On October 30, the main machine and connecting bridge of the second TBM "Dayu·Xuedun" for the Lesotho Polihali Water Transfer Tunnel Construction Project smoothly commenced stepping operations, marking a key milestone in advancing the intake TBM construction from "equipment assembly" to "tunnel excavation" and laying a solid foundation for subsequent launch and boring.

The main machine and connecting bridge of the "Dayu·Xuedun" TBM have a total length of approximately 38 meters and weigh about 560 tons. Its onboard stepping system can achieve a daily stepping capacity of approximately 120 meters. Subsequently, it will face the triple challenges of an altitude of 2,800 meters, extreme cold weather of minus 15 degrees Celsius, and 260 MPa basalt strata. Unlike conventional stepping methods, the TBM main machine and connecting bridge will, under the condition of a steep -8% downhill gradient, innovatively adopt a guide-trench-free reverse stepping technique, combined with a special stepping mode of "head facing out of the tunnel, tail facing into the tunnel," to continuously step more than 1,800 meters.

In response to safety risks such as equipment slippage that may occur under complex working conditions, the project team, based on actual site conditions, conducted in-depth analysis and assessment of technical difficulties and safety risks involved in the stepping process, including a 300-meter horizontal turning radius, a 50-meter small-radius horizontal turn, an ultra-long stepping distance of 1,800 meters, and an ultra-steep -8% gradient. By simulating the TBM stepping route in advance, preparing detailed safety technical disclosure plans and related documents, and establishing a full-chain safety control mechanism, the project ensures comprehensive support for the smooth and orderly progress of stepping operations.

Since the equipment assembly began, all staff of the project department have consistently upheld the concept of high-quality development, completing all assembly tasks for the TBM main machine and connecting bridge in just 45 days and successfully achieving the equipment stepping milestone. The project will continue to maintain high standards and strict requirements to ensure the smooth stepping of the main machine and connecting bridge to the launch chamber, creating favorable conditions for the assembly of the trailing backup gantry and connecting bridge, and making every effort to achieve the goal of launching and boring for the intake TBM.