On May 26th, the Guangzhou Foshan South Ring Road and Foshan Dongguan Intercity Railway were officially put into operation. These two lines are connected in series with the already operational Guanhui and Fozhao intercity lines, jointly constructing a 258 kilometer long "large subway" that connects five cities: Huizhou, Dongguan, Guangzhou, Foshan, and Zhaoqing, with a maximum speed of 200 kilometers per hour. What are the technical difficulties in building this "large subway"? How do builders overcome these difficulties? The reporter from Science and Technology Daily conducted interviews on these issues. "The construction process of Guangzhou Foshan South Ring Road and Foshan Dongguan intercity railway shield tunnel technology is facing many difficulties. The line has multiple interfaces with existing lines and passes through Guangzhou, Foshan, Dongguan, as well as comprehensive transportation hubs such as Guangzhou South, Foshan West, and Dongguan West." Zhao Rude, the commander of the first construction command center of the Pearl River Delta Intercity Rail Company, introduced that the geological conditions along the line are extremely complex, the river network is dense, and the surrounding environment is extremely sensitive, with a bridge tunnel ratio of up to 93%. Therefore, the safety risks of project construction are high, there are many limiting factors, and the construction difficulty is extremely high. It is reported that when the construction of the Shiziyang Tunnel between Foshan and Dongguan began, it was the largest underwater railway shield tunnel in the world at that time. During construction, the construction party uses a shield machine with a diameter of 13.61 meters, which has a large burial depth and high water pressure, with the deepest point reaching 78 meters. During the construction process, there is a significant difference in the softness and hardness of the geological strata when the tunnel passes through. The length of the bedrock section that passes through accounts for 70% of the total excavation length of 4900 meters, and it also passes through three fractured zones and two faults. Zhao Rude told reporters that the construction process of the project faced a series of difficulties such as structural design, shield tunnel selection, and construction management. Through vigorous scientific and technological research and innovation, the construction unit overcame technical obstacles such as pipe floating, excessive wear of mud pipelines, and high tool consumption, and overcame the technical difficulties of the largest diameter underwater railway shield tunnel. There are more difficulties than just these. When constructing the Dongping Waterway Extra Large Bridge of the Guangfo South Ring Intercity Railway, it is necessary to cross the Dongping Waterway and the construction difficulty is high. To ensure construction safety, the construction unit has proposed a railway prestressed concrete partial cable-stayed bridge structural system with pier beam separation after comprehensive research. Zhao Rude said that this system has been applied for the first time to a ballastless intercity railway with a speed of 200 kilometers per hour. It innovatively adopts a seismic isolation design of "viscous dampers+speed locking devices with pressure relief valves+hyperbolic supports", and through refined construction and strict quality control, the accuracy of bridge beam closure reaches millimeter level. The research results of key technologies in the design and construction of this project have won the third prize of the Railway Science and Technology Award of the China Railway Society in 2022. The construction of the largest intercity underground station on both sides of the island in China was completed at 12:08 am on the 26th, The C7999 train slowly departed from Panyu Station in Guangzhou and headed towards Xiaojinkou Station in Huizhou City. Panyu Station is the intersection of two lines, with a main length of 1194 meters and a total construction area of 116000 square meters, equivalent to 11 standard subway stations. It is currently the largest intercity underground station on both sides of an island in China. Zhao Rude introduced to the reporter that the station project is located near Guangzhou South Station, with three rivers and numerous pipelines. The construction unit has coordinated and organized the development of a multi line three-dimensional cross shaped deep foundation pit support plan in the complex and sensitive surrounding environment of the urban area, ensuring the safety of existing buildings in the surrounding area. The station adopts open excavation method for construction, with an excavation volume of about 1.75 million cubic meters of earth and rock. It is a standard super large, ultra long and ultra wide open excavation foundation pit, with extremely complex construction conditions and extremely high safety risks. Han Zhenjiang, Chief Designer of Guangzhou Foshan South Ring Road of China Railway First Survey and Design Institute Group Co., Ltd., introduced that the company has collaborated with universities and enterprises to conduct scientific research and research, using large-scale finite element analysis software to establish a three-dimensional numerical calculation model. Combined with the actual boundary conditions and engineering hydrogeological conditions on site, multi-dimensional and multi working condition coupling analysis has been carried out, successfully overcoming the technical difficulties of supporting super large irregular foundation pit structures. (Lai Xin She)