On April 23, China Railway Tunnel Group constructed the Gudauri Tunnel of Georgia North-South Corridor KK Highway and participated by China Railway Academy Co.Ltd. 30 days ahead of the overall construction plan. The tunnel uses the world's largest diameter TBM (Full Face Hard Rock Tunnel Boring Machine), "CREC Caucasus".

The total length of KK Highway is 22.7 km. The total length of LOT1 project undertaken by China Railway Tunnel Group is 10 kilometers, of which the total length of Gudoli Tunnel is 8860 meters, with two-way two-lane design, which is the largest single infrastructure project in Georgia at present. The buried depth of nearly half of the Gudoli Tunnel is more than 700 meters, and the maximum buried depth is 1121 meters. The maximum strength of the surrounding rock of the tunnel is 130 MPa, the geological conditions are complex, and there are some problems in the construction, such as carbon dioxide surge, abundant groundwater, long-distance reverse slope drainage, soil intrusion and so on, which is the key control project of the whole line.

The single-shield TBM "CREC Caucasus" jointly developed by China Railway Tunnel Group and China Railway Engineering Equipment Group is used for single-head excavation. The equipment has a length of 182 meters, a weight of 3,900 tons, a maximum thrust of 22,600 tons, a total power of 9,900 kilowatts, and an excavation diameter of 15.08 meters. It pioneered the synchronous tunneling and assembly technology to synchronize shield TBM tunneling and segment assembly, effectively improving construction efficiency. The TBM is equipped with a series of new functions, such as an active hinge, two-speed reducer, and cutter head bidirectional rotation, to prevent bad geological jamming in tunneling. Since the launch of TBM in September 2021, the highest monthly footage of "CREC Caucasus" has reached 426 meters, which has set a new record for the construction speed of super-large diameter TBM tunnels.