Seobu Urban Expressway Underground Tunnel

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On the way to Geumcheon IC on the Seohaean(West Coast) Expressway, with its habitual traffic congestion. The Geumcheon IC section - starting point of the West Coast Expressway at the southern end of Seongsan Bridge in southwestern Seoul - thanks to the opening of the western arterial road, has finally shed its notorious reputation for being a chronic traffic jam section. Hyundai E&C successfully created another masterpiece, the deepest underground tunnel in Korea, completing the construction of zone 1 of the Seobu Urban Expressway Underground Tunnel in September 2021.The construction was divided into two zones. Of the total length of 10.33km, Hyundai E&C was in charge of zone 1 to create an underground road of about 5.2km from the Seongsan Bridge point. The ground engineering and opening section which is the beginning point of the tunnel going down from the ground to underground, is 1km, and the tunnel section is 4.194km. Of the total construction cost, Hyundai E&C owns 38% of stake(230.2 billion won) and at the time of construction, the project was the largest domestic civil engineering project Hyundai E&C had ever worked on.Since meeting the completion date is important for a private investment project, employees remained laser-focused from the early stages of construction. To shorten the construction period, Hyundai E&C actively adjusted the design by ▶reducing the extension of the tunnel guide shaft (a guide shaft drilled before entering the main shaft through a vertical shaft), ▶applying the method of the vertical shaft slip form (continuous construction of structures while gradually building form work when placing concrete), and ▶pre-fabricating structures like retaining wall and in-tunnel bullhead.A typical mountain tunnel penetrates the bedrock, but the Seobu Urban Expressway Underground Tunnel, where excavation begins from the ground, also had to dig up the soil ground. In order to reinforce the soft ground at the tunnel’s starting point and preemptively respond to possible ground subsidence, the site used a high-pressure ground injection method called Grouting Method (technology of drilling a cylindrical pipe into the soft ground or spraying/injecting cement into the cracks of rocks at high pressure to ensure higher structure stability). In addition, in order to prevent water from flowing into the tunnel from adjacent Anyangcheon Stream, water-repellent Grouting technology was applied to the main line section at a depth of 80m underground. With these efforts, the site was able to successfully complete the construction in a timely manner without leaking groundwater.The tunnel is also equipped with a system that citizens can use safely and comfortably. The site was designed as a first-class disaster prevention facility placing safety as its priority. A "By-Pass" system that can directly purify harmful air-borne substances like fine dust and gas emissions inside the tunnel was applied, and CCTVs were also installed without any blind spot. In the case of underground tunnels, even small fires are likely to lead to major accidents, therefore as a response measure, a smoke extraction damper was installed, a water spray facility with intense spraying every 5 meters was installed, and 40 evacuation passages were prepared to allow users to quickly evacuate to the opposite tunnel in the event of a fire. In addition, there were four tunnel entrances and exits, three vertical shafts, and business offices, which allowed for a quick escape to the tunnel’s outside.

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