Highway Improvements A27 Everdingen-Hooipolder

Highway Improvements A27 Everdingen-Hooipolder

The A27 motorway, especially the stretch between Utrecht and Breda, ranks among the top-10 most congested roads in The Netherlands.

As a result, it is undergoing large-scale renovation and modernisation, including upgrades to existing infrastructure. ALSÉÉN, the consortium responsible for this project, has geotechnical engineers from Arthe Civil & Structure leading the geotechnical investigation and design.

Our responsibilities include:

• Settlement and stability analysis of road embankments;
• Earth retaining structures;
• Piled embankments;
• Reinforced ground structures;
• Safety assessment of levees;
• Bridge foundations;
• Assessing the influence of construction works on existing structures.

Managing challenging soil conditions

The route of the A27 runs predominantly through fluvial areas. The subsoil, extending to a depth of approximately 8 metres below the surface, mainly consists of soft peat and clay layers, combined with sand layers from ancient river channels. This dominance of soft, compressible soils presents a significant challenge for the project, particularly in managing the settlement behaviour of the motorway over its lifespan.

Traditional geotechnical investigation methods, including on-site and laboratory soil testing, are being employed. However, at Arthe, we have proposed and implemented three additional methods to enhance embankment settlement predictions and expedite the design process.

Heatmap of settlement predictions

Using our Python developments and the Building Information Modelling (BIM) model of the A27, we extract the 3D road design and populate it with thousands of data points. For each point, we determine the expected settlements by comparing required design elevation with the existing conditions. The results are displayed in a colour-coded heatmap, highlighting areas of concern.

This heatmap allows our geotechnical team to visually identify critical areas, particularly in complex geometries where existing road structures are being widened. The tool provides more detailed insights than traditional 2D calculations alone. Additionally, it integrates with the soil survey data and automated settlement calculations, allowing us to quickly test different design solutions and identify potential issues. This efficient approach helps our engineers deliver an optimal design in a shorter time.

Real-scale test embankment (proefterp)

From the outset, soft soil conditions presented a major challenge for planning and execution. To reduce uncertainties in the geotechnical design, a real-scale test embankment was proposed. This embankment was built in the same area as the tallest expected road embankment and followed the same construction sequence. The location was instrumented to collect data over a year, which was then used to fine-tune soil parameters obtained from laboratory testing.

Mapping settlement behaviour of existing motorway

At Arthe, we co-developed a Python-based tool that uses satellite data (InSAR) to map and visualise the rate of settlement along the existing A27 motorway before any modifications were made. This innovative method provides an accurate understanding of the background settlement rate.

By processing and interpolating the data, we can better understand the subsurface behaviour, which informs our geotechnical design. For example, this data allows us to analyse the soil stress history beneath the motorway using the Overconsolidation Ratio (OCR) in relation to the subsoil’s creep behaviour.

Driving innovation for a more resilient A27

Through these innovative solutions and a unified team effort, our aim is not only to optimise the A27 motorway’s structural integrity but also to enhance traffic flow and reduced long-term maintenance needs.