Capacity Change of Piles in Loess under Cyclic Axial Tension or Compression Load

Abstract

This study examines the capacity of single piles subjected to cyclic axial tension or compression load in the loess area under in situ compaction degree and extruding conditions. Four cyclic tension and compression loading tests, and two conventional tension and compression tests on single piles were carried out at a typical loess site of the Loess Plateau region of Northwest China's Shaanxi Province. A series of pretest preparations, including site leveling, steel cage production, pile formation, and soil compaction, are performed. The axial displacement of pile top, pile axial force, and frictional force of the pile side of a single pile measured in the test process were analyzed. The cyclic tension or compression load–displacement curves of the piles in loess, under the in situ compaction degree condition, show the load results in an influence of the movement trend that cannot be ignored. There is no overlap between the compression-unloading curve and tension-unloading curve. This phenomenon indicates that the cyclic loading accelerates the destruction of the pile foundation. Under an extruding condition, the difference between the maximum deformation and the minimum deformation is 2.412 mm, which is 60% of the ultimate deformation of a conventional single pile. The lateral friction of the pile shows multipeak distribution along the pile body, and the attenuation range of lateral friction strength at the pile tip is more than 50% in the failure stage.