Pullout Tests Using Modified Direct Shear Test Setup for Measuring Soil Geosynthetic Interaction Parameters
Soil geosynthetic interaction parameters and their determination play a vital role in the design of reinforced soil structures. Direct shear test and/or pullout test are commonly used to determine the interaction parameters. Often, it is economically viable to obtain these parameters through existing test setups that are conventionally used in geotechnical engineering. However, the existing test setups need certain modifications, to facilitate the requirement for the specialized tests. This paper introduces modifications to the large size (300 mm x 300 mm) direct shear test setup for evaluating the soil geosynthetic interaction parameters under pullout. The shear box in the existing test setup is replaced by a rectangular box having internal dimensions of 400 mm x 400 mm wide and 230 mm height, with a slot in the front face. Additional amendments for achieving smooth stress transfer, over entire displacement range, are explained. Typical pullout test results using the modified direct shear test set up are presented. Pullout friction coefficient values are observed to be within the range 0.55 1.69. In general, it is observed that the pullout behavior is sensitive to the normal stress and the type of geosynthetics in terms of its surface roughness.