Sustainable scope optimisation

Engineering resilience: The South Holland dike challenge

Hydraulic engineers in the Netherlands have been tasked with strengthening dikes along the country’s major rivers by 2050. As part of the Dutch National Flood Protection Programme (HWBP), Water Authority Hollandse Delta sought to optimise the scope of reinforcement work at dike section 20-3. This part located in the South Holland province between Geervliet and Hekelingen, extends for around 22 km, of which 13 km had failed to meet the legal safety requirements. The water authority needed to optimise the scope of works to minimise costs whilst reducing carbon emissions and local environmental impact.

Smart dike reinforcement: Less carbon and saving cost

Working in collaboration with engineering firm WSP, we carried out extensive research on the areas of section 20-3 that were not at the required standard and identified many opportunities for Water Authority Hollandse Delta to optimise its dike reinforcement project.

The first of the eight circular design principles advocated by Rijkswaterstaat, the Ministry of Infrastructure and Water Management of the Netherlands, resonated strongly with us and became our motto from day one: prevent all unnecessary dike reinforcement work.

By applying our in-house expertise, we:

• Accurately mapped the thickness of the clay cover layer of the dike – We conducted an electromagnetic survey and processed the acquired data to map the thickness of the clay layer on both slopes (outer and inner). This campaign enabled us to accurately detect and measure weak spots in the clay layer;

• Drastically reduced the stability scope – Using a detailed 3D ground model to feed our stability analyses, we efficiently performed a stability analysis every 100 m using specialist software developed in-house (REAL2.0). Through probabilistic and residual-strength analysis we demonstrated that the inward stability scope could be reduced by 45% and that the outward stability scope could be eliminated altogether, due to a combination of failure paths and proven strength;

• Eliminated piping scope – The failure mechanism piping, the formation of erosion channels underneath dikes, is prevalent along the Dutch dikes. By combining data from a range of sources combined with probabilistic analysis we were able to demonstrate that the initial scope could be reduced to zero (see below for details). This elimination represented a significant cost-saving for Water Authority Hollandse Delta and the HWBP.

Combining data for piping scope

To minimise the extent of piping scope in dike section 20-3, we combined data acquired from a range of sources:

• Our probabilistic and geohydrological analyses;

• Aquisense® measurements;

• Anisotropy – using the ratio of horizontal and vertical permeability to map out the soil structure and properties;

• Research into the strength of tidal sand carried out by Fugro, Deltares and Water Authority Hollandse Delta: Piping test Hedwigepolder.

Sustainability and efficiency through data integration

Bringing together these sets of data enabled us to reduce the piping scope to zero. This represented a massive saving in time and cost.

Our involvement helped the project team to:

• Reduce total reinforcement scope by 62% – Our advanced calculation techniques and in-house expertise dramatically reduced the scope of inward stability works and eliminated the need for outward stability works and for piping;

• Increase efficiency – Dike reinforcements that don’t include piping measures are simpler, faster, more efficient and far cheaper because they don’t involve expensive solutions like sheet piling. An added bonus is that future reinforcement work can be carried out more efficiently, with less inconvenience and fewer carbon emissions.