ᐅ Underground rainwater cistern damaged

Hello,

about 10 years ago, I bought a house. There is a rainwater cistern buried on the property, approximately 5m² (54 sq ft) in size and about 3m (10 ft) deep. Recently, I noticed that it no longer holds water. I inspected it from the inside and found that the bottom is heavily deformed.

This means waves have formed, which have then cracked upwards (cracks). Don’t ask me how this happened—earthquakes, no idea. My first thought was to repair it with resin and fiberglass fabric. However, I realized there are too many cracks and some areas are hard to access.

Now my question:

Can I fill the bottom with around 10% coarse gravel and then cover that with about 10% concrete? (Maybe coat it with something afterward?) Could this work?

Thanks in advance,
Andre

Is the cistern made of concrete or plastic?
If it’s plastic, you can forget about it.

If it’s concrete, I recommend doing a quick Google search for "repairing concrete cistern."
You’ll find a lot of information.