A simplified procedure to estimate the shear strength envelope of unsaturated soils

Procedures that allow the prediction of some properties of unsaturated soils or the minimization of the number of tests needed to measure them are advantageous because the control of suction during testing is a formidable task that is time consuming and involves a great degree of expertise. A simplified procedure is proposed in this paper to estimate the shear strength of an unsaturated soil. The procedure is based on an empirical hyperbolic function that has been successfully used to fit experimental data. The function requires two input values, namely the shear strength of a saturated sample and the shear strength of an air-dried sample tested without the need for suction control. Samples tested under a controlled suction larger than the maximum suction expected in the problem can, alternatively, replace the air-dried samples. Both alternatives were tested against results for various soils reported in the literature. The good agreement between the estimates and the experimental data indicates that the proposed procedure is promising and reliable for estimating preliminary unsaturated shear strength parameters.