PURPOSE: To form a water deck structure as an artificial land on soft ground by treating loads during normal or abnormal periods of time by utilizing the buoyance of a caisson and the drawing resistance of a friction wall to be penetrated into soft ground.

CONSTITUTION: A caisson 1 with a large number of bottomless hollows 2 divided in both parallel and crossing directions, as shown in Fig., is landed on the soft ground bottom 8 under water. A friction wall 12 integrally connected with the caisson 1 is penetrated into soft ground 9, receiving the passive earth pressure of continuous friction piles and during horizontal compression period by taking advantage of its high rigidity in the horizontal direction and preventing the scouring of the bottom under water by tidal current. On the upper part of the caisson 1, struts 3, braces 4, joint beams 5, water deck 6, and facilitates 7 are provided. Since total weight WG is supported by the excess buoyance Fo of the caisson 1 and the drawing resistance Rp of the friction wall 12 under the relationship Fo=WG+Rp, the water deck can be set even on soft ground.