Sinking a basement

[mike os]

Needs a proper ventilation system to prevent dampness anyway fo should handle it

The usual precautions for pits and confined spaces apply I guess

 

[Morrisman]

First establish what the drainage situation, water table, and soil saturation level is at your location, or you might find swimming pool conditions as you excavate.

When I had a gas tank sunk into my front garden they discovered a sewer pipe that runs across all the front gardens in our street....... nobody knew it was there, nothing showed on searches or water board plans.

 

[Arc Tourist]

When I had a gas tank sunk into my front garden they discovered a sewer pipe that runs across all the front gardens in our street....... nobody knew it was there, nothing showed on searches or water board plans.

My neighbour discovered an unknown sewer line which cut through a corner of their property while terracing his back garden. Fortunately it did not cross my back yard excavation. The sewer turned out to be disused from an old chapel nearby which had been torn down ages ago.

 

[jerrytug]

Out of interest how do you ventilate something like this? I'm thinking specifically for a workshop flammable gasses and gasses heavier than air.

Just use fans and ducts and filters, sucking from a low point, and msybe a spark proof fan motor.
IMO it only becomes tricky if you want to remain undetected and/or protect the space from nuclear, biological and chemical 'risks' .
If I was in a subterranean workshop, I would like to know the air intake was protected against some rioter or jealous neighbour tossing a bottle of EasyStart or something into the intake fan, and an insect filter seems a good idea, but that would be enough.

 

[AdW]

If you are considering putting in a basement below groundwater level you need to consider the effect of buoyant uplift from the hydrostatic water pressure, especially if you tank it. I have had the unusual experience of watching a large concrete basement slab deflect upwards like a membrane as a result of this. If under engineered it can crack your slab and cause water tightness issues. At the extreme, if the basement is ridged and the structure over the top insufficiently heavy, the entire structure can lift. It probably won't pop out of ground like swimming pools sometimes do but it can still be an issue.

As you are in coal measures strata you should also consider the potential need for engineering the structure to prevent hazardous gas ingress from the ground. Tanked basements where the waterproofing measures extend above ground levels are usually quite good at keeping out ground gases but not all waterproofing solutions are suitable barriers to gas - bentonite sheets being one example that springs to mind which can't cover both bases.