High-rigidity seepage-proofing combined cofferdam and construction method thereof

The invention discloses a high-rigidity seepage-proofing combined cofferdam and a construction method thereof. The manufactured cofferdam comprises two oppositely arranged steel plate piles, steel tierods for oppositely pulling the two steel plate piles, and sub-piles arranged on a foundation pit for the steel plate piles. Bagged miscellaneous fill is stacked between the two steel plate piles andstacked to the pile tops of the steel plate piles; a clay-bound macadam pavement is laid on the bagged miscellaneous fill, cement chemical churning piles engaged with one another are arranged along the clay-bound macadam pavement close to the outer side of a foundation pit, and the cement chemical churning piles are used for being inserted into a foundation silty clay layer; and bagged miscellaneous fill is stacked at the tops of the chemical churning piles close to the outer side of the foundation pit as a sub-weir, and a geomembrane is laid on the water side of the sub-weir. The high-rigidity seepage-proofing combin