The water content of sand required for the maximum strength for building sand castles

A sandy beach has a special attraction for people: Building sand castles. The required ingredients are simply sand and water. But what about the mixing ratio to achieve the maximum strength of the wet sand? In this study the influence of the moisture content on the strength of sand was investigated. For the measurement of the strength at different values of the consolidation stress a ring shear tester was used. At small moisture contents up to 2% the strength strongly increased with the moisture content. Over a relatively wide range of the moisture content, almost from 2% to 17% the influence of the moisture content on the strength was relatively small. The maximum strength was measured at a moisture content of approximately 16%. In this moisture range maximizing the applied consolidation stress is of comparatively much higher importance for the strength of the wet sand than the finding the optimum moisture content. At higher moisture contents the strength decreased as saturation with water approached 100%.