Effect of Geotextiles on Permanent Deformation in Salt-Encrusted Subgrade Soils

Abstract

The effectiveness of using geotextiles on top of salt-encrusted soil, known as sabkha in the Arabian Gulf area, used as a subgrade layer was investigated. A specific characteristic of this soil is that when it is dry (at or below the optimum moisture content) it possesses a sufficient bearing capacity and is hard enough to resist permanent deformation. However, when saturated it loses its strength and causes very large pavement deformations. An experimental model was developed in the laboratory to test and evaluate the bearing capacity and resistance to permanent deformation of the soil–fabric-reinforced system. The laboratory model consists of a cylindrical mold 320 mm in diameter and 420 mm in height in which a sabkha subgrade and a granular base are compacted and separated by a nonwoven geotextile. The testing variables considered in the study are thickness of the base layer on top of the sabkha sub-grade, the presence and types of geotextiles, the applied dynamic stress, and the moisture condition of the soil (at optimum dry versus saturated). The results indicate that the use of geotextiles significantly improved the bearing capacity and resistance to permanent deformation of the base layer on top of a sabkha subgrade. The improvement achieved is more significant for saturated conditions and is a function of the tensile strength of the geotextile. Increasing the base thickness resulted in higher levels of resistance to permanent deformation. A generalized linear regression model was developed to evaluate the permanent deformation of the soil–fabric–aggregate systems. The model is laboratory based, and its validity is restricted to the conditions investigated.

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