Content

• To step
• Part 1 of 3: Measuring the sinkhole
• Part 2 of 3: Pouring concrete into the sinkhole
• Part 3 of 3: Filling the sinkhole
• Tips
• Warnings

Zinc holes form when the soft rock - for example limestone, gypsum or another type of carbonate rock - under the top soil layer dissolves in the groundwater over time and wears away. There is then talk of karst. Eventually, the sediment settles above the underground hole because it is no longer supported, exposing the sinkhole. Homeowners are usually unaware that their homes are built on karst-covered land. Sinkholes therefore form suddenly and without any warning. To fill a sinkhole, you will first have to pour a layer of concrete into the hole. Fill the rest of the hole with clay sand and cover the clay sand with a layer of soil.

To step

Part 1 of 3: Measuring the sinkhole

1. Keep an eye on the hole to see if it gets bigger. Zinc holes are often created by weather conditions such as a heavy rain storm. Once a sinkhole has formed, the hole can get bigger because more pieces of limestone or carbonate rock wear away. Don't try to fill a sinkhole as it gets bigger by the day.
   • You can fill the sinkhole when it stops growing and has remained the same size for several days.
2. Measure the width and depth of the sinkhole. You can only fill relatively small and shallow sinkholes yourself. Grab a rod or a stick (you can even use a tree branch) and put it in the sinkhole. Note how deep and wide the hole is.
   • Be careful when walking around the edge of the sinkhole. The ground can be very unstable, so be careful not to fall into the hole.
   • Do not attempt to fill sinkholes with a diameter greater than a meter yourself. Large sinkholes can be deep and dangerous.
   • If the sinkhole is deeper than chest height, do not step into it. Deep sinkholes and holes with steep walls are likely to cause the ground to collapse.
3. Call a landscaping company. If you're concerned about your safety near the sinkhole or think the sinkhole is too big for you to fill, it's time to call a professional. Search the internet for a landscaping company and explain that you have a sinkhole in your yard that you would like to have filled.
   • Landscaping companies have more experience than the average homeowner in dealing with this phenomenon.
   • If it is a very large sinkhole, please contact the municipality.

Part 2 of 3: Pouring concrete into the sinkhole

1. Dig out the outside edges of the sinkhole. The sinkhole may be larger than it appears to be on the surface. To determine how big the sinkhole really is, use a shovel to make the sinkhole bigger. Remove the soil from the edges of the sinkhole and check that the soil around the sinkhole is stable. Keep removing soil around the edges of the hole until you get to the point where the soil and sediment are supported by solid rock.
   • Also remove all loose materials from the sinkhole such as tree branches, pine cones, etc.
2. Mix dry concrete powder with water. Start by pouring about a third of the concrete powder into a wheelbarrow or large container. Add a quart of water and mix everything thoroughly with a chop, shovel or concrete mixer. Keep adding water until the concrete is thoroughly wet and has the consistency of thick filler. Add gravel to make the concrete stronger.
   • You can buy large bags of rapid concrete at the hardware store.
   • How much concrete you need to mix depends on the size and depth of the sinkhole.
3. Pour a layer of concrete into the sinkhole. Using the wheelbarrow and shovel, pour wet concrete into the bottom of the sinkhole. This way the sinkhole cannot get deeper and you get a stable base for the other materials with which you fill the hole. Try to fill the hole for at least a quarter with concrete. When the hole is one meter deep, fill it with a 25 centimeter layer of concrete.
   • There is no need to let the concrete dry before you start filling the hole with sand and soil.
   • The intention is to reinforce the sinkhole at the bottom with a layer of concrete as the basis for the other materials you use.

Part 3 of 3: Filling the sinkhole

1. Shovel loam sand on top of the layer of concrete. Thick loamy sand is a heavy filler for the sinkhole and prevents water from accumulating in the filled sinkhole. Scoop the sand out of a wheelbarrow with your shovel and throw it into the hole. Fill the hole about three-quarters with sand.
   • You can buy sand at most hardware stores and specialized web shops. If you can't find a store that sells loam sand, contact a contractor near you.
   • Most contractors use a sand supplier with whom they can put you in touch.
2. Fill the hole with soil. Fill the rest of the sinkhole with soil. This way, the materials you used to fill the hole are at the same level as the garden or terrain around the hole. By filling the rest of the hole with soil, plants can also grow where the sinkhole was and the soil and sand become stable.
   • You can buy soil in bags at garden centers and hardware stores.
3. After a few days, throw more soil into the hole. The sand and soil that you have thrown into the sinkhole will eventually become compressed and stable. That means that the material sinks slightly and you get a hole where the sinkhole was. Use the rest of the soil to fill in the hole until the level is the same as the terrain around it.
   • Repeat the process more often if necessary. The materials you filled the sinkhole with are likely to be compressed again during a heavy rain shower or when a large amount of water enters the hole.
   • Do not plant trees or shrubs in the sinkhole site. They may not be doing well because the soil does not contain enough nutrients. They can also become uprooted and fall over if another sinkhole develops.

Tips

• There are two types of sinkholes. The first type is formed within minutes because the layer of limestone or carbonate rock above the sinkhole suddenly collapses due to a rainstorm or some other weather phenomenon. The second type is formed a lot more slowly because the layer of limestone under the ground slowly wears out and the earth and the other sediment sinks down because it is no longer supported.
• If old building materials (such as scraps of wood and planks) are buried near a construction site and start to rot, potholes can form in the ground that look a bit like sinkholes, even if they are not sinkholes. The earth then settles on top of the rotting materials.
• If a sinkhole develops in your yard and you own a home, it is your responsibility to do something about the hole. However, it may be worth contacting your insurance company and telling them about the gap.

Warnings

• Call 911 immediately if you see a sinkhole on public land, such as a parking lot or a road. If possible, stay close to the hole until help arrives to prevent people and cars from falling into the hole. For example, you can park your car near the hole (not too close) with the hazard lights on.
• If your home or any other building is threatened by a sinkhole, leave your home immediately. A sinkhole can just get bigger, and your own safety and that of your family should be your priority.
• Check that the sinkhole was not caused by a broken sewer pipe or burst water pipe. If the inside of the hole is wet or smelly, take steps to resolve the issue before attempting to fill the sinkhole.