Study of Nail Group Efficiency on Sandy Soil Using Large Scale Pull-out Box

The present study aims at investigating the pull-out resistance efficiency of single and double nails. In sandy soils, where the distance between nails is less than the minimum required distance, the pull-out resistance is reduced. Besides, when the minimum required distance is met, the nail pull-out capacity is not under the effect of the neighboring nail. The parameters affecting the efficiency of the nail group are investigated in this study; including, a type of nail, nail intervals and overburden type of pressure. One of the most important parameters – in order to determine the efficiency of the group – is the nail surface roughness coefficient, which is dependent on factors such as the number of the ribs in each unit length of nail and, also, the depth of the ribs to the size of soil particle. The nail surface roughness coefficient is used to determine the apparent friction coefficient on the nail surface. In all tests, the pull-out force-displacement curve had distinct peak values, accompanied by a reduction in the pull-out force value. The results indicated that the minimum distance required for the full involvement of the pull-out resistance of the nails was strongly subservient to the roughness coefficient of the nail surface.