Hyundai E&C announced on the 30th that it will open the longest ‘Boryeong Undersea Tunnel’ in Korea, about a 6.9km section linking Daecheon Port in Boryeong-si, Chungcheongnam-do to Wonsan-do, Ocheon-myeon, Taean-gun.
The Boryeong Undersea Tunnel is a project worth 488.1 billion won, which took about 4,000 days and 800,000 people per year. With a total length of 6927m, it is the longest tunnel in Korea and the 5th longest tunnel in the world. This tunnel is a two-lane road that penetrates about 80m below sea level from Taean (upward line) to Boryeong (downward line).
This tunnel was first opened in December 2010 for the purpose of connecting National Road 77, which was cut off near Daecheon Beach, to Yeongmok Port on Anmyeon Island. After completing the penetration of the ascending line in February 2019, the subsequent descending line passed through the center line precisely in June 2019 without error. In an undersea tunnel, it is important to reduce the error on both sides because the penetration of the starting point and the ending point is made at the same time from both sides.
Hyundai E&C has improved the accuracy of excavation by applying the NATM method and a high-tech robot drilling machine controlled by a computer. NATM is a method of excavating rock by drilling a hole in hard rock and exploding gunpowder. A Hyundai E&C official said, “In order to effectively control the seawater inflow, which is the biggest risk in undersea tunnel construction, we applied the blasting NATM method in the submarine section.” 3 Through the geological analysis using dimensional computing, the optimized excavation method penetrated the center of the tunnel without a single seawater runoff.” The longest undersea tunnel in the world, the 53.85km-long Seikan Railway undersea tunnel in Japan, started construction in 1964, and there were four seawater inflow and outflow accidents, extending the construction period.
As a result of the 3D geological analysis, there are many dangerous sections such as coal-containing layers (strata containing coal) and folding (bent geological structures) that require attention as a result of continuous monitoring and a special 1m-thick wall that allows workers to evacuate in case of emergency. Watertight doors were installed throughout to ensure safety.
In addition, the IMG (Intelligent Multi-Grouting) method was applied to minimize damage to surrounding facilities due to construction. This is a method that can block the inflow of seawater into the tunnel by precisely controlling the optimum pressure, flow rate, time, etc. of cement solution when constructing tunnel wall concrete.
In order to strengthen the durability of the Boryeong Submarine Tunnel, Hyundai E&C has strengthened the wall thickness from 30 cm to 40 cm and the concrete strength from normal (24 MPa) to high strength (40 MPa). Safety was further improved by applying
With the opening of the Boryeong Undersea Tunnel, the distance from Boryeong Daecheon Port to Taean Yeongmok Port, which took 1 hour and 30 minutes, was shortened to 10 minutes. Living conditions are expected to improve.
A Hyundai E&C official said, “The undersea tunnel construction is a battle against seawater 24 hours a day, 365 days a year. said
Reporter Jeong Jin-soo of Donga.com brjeans@donga.com
