Drainage under block paving

[Peter]

Can you compact sand?

 

Serious question, as my understanding of the partical size means that it has a lot of pore space. I also understood that block paving was acceptable under planning conditions/restraints as a permeable (semi-permeable?) surfacing. But thinking about it more, most hard surfacing goes over a compacted base or sub-base that rather reduces the permeability anyway.

 

The onsite builder, not the original contractor, suggested that as the land drain pipe comes in 50m lengths, it may have been convenient to use (inappropriately) with little thought of root intrusion in the future.

 

The next stage is some exploratory digging which I'm going to be involved with as the sycamore is TPO'ed. I suspect the whole lot will end up being dug out and re-installed properly.

 

Thanks for every- ones confirmation of my thoughts.

 

 

Sand isn't all sand.

 

If you took a sample of sharp sand from a builders merchant, and tested it like a soil sample, you would get fractions of gravel, sand, silt and clay. A surprising amount of clay too, which allows it to self bind under compaction.

[Gary Prentice]

Hope this helps https://www.google.co.uk/url?q=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/7728/pavingfrontgardens.pdf&sa=U&ved=0ahUKEwiFnq7Ao4jQAhXIAsAKHQx2AegQFggPMAE&usg=AFQjCNHRDtwzdIIeE6IV20ppqt7p7ncdKw

That's really useful, thanks.

 

 

Sand isn't all sand.

 

If you took a sample of sharp sand from a builders merchant, and tested it like a soil sample, you would get fractions of gravel, sand, silt and clay. A surprising amount of clay too, which allows it to self bind under compaction.

 

Right, that explains a lot. Cheers

[MATTMOSS]

We think there's a high probability that root intrusion has blocked the pipe. The area where water is coming up doesn't get vehicles over it because of the layout and there's no visible distortion of the blocks, there or elsewhere on the paving.

 

I was wondering if it would be possible to 'bore' the pipe to remove any roots and then use a smaller diameter solid pipe internally, to save lifting all the blocks, but suppose that wouldn't be a practical proposition?

 

Im sure that decent drainage companies have those little mole devices which can run along pipes with a light and a camera to confirm what the blockage is.

I may have dreamt it but i think they even have attachments that can clear the offending roots ,if it is roots, and run another sleeve inside.

Although i do not know if there has to be a minimum diameter pipe to do this or even whether this situation would warrent that scale of work.

[Peter]

It is possible to clear and sleeve an existing drain without digging it all up. However, I don't think you'll be able to push a new stiff pipe into a perforated land drain. The slotted pipe never sits perfectly straight in the ground, and the corrugations would make it difficult to push a stiff pipe inside with a lot of lubrication.

[Gary Prentice]

The alternative is to lift many square metres of paving. I'm a little doubtful about whether it's possible to bore a plastic corrugated pipe at all though. Then, the smaller internal pipe may prove to be inadequate for the flow rates.

 

Where's eggs?

[5 shires]

What do they put under "permeable" block paving?

 

Any compacted layer of sand or mot type limestone isn't going to let any water through.

 

Drives don't have to permeable, they have to have some way of dealing with surface run off without discharging onto the street or into the sewers.

 

You have to prepare the ground differently for permeable paving as opposed to normal. You need to dig out the ground to at least 300mm for permeable and lay different size grades of gravel starting from 15mm to 20mm down to pea gravel for top layer and no kiln dryed sand.costs more to prepare then normal but no planing permission needed if you use permeable paving.

[Peter]

That's interesting, I wonder how long it will be permeable for? Only takes a small amount of fines to filter through to block it up.

 

Sounds like a nightmare to lay too.

[Peter]

The alternative is to lift many square metres of paving. I'm a little doubtful about whether it's possible to bore a plastic corrugated pipe at all though. Then, the smaller internal pipe may prove to be inadequate for the flow rates.

 

Where's eggs?

 

 

You could bypass the slotted pipe under the block paving by moling a new drain and connecting into the slotted pipe at end of the garage.

[5 shires]

That's interesting, I wonder how long it will be permeable for? Only takes a small amount of fines to filter through to block it up.

 

Sounds like a nightmare to lay too.

 

I lay sections of marshalls drivegrid underneath to take the weight and stablelize everything,it can carry loads of up to 250 per sq metre

[eggsarascal]

The alternative is to lift many square metres of paving. I'm a little doubtful about whether it's possible to bore a plastic corrugated pipe at all though. Then, the smaller internal pipe may prove to be inadequate for the flow rates.

 

Where's eggs?

 

Evening Mr Prentice. I've been on the late shift, don't ask:sneaky2:

 

It sounds like the job was bodged in the first place.

 

You might be lucky if you can get someone in to "drain jet' it, which could solve the problem until you wind up the jacks on your caravan:biggrin:.

 

As said above land drains under block paving is a bad idea. It sounds like a dig-up job, then lay rigid pipe down to the drain/sewer.

 

A root cutter won't help in this instance, it will shatter/break/crack the land drain.