Section previously shut down for 22 months over subsidence

Incheon city pauses work after monitoring readings exceed safety thresholds

GPR, gravity and additional ground surveys under way

Main-line construction continues normally

A construction site on the Seoul Metro Line 7 Cheongna extension. [Provided by reader]
A construction site on the Seoul Metro Line 7 Cheongna extension. [Provided by reader]

Excavation at part of the Seoul Metro Line 7 extension connecting Incheon's Cheongna International City has been temporarily suspended after surface-settlement and groundwater-level readings exceeded management thresholds.

Because the section previously experienced ground subsidence that halted construction for an extended period, Incheon city has decided to identify the cause thoroughly before pushing ahead with work.

The city announced Monday that it suspended excavation at Station 006 within Contract Package 6 of the Seoul Metro Line 7 Cheongna International City extension project starting June 22, and that a detailed safety investigation is under way.

The suspension was triggered by surface-settlement and groundwater-level readings at the site that exceeded the management thresholds set out in the underground safety assessment.

Station 006 demands heightened safety management. Ground subsidence during earlier excavation forced a halt of as long as 22 months; construction resumed last August after a review of ground stability and the development of reinforcement measures.

Since work resumed, Incheon city has monitored conditions in real time, tracking groundwater levels, underground displacement, surface settlement and structural deformation.

When surface-settlement readings reached the management threshold in June, the city immediately stopped excavation and launched an investigation into the cause.

An initial on-site inspection conducted right after the suspension found no visible signs of abnormality.

Given the section's history of ground subsidence, however, the city is now conducting detailed surveys, including ground-penetrating radar (GPR) exploration, gravity surveys and additional ground investigations.

Based on the findings, the city plans to determine the precise cause, draw up any necessary reinforcement and safe-construction measures, and resume excavation once it concludes that safety has been secured.

Jang Du-hong, head of Incheon city's Urban Railway Construction Headquarters, said the city had been continuously monitoring key readings since construction resumed, given the section's history of ground subsidence. "This exceedance of the threshold was also handled in accordance with the manual — we immediately stopped excavation and began investigating the cause," he said.

He added that no anomalies had been found in site inspections so far, but that the city would resume construction only after carefully identifying the cause and fully securing safety. "We will conduct thorough site management and schedule management in parallel to minimize any additional delays to the construction timeline," he said.


gilbert@heraldcorp.com