How does the ground in Kuala Lumpur relate to sinkholes?

The sinkhole incident that occurred last Friday in Jalan Masjid India, resulting in the woman being swallowed up, has sparked a discussion regarding the foundation and terrain of Kuala Lumpur.

Many people were astonished to discover the existence of a substantial subterranean current. Nevertheless, in this instance, the woman was swept away by the powerful stream in the sewage line.

Kuala Lumpur's foundation consists primarily of limestone and quartz, which are distributed unevenly around the city. This geological composition, while providing a unique landscape, also poses significant challenges for urban development. The presence of limestone, particularly, can lead to the formation of sinkholes, especially in areas where water erosion is prevalent. This natural process, exacerbated by human activities such as construction and water drainage, can create voids beneath the surface that eventually collapse, forming sinkholes.

The limestone is abundant in the northern and central regions of Kuala Lumpur, constituting the Kuala Lumpur Limestone Formation. Quartz is abundant in the Klang Gates Ridge.

The Kuala Lumpur Limestone Formation, a geological formation originating from the Permian epoch, is prevalent in significant regions of the city. The formation played a role in the creation of caves and karst features in specific regions. These karst features, while often hidden from view, are integral to the city's underground landscape. They form intricate networks of caves and tunnels that can be both a natural wonder and a potential hazard. In urban settings, these karst systems can be destabilized by construction activities, leading to unpredictable ground movements.

Karst refers to a geologic formation characterized by the presence of weak limestone. It is characterized as extremely soft and has a tendency to become pasty, resembling a mixture of chalk and water. If the karstic limestone bedrock is not properly addressed, it can cause structural problems during building and increase the risk of sinkholes in certain regions.

The challenges posed by the karstic landscape are not new to Kuala Lumpur. Over the years, engineers and city planners have had to devise innovative solutions to mitigate the risks associated with building on such terrain. For instance, the construction of the Petronas Twin Towers involved extensive geological surveys and the implementation of advanced engineering techniques to ensure stability. These measures are crucial in preventing incidents like the recent sinkhole from becoming more frequent.

The presence of soft limestone bedrock beneath Kuala Lumpur became apparent during the construction of the Petronas Twin Towers. The distinctive construction difficulty was featured in a National Geographic documentary called "Megastructures: Petronas Twin Towers." Half of the site in its original location consisted of deteriorated limestone, while the remaining half was composed of soft rock.

In order to ensure that the structures were fully supported by the soft rock with the deepest foundations in the world, the entire site had to be relocated by a distance of 61 meters. The strong foundation consists of 104 concrete piles, which are deeply dug into the ground and range in length from 60 to 114 meters. Furthermore, each tower was constructed with a substantial concrete raft foundation, consisting of a total of 13,200 cubic metres of concrete, which was poured continuously over a period of 54 hours. The concrete raft has a thickness of 4.6 meters and a weight of 32,500 metric tonnes.

The Kenny Hill Formation is another region characterized by extensive limestone bedrock. The Kenny Hill Formation is located above the underlying graphitic schist, which is referred to as the Hawthornden Schist. This geological layering adds complexity to the city's subsurface, requiring detailed geological assessments before any major construction projects. Understanding these layers is crucial for ensuring the safety and longevity of structures built in these areas.

Is Kuala Lumpur a secure place to reside in? The recently appointed Mayor, Datuk Seri Maimunah Mohd Sharif, affirmed that the city is secure and dismissed any assertions suggesting otherwise. According to her, the Kuala Lumpur City Hall will only deem it harmful if studies present compelling evidence to contradict that. She said that the situation in the vicinity of Jalan Masjid India and Kuala Lumpur is well-managed and secure for guests. Furthermore, residents and companies can continue with their regular routines without interruption.

The Kuala Lumpur City Hall has also mobilized a task group consisting of the police, the Fire and Rescue Department, the Civil Defence Department, and the Minerals and Geoscience Department to evaluate and examine the safety of the area. This proactive approach aims to reassure the public and prevent future incidents. By conducting thorough inspections and collaborating with various departments, the city is taking steps to address potential risks and ensure the safety of its residents and visitors.

The search for the 48-year-old Indian woman who fell into the sinkhole is ongoing. Thus far, the search and rescue operation has only discovered a set of her slippers in close proximity to the sinkhole. Yesterday, the authorities conducted inspections on all six manholes along the 7km sewage line, starting at Jalan Masjid India and ending at the sewerage pond in Pantai Dalam.