Key to sandcastle construction is water – but how much should we be adding to dry sand to build the perfect palace?
Water functions to build small bridges between grains of sand, sticking them together and increasing the solidarity of the structure. Researchers from the University of Amsterdam’s Institute of Physics have shown that the optimum amount of water needed is around 1%.
The team investigated the stability of wet sand columns to account for the maximum height of sandcastles. Columns become unstable due to elastic buckling under their own weight, with the height of the column increasing as 2/3 power of the base radius of the column.
Knowing this elastic modulus can quantitatively account for measured sandcastle height – and researchers were able to build sandcastles as high as 5m. Optimum strength is achieved with a liquid volume fraction of only 1%.
Researchers also show that with specially treated water-repellent sand, underwater sandcastles can be built. The water that serves as glue when building normal sandcastles is substituted with air bubbles when building the underwater ones.
The results – published in Nature – have important implications to the civil engineering and soil mechanics sectors, where stability of soil structures is key.