| Application | PLAXIS 3D |
| Version | PLAXIS 3D |
| Date created | 20 September 2024 |
| Date modified | 20 September 2024 |
| Original author | Richard WITASSE - Principal Application Engineer |
| Keywords | PLAXIS 3D, Driven pile, Calibration, Load displacement curve |
This example deals with the modelling of pile load-tests on a single isolated pile in PLAXIS 3D using volume (continuum) elements for the pile. It will particularly illustrate different modelling techniques:
- for optimal computational efficiency of the numerical models,
- to identify independently the evolution of the shaft resistance on one hand and the base resistance on the other hand,
- to obtain accurate calibration of the target load-displacement curves,
- to efficiently consider the installation effects.
The present situation involves a driven pile with a diameter of 0.56 meters. A companion exercise “Modelling of a bored pile under axial loading” is dealing with the different scenario of a 0.8 m diameter bored pile (cast-in pile). In both cases, piles have a total length of 27 m.
The piles are to be installed in a uniform subsoil consisting of multiple sand layers of different relative densities after excavation of the 9 m top layer. Initial water level is located at h = -1m (see Figure 1). The PLAXIS numerical analysis will be considering the initial soil removal to obtain the most realistic possible state of stress at pile installation.
Defining the target pile load-displacement curves
The load-displacement curve(s) to serve as a reference for calibrating the numerical model must be evaluated. Ideally, this involves conducting experimental pile load tests on-site. However, in cases where such data is unavailable, geotechnical engineers rely on engineering codes and guidelines for pile foundation design. In this example, the suggested load-displacement curves from NEN 9997-1 (2012) have been considered. These curves provide normalised load-displacement data for both pile base resistance and shaft resistance, applicable to ground displacement piles and bored piles (refer to Figure 2).
It should be noted that the curves present the evolution of the pile base displacement for both cases. To fully develop the load-displacement curves for our specific case, it's necessary to evaluate the maximum base and shaft resistances pertinent to the current ground conditions and pile geometries. Pile load carrying capacity depends on various factors, including:
- pile characteristics such as pile length, cross section, and shape,
- soil configuration and short and long-term soil properties and
- pile installation method.
In this context, the characteristic base and shaft resistances may be determined directly from the ground parameters using the following equations given in EN 1997-1:
Rb = Ab · qb
Rb = As,1 · qs,1 + … + As,i · qs,i + … + As,Nlayers · qs,Nlayers
where qb represents the characteristic unit base resistance and qs,i the characteristic unit shaft resistance in the i-th layer for which there exist numerous methods for estimating their values.
References
NEN 9997-1 (2012). Eurocode 7: Geotechnical Design, Part 1: General rules, including Dutch national annex and NCCI.
PN-EN 1997-1 - Eurocode 7: Geotechnical design – Part 1: General rules. Part 2: Ground investigation and testing.