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The objective of the research presented in this paper, is to verify the applicability of the coefficient of interaction (COi) for geogrids. Research performed at the Otto Graf Institute (OGI) in Germany in 1990, has revealed that the behaviour of the COi is inconsistent. The test program performed with the pull out box developed at Delft University of Technology (DUT), is based on this former research to allow for a comparison of the results. A finite element program is used to study the impacts of the testing device. The data analysis reveals the distribution of shear stress along the geogrid. Dilatancy and arching of the non-cohesive soil lead to a local large increase in confining pressure, concentrated just in front of the point of mobilisation. After mobilisation, a large part of the geogrid does not contribute to the pull out resistance for no residual shear stress remains. The COi is not an appropriate parameter to determine from the current test method.