Preventing Sinkholes

It is your home, you donít want anything to happen to it!

In light of the sink-holes that fell in all around Centurion early in 2018, I thought I would explain how they are formed, and what home owners can do to help prevent them.

Before you can understand the dangers that sink-holes pose to your home, you have to understand what they are and how they are formed.

Almost all of Centurion is underlain by dolomite. This means that the rock below the ground is dolomite. Dolomite is a very hard rock, yet it is readily eroded by water. As the rock erodes it leaves behind cavities. As more dolomite is dissolved, the cavities grow bigger to form caves. Some of these caves reach huge proportions.

How big? To give you an example, here is a photo of the author climbing a 16 meter high rope ladder to get out of a cave. (Donít worry, I am safe, on a belay from above!)

Yes, that hole is 16 meters deep, and at the bottom of that is a cave that took an hour to explore. And that, folks, is one of the smaller caves in the area.

Some caves go to depths of hundreds of meters, others have roofs so high that normal torchlight cannot reach it from the ground.

(Currently, the worlds deepest cave is Krubera Cave at 2197 meters deep!)

Once these caves have formed, it is inevitable that the roof of the cave will, at some point in time, collapse. When this happens, you have a sinkhole. The problem is that sometimes, a building is situated above such a cave, and when the sinkhole forms, the building gets damaged, or in extreme cases, swallowed by the cave.

Here is a photo of a sink-hole with a circumference of 18 meters and a depth of 50 meters. At the bottom, there is a cave that is over 2 kilometers long, and has still not been completely explored or mapped. A sink-hole of that size will swallow an average sized residence with ease. This sink-hole did not form over time, it collapsed one night, in one go, without giving any warning about what was about to happen. The black spot you see in the middle of the opening is a caver in the process of descending into the cave!

So how do you prevent these caves from forming?

Cave formation is an ancient geological process, and cannot be stopped. However, there are things that speed up cave and sink-hole formation. Remember I said that dolomite is readily dissolved by water? Well, that is the secret. By feeding water into your ground system, you might be speeding up the formation of a cave or sink-hole below your home at this very moment. Iím not talking about the water you use to water your garden, that kind of water is spread over a wide area and easily absorbed by the ground.

The things that could speed up cave formation are things like:

  • Swimming pools that leak
  • Water pipes that leak
  • Damaged drainage pipes.
  • Other sources feeding lots of water into a small area.

  • Consider that two of the above points not only contribute to cave formation, but also have a negative impact on your wallet, and you can immediately see why leaking swimming pools and water pipes should be fixed without delay.

    Damaged drainage pipes, such as sewer pipes, are more difficult to identify. If you keep on having blockages on the same sewer line, in the same place over time, it is possible that the pipe is cracked or broken, most probably by tree roots. Fix this immediately and you have not only stopped the possible formation of a cave, you have also sorted out future headaches and expense from this pipe.

    Other sources of water going into a small area could be something as innocent as the water discharge from your roof. To start off with, the discharge from your roof should always be directed away from your homeís foundations. You also have to make sure that this discharge does not accumulate somewhere and then head underground, where it can cause great damage.

    If you live in the Centurion area, or any other dolomitic area, you should take these pointers to heart.


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