Skip to content

SPX formulations

This section describes what the program calculates — the methods, the assumptions, the coefficients and, above all, the limits of validity of each one.

It exists because foundation software should not be a black box. The project is signed by the engineer, and to sign it you need to know which calculation was done.

How to read these pages

Each page follows the same structure:

  1. The formulation, with the equations as the program applies them.
  2. The implementation decisions — the points where the method allows more than one reading and the program chose one. They are what explain divergence between different programs using "the same method".
  3. The limits of validity, marked like this:

Range of application

This block appears on every page and delimits where the method holds. Read it as part of the result, not as a footnote.

The calculation chain

The modules are not independent: each one consumes the previous one.

Borehole — NSPT and soil codes the input to everything
Bearing capacity — Aoki · Décourt · Teixeira consumes: borehole
Pile length consumes: bearing capacity
Settlement — Cintra & Aoki consumes: bearing capacity
Soil reaction — Kh and Kv consumes: borehole and length
Structural analysis — PyNite consumes: soil reaction
Design — NBR 6118 consumes: structural analysis
DXF detailing and calculation report consumes: design and settlement

A practical consequence: changing the borehole changes everything. The soil classification selects \(K\), \(\alpha\), \(C\) and \(m\), which in turn define capacity, settlement, spring stiffness, internal forces and reinforcement. There is no way to change the profile and reuse an earlier design.

The pages

  • Bearing capacity

    Aoki-Velloso, Décourt-Quaresma and Teixeira. How each one defines the toe \(N\), and why that is the main source of divergence between them.

  • Settlement

    Cintra & Aoki, group settlement and the Van der Veen load × settlement curve.

  • Soil reaction

    Winkler springs, \(K_h = m \cdot z\) and \(K_v\) from the allowable stress.

  • Structural analysis

    3D frame on an elastic foundation, with raked piles.

  • Design

    Biaxial bending with axial force with interaction diagram, second order and shear.

  • Parameter tables

    All the coefficients, with the logic behind the scales.