To provide a reinforcing structure of a banking which suppresses collapse of a slope surface of the banking due to overflow upon a flood, and degradation of a bearing force of an underground steel wall body by scouring of a ground surface, in a structure for reinforcing the banking with the underground steel wall body.
The underground steel wall body 2 including a steel sheet pile wall comprising steel sheet piles 3 (including steel pipe sheet piles) connected to each other is arranged within the range of a roughly top end 1c of the banking 1. The steel sheet piles 8 as diagonal braces are diagonally placed on and along the slope surface 1a inside of the dike of the banking 1 on the slope surface 1a. The steel sheet piles 8 are embedded at least in a foundation ground 5 under the banking 1 by the depth longer than the length of the slope surface 1a of the banking 1. The steel sheet piles 8 are connected to configure the diagonal steel sheet pile wall 9, and the slope surface 1a is substantially covered with the steel sheet pile wall 9.