Standing for a Crossover (X) between Rock (R) and EPB (E), the XRE has been designed and deployed by Robbins on multiple projects that feature sections of both hard rock and soft ground in the tunnel alignment. Using features of both EPB and Single Shield Hard Rock machines, the XRE has successfully been used on mixed ground projects in Australia, Turkey, Mexico, India, and more. Download a specification sheet here.
Ideal in Unstable Ground
The XRE’s unique design features make it a strong choice for mixed face rock and non-self-supporting ground. A single direction cutterhead cuts down on tool and machine wear and eliminates the problem of regrind, which causes undue wear on machine elements. Two-speed gearboxes efficiently use power to generate high torque at low RPM, allowing the XRE to get through squeezing geology and fracture zones that might leave other machines stuck.
The XRE is a versatile machine that can be customized in a number of ways. Design features often include mixed ground cutterheads with a combination of disc cutters and carbide bits. These machines may offer conversion between a fully pressurized EPB mode and non-pressurized EPB mode, as well as a non-pressurized shielded hard rock mode. Typically conversion is done by changing out the system of muck removal or by using a specialized muck removal system. Muck removal conversions may involve using a robust screw conveyor that can excavate rock, switching from screw to belt conveyor in the tunnel, or converting between an open/closed center-mounted screw conveyor.
At diameters over 12 m, the XRE design becomes even more versatile. Large XRE TBMs can be designed without compromising one machine type over the other. Current setups allow the belt conveyor to remain in place along with the screw conveyor, eliminating the conversion step between screw and belt. Instead, a hydraulic muck ring moves the conveyor into place if hard rock is encountered.
“The performance of the XRE machine has been very good given the geology we have encountered during the project. We do plan to use Robbins for upcoming projects.” — Andrés Alanís, CEO of RECSA group, contractor for TEP II
Proven in the Field