Breakwaters or retaining walls, or their bases of mass-prepaked concrete placed directly on the bedrock have been often constracted. The coefficient of friction between prepacked concrete and bedrock, which is quite important for the design of the structure, has not, however, clearified yet, and values scattered in the wide range depend on the designer are used.
　Authors proposed here a standered value for the coefficient mainly based on the analysis of data on existing structures and theoretical consideration of the mechanism of contact face between prepacked concrete and bedrock.
　Partly because this kind of problem largely depends on the execution condition and fruitfull result can not be expected by small scaele experimental studies, authors have not conducted any experiment at all this time. Therefore it should be emphasized that the value proposed here is a tentative value and problems are left for future reserch.