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Settlements

MP NX computes the settlement of the single pile with the Poulos and Davis method (1980), for an axial load Q:

s = Q/(D·Et)·I

with D the pile diameter, Et the elastic modulus of the soil and I the influence factor. The method assumes an elastic medium with Poisson's ratio ν = 0.5.

Required data

  • E of the layer containing the pile toe, in MPa: it is column E of the stratigraphy. Without a value of E the settlement is meaningless.
  • The elastic modulus of the pile Ep, taken from the concrete class in the materials archive.
  • Pile diameter and length.
  • A vertical load.

The factor I is interpolated from a table as a function of L/D (eight classes) and of the relative stiffness K = Ep/Et (linear interpolation between 10, 100, 1 000, 10⁴ and 10⁵).

Settlement options

In the Settlement options card of the Parameters tab choose:

  • the Combination the load is taken from. It is usually a serviceability combination: in the opening project the first one, "A1+M1+R3", is selected and "SLE" must be chosen by hand;
  • the Load, in kN. With 0 the program uses the vertical resultant of the chosen combination; with a non-zero value it uses that.

The settlement is computed by Calculate, together with the rest, at no extra credits.

Reading the Settlements tab

The tab shows the combination and the load used, then three tiles: the Settlement in mm, the factor I and the load Q.

Example

Q = 1 000 kN, D = 0.8 m, L = 10 m, Ep = 31 475 MPa, Et = 30 MPa. L/D = 12.5 and K = 1 049 give I = 0.147. The settlement is s = 1 000/(0.8·30 000)·0.147 = 6.1 mm. It is case 6 of the validation document.

Settlements tab: combination and load used, and the tiles with settlement in millimetres, factor I and load Q

Why the settlement is sometimes missing

If the tab says No settlement computed after a successful calculation, the chosen combination has no vertical load: Ed,v = 0 and the method needs an axial load. The on-screen message names the combination concerned.

You have two remedies:

  1. assign a vertical force Fy in the loads of that combination, or choose another combination in the Settlement options;
  2. enter the Load Q directly in the Settlement options.

It happens, for instance, with Bowles' example 16.3, which has the ultimate load only and no design action.

Limits

  • The settlement is that of the single pile: there is no group effect.
  • The method uses a single modulus Et, that of the toe layer: in strongly layered ground the result is an order of magnitude to be assessed with judgement.
  • Settlement with Fleming's hyperbolic method, available in the desktop program, is not in MP NX.

Found an error on this page? Let us know or open a Pull Request.