Bearing Capacity of Model Footings in Unsaturated Soils Sai K. Vanapalli and Fathi M.O. Mohamed Department of Civil Engineering, 161 Louis Pasteur Str., University of Ottawa, Ottawa, K1N 6N5 Ontario, Canada vanapall@eng.uottawa.ca, fmoha035@uottawa.ca Summary. A simple technique is proposed to predict the variation of the bearing capacity of an unsaturated soil with respect to matric suction. This technique is based on extending conventional bearing capacity theory proposed by Terzaghi. The proposed equation in this paper is presented as a functional relationship such that the variation of the bearing capacity of an unsaturated soil with respect to matric suction can be predicted. This technique is developed extending the concepts for predicting the shear strength of unsaturated soils proposed by Vanapalli et al. (1996). Using the approach presented in this paper, the bearing capacity of an unsaturated soil can be predicted using the saturated shear strength parameters, c ′ and φ ′ and the soil-water retention curve (SWRC). Key words: bearing capacity, unsaturated soils, shear strength, matric suction, soil–water retention curve, model footings Introduction The bearing capacity is one of the key parameters required in the design of shallow foundations. Several approaches are available in the literature for determination of the bearing capacity of soils based on the saturated shear strength parameters (Terzaghi 1943, Meyerhof 1951). However, in several situ- ations, shallow foundations are located above the ground water table where the soil is typically in a state of unsaturated condition. Nevertheless, the bearing capacity of soils is commonly determined assuming fully saturated conditions ignoring the influence of capillary stresses or the matric suction. Due to this reason, estimation of the bearing capacity of shallow foundations using the conventional approaches may not be reliable leading to uneconomical designs. Foundation designs for unsaturated soils are complex and require not only the soil–structure interaction but also a fundamental understanding of soil be- haviour that comprises the combined role of suction and cementation (Schnaid et al. 1995). Several researchers carried out investigations on the bearing ca- pacity of unsaturated soils (Broms 1963, Steensen-Bach et al. 1987, Oloo 1994, SOFTbank E-Book Center Tehran, Phone: 66403879,66493070 For Educational Use.