Class Codes & Rates:

 Code 6251 is assigned to specialist contractors engaged in non-pneumatic tunnel construction. The classification contemplates all operations including lining. It does not contemplate subway construction or any operations performed under air pressure. The operations include earth, rock, and water removal by mechanical equipment, explosives and pumps and drains piped to the outside of the bore which will vary in size depending upon the ultimate use of the tunnel. Shaped steel I-beams are placed as the bore progresses, to which horizontal beams or solid bar stock are welded or bolted for support. Shielding the bore, between the I-beams, requires bolting wood bulkheads or welding steel plates to the beams followed by filling gaps between the face of the bore and shielding with sand or concrete grout. The tunnel will then be lined with concrete, steel or tile, if required, and lighting, ventilation and drains installed.