A new series of guide rod swivel cutterheads for the Akkerman guided boring machine line will allow installation of steel casings in deep, densely compacted ground and soft rock. With a universal bearing swivel, the robust range of guide rod swivel cutterheads, the GRS-50 series, contains four sizes of high thrust bearing upsizing tools able to withstand up to 50 tons of continuous thrust on guided boring, guided auger boring, and soft rock pilot boring projects.
The GRS-50 units are suitable for a wide range of pilot boring projects. It can be used during guided auger boring to upsize from the pilot tube to the steel casing diameters and also follow the rock drill adapter (RDA) in weathered rock conditions. On projects with space constraints, the GRS-50 is compatible with a 4800 series jacking frame with an auger boring adapter for spoil discharge.
The new cutterheads match the outside diameter of common steel casing pipe in 24in (610mm), 30in (762mm), 36in (914mm) and 42in (1,067mm) diameters. The GRS-50 is an economical solution since the 7in bearing swivel is universal to all GRS-50 cutterheads and securely bolts onto the cutterhead collar. Two seals inside the bearing swivel prevent contaminants entering the main housing.
The guide shaft extends beyond the face of the cutterhead and connects to the last length of pilot tube with a 3in hex connection to firmly hold the bore on line and grade. During steel casing installation, the bearing swivel absorbs the rotational torque while the cutterhead excavates in a clockwise direction. Excavated spoil flows through the auger flights for removal in the launch shaft.
The durable, carbide gauge cutter bits around the perimeter of the cutterheads are mounted on collapsible wings that retract into the casing sleeve for pullback, should an obstacle be encountered. In such events, the guide shaft can reconnect to the hex connection on the pilot tube to resume boring. The round shank gauge cutter bit allows it to turn as it excavates for optimal wear and longevity and if necessary, can be easily replaced.
The complete boring assembly is 42in (1,067mm) long from tip of the guide shaft to the rear auger drive adapter and includes a GRS-50 cutterhead, a bearing swivel, an auger drive adapter for 5-6in lead auger hex connection and a casing sleeve.
To upsize from the pilot tubes in ground conditions requiring less jacking force, a single or two-step weld-on reaming head remains the appropriate choice.