Experience of installing bored piles with a spread foot

Abstract

The two basic methods of installing bored piles with a spread foot (method of boring and concreting with the use of drilling mud, and the method of dry boring) are outlined and the problems encountered are discussed. For installing piles in compact dry soils drilling with a auger machine is most expedient. The use of piles with a spread foot led to the construction of an expander (for making widened cavities) which consists of a hinged quadrangle whose sides are made of pipes, angle iron or square iron. Blades are attached to the lower side of the quardangle. The upper component of the expander is connected with the rod of the drilling machine and the lower component is hinged to the scoop for the drilled-out soil. Details of other expanders are briefly described. The design resistance of the bored piles with the spread foot with respect to the material of the stem is determined as for a centrally compressed element based on the norms. The test of the piles with the spread foot showed that the "settlement load" curve in most cases does not have a break at which the tangent to the settlement curve becomes almost vertical and which characterizes the limiting state. Therefore the ultimate load for piles with a spread foot should be established by the value of the limiting settlement which is regulated in the norms. Tests indicate that bored piles with a spread foot have a large bearing capacity. Data is cited on the installation of piles with 2-level expansions, and it is shown that the resistance of such piles are greater than that of piles with one expansion.