Jinan Metro Line 4 Tunnel Breakthrough in Complex Water-Rich Sand Layer, Tail Seal Brush Ensures Safe Long-Distance Shield Tunneling

Jinan Metro Line 4, an important urban rail transit project running through the central area of Jinan, plays a significant role in optimizing the city’s transportation network and improving public mobility. Recently, the shield tunneling section between Yuhan Road Station and Shandong Sports Center Station was successfully completed. As one of the most challenging sections of the entire line, this area involved the most complex geological conditions, highest construction risks, and strictest technical requirements. During the construction process, multiple earth pressure balance shield machines were used for alternating excavation. Facing complex environments including water-rich sand layers, fractured rock formations, and densely distributed buildings, the tail seal brush served as a critical sealing component of the shield machine, providing essential protection against water leakage, sand intrusion, and slurry leakage, ensuring safe and continuous long-distance tunneling.

The shield tunnel section has a total length of 2,346 meters, with a burial depth ranging from 14 to 26 meters. The excavation route mainly passed through composite geological conditions including water-rich sand layers, silty clay, and moderately weathered rock formations. The area contains abundant underground water resources, frequent changes in water pressure, and highly mobile sand layers, creating potential risks such as shield tail slurry leakage, water and sand inflow, and water penetration between tunnel segments. For earth pressure balance shield machines, the tail seal brush acts as the final physical barrier preventing external soil and groundwater from entering the shield body.

Through a multi-layer steel wire brush structure, the tail seal brush closely contacts the outer surface of tunnel segments to form a sealed grease chamber. By continuously injecting shield grease, stable sealing pressure is maintained to effectively block groundwater and soil intrusion. If the wear resistance of the tail seal brush is insufficient, installation accuracy is not properly controlled, or grease supply is interrupted, sealing performance may be affected, leading to equipment shutdown, brush replacement, and ground disturbance, which could significantly impact construction safety and progress.

To overcome the challenges brought by water-rich sand layer excavation, the project team optimized the shield construction plan according to geological characteristics. During the selection of sealing components, high-performance tail seal brush products with excellent wear resistance, pressure resistance, and long-distance tunneling adaptability were selected. Before construction, strict inspections were carried out on product quality, transportation acceptance, and installation positioning to ensure that brush flatness, steel wire density, and steel plate fitting accuracy met construction requirements.

During the tunneling process, dedicated personnel monitored key parameters including shield grease pressure, injection volume, excavation speed, and grouting pressure around the clock. According to changes in sand layer conditions and groundwater pressure, operating parameters were adjusted dynamically to identify and address potential issues such as brush wear, wire separation, and local leakage at an early stage. These measures ensured stable operation of the shield tail sealing system throughout the construction period.

During nearly four months of continuous excavation, the shield machine maintained a stable daily advance rate of 11 to 13 tunnel rings and completed a total of 782 rings of safe excavation. The project successfully overcame multiple challenges, including sudden changes between soft and hard geological layers, local boulders, and tunneling beneath densely populated residential areas and municipal pipelines. Throughout the entire process, the tail seal brush sealing system remained stable, with no shield tail leakage incidents occurring. This significantly reduced downtime caused by sealing system maintenance and improved overall construction efficiency.

Behind the reliable performance of the tail seal brush system is also the continuous innovation and manufacturing experience of professional suppliers. As a company specializing in shield tail brushes, Chenxing Machinery has accumulated extensive experience in the research, development, and production of tail seal brush products. The company has produced more than 1.2 million sets of shield tail brushes, and its products once achieved approximately 70% market share in China, making it a recognized hidden champion in the domestic shield tail brush industry. Among companies exporting similar products, Chenxing Machinery is one of the few manufacturers that focuses exclusively on shield tail brushes rather than producing a wide range of shield machine accessories.

With years of professional manufacturing experience and large-scale engineering applications, Chenxing Machinery’s tail seal brush products have been widely applied in metro projects, highway tunnels, water conservancy projects, and other underground engineering construction. The company continues to optimize product structures, materials, and manufacturing processes to improve sealing performance under high water pressure, long-distance excavation, and complex geological conditions.

The successful breakthrough of the Jinan Metro Line 4 shield section not only represents an important milestone in the city’s rail transit development but also provides valuable experience for similar shield tunneling projects in water-rich sand layers. With the continuous expansion of global tunnel construction, shield machines are being applied in increasingly complex environments, creating higher requirements for key components such as the tail seal brush. Relying on professional manufacturing capabilities and accumulated engineering experience, high-performance tail seal brushes will continue to play an important role in ensuring safer, more efficient, and more reliable shield tunneling operations in the future.