STUDY OF BEHAVIOUR OF HELICAL SCREW ANCHORS

Abstract

Experimental investigations on ultimate pullout capacity of vertical helical screw anchor piles in sand have been presented in this investigation. A brief literature review depicts a consolidated view of the work done by the previous researchers in studying the behavior of 1-lelical Screw Anchors. The behavior of helical anchors in reinforced as well as unreinforced sand has been analyzed through several tests conducted via, single vertical anchor pile in the testing apparatus in each test. Two sets of model helical anchor piles with different diameters (one set of 50 mm. dia. and other of 80 mm. dia.) with diverse helical blades (one, two and three in numbers) of same geometrical properties have been used in this study. The anchors were pre-installed in cylindrical test tank and sand (with relative densities of 50% and 80% in different tests) was hand packed in 100 mm. thick layers around the pile, held in position in the tank's center, to achieve uniform density. For the unreinforced sand, the parameters such as sand relative density, helical blade number and diameter were varied and test results (Ultimate Pullout Capacity. Q) values were compared with each other. Whereas, for the reinforced sand, the geosynthetic material. geogrid. was used in the form of circular cut strips whose diameter was taken in proportion with the helix diameter of 50 mm. triple helical screw pile. The parameters of width, spacing and number of layers of geogrid were changed and Q values in these cases were also compared with each other of their combinations. The results indicate that the Q values improve by significantly increasing the relative density values of the sand, the diameter of anchor pile and the number of helix blades as well. The inclusion of geogrids also increases the Q values to much extent but to an optimum values of width, spacing and number of layers ofthe geogrid.