Soil-geosynthetic interface strength and stiffness relationships from pullout tests

Pullout tests are commonly used to describe the ultimate shearing resistanc e developed along the interface between the confining soil and the geosynth etic as a function of normal stress confinement. Pullout tests can also be used to define the complete soil-geosynthetic interface relationship betwee n shear stress and shear displacement interaction. Such a description of in terface strength and stiffness characteristics is needed in analytical mode ls used to predict a displacement response of geosynthetic-reinforced soil structures. Due to the extensibility of geosynthetics, data from pullout te sts cannot be used directly to calculate strength and stiffness interface p roperties. The pullout test must be analyzed as a boundary-value problem wi th appropriate assumptions made regarding the constitutive relationship of the geosynthetic itself and for the interface interaction. An analytical me thod is presented that allows for the relationship between shear stress and shear displacement to be back-calculated from pullout test data. This meth od is used to evaluate interface shear stiffness and shear strength for a g eogrid and geotextile product for three normal stress confinement levels. T he significance of material models used in the formulation is examined.