Abstract: An underground excavator includes a chamber defined in the forward section of an excavator body for receiving excavated material such as soil, sand, gravel, clay and their mixtures. A rotary cutter is mounted to the forward end of a rotary shaft for penetrating through the chamber for axial rotation and simultaneous rocking in an axial direction. The cutter has a conical cutter face plate having holes for passing the excavated material of a diameter smaller than an opening disposed in the chamber. Any gravel or the like present in the advancing route to the underground excavator and smaller than the holes of the cutter is received into the chamber to be discharged from the excavator. Any gravel larger than the holes or the like not receivable into the chamber is moved quickly along the conical cutter face plate toward peripheral ground layer by being subjected to the rocking motion of the conical cutter face plate simultaneously with the rotation of the cutter during advancement of the excavator.

Abstract: A caisson sinking method comprises the steps of excavating the ground to make a support ditch having the same plan-view shape as a caisson to be sunk, casting into the excavated ditch a bearing material that can carry the caisson as supported in the ditch but collapses easily by itself, placing entire tapered bottom edge of the caisson on the bearing material cast in the support ditch as aligned therewith, and sequentially removing the bearing material immediately below the bottom edge of the caisson, the caisson being thereby smoothly sunk down to a caisson sinking position without any tilting of the caisson.

Abstract: A shield tunnel boring machine having at its boring head a pressure-resisting mud kneading chamber defined by a bulkhead, wherein the bulkhead is divided into outer peripheral and central bulkhead parts. The outer peripheral bulkhead part is fixed to the inner periphery of a cylindrical shield. The central bulkhead part is made rotatable in association with a head-positioned rotary cutter as driven by a main motor. The sealing means required for the bulkhead is limited to seal one for a gap between the fixed outer peripheral bulkhead part and the rotatable central bulkhead part and the number of necessary related parts can be remarkably reduced.