The Decrease of the Strength of Unsaturated Silty Sand

J. C. Leal-Vaca, G. Gallegos-Fonseca, E. Rojas-González


It is generally considered that the shear strength of fine soils continuously increases with suction; however, this is not the case for all types of soils. There are some soils whose strength reaches a maximum at certain suction and then reduces with further of suction. Nevertheless, such cases have not been completely documented and analyzed. This paper presents the results of a series of suction controlled triaxial tests made on silty sand. The tests were made for both the wetting and the drying path. Suction was controlled by circulating air at a constant relative humidity. The retention curve was also obtained for the wetting and the drying path. The variation of cohesive stress was determined using some of the existing equations and the solid-porous model proposed by Rojas (2008a y 2008b). These equations include Bishop’s χ parameter, evaluated theoretically and experimentally. The triaxial tests results show that the strength of the soil increases to a maximum at certain suction and then decreases when suction is further increased.

Palabras clave

unsaturated soils; silty sand; effective stress; strength; triaxial test; retention curve.

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