The overall inadequacy of underground excavation work has been identified as the cause of a series of recent large-scale sinkhole accidents. The ground investigation reflected in the design when developing urban underground space is inadequate, and it has been pointed out that there are limitations to on-site supervision regarding the poor construction despite the construction company not applying ground reinforcement and waterproofing methods due to budget and time constraints, which raises the risk of sinkholes.
On the 24th, an emergency seminar on the topic "What are the solutions to the continuous ground subsidence accidents?" was held at the National Assembly Member's Office Building in Yeouido, Seoul, hosted by Representative Park Yong-gab's office.
◇Insufficient geological investigation... Groundwater discharge also a cause
Lee Ho, president of the Korea Underground Safety Association, noted in a presentation titled "Causes of ground subsidence accidents and fundamental solutions" that "a commonality in typical sinkhole accidents is that excavation work was underway in the vicinity," adding, "This cannot be ruled out as a direct or indirect cause." He further remarked that "even in the metropolitan area, construction is being carried out at 70 to 80 meters underground, which could be suspected to correlate with the scale of underground space development and the frequency of accidents."
There are criticisms that the overall inadequacy of underground construction processes is linked to the occurrence of sinkholes. Concerns have been raised about the inadequate geological investigations reflected in the design.
Baek Yong, a senior research fellow at the Korea Institute of Civil Engineering and Building Technology, pointed out that "the money invested in ground investigations is extremely low according to national construction standards," explaining that "for example, a single borehole is made for basic design and a ground investigation is conducted. It's not even 2 or 3 boreholes." He continued, "Especially in urban areas, if local residents oppose, ground investigations cannot be conducted, leading to the use of nearby data. If a geological vulnerability appears during construction, it becomes practically difficult to conduct additional ground investigations, and there are many cases of reinforcing and excavating without proper verification."
Choi Myung-ki, a professor of the Republic of Korea Industrial Field Professors Association, criticized that "there is a tendency to attribute the cause of ground subsidence to aging water supply and sewage pipes, but this is pointed out as a cause in the context of avoiding responsibility for the poor construction due to inadequate ground reinforcement and waterproofing during the excavation work," adding that "for the sake of cost reduction, paperwork and photographs for ground reinforcement work are often prepared, but in practice the construction is inadequately and poorly done."
In particular, groundwater discharge occurring during excavation work or underground construction structures has also been cited as a cause of sinkholes. Jo Bok-rae, director of the Underground Space Research Institute, stated that "when groundwater is forcibly discharged during construction, soil particles are also washed away with the water, leaving the space where the water was empty and causing overall weakening and voids in the ground," adding, "Under these conditions, conducting underground work while excessive groundwater discharge and poor construction management leads to an inability to detect multiple signs of collapse in advance, leaving us exposed to large-scale social disasters."
◇Strengthen penalties for arbitrary method changes... Introduction of sinkhole forecasting system is also necessary
Experts have pointed out the need to strengthen the enforcement of the Underground Safety Act to prevent sinkhole accidents. The chairman noted that "it has been 7 years since the Underground Safety Act was implemented, but continuous ground subsidence accidents have occurred, indicating a need to enhance the effectiveness of the law," suggesting that "there is a need to strengthen safety investigations and on-site inspections after the commencement of excavation work." He added, "Penalties for unfair method changes should also be strengthened."
As excessive groundwater discharge raises the risk of sinkholes, there are opinions that regulations on groundwater discharge are necessary. Professor Choi stated, "Groundwater discharge limits should be set for underground excavation sites and existing buildings to regulate groundwater discharge below a certain amount, and if permanent drainage continues to be permitted, sinkholes will keep occurring."
The need for a prediction and prevention-centered underground safety management system was also raised to prevent sinkholes. The chairman stated, "Until now, when sinkhole accidents occurred, the response was the focus, but now we must predict and prevent to reduce accidents," emphasizing that "the calibration and testing of measurement instruments used at construction sites should be mandatory and advanced techniques for analyzing prediction results should be introduced." He further noted, "The implementation of ground-penetrating radar (GPR) technology should be realized, and standards for equipment performance, training of experts, and regulations for registering specialized equipment companies are needed."
Proposals for a sinkhole forecasting system have also been made. Professor Choi said, "There needs to be a system that can forecast ground subsidence by analyzing conditions of communal infrastructure, geological status, and construction status using big data and artificial intelligence (AI)," adding, "We need to find ways for citizens to respond in advance." He continued, "When there are reports from citizens regarding (sinkholes), a central tower that comprehensively examines these should be established."
There is also a need for institutional improvement concerning the identification of causes of accidents. Currently, in South Korea, when a sinkhole occurs, an accident investigation committee is formed, and it takes about two months to identify the cause.
The chairman pointed out that "in Japan, a large-scale sinkhole recently occurred, and the investigation procedures for identifying the cause are underway at the accident site for nearly 90 days," stating that "in our country, there is a lack of investigation procedures after a ground subsidence accident occurs." He continued, "In our country, investigation committees are usually formed around ground subsidence accidents that gain media attention, and there is a need for regularization of the cause identification and investigation system, emphasizing that "a separate organization capable of conducting investigations should be established."