Advanced design optimisation drives dike reinforcement

Improved reinforcement for safety, sustainability and quality

The aim of the National Flood Protection Programme in the Netherlands is to strengthen the dikes along the country’s major rivers by 2050.

The Water Authority Rivierenland commissioned De Betuwse Waard – a building consortium comprising GMB, Ploegam and Dura Vermeer – to reinforce a 13 km section of the 15 km dike located between Wolferen and Sprok, to bring it up to the current safety standard.

The Water Authority wanted a reinforcement design that optimised safety, minimised the project’s environmental impact and improved the quality of the entire area.

Extensive ground investigation for data and insights

In 2019 the consortium asked Fugro to carry out an extensive geotechnical investigation to provide data and insights about the site, including:

• Electromagnetic surveys – measuring and mapping the thickness of the clay layer in the floodplains;

• Cone penetration tests, drilling and in-house laboratory research – identifying and characterising soil and erosion through laboratory tests;

• Continuous, remote monitoring – measurements taken at nearby monitoring wells;

• Borehole permeability testing – a cost-effective permeability test using constant water pressure with minimal environmental impact;

• Hydraulic resistance testing – carried out with monitoring wells at gullies and nearby ponds;

• Design optimisation by:

  • Scope reduction – One of the key failures in dikes is due to piping – this is where water flows through the foundation of a dike, gradually eroding soil and forming underground channels that can lead to collapse. A major influence on this is the soil‘s permeability. Our Aquisense® technology was able to measure the movement of groundwater in the nearby ground layers, and investigate the permeability of deep sand layers. This showed the overall piping scope could be reduced by 30% - from 13 km to 9.1 km;

  • Sustainability – 30% less carbon emissions due to:

    • the production of plastic heave screens (=95% lower than traditional steel sheet pile planks);

    • 3.9 km less steel or plastic sheet piles due to a 30% scope reduction;

    • 16% reduction in screen length - on average by 1 m - by optimising the heave criterion to limit the piping scope. The shorter sheet pile length contributed to the feasibility of installing the plastic heave screens. We chose the heave screens, because these were most efficient and were space-limiting compared to classic berms;

  • Cost-savings – Our advanced failure probability analyses for outward stability (gully erosion caused by overflow at the channels crossings), confirmed that an outer slope of 1:3 provided the required level of stability and that an outer berm was unnecessary. This insight resulted in a significant reduction in the materials and space required, reducing costs and carbon emissions;

  • Improved dike stability – The dike design is optimised for flood events. During flooding, water can flow over the dike at a maximum rate of 10 litres per second per linear metre. These incidents can destabilise the dike structure, so a lot of attention went into stabilising the dike for these conditions. For this design, the in situ permeability tests and advanced PLAXIS models were crucial.

Innovative highlights

Aquisense® measurements and floodplain piping study

We accurately mapped the permeability of the aquifer using our innovative Aquisense® technology. Additionally, the findings from our floodplain piping study formed the basis of a generic guideline that enabled the inclusion of more floodplains for natural flood protection and enhanced climate resilience. The acquired measurement data and insights combined with the findings from the study of the floodplains, contributed to the overall reduction of the piping scope by 30%.

Heave screen design optimisation

We applied the results of our soil investigations (including Aquisense®) and our in-house laboratory research to optimise the heave criterion for the heave screen designs. This led to a 16% reduction in screen length.

Impact on sustainability and piping

Our research, analysis and subsequent recommendations delivered a range of benefits, including:

• Improved sustainability: carbon emissions from the plastic heave sheets are 95% lower than the equivalent steel sheet piles;

• Enhanced understanding of the formation of erosion channels under the dike (piping). The resultant guidelines can be applied to future dike reinforcements;

• 30% reduction in carbon emissions compared to the initial designs by  optimising the design (in terms of dimensions and material used) and the combined effort of the project-team.