Experiment study on bearing capacity of large-diameter long pile in large thickness backfill loess site

Abstract

The characteristics of backfill loess is different from undisturbed loess. Researches on pile foundations of large thickness backfill loess sites are relatively scarce. Based on a large thickness Q4 backfill loess site, with the backfill loess depth of 25 m, the concrete strain gauges and reinforcement stress meter were arranged on the pile shafts, and the soil pressure cells were installed on the pile bottom for field load test of three test piles. Results show that: in the backfill loess layer, the piletop load is proportional to the depth of negative skin friction, and inversely proportional to the time of occurrence of positive skin friction. The depth ratio of neutral point (Neutral point depth/Loess thickness) is less than the range proposed by Technical Code for Building Pile Foundations (JGJ 94-2008). The loess collapsibility is obvious in the range of about 2/5 from the surface, and in this range, negative skin friction measured from test piles was far greater than the numerical value recommended by the Code for Building Construction in Collapsible Loess Regions (GB50025-2018). The largediameter long pile rendered as the frictional end-bearing pile, and it can give full play to the bearing capacity of soil. When the ratio of pile-top load and limit value of pile-top load reaches 0.705, the settlement of a single pile cannot be equivalent to the compression of the pile, and it should be the sum of the compression of the pile and the settlement of soil at the pile bottom.