On September 7, Caucasus, the world's largest diameter full face rock tunnal boring machine (TBM), was successfully assembled on site at the southern foot of the Caucasus Mountains at an altitude of more than 2,000 meters and began its march towards the start of the cave.

With a boring diameter of 15.08 meters, a total length of 182 meters, a total weight of 3,900 tons, a maximum full thrust of 22,600 tons and a total power of 9,900 kilowatts, the 'Caucasus' is currently the world's largest single-shield rock tunnel boring machine. TBM 'Caucasus' was jointly developed by CREG and CRTG, designed by China on China’s standard and manufactured all by China. It is used for the North-South Highway Tunnel Project (KK Highway Project) in the territory of Mtskheta-Mtianeti Oblast, Georgia.

The boring length of TBM in the KK highway tunnel is 8,860m, the maximum burial depth of the tunnel is 1121m, and the general depth is more than 600m. The lithology is mainly tuff and marl. In view of the construction problems caused by the long distance and large depth of burial, the CREG design team designed in the way of using active articulation system, bi-directional rotating cutter, two-speed reducer system and box culvert synchronous assembly to realize precise adjustment of the host attitude and have the strong ability of relieving from large depth of burial, enabling the equipment to have efficient boring capacity under different geological conditions.