Introduction

Geosynthetic-reinforced pile-supported (GRPS) embankments were developed for areas with compressible soil and subsidence.

Up to date, nearly all GRPS piled embankments in the world are dry, and therefore, no measurements were available of those structures where the embankment was partially or completely submerged into groundwater.

As a result, in wet conditions, unsustainable and unnecessarily expensive solutions such as concrete slabs are chosen.

This research will quantified the influence of extreme rain (climate change) or a high groundwater level (subsidence, sea level rise) and develop a design procedure to take groundwater into account.

Furthermore, efforts have been made to understand the impact of dynamic loading on piled mattresses through field measurements and numerical analyses.

Activities

• Field measurements
• Small-scale experiments
• Finite element analyses

Field measurements

A regional road in the Krimpenerwaard, Netherlands, was constructed on a geotextile-reinforced pile-supported embankment. A section was monitored for four years. Geotextile strains, the changing groundwater level and settlements were measured.

GRPS embankment in the Krimpenerwaard, Netherlands. Installation of geotextile reinforcement, at the bottom of the embankment. (a) across road way, (b) along road way. The concrete pre-cast pile caps were covered by a non woven for protection of the reinforcement

Installation monitoring

Cross section test section, the ground water level was measured with pore pressure transducers. The groundwater table varied strongly.

Measured groundwater  level (ppt1). Air bubbles disturbed the measurements of ppt6.

Measured strains in the geotextile reinforcement

The geotextile strains did not respond clearly to the changing groundwater table 

The geotextile strains seem to relate with the average day temperature

The measured geotextile (GR) strains are smaller than the values calculated with the Concentric Arches model, that is utilized by the Dutch Design Guideline CUR226 for basal reinforced piled embankments

The analytical Concentric Arches model (van Eekelen et al., 2013 and 2015). The load is transferred via the arches towards the subsurface and pile caps. 

Conclusions field experiments

• The analytic Concentric Arches model calculates larger geotextile strains than measured and therefore gives a safe prediction
• The groundwater level does not affect the geotextile strains
• The air temperature affects the geotextile strains
• For this case, with these geotextiles, and this high ground water level, design guideline CUR226 for basal reinforced piled embankments, that applies the Concentric Arches model, gives a safe design.

Experiments

Consortium

Private partners

• Keller Polska, Poland
• Keller Holding GmbH, Germany
• Keller Fondations Spéciales, France
• SHM System, Poland

Knowledge Institutes

• TU Darmstadt, Institute of Geotechnics, Germany
• Deltares, Delft, The Netherlands

Public partner

• GEOLAB (a four-year Horizon 2020 project (2021 – 2025) funded by the European Union H2020 Research and Innovation Programme (project-geolab.eu)

Small-scale model tests (Deltares). Test set-up, DFOS sensors, cross-sections, installation of displacement transducers.

Activities

• Small-scale tests at the Deltares Model Hall.
• Nearly full-scale tests in a deep test pit at the University of Darmstadt.
• The application of modern DFOS technology to gives a 3D picture of the deformations and soil strains in the embankment and steel strains.
• Analytical and 3D FEM simulations and analyses.
• Development of a calculation model to design the steel reinforcement of a piled embankment.

Large-scale test (TU Darmstadt), 16 piles centre-to-centre 1.25 m, sand being pluviated, DFOS sensors for measuring 3D deformations installed, cross-section, DFOS for soil strains and pressure cells installed.

Selection of Results

First small-scale test: measured and calculated soil arching A (load exerted on the piles, above the basal reinforcement), using three European models. H&R refers to the model of Hewlett & Randolph 1988. Surcharge loads are indicated (0 to 100 kPa).

First small-scale test: Steel strains, measured on top of the top steel bar in x-direction. a. after consolidation without surcharge load, b. after increasing the surcharge load to 25 kPa, and c. after consolidation with surcharge load at 25 kPa.

DFOS result in the large-scale test: vertical deformations at Level 1 after the installation of the first 1.05 m of the embankment.

Comparison of the measured (DFOS result) and calculated deformations of the steel reinforcement in the large-scale test. Calculations with the CA model, that was adopted in CUR226.

Products / planning

The official products of this TKI project are:

More information?

Please, contact Suzanne.vanEekelen@deltares.nl.