ABSTRACT
This chapter focuses on the stability of loose non-cohesive grains, like rock and gravel. In addition, it presents some stability considerations for coherent material. Natural rock is a very important construction material for protections. It is almost omnipresent in the world and relatively easy to obtain. The specific mass of natural rock normally lies between 2500 and 2700 kg/m3, while extremes of more than 3000 kg/m3 can be found. This is favourable for the stability and is difficult to match by artificial material like concrete. Rocks come in all sizes, varying from millimeters up to one or two meters, corresponding with a stone mass of around 10000 kg. Only for very heavily attacked structures, like breakwaters in deep water with high waves, this will be insufficient. Thus, as a construction material for hydraulic engineering, rock is still indispensable. Sand and gravel also consist of non-cohesive, but much smaller and rounder grains. They are not much stable construction materials.
