Conf. on Soil Mechanics and Foundation Engineering, Vol. 1, International Society for Soil Mechanics and Geotechnical Engineering, London, 72–77.
Springman, S. M., Jommi, C., and Teysseire, P. (2003). “Instability on moraine slopes induced by loss of suction: A case history.” Geotechnique, 53(1), 3–10.
Steensen-Bach, J. O., Foged, N., and Steenfelt, J. S. (1987). “Capillary induced stresses—Fact or fiction?” Proc., 9th European Conf. on Soil Mechanics and Foundation Engineering, Balkema, Rotterdam, Netherlands, 83–89.
Terzaghi, K. (1943). Theoretical soil mechanics, Wiley, New York.
Terzaghi, K. and Peck, R. B. (1948). Soil mechanics in engineering practice, Wiley, New York.
Vahedifard, F., Leshchinsky, B., Mortezaei, K., and Lu, N. (2015a). “Active earth pressures for unsaturated retaining structures.” J. Geotech. Geoenviron. Eng., 04015048.
Vahedifard, F., Leshchinsky, D., Mortezaei, K., and Lu, N. (2015b). “Effective stress-based limit equilibrium analysis for homogenous unsaturated slopes.” Int. J. Geomech., in press.
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.” Can. Geotech. J., 33(3), 379–392.
Vanapalli, S. K., and Mohamed, F. M. O. (2007). “Bearing capacity of model footings in unsaturated soils.” Experimental unsaturated soil mechanics, T. Schanz, ed., Springer, Berlin, 483–493.
Vanapalli, S. K., and Mohamed, F. M. O. (2013). “Bearing capacity and settlement of footings in unsaturated sands.” Can. Geotech. J., 5(1), 595–604.
van Genuchten, M. Th. (1980). “A closed-form equation predicting the hydraulic conductivity of unsaturated soils.” Soil Sci. Soc. Am., 44(5), 892–898.
Vesic, A. B. (1973). “Analysis of ultimate loads of shallow foundations.” J. Soil Mech. and Found. Div., 99(1), 45–73.
Wuttke, F., Kafle, B., Lins, Y., and Schanz, T. (2013). “Macroelement for statically loaded shallow strip foundation resting on unsaturated soil.” Int. J. Geomech., 557–564.
Yeh, T.-C. (1989). “One-dimensional steady state infiltration in heterogeneous soils.” Water Resour. Res., 25(10), 2149–2158.
Zhou, A., and Sheng, D. (2015). “An advanced hydro-mechanical constitutive model for unsaturated soils with different initial densities.” Comput. Geotech., 63, 46–66.
Zhou, A.-N., Sheng, D., Sloan, S. W., and Gens, A. (2012a). “Interpretation of unsaturated soil behaviour in the stress-saturation space. I: Volume change and water retention behaviours.” Comput. Geotech., 43, 178–187.
Zhou, A.-N., Sheng, D., Sloan, S. W., and Gens, A. (2012b). “Interpretation of unsaturated soil behaviour in the stress-saturation space. II: Constitutive relationships and validations.” Comput. Geotech., 43, 111–123.
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Journal of Geotechnical and Geoenvironmental Engineering
Volume 142 • Issue 4 • April 2016
Copyright
© 2015 American Society of Civil Engineers.
History
Received: Mar 31, 2015
Accepted: Oct 5, 2015
Published online: Dec 17, 2015
Published in print: Apr 1, 2016
Discussion open until: May 17, 2016
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