Safe and fast construction method of down-traversing river shallow depth bored tunnel

The invention discloses a safe and fast construction method of a down-traversing river shallow depth bored tunnel. The method includes the steps that on the two sides of the tunnel, the upstream and the downstream of a river are each provided with a clay cofferdam so that the river can be intercepted, and a dry river bed is formed in a tunnel construction area; the two constructed clay cofferdams are communicated through a flow guiding pipe, and therefore upstream river water and downstream river water can flow; the two sides of the tunnel are each provided with at least one row of Larsen steel plate piles, and the tunnel is excavated after the Larsen steel plate piles extend to a river bank in the axial direction of the tunnel. The clay cofferdams, the flow guiding pipe and the Larsen steel plate piles are matched coordinately and comprehensively utilized, and tunnel construction safety is guaranteed by the clay cofferdams, the flow guiding pipe and the Larsen steel plate piles jointly. The method is good in construction safety and high in construction efficiency, treatment measures are flexible, pertinent adjustment can be performed according to different geological conditions, and manufacturing cost of projects is saved as much as possible on the premise that safety is guaranteed.