This article explains in detail what sinkholes and potholes are, why they occur, the main factors that contribute to their occurrence in cities, how to prevent and repair them, and emphasizes the importance of urban planning.

What is a sinkhole?

A sinkhole is a hole, usually shaped like a flat bowl, cone, or funnel, created by the subsidence of an underground void. They don’t all look the same, and there are three main causes of sinkholes, so it’s important to understand the exact cause in order to take action.

Causes of sinkholes

First, let’s look at the causes of sinkholes, which can be categorized as collapse, melt, or subsidence. Cover-collapse sinkholes occur where there is a thick layer of clay, and due to the adhesive properties of clay, they last for a period of time before suddenly collapsing and causing great damage. Dissolution sinkholes are created when surface water or rainwater dissolves limestone exposed at the surface. A cover-subsidence sinkhole is a hollow space in a bedrock layer that is created when sandy soil slowly subsides over a long period of time. In Korea, collapse-type sinkholes occur mainly. Natural sinkholes are caused by groundwater dissolving rocks or sudden changes in groundwater flow. When groundwater creates a void in the bedrock, the upper soil and groundwater fill the void, creating an arch-like pupil in the soil, which then collapses. In particular, when the bedrock is composed of water-soluble materials, groundwater dissolves the bedrock, creating a void, and when the groundwater level drops, the top collapses, creating a sinkhole.

Causes of sinkholes in cities

The main causes of sinkholes in cities are falling groundwater levels and increased groundwater use. This compromises the stability of the ground, causing sinkholes to form. Excessive groundwater use, disturbance of groundwater flow during development projects, and leaks in water and sewer pipes are the main causes. Over-utilization of groundwater causes groundwater in the bedrock layer to escape, creating a void in the bedrock and causing sinkholes, while sinkholes occur when groundwater flows to the surface or changes in groundwater flow during or after development projects. Sinkholes also occur when water and sewer pipes leak, weakening the cohesion of clay and causing water and soil to settle.

What is a pot hole?

Sinkholes that form on concrete roads in cities are called pot holes. Potholes are caused by voids in the asphalt. While sinkholes require an understanding of the properties of the ground, potholes can be easily prevented and repaired by understanding the asphalt paving process. To prevent potholes, you need to understand asphalt paving. The key to asphalt pavement is the aggregate. Aggregates are stones of different sizes that are responsible for the strength of an asphalt or concrete pavement. They literally act as the skeleton of the structure. The hot asphalt is then melted and infiltrated between the aggregates, which creates air bubbles. These layers of bubbles are called voids, and they’re the main cause of pot holes. Since asphalt is not a rigid solid, it expands in the summer and contracts in the winter. The pores expand and contract accordingly, but the problem is when moisture gets into the pores. The repeated expansion and contraction of moisture causes potholes to form. Minimizing potholes is an easy way to prevent them.

How to repair urban sinkholes

There are two main ways to repair a pot hole. The easiest way is to just pour an asphalt solution and temporarily fill it. However, as we mentioned earlier, asphalt solution alone can cause secondary damage because it’s too soft and doesn’t have a certain amount of strength. The second method is a type of milling. Unlike milling, it involves rebuilding the asphalt from the formulation design to the injection, so it’s more time-consuming and expensive, but it’s a surefire solution.
Preventing potholes is simple in theory, but the reason why potholes are so common on roads is that it is difficult to minimize voids as theoretically possible. In addition, apart from the above explanation, there are cases where voids are caused by cracks due to the aging of the road. We look forward to new technologies that minimize potholes in the future. This also reflects the unavoidable reality of Korea’s rapid urbanization. I hope that Korea can avoid such problems by thoroughly planning cities.