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The contours of the future A16 are beginning to become visible. Sand tracks, foundation machines and sheet pile walls are laying the underground foundation for all above-ground infrastructure. In this phase of the project, the geotechnical and geohydrological implementation design of De Groene Boog is being realized, to which CRUX Engineering is making an important contribution.
It is one of the key components of this major infrastructure work: preparing the existing subsoil for all the traffic that will be using the new highway in the coming years. The foundation in this Rotterdam region, one of the lowest-lying parts of the Netherlands, has a very erratic structure. Clay and peat layers crisscross each other with no apparent logical coherence. Before a solid bearing sand layer is found, we are generally already eight to ten meters below ground level. This erratic structure called for a site-specific approach to the geotechnical design of sand bodies, earth courses and pile foundations for the structures.
In order to keep the subsoil stable during construction, on most sections the sand for the earth tracks (a total of four million cubic meters!) is slowly raised in increments of half a meter every one or two weeks to a maximum of fourteen meters. This gradual uplift schedule, combined with additional stabilizing measures, is necessary to still allow safe elevation on the poor ground. The lanes then lie there for a year, to give the subsoil time to compress under the new load. In the process, about thirty percent of all the clean sand disappears under the existing ground level. For De Groene Boog, CRUX provides experienced professionals who, based on risk-based stability and settlement calculations, enable safe work and ensure that the set quality requirements, such as residual settlement and flatness, are met on this challenging subgrade.
Designing with finite elements in view of the environment.
Many of the structures disappear into the subsurface and are designed to protect existing roads, underground infrastructure and neighboring buildings and objects during the work. This minimizes the impact on the surroundings. The impact of the work and the required control measures are examined with advanced finite element software and then monitored outdoors.
Due to the low position and relatively light soil layers in combination with deep stress water, digging a watercourse can already lead to subsurface erosion. Sufficiently reliable information about (ground) water levels is unfortunately often limited. CRUX has therefore built a complete groundwater model so that, based on calculation, data are available at all locations and this risk is controlled.
To carry out the work outside safely and according to plan, close contact between the work preparation, superintendents and engineers is necessary. This is often a dynamic process in which the geotechnical professional must keep a finger on the pulse and regularly visit the site to check whether practice and design correspond. It is constantly a game of agreeing starting points, designing and retesting, to keep up with the dynamics outside. By recognizing the importance of clear communication and quick response, CRUX professionals prove their added value.
