SINGAPORE, Aug 31 — Rescue operations are underway after a woman fell into an 8m-deep sinkhole along Jalan Masjid India in Kuala Lumpur, Malaysia, last week.

Last Friday (August 23), 48-year-old Vijayaletchumy, a tourist from India, was walking along the pavement when the ground suddenly collapsed beneath her at 8.22am.

Efforts to locate her have been trying due to strong undercurrents — likely exacerbated by heavy rain the city experienced earlier — and poor visibility. So far, the only sign of her presence that rescuers have found was a pair of slippers believed to have belonged to her.

In the early hours of Wednesday, a second sinkhole opened up some 50m from the site, believed to be caused by a downpour.

The Masjid India area has since been cordoned off, but footpaths remain accessible.

TODAY spoke to engineering experts from Malaysia and Singapore to gain insights into the possible causes of the sinkhole, the likelihood of such incidents becoming more common in Kuala Lumpur, and whether similar events could occur in Singapore.

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What caused the sinkholes in Kuala Lumpur?

Although investigations have yet to ascertain the cause of the sinkhole that opened up on August 23, Malaysian geological and engineering experts said that some possible causes may be soil erosion and heavy rainfall.

Dr Nor Shahidah Mohd Nazer, an expert in geological engineering and soil mechanics, believes that the water flow below the surface could be eroding the soil internally.

There is also the possibility of pipe leakage, which might be loosening soil grains and creating hollow spaces, contributing to the collapse.

"Kuala Lumpur also experienced heavy rain before the incident, with some areas reportedly flooded and saturated. This likely contributed to ground softening and undercutting erosion caused by the flowing water,” she added.

Similarly, Professor Dr Jeffrey Chiang, president of Malaysia’s Institution of Engineers, said that the cause may also be associated with utilities infrastructure such as water pipes and cables underground.

"(The Masjid India) location is a very busy spot in Kuala Lumpur. I believe many utilities networks have been layered there for years, which may have contributed to soil erosion and potential instability, possibly due to pipe leaks beneath the surface.”

The geological makeup of Malaysia’s capital city, particularly its limestone-rich soil, is also under scrutiny.

Limestone formations — such as those found beneath some parts of the city — are prone to erosion, especially when water flows through the soil over long periods.

However, the presence of limestone under the Masjid India area was refuted by Zamri Ramli, director-general of the country’s minerals and geosciences department.

In an article by Malaysian daily New Straits Times on Thursday, Zamri said: "Based on geological assessments, the area is not underlain by limestone, indicating that there are other non-natural factors involved.”

He added that only 30 per cent of Kuala Lumpur is underlain by limestone and this does not hinder development in the area.

Even if there was limestone, Prof Chiang said that modern engineering technology can address these issues with the right design approach, construction methods and a commitment to proper upkeep and maintenance.

Responding to concerns over infrastructure, geologist Azmi Hassan said that Kuala Lumpur’s above-ground infrastructure is not the main cause of the sinkhole.

Dr Azmi, who is with the Nusantara Academy of Strategic Research, told Malaysian news site Sinar Daily: "When constructing large structures, it is crucial to consider the geological factors beneath, especially the type of rock.

"If it is limestone, certain precautions are necessary. To say that KL’s infrastructure is overloaded and causing sinkholes does not seem accurate to me, since sinkholes occur worldwide.”

Is Kuala Lumpur still safe?

With two sinkholes occurring over the past week, there is a possibility of more collapses due to damage caused by the first one, Prof Chiang said.

"The first sinkhole could have accelerated or exaggerated further damages to the service pipes underground, either upstream or downstream. But this is subject to a detailed investigation.”

As part of the rescue and investigative operations, all six manholes on the road have been opened for inspection. The sewage line is 7km long and leads to a sewerage pond in Pantai Dalam.

Sewage water was pumped out to allow eight rescue divers from Malaysia’s fire and rescue department to enter the site at 2am on August 30, Malaysian news media reported.

The operation, supported by 75 crew members handling machinery and logistics, has since been halted. It is set to continue at the Pantai Dalam sewage plant.

To those walking around the city, Dr Shahidah advised: "As a precaution, just be careful and look out for signs of unstable ground.”

Two days after the tourist went missing, Kuala Lumpur’s mayor Maimunah Mohd Sharif told reporters at a press conference that the city "remains safe”.

"We will only consider it unsafe if there are studies that provide evidence to the contrary, especially given the alarming media reports,” New Straits Times reported her as saying.

A task force has been set up to assess the area’s safety. It comprises Kuala Lumpur City Hall, the police, the fire and rescue department, the civil defence department, and the minerals and geosciences department.

Sinkholes have occurred in the city before this recent case. Just last month, a similar cave-in occurred about 50m away in front of the Masjid India community police station.

In January 2020, a large sinkhole appeared along Jalan Maharajalela, roughly 3km from Jalan Masjid India, causing significant traffic disruption. The authorities attributed the incident then to a burst underground water pipe that led to soil erosion.

Could something similiar happen in Singapore?

Two analysts from Singapore told TODAY that an incident similar to the one in Kuala Lumpur — where a person suddenly falls through the ground due to a sinkhole while walking on a busy street — is unlikely to occur here due to the difference in ground formation.

Associate Professor Wu Wei from Nanyang Technological University (NTU), who specialises in rock engineering, said that in contrast to Kuala Lumpur’s limestone formations, the ground on this island city consists mainly of solid bedrock.

The ground is then overlaid by residual or deposited soil formations with no known strong subsurface currents.

Sharron Ng, a council member of Singapore’s Institution of Engineers, said that such deep foundations mitigate the risk of impact caused by sinkholes.

Assoc Prof Wu said: "As far as we know, small cavities exist in the limestone areas scattered throughout the Jurong sedimentary rock formations, but these have not been known to cause any significant ground settlement or sinkholes.”

Over the past decade, sinkholes have appeared sporadically on Keppel Road, in Clementi and on Upper Changi Road.

Ng said that although every case was different, these sinkholes were generally caused by underground work activities.

Assoc Prof Wu agreed, saying that natural sinkholes are "unlikely” to occur in Singapore, but they could still happen due to man-made activities such as excavation work, pipe leaks, or subsurface streams from heavy rain, which can weaken the soil and cause it to shift.

"The difference is that sinkholes in Singapore are commonly localised or isolated, while those in KL are possibly interconnected with limestone cavities.”

What can the authorities do to mitigate risks?

To reduce the risks and prevent a similar incident, Prof Chiang from Malaysia said that the authorities must carry out a more thorough mapping of the Kuala Lumpur city area using up-to-date technology, such as sonar wave or geophone mapping with satellites, targeting potential hot spots.

"In due time, this would give a clearer picture of how risky certain areas are, which could have potential sinkholes in the near future.”

Dr Shahidah said that there is a need to inspect utility pipes for leakages.

"Utility pipes, especially water pipes that have been buried for more than five years, must be thoroughly checked for leakages to prevent internal erosion from worsening,” she added.

As for Singapore, systems are in place to mitigate the risks of sinkholes caused by underground construction activities.

Assoc Prof Wu said that contractors are required to use piezometers to monitor groundwater pressure and settlement markers to track ground deformation during underground construction.

He added that NTU is developing smart technology to detect the early stages of sinkhole formation during tunnel boring.

In terms of infrastructure, Ng said: "There is no need for monitoring or concern because there is no building prone to sinkholes.” — TODAY