The soil-geosynthetic interface resistance, usually obtained by pullout or direct shear tests, is an essential parameter for design analysis. Interface shear strength between soil and geosynthetics depends of particle shape and size, moisture content of soil, type of geosynthetic normal stress acting at the interface. In the case of sandy soils, volumetric changes at interface during shearing has a significantly effect on pullout strength of geosynthetics. In addition, soil suction and dilation developed during shearing of partially saturated soils are strictly related parameters. However, the behavior of geosynthetic-soil interface and its association with dilation and suction is not fully understood. This study consisted of a series of pullout tests performed in order to assess the effect of dilation-suction developed at the interface shear strength of a geogrid embedded in a sand. The experimental program was conducted using an extruded HDPE geogrid reinforcement and a well-graded sand compacted at different water contents. A small-scale pullout apparatus was instrumented to monitor soil suction and vertical displacements during shearing. The results showed that pullout strength of geogrid-sand interface was greater at moisture conditions and normal stresses that conditioned to dilation. In addition, dilation led to suction increases during shearing.
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