AXIAL BEHAVIOR OF SCREW PILE IN SOFT CLAY OVERLAYING SAND LAYER

Abstract

ABSTRACT The screw pile is a famous solution used in various engineering applications, which have relatively low capacity foundations offering stability against compression, overturning moment, uplift tension, and horizontal loads. This study presents a series of model experiments conducted on single screw pile embedded in soft clay soil over laying a sandy soil under compressive loads. The effects of different parameters, such as screw pile length (L), number of helix plate, helix diameter (Dh), inter helix spacing (s) and screw pile settlement, are studied. Three different pile length (300, 350 and 400) mm, single and double helix and pile without helix, (1.5D, 3D and 4D) helix diameter, (30 and 50) mm spacing between helix plate are used in this study (where D is the diameter of the pile shaft). Also, buckling in screw pile is checked and a comparison between the measured and predicted compressive forces on the screw piles is investigated. The results of the experiment showed that the screw piles settlement for piles embedded in soft clay soil overlaying a sandy soil layer decrease (59-182)% with increasing depth of embedment in the sandy layer L/D from 35 to 40, helix diameter and number of helix those provide anchorage against settlement. Deeper screw piles with higher L/D ratios showed compressive capacity (24-55) times greater than the shallower piles (screw pile embedded in soft clay). In addition, screw piles showed resistance to the applied compressive forces (9-16) times more than ordinary piles. II The compressive force increases with increasing diameters and number of helix plates. Furthermore, from this study, it is found that the screw piles with double helix principally failed by cylindrical surface occurred in the region between two helix plates. Another failure mode is individual bearing that occurred at double helix screw pile with spacing ratio (s/Dh) greater than 2 and at the base of screw piles, which has single helix plate. Comparing the predicted theoretical results with the actual measured load test results, it was found that the failure criterion (20% helix diameter) used to determine the ultimate compressive capacity was best suited for a valid comparison than other failure criteria (5%, 10% and 15%).