Trench digging, found hollows? holes

[garden4ork]

Little concerned/curious over these 'hollows' I've found when digging out a foundation trench. They seem to only be close to rocks, the one nearest to camera goes deeper into the hollow. Not very deep but I've not really delved into it. This is the only place I've found them after digging around 7m length

 

First thoughts were an old well, as in this area it does tend to flood under heavy downpours from groundwater however also could be rat tunnels? Figured I'd share here and get some 2nd opinions

 

Thank you

 

 

Edited June 29, 2023 by garden4ork

[ProDave]

Could it be infilled ground? A load of rocks or concrete blocks thrown in and the spaces in between never properly filled?

[Temp]

Think I would dig a bit deeper in those areas to see how deep they go. Be careful you don't fall down a mine shaft or old well. Tie a bowline around your waste if you go in the trench.

[Jenki]

It's close to the ground so I'd suspect backfill, but take care and dig some more, pull out the rock and see what your left with, if it's backfill and you get ground water it may well have washed away leaving the voids in the poorly compacted backfill.

[garden4ork]

Thank you. The void backfill description does sound likely now you've said it but reading about falling down a mineshaft made me shudder a bit! Will take care...

Edited June 29, 2023 by garden4ork

[saveasteading]

The holes on the side  are where rocks have neen pulled out. And to the bottom they have voids beneatg.

The ground is infill which is normal enough but not suitable for a foundation.

[Dave Jones]

keep digging until you find virgin ground or hit 3m in which case call in the pilers.

[twice round the block]

What's the footings for? garden wall or a building