Abstract

LEAL-VACA, Julio César; GALLEGOS-FONSECA, Gustavo  and  ROJAS-GONZALEZ, Eduardo. Estimation of Effective Stress From Bishop's Parameter χ for a Silty Sand. Ing. invest. y tecnol. [online]. 2013, vol.14, n.2, pp.139-151. ISSN 2594-0732.

The behaviour of resistance and volumetric changes of a saturated soil are controlled by effective stress, however in the case of unsaturated soils it has not been possible to clarify this argument. There is not an equation for the effective stress of unsaturated soil that is applicable to all soil types. Bishop (1959) proposed an equation for effective stress to unsaturated soils, this equation contains the parameter c, to determine this parameter there are several equations but none covers all the cases. Moreover, the soil mechanics has considered that the shear strength of fine soils increases with suction, but this is not the case for all soil types. There are some soils whose resistance reaches a maximum for certain suction and then decreases for higher values of suction. However, such cases have not yet been fully documented and analyzed. This article presents a series of triaxial tests with controlled suction made in a silty sand. The tests were made on wetting and drying trajectories. The suction was controlled by circulation of air with constant relative humidity. The water retention curve was obtained for both trajectories of wetting and drying with filter paper technique and other tests were made with the cylinder membrane extractor for drying trajectory. The results of triaxial tests are shown in p'-q diagram, and can be observed that the resistance of soil increases to a maximum for certain suction and then decreases for higher values of suction, it also includes the χ values obtained from some existing equations for this parameter and experimental results.

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

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