Bearing platform island-building cofferdam structure under torrent and large-variable-amplitude water level environment and construction method

The invention discloses a bearing platform island building cofferdam structure under the torrent and large-amplitude water level environment, and relates to the technical field of bridges, municipal administration and water conservancy projects. The structure comprises a embankment structure, an island-building cofferdam center structure and an island-building cofferdam scour-preventing structure, wherein the embankment structure is sequentially provided with a first gravel slag layer, a block stone layer, a first nylon net bag gabion and a first reinforced gabion-nylon net bag gabion combination from a river bank to a river bed; a second gravel slag layer, a clay layer and a sand gravel soil layer are sequentially arranged in the island building cofferdam center structure from outside to inside. The island-building cofferdam anti-scour structure comprises a second nylon net bag gabion and a second reinforced gabion-nylon net bag gabion combination. The device can adapt to river construction conditions of dee