On June 29, the "Jincheng No. 32" shield machine was successfully received, and the shield-driven section from Jinan West Station to Dayang Station on Jinan Metro Line 4—the longest section tunnel on the entire line, constructed by China Railway 21st Bureau Group—achieved twin-tube breakthrough.

Construction site at Jinan West Station of Jinan Metro Line 4

The twin tubes of this section total 4,582 meters in length, continuously passing beneath three operating high-speed railways, Metro Line 1, major urban arterial roads, and multiple large-diameter water supply, rainwater/sewage, and natural gas pipelines. This is the first case nationwide of a single shield-driven section passing beneath four operating railway lines, with one train passing every four minutes on average. The horizontal clearance between the shield tunnel edge and the piers of the operating high-speed railway bridge is 9.4 meters, and the clearance to the bottom of the operating metro line is only 3.01 meters.

This section is located in the core area of the "Jixi Grand Reservoir," where the groundwater level is high, water pressure is great, and water content is abundant. It passes through silty clay layers, with local cobble layers at the crown, exhibiting extremely strong vertical permeability.

Shield personnel monitoring real-time tunneling parameters

The project team carefully studied the engineering data, conducted comprehensive above-ground and underground surveys and statistics of the construction area, carried out diagnostic analysis and verification, selected the optimal shield machine model, and formulated the best construction plans for "railway-related," "track-related," and "road-related" works. They strictly enforced the node verification procedures to control risks to the greatest extent, laying the foundation for smooth tunneling of the shield-driven section.

Before construction, the participating personnel set up a trial section to determine the optimal tunneling parameters, installed isolation piles to shield the high-speed railway bridge piles from construction disturbance, and took the lead in adopting an automated monitoring system for high-speed railway piers to monitor settlement data changes of the piers in real time, with manual re-inspection of tunnel structural changes. During construction, various tunneling parameters of the shield machine were dynamically adjusted based on monitoring data, the setting time of the synchronous grout was shortened, and anti-settlement filling material was injected around the shield body. After construction, deep-hole grouting reinforcement was carried out inside the tunnel, and all safety measures were comprehensively strengthened to ensure the safe breakthrough of the section tunnel.

Inside the shield tunnel

To prevent potential water leakage risks during tunneling, the construction personnel scientifically selected a shield machine equipped with four rows of tail brushes to enhance the sealing effect of the shield tail and prevent water leakage there. Water-swelling sealing strips were added at the segment joints to block seepage through the gaps. For shield launching and reception, a double-seal design for the portal and a fully wrapped sleeve design for the portal were adopted respectively to improve portal airtightness. After construction, a water-stop ring was installed every 6 meters in the tunnel to block water coming from behind the shield machine. The synchronous grouting pipelines were modified to inject quick-setting materials, shortening the grout setting time, ensuring waterproofing safety, and achieving "zero settlement."

The twin-tube breakthrough of this section plays a major role in promoting the early breakthrough and operation of the entire line. Once Line 4 is completed and opened to traffic, it will further improve the layout of Jinan's metro network and is of great significance for alleviating east-west traffic pressure in Jinan, especially on Jingshi Road, and for advancing Jinan's construction of the provincial capital economic circle.