Method for constructing tunnel with uncovered hole section in middle

The invention relates to a method for constructing a tunnel, in particular to a method for constructing a tunnel with an uncovered hole section in the middle, aiming to the solve the problems of single working surface, large construction amount and long construction period of the prior method for excavating the tunnel. The method comprises the following steps: (1) building water drainage systems on the upstream of uncovered holes and on the ground surface; (2) excavating the uncovered holes, protecting side slopes, and reserving upper leading-in hole core earth at the joint of the uncovered holes and the covered holes; (3) constructing the middle leading-in holes of the uncovered holes, and constructing the upper leading-in holes of the covered holes on two sides; (4) constructing the lower leading-in holes of the uncovered holes, and constructing the middle leading-in holes of the covered holes on two sides; (5) constructing the lower leading-in holes of the covered holes on two sides; (6) constructing inverted arches at the entrances to the covered holes, and excavating by troughs to construct inverted arches of the uncovered holes; (7) constructing the linings of the uncovered holes for the second time; (8) constructing the waterproof layers of the uncovered holes; and (9) sealing and backfilling the uncovered holes. The working surface is doubled under the condition of not increasing the cost, the cross operation is carried out, the construction period is shortened, the construction cost is saved, and good social and economic benefits are achieved.