Pullout behavior of geostrip reinforcement inserted in Ponza-modified clay under different confinement conditions has been studied. Natural low-plasticity clay obtained from the Al-Amiriya area in western Baghdad was used as the base soil, while Ponza a lightweight aggregate used as a granular volcanic modifier for enhancing soil–reinforcement interaction. Large pullout tests were conducted using a rigid steel box that measures 600 mm × 400 mm × 400 mm. The geostrip reinforcement was installed at 150 mm in depth, while the geostrip possessed a width of 90 mm and an embedded length of 500 mm. Three normal stress levels (173, 207, 250 kPa) were used for testing overburden pressure, with Ponza contents ranging from 0% to 50%. The pullout force and displacement were recorded continuously to determine load–displacement response, maximum pullout resistance, apparent friction coefficient, interface shear stress. The implementation of Ponza increased pullout resistance and mobilization of interface shear resistance for movement between clay and geostrip. Results showed that with increase in Ponza % and normal stress, the maximum pullout force increased to approximately 39.19 kN at 50% Ponza under 250 kPa instead of 29.42 kN. Although apparent friction coefficient decreased with increasing normal stress, the maximum interface shear stress increased. The higher Ponza content also led to large peak displacements and indicated a progression to more ductile behavior. These results show that clay modified with Ponza can significantly enhance pullout of geostrip and can be useful in application of reinforced soil structures and mechanically stabilized earth systems.
