Recently, the longest single-line shield tunnel on the Guangzhou-Foshan East Ring Intercity Railway's Guangzhou South Station to Baiyun Airport section (hereinafter referred to as the "Guangzhou-Foshan East Ring Intercity") — the "Dayuan Station-Taihe Station" section (hereinafter referred to as the "Datai Section") — saw its upward line successfully breakthrough, marking that all tunnels on the entire Guangzhou-Foshan East Ring Intercity line have achieved "tunnel holing-through."

According to reports, the Datai Section of the Guangzhou-Foshan East Ring Intercity, constructed by China Railway 19th Bureau Group Co., Ltd., is a controlling project for the entire line. The upward line is 6,144 meters long, with a tunnel outer diameter of 8.8 meters, an inner diameter of 8 meters, and a ring width of 1.8 meters. The geological conditions of the tunnel in this section are quite complex, passing through typical composite strata of the Pearl River Delta region, including Quaternary alluvial-proluvial and residual slope deposits, as well as Carboniferous siltstone, quartz sandstone, sandy conglomerate, limestone, carbonaceous limestone, carbonaceous slate, and Sinian gneiss and Yanshanian granite.

"The tunnel burial depth varies from 12 meters to 158 meters, with abundant groundwater and extremely high water pressure. It crosses long-distance hard rock sections such as gneiss and granite, with high hard rock strength — especially the moderately weathered gneiss section, where the maximum saturated compressive strength is about 155 MPa," introduced Zhang Guang, an engineer of the construction section from the Pearl River Delta Company of Guangzhou Metro Group. "There are numerous hard rock protrusions and soft-over-hard sections in this interval, crossing 8 fault fracture zones, multiple weathered perched-water troughs, and boulders, and passing under (or alongside) many structures such as expressways and operating railways. The construction difficulty is extremely high."

Because no intermediate shaft could be added in the middle of the 6,144-meter tunnel, the shield was driven as a single-head excavation, making equipment selection extremely stringent. After multiple rounds of demonstration and research, the construction unit, together with the design unit, shield manufacturer, and well-known domestic tunnel industry experts, proposed and successfully applied the construction method of "single-shield and earth pressure balance dual-mode tunneling machine construction and process mode conversion," solving the problem of no space for intermediate shaft layout in a long and large tunnel. The successful tunnel holing-through verified the feasibility of large-diameter EPB and TBM dual-mode machines, and it is also the first time in China that a "single-shield and earth pressure balance dual-mode" tunneling machine has successfully achieved single-head excavation of a large-diameter railway tunnel of more than 6 kilometers, providing valuable reference experience for existing dual-mode shield construction technology and similar projects.

To ensure the smooth breakthrough of the tunnel, the Pearl River Delta Company also specially established a dedicated work task force for the Guangzhou-Foshan East Ring Intercity construction scheduling plan, strengthened progress control measures, ensured weekly progress by daily progress and monthly progress by weekly progress, strengthened the information reporting system, intensified supervision and inspection, and corrected deviations promptly when problems were found. At the same time, the construction unit was urged to establish bureau- and division-level supervision groups to strengthen on-site supervision.

With the joint efforts of all parties, the shield construction successively overcame a series of technical difficulties, including the shield in earth pressure balance mode passing under numerous structures, the shield in TBM mode crossing unconformity contact zones, the earth pressure mode crossing soft-over-hard strata with muck volume control, the TBM/EPB dual-mode shield in complex rock strata with long-distance continuous belt conveyor and vertical hoist muck removal construction, and the high-water-pressure dual-mode shield with chamber-filling grouting construction, ultimately achieving the breakthrough of the longest single-line shield tunnel and creating favorable conditions for the Guangzhou-Foshan East Ring Intercity to be completed on schedule.