GGU-AXPILE: Driven piles according to FRANKE
The approach after FRANKE is applied to driven piles (e.g. in the Geotechnical Engineering Handbook 2003, Part 3), allowing calculation of a resistance-settlement curve also for driven piles. The relationship given by Franke is:
Base resistance σ = β · (s/b*)1/c
Skin friction τ = α · qs
With:
s = pile settlement [mm]
qs = cone resistance of the CPT to DIN 4094 [MN/m²]
α, β, b*, c = coefficients according to the following table
Pile type | β | b* | c | α |
Reinforced concrete driven piles | 1.0 | 0.25 | 1.63 | 0.003 |
In-situ concrete driven piles | 1.0 | 0.55 | 1.55 | 0.004 |
"Franki" piles | 2.0 | 0.55 | 1.55 | 0.004 |
Plain steel piles | 1.0 | 0.65 | 1.90 | 0.002 |
The above values can be adopted directly from within the program. However, you can also use your own values.
The values for the base resistance increase uninterrupted. A failure settlement cannot be read from the curve after Franke. You must therefore additionally define a failure settlement sg. This can be achieved either by means of an absolute value (e.g. sg = 0.5 cm) or a relative value as a function of the pile diameter (e.g. sg = 0.025 · pile diameter).
The GGU-AXPILE program does not check a minimum embedment in the load-bearing subsoil in accordance with the standard when this pile type is selected. The parameters β, b*, c listed in the table above describe the base resistance of a driven pile. The base resistance of a driven pile that can be activated is therefore completely independent of the soil parameters entered in the "Edit/Soils" menu item. You must therefore check yourself whether the soil in the pile toe area fulfils the parameters β, b*, c.
In general, this is the case if there is at least a medium dense compaction or at least a stiff to semi-solid consistency. The entered soil parameter qs together with the parameter α is solely responsible for the skin friction. The entered soil parameters γ' and γ are only relevant when working with tension piles.