How to deal with a waterlogged site prior to building a shed base

[JayW]

Hi All

Not sure if this needs to be in the garden sub forum but I thought it would benefit from general building input in terms of foundations etc.

Essentially I want to build a raised timber frame sitting on concrete blocks to support a 17ft plastic keter shed (storing general items nothing heavy). My plan was to dig individual holes and fill with compacted mot type 1, followed by mortar, blocks, doc and 5x2 timber. (See example plan)

Due to the garden being slightly sloped and with all the heavy rain recently it has been quite flooded and hasn't returned to a firm surface as of yet.

I'm aware I should be thinking about french drains or a soakaway but because this is the furthest part of the garden and on a slope in quite limited. It's also clay based which makes draining even more difficult.

I also know pouring a concrete slab would be better but I have already spent almost £500 on timber, blocks, type 1 and everything else needed.

Would you say adding 2-4 tonnes of recycled crushed concrete or 40mm stone compacted first, followed by a geotextile membrane and then type 1 on top of that be enough so create a stable ground for the blocks?

The timber and half the blocks will always sit above any standing water, my concern is the sinking of any supports or the integrity of any mortar joint if it becomes waterlogged. I'm hoping however if I have a layer of 40mm stone then this will aid drainage of the area.

Thanks

 

[blup]

I would look to ke3p it as simple as possible and bolt a timber skirt to concrete spurs buried in the ground.

 

[^woody^]

Wait until the spring, to avoid loading saturated ground and getting movement later when it dries

 

[JayW]

Thanks, I don't have the luxury of waiting until spring. We are having our existing garage demolished and this shed needs to be built to house the stuff (ideally next 4-5 weeks) I already have all the materials ready to go (timber, blocks and type 1)

Just trying to gauge the best way to attack, I either need to order some more type 1 or clean stone and create a firm base on top of geotextile, or stick with my original plan of individual pads. (obviously one uses way more material than the other)

I am just concerned about sinkage over time with pads if the ground is on the softer side or at times like now where it's just so saturated. I'd rather get it right now than see the shed twisting in 2 or 3 years. If someone can confirm that digging down a sufficient depth and having a thick type 1 base under each concrete block would be ok and cope with water (in the future, not while its setting) then i'd be more confident about starting once its dried up a bit.