Mechanical characteristics and calculation method of static pressure pile installation for PHC pipe piles in sandy soil foundation with pebble interlayer.

The static pressure pile installation technique is extensively utilized in the construction of bridge pile foundations. However, the presence of pebble interlayers within the strata is a common occurrence. To examine the impact of such pebble interlayers on the installation of pipe piles using static pressure, model tests were executed to scrutinize parameters including pile penetration force, ultimate bearing capacity, lateral soil pressure, and the distribution of pile penetration resistance under two distinct working conditions: standard sand and pebble interlayer during pile penetration. The objective was to elucidate the effect of pebble interlayers on pile penetration. The findings indicated that a pebble layer with a thickness equivalent to 2.5 times the diameter of the pile could result in a 1.3-fold increase in the average pile penetration force, and at its peak, could elevate the pile penetration force by as much as 1.8-fold. Furthermore, the lateral soil pressure surrounding the pile exhibits a nonlinear escalation. In scenarios where the foundation soil is uniform, the lateral soil pressure at a specific point around the pile will markedly increase due to the soil compression effect generated as the pile head approaches that location. Nonetheless, after the pile head surpasses this point, the lateral soil pressure will experience a rapid decline due to the unloading effect precipitated by the failure of the soil surrounding the pile. When the pile head traverses through the pebble interlayer, it induces an augmentation in the lateral soil pressure within the underlying soil stratum. Additionally, drawing upon Meyerhof's theory of ultimate bearing capacity, a revised calculation formula for pile penetration resistance in both uniform and pebble-interbedded sandy soil foundations has been formulated. This formula can be employed to estimate the pile penetration resistance of static pressure piles.