The invention discloses a reinforcing treatment structure for a tunnel middle-lower portion
karst cave and a construction method of the reinforcing treatment structure. The treatment structure comprises a tunnel;
karst caves located on one side and the lower portion of the tunnel in the horizontal direction; and a
rubble layer, a gravel layer, concrete, a reinforcing beam, a sprayed concrete layer, a local anchor rod and a
cartridge anchor rod are arranged in the lower
karst cave of the tunnel from bottom to top in sequence, wherein the reinforcing beam is connected between the concrete and an inverted arch of the tunnel, the sprayed concrete layer is connected between the horizontal karst
cave and the tunnel, the local anchor rod is connected between the horizontal karst cave and a rock
mass, and the
cartridge anchor rod is connected between the tunnel and the rock
mass. According to the reinforcing treatment structure, the lower karst cave of the tunnel is filled with the
rubble layer and the gravel layer, so that the bearing of the bottom of the tunnel and the construction progress are guaranteed; through the arrangement of the reinforcing beam, the concrete filling layer below the inverted arch of the tunnel can be reinforced, and the reinforcing beam has buffering and weakening effects on asymmetric acting force; and by arranging the sprayed concrete layer, on one hand, connection between the karst cave and the tunnel is strengthened, and on the other hand, contact between the boundary of the karst cave and the rock
mass is strengthened.