Analytical and Field Evaluation Methods of the Bearing Capacity of Deep Piles and Barrettes in Soft Soil at St. Petersburg

Abstract

The standard procedure of the field evaluation methods of the bearing capacity of piles used in Russian Federation is described.

A pilot deep pile (length L=52.8m and diameter D=1,2m) constructed under a multi-story building within large layers of soft soil is utilized as an example of the in-situ loading system at a construction site; the results of such a static test are presented and compared with analytical predictions of the bearing capacity for such a pile. Similarly, a pilot deep barrette with rectangular cross section (3,3m x1,1m) and a length of 65 m was also constructed at the same construction site with its bottom end reaching a layer of stiff Vendian clay (bed-rocks of pre-glacial origination). The tests of the pile were performed by using O – cells. The deformation sensors were mounted into the reinforced frame of the pile at 9 levels during the installation of the pile. The tests of the pilot barrette were performed in two stages. During the first stage the standard Top-Down tests were done along the whole length of the pile. During the second stage tests using O-cells were performed transferring the loading in two directions (up and down) after reaching maximal load. An O-cell was placed at the depth of 50 m within the layer of stiff clays.

The diagrams of the pile movement against the applied loading during the first and second test stages are presented together with the predicted total bearing capacity of the barrette found by employing different analytical methods.