Sinkholes are one of Mother Nature’s most unpredictable occurrences, however, they’re not completely impossible to detect. In the United States, 7 states are known to be ‘sinkhole prone’ due to the bedrock being composed of evaporites and carbonate rocks, with Kentucky being one of the most karst terrains in the world! While many think of sinkholes only being large enough to swallow a bus, there are sinkholes that can be small and non-threatening. Luckily, there are ways to analyze the land and make sound decisions to not only prevent the occurrence but hopefully avoid it.
The first factor in sinkhole creation is the ground makeup. Sinkholes are most prominent in areas where the bedrock is made up of evaporites (salt, gypsum, and anhydrite) and/or carbonates (limestone and dolomite). While evaporites make up roughly 40% of the U.S., they’re typically at deep levels and nowhere near the surface. When the ground has the capability of eroding and dissolving away, this is known as ‘karst terrain’, which are recognized as sinkholes, caves, and springs. Karst terrain addresses the water factor of sinkhole creation, as there are water passages throughout the bedrock. Carbonates and evaporites are sedimentary rocks, meaning there are small holes and passages throughout. This creates passages for water to pass through causing the bedrock to break apart and dissolve. As the bedrock dissolves, the ground will begin to break down and cave in.
How would construction play a part in causing a sinkhole if it’s naturally occurring? It’s unfortunately simple. During the construction of a new building, the first step is excavation. Contractors will level the ground so the building will not lean, and cause pressure in places not meant for bearing weight. However, in areas that are sinkhole prone, contractors are more likely to use ground penetration radar (GPR) prior to breaking ground. This allows them to see below the ground, identify any weak points in the bedrock, and excavate in the safest way possible. Information regarding the type of bedrock is also studied as the contractors must know whether the ground is too weak for more weight, or the vibrations of machinery could cause breakage. Another step in preventing future sinkhole occurrences is the plumbing contractors. Many sinkholes found at residential and commercial spaces are due to poor plumbing installation and maintenance.
Fraser, Michigan was met with a sinkhole disaster on Christmas Eve 2016 due to a broken sewer pipe running through the suburb. The pipe cracked in 2014 due to a ‘flood of sewage’ from contractors performing maintenance allowing gallons of water to rush through within minutes rather than hours. The water pressure around the crack caused the sediment from under homes to be pulled into the pipes and caused the ground to wash away. The sinkhole measured the size of a football field and 65 feet deep, causing a dozen homes to be evacuated. Plumbing has many inspections that take place during construction and are recommended to be done every 2 years after project completion. It’s also important that should a blockage occur, the flush out should drag out as long as possible to avoid a surge of water like in the Fraser disaster. Believe it or not, Detroit is actually a sinkhole hotspot! Due to the immense infrastructure, suburbs, and having a limestone bedrock along a high-traffic shoreline, it makes this (unfortunately) a perfect place for a sinkhole to occur.
Although GPR is helpful pre-construction, a sinkhole develops throughout time. There are ways to identify if a project is on a current sinkhole, but it’s important to note that these incidents don’t mean you’re located on a sinkhole for a fact. If a building begins to crack on the walls or floors, this implies there is settling occurring and the areas that used to safely bear weight, no longer have an opposing force to do so. Your windows and doors would also no longer shut properly, due to bending. An incident that isn’t common in urban areas is a change in the color of well water. This means there is sediment entering the plumbing, which could lead to a sinkhole if not addressed. However, you should address this anyways because you’d be bathing in and drinking dirt, and who wants that?
There are also ways to identify sinkhole occurrences outside, which can be useful if you live in the city. Buried items will start to show due to the ground sinking, and ponds will form in dipped areas. You also might notice the vegetation is dying no matter the amount of water or rain, meaning the water isn’t staying in the soil. Again, these incidents don’t only point to a sinkhole occurring! However, these things should be checked throughout construction and after completion to ensure that a sinkhole hasn’t begun occurring, as they can occur anytime and anywhere. There is some good news though! Sinkholes aren’t just large holes in the Earth that swallow whatever is above. Sinkholes can also be small depressions in the Earth where the ground simply deflates. These are known as ‘cover subsidence’ sinkholes. The bedrock is stable, however, the sediment above falls to fill in holes or cracks that have emerged. This occurrence is common in cemeteries, due to the ground settling back into the grave site that was once packed tightly and must now resettle.
Sinkholes are scary as they are unpredictable. Luckily, geological science and technology has advanced in ways that allow us to understand the probability of them happening, but also how to avoid them when possible. Construction can play a role requiring contractors to have the project well thought out and planned safely to protect the client and surrounding areas and people, regardless of the chance of creating or crossing a sinkhole. If you’ve enjoyed reading, please share this article with your friends and family via the icons below or leave a comment!
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