Recently, the west line tunnel of the Beijing East 6th Ring Road Reconstruction Project, organized and implemented by Beijing Capital Highway Development Group Co., Ltd. and constructed by China Railway 14th Bureau Group, surpassed 1,500 meters of tunneling. Since the beginning of this month, the "Jinghua" shield tunneling machine has achieved a monthly tunneling advance of 542 meters, once again setting a new monthly advance record for 16-meter-class super-large-diameter shield tunneling machines. This is of milestone significance for the construction of the shield tunneling sections along the entire East 6th Ring Road Reconstruction Project and has also greatly encouraged the builders.

According to reports, the shield tunnel of the Beijing East 6th Ring Road passes through high-density water-rich sand layers, with a maximum burial depth of 59 meters. The deeper such strata are, the more complex the geological conditions and the poorer the self-stability; if the machine stops for a long time, it may bring the risk of face instability. For this reason, from the very beginning of the project, the builders attached importance to the running-in between people and the shield machine and between geology and the shield machine. They used the first 200 meters of the tunnel as a trial tunneling section, advancing at a rate of 4 to 5 rings per day, gradually exploring suitable tunneling parameters, improving proficiency in equipment use, and carrying out partial modifications to the equipment, laying the foundation for stable tunneling later. The tunneling speed gradually increased to 6 to 8 rings per day, and has now reached about 10 rings per day.

Like people, a shield machine can also become "fatigued" after working for a long time. Therefore, during tunnel tunneling, the builders did not simply pursue high output but adhered to the concept that "stable output is high output." They rationally coordinated the construction schedule, and on the basis of ensuring safety in production and project quality, closely followed time nodes, proactively controlled the daily tunneling advance, and used the 3 to 4 hour shift-change interval for planned repairs and preventive maintenance of the equipment. In a single month, inspection and lubrication alone reached 126 items, and the equipment failure rate was kept within 5% at all times.

At present, the "Jinghua" shield tunneling machine has safely and smoothly tunneled 1,500 meters, successfully passing through multiple risk sources with almost no disturbance, laying a solid foundation for the full breakthrough of the tunnel section of the East 6th Ring Road Reconstruction Project in the next step.

Next, the shield tunneling machine will continue to face many risks and challenges, including tunneling in high-density water-rich sand layers, tunneling beneath highly dense aboveground risk sources, and cross-construction of the tunnel's large-volume internal structure. "In particular, the upcoming underpass beneath the Tongyan Expressway has a relatively high content of fine particles such as clay and silty clay in the strata below it. These fine particles will increase synchronously with the circulation of slurry, causing the relative density of the slurry to rise rapidly and adversely affecting the advancement of the shield machine and slurry discharge. In addition, the Tongyan Expressway has dense traffic flow. If collapse occurs during the shield underpass, it will cause serious safety accidents. All of these bring new challenges to our subsequent tunneling," said He Lichao, head of the East 6th Ring Road Project Department of Capital Construction Company.

To this end, Capital Group planned in advance and deployed precisely, formulating a safe and scientific special construction plan and clarifying the 15-character basic operating principle of "maintain slurry pressure, prevent blockage, strictly synchronize, tightly seal, and do not stop the machine." The group continuously strengthened on-site safety and quality management, optimized construction technology, increased resource allocation, and insisted on planned repairs and preventive maintenance for the shield machine and auxiliary equipment to reduce the equipment failure rate and ensure "safety first, quality foremost, and efficient advancement."