Piles and micropiles is an application for the calculation of the bearing capacity of the foundation soil for a pile or a micropile loaded by any distribution of loads (moment, axial force, and shear). It also performs the settlement calculation using the Davis-Poulos method, according to which the pile is considered rigid (undeformable) immersed in an elastic medium, half-space or layer of finite thickness.
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The vertical ultimate bearing capacity is calculated through the Berezantzev formula depending on the pile geometry, soil characteristics, and the pile-soil interface. Since the execution of a pile, whether driven or bored, always modifies the soil characteristics around it, it is proposed to assume a shear strength angle equal to:
For driven piles
φcorr= φ+3
tanδ = tan(0.66 · φcorr
For bored piles
φcorr= φ-3
C = C·0.9
tanδ = tan(0.66·φcorr)
where φ is the shear strength angle before pile execution. For calculation purposes, the ultimate bearing capacity QLimit is conventionally divided into two components, the tip resistance Qp and the shaft resistance Ql
Qp = π·D2/4 · (γt·L·Nq + Nc·C)
Nc and Nq bearing capacity factors already including the shape effect (circular)
The method used for the calculation of the shaft bearing capacity is the α method, proposed by Tomlinson (1971); the shaft resistance is calculated as follows:
Ql = (α·C+γt·L·K·tanδ )·π·D·L·fw
Wpalo = (π·D2/ 4)·L·γp
QLimite = (Qp + Qs – Wpalo)
γt unit weight of the soil
L pile length
fw correction factor related to the taper of the pile, i.e., the percentage decrease in the pile diameter
c average value of cohesion (or undrained shear strength)
σ’ effective vertical pressure of the soil
K coefficient of horizontal earth pressure, depending on the pile execution technology and the previous state of compaction
γp unit weight of the material the pile is made of