Open ended drainpipe under slab

[askman]

After knocking down what was the old rear wall of my house, I’ve noticed that some of the dust / earth which sits in the resulting channel has gotten slightly damp. There is a pre existing extension on the back roughly 30 years old so I know that the following isn’t directly from the weather outside.

After digging out a little with my hand it looks like earth rather than dust or rubble from the building work, and have also found an open ended clay pipe approx. 3” poking towards the back of the house and sitting under the concrete slab of the house.

I’m thinking that this is an old rainwater pipe as when I run water down the soil pipe I can’t hear it through this other one.

Is it likely that the unknown pipe is causing this dampness? If so, what’s the best way to combat the issue? Cap it off with a rubber cap and jubilee clip it tight?

On a separate note, the extension floor was done really poorly so I’m going to be getting this floor pulled up and re-layed with insulation and a new dampproof course so can get this area covered as well, just wondered if there was something else I need to do.

 

[John D v2.0]

really you shouldn't have redundant drain branches, it should be capped off at the manhole with something the rats cant chew through to make a nest in the pipe. If it's uphill from the wet part to this part, it shouldn't be causing damp unless your drains are filling up regularly.

The ground is just generally damp at all times, so if your old wall footing is wet it's not a big issue. But it is a good idea to make sure no water is being channeled under your house, no leaks etc.