Recently, at the construction site of Shield Shaft No. 2 (hereinafter referred to as "Jingbai Shaft No. 2") on the Jingxi Road–Baiyun Dongping section of the Guangzhou East–Huadu Tiangui Intercity Railway (hereinafter referred to as the "Guanghua Intercity Railway"), as the "Future" vertical shaft boring machine completed the assembly of the final segment ring of the left-line shaft, it marked the successful verification of the vertical mechanical shaft construction technology applied for the first time in China's rail transit construction sector, accumulating experience for the application of this technology in the domestic rail transit construction field.

This construction method adopts a non-drainage excavation process within the shaft, greatly reducing the cost of the retaining structure and minimizing the impact on the surrounding environment, while achieving unmanned operation underground and minimal personnel on the surface, significantly improving the safety of shaft construction.

The segments of Jingbai Shaft No. 2 have an outer diameter of 14 meters, an inner diameter of 13 meters, and a depth of 37.2 meters. This shaft boring machine successively traversed backfill soil, silty fine sand, silty clay, sandy cohesive soil, completely weathered granite, strongly weathered granite, moderately weathered granite, and slightly weathered granite strata, which are typical composite strata in South China, and there exist adverse geological conditions such as numerous boulders and large undulations of the rock surface, along with abundant groundwater, placing extremely high demands on equipment reliability and making construction extremely difficult.

In response to the challenges of high water pressure, high hardness, large boulders, and large rock-surface undulations, the CRCHI research and development team conducted extensive investigation and thorough research, and carried out targeted design of the equipment through theoretical model analysis, technical verification, and other methods. On the basis of completing the right-line shaft construction, they summarized experience and optimized and improved the equipment and construction technology, enhancing the equipment's adaptability and excavation efficiency in hard rock and boulder strata, and completed the left-line shaft construction task in only 34 days.

First Use of New Equipment   Successful Completion of the Set Task

Jingbai Section Shaft No. 2 is located in the plot on the west side of Tonghe Road, Baiyun District, and comprises two mechanical shafts with an inner diameter of 13 meters and an outer diameter of 14 meters. The upper sections of both lines are excavated using the boring machine, while the lower sections are constructed by open-cut method, with an excavation depth of 27 meters. The "Future" shaft boring machine used in the project has an excavation diameter of 14.2 meters and weighs about 120 tons. It adopts two excavation modes—the cutting-type cutter head and the ring-shaped cutterhead—as well as advanced technologies such as a slurry circulation mucking system, a central high-pressure scouring system, and an online real-time monitoring system for excavation parameters, achieving an excavation efficiency of more than 1 meter per day in moderately weathered granite and boulder layers.

Since the "Future" caisson-type shaft boring machine was successfully launched on the right line on December 20 last year, in order to ensure smooth mechanical shaft excavation, Guangzhou Metro, together with the construction contractor China Railway Construction Corporation South China Company Guanghua Intercity Railway General Contracting Department, China Railway 15th Bureau, and other participating parties, overcame problems such as the wear and replacement of roller cutters, clogging and repair welding of the drum grille, and the滞留 and discharge of large stones inside the shaft, avoiding risks such as over-excavation of the shaft, foundation pit collapse, settlement of surrounding strata, and damage to the cutter head of the shaft boring machine. By improving the equipment's stratum adaptability and construction efficiency, the right-line shaft construction task was completed first on March 8, 2023.

Summarizing During Construction   Improving Operational Efficiency

As the most advanced urban deep foundation pit construction technology at present, the mechanical shaft construction method still lacks national and industry-local standards, and domestic equipment and construction technology are still in the initial stage of exploration. Before construction, the builders of the Guanghua Intercity Railway conducted repeated "simulations" of the new technology through extensive preliminary investigation, theoretical model calculations, technical verification, and other methods.

"Research and Application of Key Technologies for Deep Foundation Pit Shaft Boring Machines" is a key research and development project of Guangzhou City under the "revealing the list and taking command" mechanism. In order to further improve the application and research of the new technology, after completing the right-line shaft construction, the builders immediately held a technical summary meeting and invited authoritative experts in the industry to analyze the problems encountered during construction, the measures taken, and the application of digital technology. On the basis of summarizing experience, the construction technology was optimized and improved, significantly increasing the construction efficiency of the left-line shaft. Among them, the right-line shaft construction took 78 days, while the left-line shaft construction took only 34 days to complete the task, saving nearly 60% of construction time.

The project team will continue to optimize the subsequent research and application of the shaft boring machine, adhere to the goal of building high-quality projects, carry out special research and summary work on shaft construction technology, and strive to advance the research and application of key technologies for shaft boring machines to a deeper level, achieving intelligent, information-based, unmanned, and greatly improved efficiency in mechanical shaft excavation technology, and opening up new construction fields.