A new type of machine has been designed for line- and grade-sensitive utility bores at small diameters in hard rockrnand mixed ground. With remotely controlled steering, the small diameter Motorized Small Boring Unit (SBU-M)rnfills a niche traditionally occupied by slurry microtunneling machines adapted for hard rock. In any size from 30 torn44 inches (762 mm to 1,118 mm), the smaller diameter SBU-M is a cost-effective alternative to conventionalrnmicrotunneling and pipe jacking operations.rnThe compact machine allows for line and grade control within 1 inch (25 mm) for bores up to 500 ft (150 m) andrnuses laser-guided steering for increased accuracy. The machine employs existing cutterhead and disc cutter designsrnable to excavate in ground conditions up to 25,000 psi (172 MPa) UCS. During excavation, a unique vacuumrnsystem removes spoil at small diameters rather than an invert auger. The small diameter SBU-M is typically usedrnwith welded steel casing; however on longer projects, the casing can be bolted and pushed out with ReinforcedrnConcrete Pipe (RCP).rnThis paper discusses the development of the new machine design and application at its first project in Muscat,rnOman. A 38-inch diameter machine is being used for six mixed ground crossings on the Bausher WastewaterrnProject for contractor AFAQ AL-MUSANA Trading LLC. Performance of the machine, successes and challengesrnof tunneling, and any necessary design modifications will be examined.
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