Shear Strength Behavior and Soil Water Retention Curve of a Dual Porosity Silt-Bentonite Mixture


Department of Civil Engineering,Shiraz University


Evaluation of soil shear strength is an important step in the stability analysis of earth
structures, foundations and natural slopes. The shear strength profile of unsaturated soil is dictated by the
suction profile. This pro le depends on the evaporation rate, depth of the water table and the soil water
retention curve. In this paper, the soil water retention curve of a dual porosity silt-bentonite mixture is
determined; employing the vapor equilibrium method and osmotic suction technique, and the validity of
these approaches is examined against the results from the filter paper technique. Besides, the effect of
the stress state on the suction value is studied employing the filter paper method. Furthermore, the shear
strength response of the material is evaluated for a wide range of suction values (0-287MPa) employing
the direct shear apparatus. Results of direct shear tests show that the expansive clay behaves like a normal
consolidated soil at suction values less than, or equal to, 20.5MPa, while its behavior is similar to the
heavily over consolidated soils for suction more than 20.5MPa.