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Sinkholes - a matter of water erosion

Sinkhole in the United States, Source: Nationalgeographics, by Octavio Jones
Sinkhole in the United States, Source: Nationalgeographics, by Octavio Jones


Anywhere in our world different kind of erosions happen which form our landscape – on the surface as well the subsurface. The most significant factor of erosion is water (beside wind, landslide and abrasion) which is causing a challenge in engineering problem. The ability of water to move soil and rock depends on several factors. The faster and more turbulent the flows of water, the more erosive characteristics are appearing. Larger particles like gravel are more resistant to erosion than small particles like silt or clay. Finally, rather than physical erosion, some materials dissolve in water, just like sugar or salt. It can be eroded just by dissolving into the ground water from time to time.

Some kinds of soil are more affected than others – i.e. dolomite areas, etc. Most natural sinkholes occur in areas with large deposits of carbonate rocks like lime stone. Over long periods of time, ground water flowing through the subsurface can dissolve the rocks, creating voids and open tunnels. In fact, this is how most caves are formed – a creative name of sinkholes is also „Internal erosion“. A sinkhole is a feature that occurs suddenly and manifests as a hole in the ground.

Huge sinkhole , Source: Nationalgeographics, by Octavio Jones
Huge sinkhole, Source: Nationalgeographics, by Octavio Jones

The consequences are a catastrophic collapse which may lead to death, injury or heavy structural damages. Many photos and videos are collected and published on the internet; - just search for “Sinkholes” and you will be impressed.
Sinkholes are usually circular, up to a diameter of 125 meters, with a depth up to 50 meters. Cracks in walls and in the ground of the settlements are often early warning signals of an upcoming sinkhole appearance. As a matter of fact, a sinkhole is a nightmare for every municipality and the damages are huge.

Sinkhole - by nature

A sinkhole is generally what we call a karst terrain. Karst terrains are basically areas that are underlain by soluble rock, rocks that can dissolve like lime stone, gypsum and salt. Rain water naturally is a salic when it gets underground into these rocks. Over long periods of time, hundreds, thousands or tens of thousands of years, the rocks will dissolve and will leave cabins and voids underground. As these voids grow upward, the soil on top can no longer sustain itself, and we get these catastrophic collapses.

Beside the process of creating cavities under the ground and lowering the ground water table which is another reason for sinkholes - cavities exist within the bedrock or the overburden which are in a stable balance. The cavities are accompanied by groundwater. Lowering the water table disturbs the balance and the active erosion under the soil will be accelerated. The process of erosion is gaining an unstoppable process and the collapse will be the final result.

failure broken pipeline
The failure here was a broken drainage pipe. Source: ABC News

Sinkhole - human made

But not every sinkhole is formed through natural processes. In fact, many of the most famous sinkholes in recent times have been human-created. Just like a cave dissolved into the bedrock can act like a pipe and allow ground water to carry away the soil – a current pipe can do the same thing and current pipes are limited to areas with specific geology. If you could take a look into the subsurface of any urban area, you will see miles of water, sewer and storm water drainage pipes.

All it takes is a little bit of settlement or shifting to create an opening in one of these pipes and allow internal erosion to start. Other possible reasons of ex-filtration are abrasion, corrosion, pipe aging and wrong installation. During this exfiltration, water moving through this pipe is able to dislodge the soil and carry it away. On the same leakage infiltrations can happen to speed the time of creating cavities. Notice that there is no signal on the surface that anything is going on below. As more soil is washed away, the subsurface void grows. Depending on all those soil properties we were talking about earlier, this process can take days to years before anyone notices. Many of our subsurface utilities are placed directly below roadways and the paving often acts as a final bridge above the sinkhole, hiding the void below.

Beside wrong piping systems other human activities can have a great impact on sinkholes like mining, fracking and geothermic works, where cavities are formed or opened – due to their impact on the soil-structure subsurface. But the main origin of sinkholes made by humans is the result of leaking pipelines.

repairing sinkhole japan
Repairing a sinkhole sewage line with Krah-Pipes – within 48 hrs.


Sinkholes created by nature cannot be avoided, but man-made sinkholes – result of our fast growing infrastructure - can be avoided by using the right sustainable pipe system. One of the main points for installing new pipelines should be – flexible pipe system – resistance against soil movements – occurred by several impacts, like earthquakes. Modern and sustainable flexible pipe solutions (even in large diameters) are available, they are absolutely tight jointed – preferably welded. All components in the pipe system should have the same high quality requirements as the pipe.

Manholes, fittings, etc. Flexible instead of rigid - the Krah pipe system is providing all features, to be a sustainable solution for infrastructure projects. Not only to repair sinkholes – like the quick repair in Fukumato / Japan, where a sinkhole was repaired with a Krah pipeline – and that only over a weekend! On the internet many project reports can be found regarding this project.

Think about the consequences before you act (installing the wrong pipe system)!
A right solution is available – Krah Pipes.

Alexander Krah
Krah Pipes GmbH & Co. KG