If we assess dikes with a sandy subsoil using calculation rules that have been developed for clay dikes, do we make the right decisions when it comes to strengthening or replacing them? Techniques and insights change, specific knowledge is lacking; this was reason enough for the Drents Overijsselse Delta Water Board to look at the safety of the Vecht dikes in an innovative and situation-specific manner. Infram Hydren was asked to write a Plan of Approach for research into the applicability of the currently used warning values. This plan formed the basis for the Grass on Sand project of the Flood Protection Programme (HWBP). In this project Infram Hydren is responsible for research into the strength of the grass cover at various locations along the Vecht.
Research into the strength of the turf on sand and the load-bearing capacity of the dikes can clarify whether the statutory calculation rules correspond to practice. Or whether they require adjustment. The aim is always to guarantee safety, but also: to do no more than necessary (and thus save costs). Research should take into account the impact of climate change and subsidence. Infram Hydren is an expert in the field of dike revetments and is the only party with experience in this type of research and the resources to carry it out.
Our Plan of Approach formed the basis of the project and gave the go-ahead for the research. We have engaged the necessary parties and jointly determined the locations for the research on the Vecht dikes. Infram Hydren carried out research into the soil, grass, cover and structure of the dikes. Using our sod pulling device and our wave overtopping and wave impact simulator, we investigated the critical limit values.
Infram Hydren is also involved as a consultant and reviewer in delivering the final report to the Assessment and Design Instruments programme (BOI2023) at the end of 2021.