The Pull-Out Resistance of Model Soil Nails

Abstract

As an adjunct to a series of centrifuge model tests on nailed soil slopes, a comprehensive series of pull-out tests have been conducted on model nails. The objectives of the tests were to investigate the fundamental interaction mechanisms between nail and soil during pull-out, and to obtain basic data needed for the analysis of the centrifuge tests. Three different soil types were used, all dry sands, and the parameters varied in the tests were the nail length and diameter, nail stiffness, and surface roughness of the nail. Results of the tests are presented and considered in the context of a simplified theoretical model. The apparent coefficient of friction (bond) between stiff rough nails and soil is shown to be dependent on the friction angle of the soil, the rate of soil dilation during shear, the stiffness of the soil and the diameter of the nail in relation to the mean particle size of the soil. For smooth nails the bond resistance is much smaller, and such nails should not be used in practice. For relatively extensible nails the interaction mechanisms are complicated by the occurrence of progressive failure along the nail.