EFFECT OF SKIN RESISTANCE AND ENLARGED BASE ON PULL OUT CAPACITY OF MODELED PILES

Abstract

Piles supporting high structures, such as tall chimneys, transmission towers, water towers, tents, electric poles, silos are required to resist uplift force due to wind. So piles are designed to resist this tensile uplift force. Resistance to uplift is given by the friction between the pile and the surrounding soil plus weight of pile itself. The uplift resistance of vertical pile can be computed similar to friction piles. Uplift piles are invariably provided with an enlarged area at the base in the form of a bell or a bulb. Piles develop resistance to pull-out only from the skin friction developed along the embedment length. Point bearing is not included, but weight of the pile is included in uplift capacity. An experimental and theoretical analysis is carried out to predict the ultimate uplift capacity of piles embedded in sand. The method takes into consideration the length, diameter, surface characteristics of piles and soil properties. Charts for evaluating uplift capacity of piles are presented through figures. Experimental and theoretical results of model tests of modeled piles buried in sand are described. Comparison tests were done to determine the influence of factors on uplift capacity such as size of pile (diameter), embedment depth, roughness and enlarged base of modeled piles. Pile uplift capacity not only depends on denseness of sand it also depends on method of installation, depth of embedment, size of pile, material of pile. As pile uplift capacity is sum of frictional resistance and weight of pile, frictional resistance attains a constant value beyond critical depth.