Soil-Geosynthetic Interface Strength and Stiffness Relationships From Pullout Tests

Pullout tests are commonly used to describe the ultimate shearing resistance developed along the interface between the confining soil and the geosynthetic as a function of normal stress confinement. Pullout tests can also be used to define the complete soil-geosynthetic interface relationship between shear stress and shear displacement interaction. Such a description of interface strength and stiffness characteristics is needed in analytical models used to predict a displacement response of geosynthetic-reinforced soil structures. Due to the extensibility of geosynthetics, data from pullout tests cannot be used directly to calculate strength and stiffness interface properties. The pullout test must be analyzed as a boundary-value problem with appropriate assumptions made regarding the constitutive relationship of the geosynthetic itself and for the interface interaction. An analytical method is presented that allows for the relationship between shear stress and shear displacement to be back-calculated from pullout test data. This method is used to evaluate interface shear stiffness and shear strength for a geogrid and geotextile product for three normal stress confinement levels. The significance of material models used in the formulation is examined.