SBU Division Small Boring Unit (SBU-A) Technical Description The Small Boring Unit (SBU-A) is a proven solution for medium to hard rock utility installations up to 150 m in length. The SBU-A can be used with any conventional auger boring machine (ABM) from 0.6 to 1.8 m in diameter and utilizes a full-face auger for spoils removal. For excavation, the SBU-A is welded to the lead casing. An ABM provides both torque and forward thrust to the cutting head. In hard rock, the circular cutterhead is fitted with disc cutters, while in mixed ground a combination of ripper teeth, drag, bits, and disc cutters are used. Cutting Through Rock Small Boring Units utilize disc cutters from 6.5” to 14” in diameter to excavate rock. Disc cutters penetrate the rock face and create a “crush zone” through which fractures propagate. Material between adjacent crush zones is then chipped from the face. Muck scrapers scoop the muck into openings on the cutterhead (called muck buckets), which transfer the material to a full-face auger for removal. Improved Boring Efficiency Unlike typical carbide bit or roller cone cutting heads, the SBU-A can power through rock over 175 MPa UCS. Most tungsten carbide cutting tools tend to break off in rock above 75 MPa UCS, requiring expensive replacements and machine downtime. A Cost Effective Solution The SBU-A has been successfully used on hundreds of projects around the world to efficiently excavate hard rock. By maximizing machine availability and minimizing labor costs, a typical SBU-A/ABM setup is economically better than carbide bit or roller cone cutting heads. SBU-A APPLICATIONS • Full-face auger boring • Replacement for carbide bit and roller cone cutterheads • Bore lengths up to 150 m (depending on geology)

MACHINE DIAMETERS ROCK STRENGTHS GROUND CONDITIONS Medium to hard rock, or mixed ground Bore Diameter Cutter Size Bore Diameter Cutter Size Bore Diameter Cutter Size Bore Diameter Cutter Size Bore Diameter Cutter Size Bore Diameter Cutter Size Bore Diameter Cutter Size Bore Diameter Cutter Size CORPORATE HEADQUARTERS Visit www.TheRobbinsCompany.com for more information. © Copyright 2009 The Robbins Company