Abstract: An air-pressure impact type drilling method and an apparatus for the same in which a piston of an air hammer drill is moved up and down by pressure air to produce impact energy and the impact energy of the piston is used to give impact vibrations repetitively to a drill bit. In the air-pressure impact type drilling method and the apparatus for the same, the air hammer drill is operated by the pressure air to be supplied from the ground, the air that has already been used for operation of the air hammer drill is exhausted onto the ground through an air exhaust pipe provided in a drilling pipe and communicating with an air exhaust passage formed in the air hammer drill, and substances cut out by the air hammer drill together with muddy water within the trench are discharged by means of a reverse circulation system while drilling on through the earth.

Abstract: A trench excavator capable of excavating a trench of a rectangular section suitable for formation of an underground diaphragm wall. The underground diaphragm walls are now applied as underground structures replacing caissons, rigid foundations for multistory or tower like buildings, underground tanks and the like. In the trench excavator according to the invention, a pair of drum cutters and a ring cutter interposed therebetween form one unit and a plurality of such units are arranged parallel to one another, whereby an unexcavated portion produced between the drum cutters can be cut out by the ring cutter, leaving no unexcavated portion.