PURPOSE: To prevent the retension of water and to prevent the breakdown of a bedrock by laying a porous hardening material or a porous drain board between the bedrock and a construction, and getting through the running water from above or springs in the bedrock.

CONSTITUTION: A projection from a bedrock 1 of an anchor 5 driven to the bedrock 1 is penetrated through a porous drain board 2 and a construction 3, and is fixed on the construction 3 with a nut and the like. A porous hardening material 6 is driven between a retaining wall 7 on which existing piles and others are piled up at proper intervals from the bedrock 1 and the bedrock 1. According to the constitution, the retention of running water and springs can be prevented as well as the breakdown of the bedrock.