Heavy clay drainage help

I have checked the manhole a few times now on different days and never seen so much as a drop leaving the pipe, yet the garden is absolutely sodden still, and I mean three inch deep surface puddles, so boggy all over I properly sink into it soaked, so it doesn't seem like anything is working, especially since it's been 4 weeks now with no improvement and per meant standing water. I don't know, if it is working it is certainly a far cry from the drainage solution we were told to expect.

Ive just phoned a different drainage company who have said it sounds like a lot of mistakes were made-

-Heavy machinery should never have been used on waterlogged clay, it just compacts it and makes the problem worse, and makes a mess of the area. it should be done by hand with a spade.
-it should have been backfilled with gravel or any other free draining aggregate, but never just the same heavy clay. For the drains to work the water has to reach them. If the water could easily permeate a foot down through the heavy clay then drainage wouldn't have been needed to start with!
-the subsoil removed to dig the trenches should have been removed from the garden not just left on top
- weed membrane is completely inappropriate and shouldn't have been used.

They have basically said it sounds like it will never work properly the way it's been done, but they can come and properly assess it in person Saturday morning, so I've said yes (as I'm waiting for the original contractor to come back from holiday anyway.) If the company will give me a written report of sorts, of what they have found wrong with it and how it won't work, would it be a good idea to show the first contractor when he comes back to look at everything?

 

One thing that comes to mind is that you rotovated the site first,then the digger came in, turning up soil in the winter months will make things worst and will take a alot longer to dry out IMHO
edit
Also you now have a air gap in the soil through pipes and gravel which will help dry out the sub soil better, just because a land drain is not running water it's not working

 

Just for extra reading, I've put in many land drains for local landowners,
just some examples of how some are done

trench to a ditch,4inch pipe, clean gravel then back filled

trench to a ditch, 4inch pipe, then back filled

trench to ditch, clean gravel, then back filled

trench to ditch, builders rubble, then back filled

15 years later they're still working, but the last one is the not working as well when it was done, but it depens on soil types, rain fall and slope

 

Thanks @Jiffy thats really good to know that the same method might have worked in a different situation, it gives me hope that this was a genuine mistake by the contractor and he hasn't intentionally done a bad job, hopefully he will be happy to rectify it once he sees it hasn't worked.

Going back to the issue of amending the clay topsoil to improve drainage by adding organic matter, Ive found a local company who grow mushrooms and they can deliver 7.5 tonnes of loose mushroom compost for £130, which is very good value compared to other options, is that likely to be enough/too much? Or is that something that can really only be assessed as it is added? I'm terrible with sizes/quantities!

 

7.5 tonnes is a huge, nay HUUUGGGEEE amount of mushroom compost.

The 60 bags I did mine with probably totalled about half a tonne, if that.

In fact, some approx calcs. I'd say each sack weighed about 15 kg. Times 60 is about 900 kgs.

 

Haha oh right!! More than I need then? So will it be done by weight and not mass? I hate to be having a dumb blonde moment but I get really confused with how things are measured if I'm honest. I've seen it sold in bulk bags with no listed weight and in large bags listed in litres, and as loose in ton loads. I assumed that 7.5 tonnes was the capacity of the vehicle and it would be just a full load so to speak, rather than the actual weight of the compost itself, is that completely wrong?

 

Another way of draining the ground (fields) is with one of these, which is pull through the ground and make a tunnel the size of your arm and water trickle into them and down to a ditch but these will fill up in time and will have to be done again

 

I couldn't really guess how much you'd in terms of weight. It's easier to estimate by volume. Take the area to cover in metres square, multiply by the desired depth in metres to get the required number of cubic metres.

The thing to be careful of, us actually using too much. A depth of 10cm should be more than enough (10cm being 0.1m). Clay is actually good. UN fact it's excellent. Just not when it's 'just' clay. A few inches of mushroom compost mixed in near the surface will serve to hold the clay particlesapart, allowing drainage when wet, while retaining moisture when it's dry outside.

Something else happens when you loosen the clay with compost. All the earthworms love it. As they tunnel about to munch on the compost, they drag it under, mix it up, and keep little tunnels that further aid drainage

Go too far with it, and it will be too soft to support a nice lawn, and will be boggy in wet weather, and dry to the point of your grass dying in summer.

 

Love the photo!

Oh thank you for that @JWK I'm bobbins with figures so that's a huge help. Ended up having a 25 minute argument with my husband about whether a tonne was a measurement of mass or weight and got absolutely nowhere with the actual compost quantity problem!

 

9.15 m x 9.15m x 0.1m = 8.37m3.

Can't find a weight per cubic metre (I'd ask the supplier) but wondering about how much the ground will be raised by adding 100mm of SMC (as it may not be the obvious answer of 100mm, as as for example adding 1m3 of pebbles to 1m3 of sand will not result in 2m3 of ballast), and whether raising the topsoiled area would cause flooding of the adjacent patio (I think that's what I can see in that pic taken through a window).

P.S. Is "100mm" the amount the ground is to be raised by, or the depth of SMC to to spread on the surface prior to digging in? Because the latter will be for 'bulked up' quantities and require much less SMC.