Recently, at the construction site of the Kvesheti-Kobi highway tunnel as part of the North-South Road Corridor in Georgia which is a key traffic construction project of the Belt and Road Initiative, the high-end equipment 'Caucasus', the world's largest diameter full face hard rock TBM developed by China Railway Engineering Equipment Group under CRHIC, was successfully applied to tunneling in complex geological conditions and advanced for 4,000m.

The hard rock TBM 'Caucasus' (CREC 859) has a diameter of 15.08 meters and a total length of 182 meters, making it the world's largest diameter full face hard rock TBM till now; it weighs 3900 tons, equivalent to the weight of 50 Airbus A320 passenger aircrafts; its maximum thrust is 22,600 tons, equaling to the weight of 1500 F22 aeroengines; it has a total power of 9,900kW, the same weight of 1,000 sedans; the machine is completely designed and manufactured by China to Chinese standards.

The machine is equipped with dual speed reducer technology that meets different tunneling requirements such as high speed tunneling in stable wall rock and high torque tunneling in soft wall rock. The continuous tunneling technology is applied for the first time, with tunneling and assembly being implemented concurrently. During traditional TBM construction, the shield machine needs to stop every time it advances for one ring and continues tunneling after assembling a ring of segments. The continuous tunneling technology helps improve the tunneling efficiency by 20% to 30% and enables the parallel operation of tunneling and assembly, thus greatly boosting the construction efficiency. With a maximum daily performance of 20 meters and a maximum monthly performance of 420 meters, the machine has been highly praised by Georgian owner and representatives of Italy's largest international contractors.