Residents on edge as sinkholes strike near construction zones

Residents on edge as sinkholes strike near construction zones

2023-07-16

In April of this year, a startling sight unfolded near a construction area in Hsinchu. A section of a road suddenly caved in, creating a sinkhole that swallowed up a nearby Tesla. Just half a month earlier, a similar incident occurred in Taipei a giant sinkhole appeared near a construction site, causing nearby homes to lean precariously and prompting the residents’ evacuation. These incidents are not isolated. Sinkholes are showing up all across urban Taiwan, damaging roads and threatening the safety and property of locals. But what’s causing this alarming rise in sinkholes? And is there a way to predict when and where the next one will occur?

Even in a casual conversation with neighbors, anxiety is visible on the face of Zhubei community leader Mao Zhenfu.

Mao Zhen-fu
Zhubei community leader
The businesspeople here are either tenants or property owners who live on the property themselves. The tenants suffer the most. Why? Because when the road is sealed, they can’t do business. Any one of these shop fronts cost NT$30,000 or NT$40,000 in rent each month.

Over the past nine months, the roads surrounding this Zhubei construction site have collapsed five times. One of those roads, Shengli 2nd Road, has been closed for more than half a year, leaving a long row of desolate shops.

This year in April, another sinkhole at the worksite devoured a Tesla.

Residents in Zhubei live in fear, and less than half a month later, another sinkhole appeared in Taipei’s Xinyi District, swallowing up scooters and bicycles.

Sinkholes have become an increasingly common phenomenon. One struck in Yonghe, New Taipei in 2020, in Changhua City in 2021, in Cianjin, Kaohsiung in 2022, and in Longjing, Taichung in 2023. What’s driving this unsettling phenomenon?

Ni Chun-fa
National Central University Graduate Institute of Applied Geology
Many of the sinkholes that we see are the result of human interference. It has to do with the mechanical balance between water and soil. Anything that causes an imbalance of water in the soil can lead to the rearrangement of soil particles, resulting in a collapse.

To get a sense of this water-soil imbalance, consider this scenario: A water pipe bursts under a road. Water comes rushing out, washing away the nearby soil and leading to the formation of voids in the soil layer. Once the road begins to cave, a sinkhole is created.

Ni Chun-fa
National Central University Graduate Institute of Applied Geology
Typically, building a high-rise involves deep excavation, which lowers the level of the groundwater. Particularly at the construction site itself, the groundwater level is very low. If the groundwater level is significantly lower than the level outside of the construction site, fine particles of soil can be washed away.

When a high-rise basement is excavated to a depth that’s lower than the groundwater level, water infiltration can hinder construction. To keep this from happening, wells are often set up to pump groundwater and lower the water level. The discrepancy between the water levels inside and outside the worksite causes water to flow out, toward the area with the lower level. This becomes a problem if the ground composition is a mix of gravel and sand. Flowing water can sweep away the sand, depriving the gravel of its supportive structure. The gravel then repositions itself, leading to the creation of voids.

But before a high-rise is built, wouldn’t a construction firm conduct a geological survey?

Tseng Ho-teng
New Taipei geological technicians association
In the early years, we’d heard of cases where geological surveys were falsified or even skipped entirely. But nowadays, we don’t hear about such things happening. Each worksite will conduct a geological survey at the very start. I believe that the survey requirement is fulfilled at this stage, and that after the survey is completed, there’s an efficient review mechanism.

Next, the geological report is turned over to professional technicians. They use it to design supports for the sides of an excavated basement, to prevent soil or water from collapsing. Three types of supports are commonly used in the industry: sheet piles, earth-retaining piles, and continuous walls.

Tseng Ho-teng
New Taipei geological technicians association
The continuous wall is the most expensive and it takes the longest time to set up. However, it’s the best at retaining soil and water. The next best thing is the earth-retaining pile. But there are gaps between each one, so of course groundwater can seep in, reducing its effectiveness. Then there’s the sheet pile. The crevices in sheet piles make it easy for groundwater to seep in.

Technicians will recommend which support to use, based on the geological conditions. With modern engineering designs, safety isn’t an issue. But even the highest-performing continuous walls can’t prevent sinkholes from forming.

Chan Jung-feng (July 2020)
Former head of New Taipei Public Works Department
The preliminary assessment is that water leaked from the seams of the wall.

No matter what form of construction is used, the appearance of muddy water at a construction site is a warning sign. Here in the basement of this Zhubei construction project, you can see muddy water where the sandbags are piled up.

Ni Chun-fa
National Central University Graduate Institute of Applied Geology
The leaking water – if it carries materials such as sand, you’ll be able to see color. Seeing color means that the water has started to bring out fine particles. That’s a very important message. Disasters caused by groundwater actually occur very slowly. There are opportunities to resolve them, there’s time.

Sinkholes are problems with warning signs, and there’s time to prevent their formation. So when they occur anyway, over and over again, is man solely to blame? Over in Zhubei, Hsinchu, locals now find it hard to trust developers.

Eight years ago, Casey moved to Zhubei with her husband, an engineer. They live near the construction site where multiple sinkholes have occurred. On the day a Tesla fell into a crater, she was not far away.

Casey
Zhubei resident
It felt like a stunt from a movie. You could see a car stuck inside, and it felt so unreal. I took a picture on my way back. The soil erosion inside – by that time, the car had been already been removed, and I discovered that all the soil inside was gone, the hole was super empty. When I saw it, I was shocked at first glance, and then later I felt scared.

The looming threat of sinkholes has caused anger and distress among the people of this neighborhood.

Each day, cracks expand in their sidewalks and flower planters.

Mao Zhen-fu
Zhubei community leader
Everybody is worried about their house collapsing. They worked so hard to buy a house. You’re lying to them if you tell them not to worry. Through a friend’s referral, I personally invited a structural engineer from Taipei to provide an explanation to our residents. Last Friday, through a neighbor, we brought in another structural engineer from Kaohsiung.

Repeated sinkholes have forced residents to seek out experts on their own. They don’t believe the narrative of construction companies. They’re also suspicious of the local government.

Chiu Hsien-chih
Lawmaker
What Hsinchu County Commissioner Yang Wen-ke does is, he goes to the site, he performs his outrage – that’s his SOP. After his performance of rage, construction stops, it stops for a while, and then it resumes. The reality is, there’s a relationship between construction companies and local governments. These politicians are too close-knit with builders, who provide political donations or campaign headquarters and things like that. This leads to the inability to assert public power over people you need to manage.

But what can these locals do to help themselves?

Assistant professor Lin Chen-hua pushes a ground-penetrating radar, a machine that costs nearly a million New Taiwan dollars. It offers a window to the world below ground.

Lin Chen-hua
Chung Hua University Dept. of Civil Engineering
It’s just like doing an X-ray scan of the human body. The depth of its detection is determined by the high and low frequencies of the antenna. In good geological conditions, low frequencies can detect up to 30 meters, no problem.

Based on the waves reflected from the ground, this radar can distinguish between different materials such as metal, plastic, and air. It can help residents judge whether the ground of their neighborhood is safe.

Experts can use these ripples to decode information from underground. Even a hole measuring 15 centimeters in diameter can be detected. Such a radar, if incorporated in the standard protocol of building construction, could eliminate many hazards and disputes.

Lin Chen-hua
Chung Hua University Dept. of Civil Engineering
Prior to excavation, you could do a survey. For example, regardless of the construction site, you must survey the neighboring properties. Do a test first, to get some baseline information. So in the process of excavation, if anything happens to the neighboring properties, another test can be done, to see the problem was caused by the soil.

To reduce the frequency of sinkholes over the long run, the central government needs to strengthen its regulation of the construction industry.

Chiu Hsien-chih
Lawmaker
We asked the Construction and Planning Agency to help local governments set up a standard for resuming work. After all, what are the criteria for resuming work? Secondly, there needs to be an SOP for follow-up safety monitoring. The website should let citizens know which builders are extremely terrible, with a record of frequent construction accidents and multiple fines from the construction agency.

Mr. Huang
Resident affected by Xinyi District sinkhole
They sent cement mixer trucks to do the grouting. They used 58 trucks.

With the arrival of each new building, one question invariably arises, “Will it be a good neighbor or a bad neighbor?” The answer is largely up to the government and the construction industry, and whether they can restore the people’s right to live in peace and without fear.