Scaled model tests on pile types influencing the stability of stiffened deep mixed pile-supported embankment over soft clay

Abstract

Stiffened deep mixed (SDM) piles can be classified into three types based on the relative lengths of the core pile and the outer DM pile: the length of the core pile is shorter than, equal to, or longer than that of the outer DM pile. Limited research has been undertaken to investigate the performance of embankments supported by various types of SDM piles over soft soil. This study carried out a series of model tests to investigate the stability of embankment over soft clay improved by different types of SDM piles. The test results indicated that the improvement factors for embankment stability were 1.37, 1.87, and 1.75 for the tests with short-core, equal-core and long-core SDM piles, respectively. Significant vertical stress was concentrated onto the core pile due to its high stiffness, while the outer DM pile yielded earlier. Under the embankment crest, SDM piles generally failed by compression, while the short-core SDM pile exhibited bulging beneath the core pile tips, and the long-core SDM pile fractured at the unwrapped section. The SDM piles under the embankment slope mainly bore bending moments, and the type of SDM piles affected the bending pattern. The stability of SDM pile-supported embankments can be reasonably evaluated by considering the resisting moment of the piles due to lateral force. The position parameter of equivalent lateral force in an SDM pile-supported embankment ranges from 1/4 to 2/5.