Recently, Guangzhou Metro Line 12 and Phase II of Line 14 have achieved multiple milestones. On Line 12, the left-line shield tunnel of the Yunxi Park to Xiaojinzhong section (hereinafter referred to as the "Yunxiao section") has been completed, and Chigang Station, the deepest station on the entire line, has been topped out; on Phase II of Line 14, the left-line shield tunnel of the Guangle No. 2 Intermediate Ventilation Shaft to Lejia Road section (hereinafter referred to as the "Zhongle section") has also been successfully completed.

Shield diameter 11.7 meters: Line 12's largest shield successfully breaks through

The left line of the Yunxiao section on Line 12 starts from Yunxi Park Station in the north. After leaving Yunxi Park Station, it runs along Baiyun Avenue South, then passes beneath the Jinyuan Road tunnel and a cluster of buildings before reaching Xiaojinzhong Station. The Yunxiao section has a total length of 457 meters and was constructed using the slurry balance shield machine "Rongtong Hao," with an outer diameter of 11.71 meters. "Rongtong Hao" is also the largest-diameter shield machine on the entire Line 12.

The geological conditions along the section are complex, with various strata overlapping and interlocking. The section has strongly developed karst and shallow cover, with a karst cave encounter rate as high as 42.5%. At the same time, underground pipelines above the section tunnel are dense, with gas, water supply, rainwater and sewage pipelines distributed in a complex manner—a total of 68 pipelines are crossed beneath or alongside—and the tunnel must pass beneath the Jinyuan Road municipal tunnel at a close distance with a clear spacing of only 0.8 meters, posing extremely high risks during shield tunneling.

To ensure the smooth completion of the left-line shield tunnel in the Yunxiao section, Guangzhou Metro's builders conducted multiple rounds of technical research, using ground-penetrating radar and seismic cross-hole CT methods to carry out advance detection of karst cave development in the section, and investigated and resolved the shield attitude control problems caused by slurry overflow and pressure loss during shield tunneling in karst strata. At the same time, they summarized and analyzed data such as tunneling parameters, ensured the stability of the shield tunneling area through simultaneous in-tunnel grouting and secondary grouting, carried out round-the-clock uninterrupted monitoring and early warning, and established an "above-ground and underground" emergency linkage mechanism, thereby maximizing the safety of shield construction and successfully achieving tunnel breakthrough.

Equivalent to a 13-story underground building: Line 12's deepest station topped out

Chigang Station on Line 12 is located in the triangular area at the intersection of Liede Bridge and Xingang Middle Road. It is an interchange station, with the main structure being four levels underground and the future interchange area designed as six levels underground. The deepest part of the foundation pit reaches 39.8 meters, the deepest foundation pit on the entire line, equivalent to a 13-story underground building. The station crosses over and passes beneath existing operating metro lines at zero distance, and the foundation pit is adjacent to existing operating metro lines, bridges, and rivers, with a complex surrounding environment.

During the construction of the station's retaining structure, the construction site was constrained by the space beneath the bridge, and conventional large equipment could not operate. The work area was less than 1 meter from the main pier of the existing bridge, and the rock strength was high. The construction party, based on actual site conditions, organized multiple technical analysis meetings and conducted comparative analysis of tooling and equipment. Ultimately, it adopted a combination of low-headroom rotary drilling rigs, percussion drills, rotary drilling rigs, and other equipment to form holes, creating a situation of "drilling side by side and working at multiple points simultaneously." During construction, to reduce noise impact on the surroundings and improve construction efficiency, an additional set of drill bits was added to each rotary drilling rig, ultimately completing the station's retaining structure construction task ahead of schedule.

The main structure of Chigang Station crosses over and passes beneath the existing line section at "zero distance." Construction risks are high, rock strength is high, and construction is difficult, making it easy to cause settlement or significant deformation of the existing line's track area. In response to the highly difficult and high-risk industry challenge of mined construction beneath existing lines, metro builders, drawing on past construction experience and process exploration, actively promoted measures such as design change optimization and creatively proposed the "semi-cavern column close-fitting" construction technology. This uses six newly built columns as vertical supports and the existing line box structure as a cover, rigidly locking the spatial position and shape of the existing structure, and carries out mined construction under the protection of the cover, thereby reducing settlement of the existing line, improving construction safety, and ensuring the structural forces and operational safety of the existing structure. During construction, an emergency linkage mechanism was established with the operating unit, data monitoring was strengthened, various measures were implemented, safety risk control was put in place, and the construction task of Chigang Station passing beneath the existing line was successfully completed.

Karst cave encounter rate exceeds 90%: the section with the highest cave encounter rate on Phase II of Line 14 breaks through

The left line of the Zhongle section tunnel on Phase II of Line 14 has a total length of approximately 632 meters and a burial depth of about 14 to 16 meters. The section lies in limestone strata with strongly developed karst, and the karst cave encounter rate in the section reaches 91.2%. The geological conditions are complex, and most of the tunnel excavation lies in strata that are soft at the top and hard at the bottom. Construction risks are high, and shield tunneling control requirements are stringent.

To ensure safe and controllable shield construction in the section, Guangzhou Metro's builders comprehensively reviewed the shield construction risks in the section and formulated corresponding risk control measures, refined construction plans for shield launching, tunneling, and underpassing, implemented a 24-hour ground personnel patrol and duty system, and intensified monitoring measures during the underpassing of important structures and buildings. In view of the geological complexity of karst-developed strata, an advanced geological detection system was applied in the section to identify the strata conditions ahead of shield tunneling in advance, preventing undetected karst caves from affecting shield tunneling safety and making every effort to ensure safe and controllable shield tunneling.

During shield breakthrough, water and sand inrush risks are likely to occur due to strata pressure. The shield in this section adopted steel sleeve sealed launching and sealed reception, that is, a cylindrical sealed steel structure with a diameter slightly larger than the shield machine and a length slightly longer than the shield body was installed at the shield receiving shaft. The open end of the steel sleeve was connected to the embedded steel ring at the portal to form an integrated sealed container, maintaining balance with the soil pressure and ensuring safe shield breakthrough.

As of now, the civil engineering works of Line 12 (Xunfenggang–Higher Education Mega Center South) have cumulatively reached 86%. Of the 25 stations, 22 have been topped out and 3 are under civil engineering construction; of the 24 sections, 21 have been completed and 3 are under civil engineering construction; the depot access line has been completed; a total of 5 shield machines are currently tunneling; electromechanical construction is underway at 20 stations across the line; and electromechanical construction is underway at the Chatou Depot.

The civil engineering works of Phase II of Line 14 (Jiahewanggang–Guangzhou Railway Station) have cumulatively reached 62%. Of the 8 stations, 6 have been topped out, 1 is under civil engineering construction, and the remaining 1 is in preliminary preparation; of the 8 sections, 7 have been completed and 1 is under civil engineering construction; a total of 1 shield machine is currently tunneling. Electromechanical installation and decoration construction is underway at 6 stations.

(Note: Station names are provisional names for the project only; standard station names shall be subject to those approved and announced by the municipal government.)