Robbins’ Crossover series of TBMs is a line of field-tested, rugged Dual Mode-type machines. Crossover TBMs feature aspects of two TBM types and are ideal for mixed ground conditions that might otherwise require multiple tunneling machines. The XRE (standing for Crossover Rock /EPB) is the most common type of hybrid machine, and features characteristics of Single Shield Hard Rock machines and EPBs for efficient excavation in mixed soils with rock. Additional types of Crossover machines include the XSE (Crossover between Slurry/EPB). The Crossover series is quickly gaining in popularity, with Robbins Crossover TBMs currently boring in locations including the U.S, Turkey, China, and India.
The Crossover terminology embodies the concept that the machines are able to “cross over” between modes, says Robbins President Lok Home. The unique machines are a top focus point for the company: “Robbins comes at this business with extensive rock experience so everything we design comes with the assumption that there will be tough conditions. When you have to “cross over” to another mode then already you are in difficult conditions, and contractors need robust machines to get through these challenges.”
Throughout the world, Crossover machines have seen a multitude of successful projects. In March 2021 in Guangzhou, a 9.2 m (30 ft) diameter XRE machine had the honor of being the “Largest ever Crossover to launch in China”. The machine is boring the 2.5 km (1.6 mi) long Pazhou Line Lot PZH-1 of the Pearl River Delta Intercity Railway Project. This launch is one of several including two Crossover machines for Chongqing Metro, in a growing trend towards more complex mixed ground projects within China.
In India on the Mumbai Metro Line 3, there have been multiple breakthroughs with two 6.65 m (21.8 ft) diameter Crossover XRE TBMs for the L&T/STEC JV. These TBMS have both bored over 2,000 m of basalt rock with transition zones of shale, tuff, and breccia underneath the city and are making three to four breakthroughs each.
For more on Crossover TBMs and the latest project updates, visit www.robbinstbm.com.