Which Types of Ground are Most Susceptible to Sinkholes?

In the most recent episode of IAM News, we explored how sinkholes, while seeming to appear suddenly, actually form over many years. Let’s delve into the geotechnical aspects that make some ground more prone to sinkholes than others.

One of the most common landscapes for sinkhole formation is in regions with limestone or karst terrain. Limestone is a sedimentary rock that is composed of mostly calcium carbonate. Rainwater with naturally dissolved carbon dioxide forms a weak carbonic acid. Over time, this dissolves and erodes the limestone, creating underground cavities and networks of interconnected voids. Eventually, the overlying ground can no longer support its own weight, and a sinkhole forms as the ground collapses into the underground cavities.

Gypsum is another type of sedimentary rock, rich in calcium sulphate. Like limestone, it is susceptible to dissolution by water. Areas with extensive deposits of gypsum and other evaporite minerals are also prone to sinkhole formation. Water slowly dissolves the minerals, leaving behind hollow spaces. Again, when the ground can no longer bear the load above it, sinkholes can form.

Finally, loose sediments like sand and clay may not be solid rock, but they can still play a role in sinkhole formation. In regions with a lot of unconsolidated sediment, water can easily percolate through the ground and create voids. These voids weaken the ground’s ability to support weight, and, under certain conditions, the surface can collapse to form a sinkhole. These are often called “cover-collapse” sinkholes.

It is important to know that, while these are the general types of ground most susceptible to sinkholes, sinkholes can form in a variety of geological settings. Human activities, such as mining and construction, can also influence sinkhole formation by forming voids underground that can also collapse overhead.

Sinkhole collapse is often triggered by heavy rain because the soil comprising the roof to a sinkhole becomes heavier and weaker with more moisture until it can no longer span the void and it collapses under its self-weight.

Studying and understanding the geotechnical properties of different types of ground is crucial for predicting and mitigating the risks to infrastructure associated with sinkholes. Geotechnical engineers work alongside infrastructure stakeholders to recommend appropriate remediation techniques to minimize the potential for sinkhole related problems.

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