The shear behavior obtained from the direct shear and pullout tests for different poor graded soil-geosynthetic systems

This paper discussed the difference between the test results obtained from ASTM D5321, the direction shear test, and ASTM D6706, the pullout test for poor graded soil/geosynthetic systems. If the soil particles could be able to penetrate through the geosynthetic openings and to develop the passive bearing capacity resistance, the pullout resistance would not increase in proportion to the increase of soil normal pressure. The pullout interaction coefficient, Ci, would decrease as increasing the normal pressure. Otherwise, the efficiency on friction for the direct shear test can be correlated to the interaction coefficient for pullout test for the most test conditions. The interaction coefficient is about 50% to 65% of the friction efficient for the direct shear test. Pullout interaction coefficients ranged from 0.182 to 1.251 for the test conditions. For direct shear test, if the soil particles are smaller than the geosynthetic openings, this could cause the shearing surface occurred above the soil/geotextile interface, and the frictional behavior would quite similar to that of the test soil itself. If not, the soil particles were expected to turn around and slide along the geosynthetic surface, and low friction efficiency at ultimate strain was commonly obtained. These friction efficiencies varied from 0.36 to 0.98 for the test conditions.