Why did eight sinkholes appear in Taipei in half a year when the road collapsed deep enough to accommodate a car?
Text: Cai Lixun Picture source: Provided by Taipei City Councilor Chen Yijun
Taipei City, the capital of the world, has experienced eight road collapse incidents since May. The potholes are even big enough to accommodate a car. The reason behind them is mostly problems with underground pipelines, which hollowed out the roadbed. In the face of systemic problems in road safety, how should we respond and improve so that people and cars can drive with peace of mind?
Is it caused by climate factors or human error?
The New Construction Engineering Office of the Taipei City Government’s Public Works Bureau responded to “The World” that the main reason is climatic factors. The increase in the frequency of extreme rainfall has greatly increased the intensity and frequency of water pipelines being washed, and intensified the corrosion of pipe walls. The old pipe body was damaged in advance, the joints were loose, and the overflowing water caused the surrounding soil to become soft.
However, extreme rainfall is not new this year. Taipei City also had a record rainfall of 209 millimeters in June last year, a record high in the past 20 years. Therefore, the cause of road collapse is not only caused by climate.
Insufficient construction work is indeed one of them. Pipelines buried under roads usually include lines managed by different units such as gas, electricity, telecommunications, tap water, sewage, and rainwater sewers. However, Taipei City has a dense population and frequent road construction, with about 7,000 projects a year. “The 5 or 6 meters below the road surface are subject to severe human disturbance,” explained Chen Wenshan, a researcher at the New Carbon Exploration Technology Research Center of National Taiwan University.
The road surface was redone without backfilling with specified materials.
Roads must be restored after excavation. Gong Xiangsheng, executive director of the National Federation of Civil Engineers Association of the Republic of China, pointed out that the materials are usually backfilled first, and then heavy objects are repeatedly used to freely fall to pound the foundation or filled earth and stone materials to increase the density, and then Carry out road paving.
In the past, common backfill materials were sand and gravel-grade ingredients. However, if the material is of poor quality and is not compacted according to specifications, the material will not be dense enough, which will increase the probability of road collapse. Therefore, various competent authorities have gradually stipulated that backfill must be filled with “controlled low-strength materials” (CLSM).
However, the cost of backfilling CLSM is at least 10% to 20% higher. Some manufacturers will choose other materials, which also increases the risk. For example, County Road 165 in Yunlin County, which was reopened to traffic in September last year, suffered road surface collapse six months after it was opened. It was precisely because the construction unit did not backfill with CLSM.
Monitoring after backfilling may not be fully implemented. There are an average of 20 road construction projects in Taipei City every day. Chen Zhaozhi, director of the Road Excavation Management Center of the Taipei City Government Works Bureau, pointed out that each pipeline unit will station a person at the pipeline management center to monitor all construction cases of the unit at that time. On the on-site side, each unit has its own supervision practices. However, Taipei City Councilor Chen Yijun, whose constituency has experienced five collapses, observed that construction units often only take photos and send them back, and the supervisory unit does not send personnel to on-site inspections, making supervision a mere formality.
The central government should formulate road maintenance standards
To solve systemic road safety problems, the first step is to ensure pipeline backfilling and strengthen monitoring. Gong Xiangsheng emphasized that even small-scale pipe excavation should be supervised according to the Luping project.
The second step is to investigate and establish a 3D map of the pipeline. Gong Xiangsheng said that currently there are only 2D drawings of pipelines, but the construction unit must know the diameter, depth and location of the pipeline in order to improve construction accuracy and reduce the chance of accidentally digging the pipeline.
After a series of collapse incidents, the Taipei City Government has initiated response measures. The New Construction Office will prioritize areas where potholes, depressions or bulges have occurred within a 5-meter radius of the pipeline unit’s emergency repair location within the past three years, as risk hot spots, and conduct ground-penetrating radar surveys.
In fact, although road maintenance is the responsibility of local governments, the central government cannot shirk its responsibility. According to the provisions of the “Local Institutions Act”, urban road improvement and maintenance are handled by county and municipal governments themselves. However, local budgets are limited, which further highlights the importance of systematic road maintenance operations. The Ministry of the Interior has not formulated relevant urban road maintenance regulations to provide Local administration follows.
When extreme weather has profoundly affected daily life, and road collapses have also occurred in many counties and cities, it is even more important at this time to have a set of nationally consistent road maintenance standards to build a more resilient and safe environment.
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2023-09-28 01:23:33
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