Cutterhead Hoisting
Following the successful breakthrough of the left-line shield tunnel on the Zhongle section (the intermediate ventilation shaft of Guangle No. 2 to Lejia Road) of Metro Line 14 Phase II, the right-line shield of the Zhongle section recently completed its excavation task as well, achieving a double-line breakthrough for the section. At this point, all shield tunnels on the Jiahewanggang–Lejia Road section of Metro Line 14 Phase II have been fully connected.
According to Guangzhou Metro, Line 14 Phase II runs north-south through Baiyun District and Yuexiu District, with a total length of 11.9 kilometers and 8 stations. Four sections lie in complex geology consisting of karst-developed limestone strata and coal mining goaf areas, and the alignment runs parallel to an expressway viaduct for about 6 kilometers.
As of now, the civil engineering work for the entire Line 14 Phase II (Jiahewanggang–Guangzhou Railway Station) has been completed cumulatively at 63%. Of the 8 stations, 6 have been topped out, 1 is under civil construction, and the remaining 1 is in preliminary preparation; of the 9 sections, 8 have been connected, and the remaining 1 is in preliminary preparation. Electromechanical installation and decoration are underway at 6 stations.
Cave encounter rate exceeds 90%; section faces complex geological challenges
The right line of the Zhongle section, which has now broken through, is about 640 meters long with a burial depth of about 14 to 16 meters. The section lies in limestone strata with strong karst development, and the cave encounter rate reaches 91.2%, the highest among all sections of Line 14 Phase II. During shield excavation, most of the geology is soft on top and hard below, and above the section lies an important municipal road with heavy traffic. The shield excavation had to overcome problems such as high rock strength and difficult control of ground settlement.
In response to the geological complexity of the karst-developed strata, Guangzhou Metro, together with the contractor Guangdong Huasui and the supervision unit China Railway Jinan Supervision, added advanced geological radar and advanced grouting equipment to the shield machine during the early equipment selection stage for the Zhongle section, so as to detect the strata conditions ahead of the shield in advance and prevent undetected karst caves from affecting shield excavation safety. At the same time, prepared grout was injected into the surrounding strata ahead of the cutterhead to improve soil strength, effectively control surface settlement, and ensure safe and controllable shield excavation.
Additional explosion-proof measures for the shield; safe underpassing of coal mining goaf
On the Jiahewanggang–Lejia Road section of Line 14 Phase II, the Lejia Road–Gangbei section (the "Legang section") also lies in strongly karst-developed limestone strata, like the Zhongle section. In some parts of the section, the cave encounter rate reaches 100%, with a maximum cave height of 13 meters. More challenging still, the Legang section also has to pass through a coal mining goaf.
Combustible gas exists in the coal mining goaf. To prevent disasters such as gas explosions, Guangzhou Metro and the contractor added explosion-proof measures to the shield machine during the early equipment selection stage, formulated a targeted implementation plan for underpassing the coal mining goaf, and installed gas detection devices inside the shield machine for real-time gas monitoring in the tunnel.
(Note: Station names are provisional engineering names only; the official station names shall be those approved and announced by the municipal government.)
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