Wet soft sub base - Block paving

[MASURepair]

Hello All. I am currently in the middle of block paving my 75sqm drive. So far i have managed to get the sub base down and the edges concreated in. However due to the cold, frost, and some recent rain i have found that my sub base seems soft under foot. I have layed 150mm of 803 20mm to dust and compacted it in 50mm layers using a wacker DPU2550H weighing 157kg and i have wacker it untill i am blue in the face i must have made about 20 passes over each layer. But i've come out this morning to give it a final wack before
laying the grit sand over the top and found the wacker just sinking in and pushing all the sub base to the side resulting in a lot of water coming to the surface. Would it still be ok to lay the grit sand down or should i wait for the ground to dry out a bit. Thanks.

[msh paving]

I have layed 150mm of 803 20mm to dust and compacted it in 50mm layers using a wacker DPU2550H weighing 157kg and i have wacker it untill i am blue in the face i must have made about 20 passes over each layer. But i've come out this morning to give it a final wack before

the material is to small lump size, Type 1 should be used 40mm down to fines, your material is very small to compact the plate is a good size i use one myself like it 50mm layers are probilly to thin to compact well 100mm at a time is ideal, if water is comming up and soft you need to leave it well alone till drys out or lift the sub base to allow it to dry and re-do it MSH

[DNgroundworks]

If its soft underfoot its no good IMO, should be using MOT TYPE1 hardcore under a driveway.

Maybe try leaving it to dry as you say then see how it is but if it were me id pull the wet mess you have at the moment out and put some fresh type 1 down, with terram and compact asap.

what is 803?

[DNgroundworks]

sorry msh must of been typing at the same time!

[MASURepair]

803 is the the number given to the road construction act. Clause 803 states what materials to use and the process in which to build a road.

Hi, thanks for your quick replys guys, The stuff i've been using was recommended by a local patio and driveway supply centre, he also refered to it as 20mm binding.

I have put a layer or tarram down under my sub base however are you suggesting i am using the wrong stuff for my sub base?

Kind Regards.

[DNgroundworks]

well sort of, i always use type 1 for subbase construction, but i have met other lads who use 20mm down as you have done and had no problems :p

But in your circumstances type 1 is the material id choose only because ive never had much to do with the other stuff!

[DNgroundworks]

some one else might be able to give you a more detailed explanation as to why type 1 is better - better load bearing capabilities maybe? better compaction?

[MASURepair]

Thanks for the advice, so should i leave it to try and dry it out a bit before laying the grit sand?

[DNgroundworks]

You will probably find that once it is dry, you will be able to re-compact it, and crack on with the rest of the job, just make sure there is no give at all or any wet sloppy patches before putting down the grit sand, i think it should be ok.

[GB_Groundworks]

20mm to dust as a lot more fines and small particulates resulting in more chance of it becoming thixatropic. 20mm to dust is nice to use to blind off with as it rakes by hand better and binds nicely how ever your main sub base should have been dtp1 as per the 803 clause. If you actually read the 803 clause it's more about the Los Angeles test on aggregate wear resistance and it's suitability to a trafficked road. Over kill for patio, but as your sub base is thixatropic you are going to have to let it dry out. Otherwise the vibration will just turn it into a liquid every time.

Thixotropick Becoming a fluid when agitated but solid or semi-solid when allowed to stand

[Tony McC]

803 is the term used in Ireland for Type 1, and as the OP pointed out, it stems from the very same clause as the UK spec for Type 1, (SHW Clause 803 - unbound granular material for sub-bases). However, it should be 40mm to dust (ish) as pointed out by MSH, not 20mm to dust, which is NOT an 803 spec.

20mm down, assuming that is what has been used, *is* too small, and will result in more movement of the sub-base in its early life, but, if there are sufficient fines, it will firm-up over time, especially once it's had a chance to dry out properly.

I'd be sorely tempted to leave it untrafficked for at least a couple of weeks and then see how it's behaving.