Path above drain sounds hollow ...

[JP_]

The concrete path that runs alongside my house, under which is the main drain, sounds hollow in part - when tapped. Should I worry? Concrete has been built up at some point - we had damp issues in the floor inside, but I think just an airbrick issue. Also, gutter seems to be leaking a little at the join. I think that is the cause of the wet patch on the ground.
I have a video, but just realised its on my phone, so will add that later.

 

[Nige F]

Nothing to worry about The footings of the house will be deeper than the drain - it's part of the sewerage undertakers network, and not your responsibility. Get the gutter fixed. The concrete is probably over voids in the hardcore under - just what I have outside my front door, but as the slab has cracked and dropped I'm going to re do it this sumer.

 

[JP_]

Here's the video, hopefully..
https://drive.google.com/file/d/1kXlE5ZOQrDsxhLxuSeO07-4nUjY7kGZ_qQ/view?usp=sharing

 

[Hugh Jaleak]

Possible ground below had shrunk/subsided, creating a void. Without breaking the concrete out you wont know for sure, depends what traffic is using that path and how far you want to go.

 

[JP_]

Zero traffic, will ignore.

 

[JohnD]

looking at your video, I think it's very likely that you have a clay gulley which is cracked or broken, and the long-term escape of water has washed away the soil around it, so there is now a cavity under the concrete.

You can drill a hole through the concrete if you like and poke down it. Probably you will find soap-scented mud, and some red worms.

 

[JP_]

Hmm, that doesn't sound good....

 

[Ian H]

I've got 50p saying the concrete has been poured over broken bricks and there's ash stuff under it that's settled.

 

[JohnD]

I wonder how it knew it should only settle near the drain.

 

[Ian H]

Maybe because it's been excavated previously?

 

[Nige F]

A main drain is mentioned by the OP- are there any laterals or gullies ?

 

[Hugh Jaleak]

Assumed rainwater gulley spotted in the video Nige.