Experimental investigation of bearing mechanism of closed- and open-ended piles supported by thin bearing layer using X-ray micro CT

Abstract

In order to clarify the bearing mechanism of closed-ended and open-ended piles supported by a thin bearing layer, pile-loading tests are conducted on model grounds with different bearing layer thicknesses, and the soil deformation characteristics around the pile tips are observed by X-ray micro CT. In the case of open-ended piles supported by a thin bearing layer, the soil in the pile greatly displaces following the downward displacement of the soil located more deeply than the pile tip, and the soil density in the pile becomes lower than when the bearing layer thickness is sufficiently large. These characteristics probably cause lower inner friction and lower base resistance, resulting in a lower bearing capacity. When the bearing layer thickness is more than three times the pile diameter, the bearing capacity is much higher than when the bearing layer thickness is the same as the pile diameter. In addition, soil deformation which occurs is almost entirely in the bearing layer, and the changes in bearing capacity are hardly affected by the soft layer below the bearing layer. The experimental findings obtained in the present study support the idea that the criterion for the bearing layer thickness, where the influence of a thin bearing layer on the bearing capacity can be ignored, is three times the pile diameter, regardless of whether the pile tip is open or closed.