PURPOSE: To prevent the sinking of a block on a soft ground and stabilize laying by arranging the projecting stripes having each triangular section in the longitudinal direction along a waterway, on the undersurface of the ground contact part of the block which forms the waterway.

CONSTITUTION: Projecting stripes 2 having a triangular section are arranged in the longitudinal direction along a waterway. On the undersurface (bottom part) of the ground contact part of a concrete block body 1 which forms the waterway. In case of a block having a flange, projection stripes are formed on the undersurface of the flange. Sinking is prevented by providing the load dispersion and the floating-up force onto the block body 1, and when the blocks are joined, the shift in the axial direction is facilitated, and also the close adhesion with the contiguous blocks is facilitated. Therefore, the concrete block which is laid on the waterway and is exceedingly advantageous for the execution and strength can be obtained.