Soft ground - How should i deal with a soft area

[Red]

Please help, I am stuck and I need to find a way forward. I am blocking the driveway and I have hit soft ground down the left hand side and it is giving me a headache.

The problem area is about 5m x 2m strip down the left hand side of a 73sq m drive way.

When I was digging out, the ground in this area was really wet and soft so I went down a bit deeper until I hit clay. This seemed quite a bit firmer so I banged some old bricks into it and covered it with a geotextile and 20cm of type 1 hoping it would be ok. When I drive the rollers across the top it feels spongy, it’s a little like driving over a mattress it compresses and springs back into place.

The property is at the bottom of a hill and thinking about rain water running down makes me wonder if I could ever cure the problem for a justifiable cost.

I read ‘keep digging until you hit solid ground’ but I’m reluctant to keep digging as I feel it will be a long way down and the waste is expensive to get rid of.

We have been pondering some options but lack of experience makes me unsure.

Do we:

Keep digging and hope for the best.

Dig a little and put a concrete raft in to provide support.

With fingers crossed raise the level a bit in the soft area with more type 1

Abandon the idea of a nice wide driveway and put a decorative gravel area in for pedestrian traffic only.

Any helpful thoughts or experiences would be greatly appreciated.

I can post some pics if that helps.

[rxbren]

For a start the old bricks are not a good idea should have built it up in layers of compacted type1 stone you could try digging it all back out going a wider than you need, geotextile down first then type 1 compacted in layers

[Red]

Hi rxbren, thanks for the reply; I put the bricks in the clay under the type 1, I thought they would help stabilize things by spreading load, geotex over the top then the type 1. I didn't compact in layers as I thought the 1.5 tonne vibrating Bomag would rattle through 20 cm of type 1 without a problem. Sorry if i am missing something but why would going wider help?

[seanandruby]

Hi Red. You need to dig out till you arr satisfied with the sub grade. Cover the unstable ground with GEO GRID, this is a netting type for use on ground stabilisation. You need to bring fill up to the start of your sub base level, crush and run would do but you have to be careful of the quality of it so best to use mot, oops i mean dtp1. once your capping layer is in you can start your make up of the driveway. Pay attention to any drainage you will be placing in your drive. Is it to late to dig out the 200ml and replace your geo- text to geo -grid ? Also don't overdo the bomag on the damp bit and yes 200 with a roller is ok but try do 100/ 150 layers, or 75ml with a plate compactor. Hope this helps.

[Red]

Thanks Sean, i'm going to pull all the type 1 as you suggest and dig out more to see where we are at with the ground beneath. I was trying to avoid the cost of more skips but It looks like i'm going to have to take it on the chin.

[Red]

Ok I have dug well down, about 2.5 feet, and and the ground is firmer and dryer but i'm not hitting anything really good its all a sandy clay material.

I back filled but found after a while the ground was water logged and the type 1 was back to being un-compressible with water coming up to the surface. I'm guessing I need to put field drainage in to dry the ground.

Any thoughts folks?

[seanandruby]

Do you know from where the water is coming from?
You can't just back filll dodgy ground with dtp1 Red. As i stated before " you need a geo- grid", also you need more robust capping layers ie crushed rock, old hardcore etc: heavy roller will just pump the water up through the dtp1. I would place a geo grid over the dodgy sub soil, lay capping layers 225 layers, once at formation level cover with geo- text' and start your formation. As we don't know from where your water is coming from, high water table, leaking pipe it's hard to advise on drainage from or to where ?

[Red]

Before saw your post Sean I had grasped the nettle and ran drainage in to deal with the water problem. In fact I have been so busy I have only just managed to get back to the forum. I might be speaking too soon but it seems to have done the trick. The back filled ground feels pretty solid now.

The water is coming from a terraced garden on the left of the driveway which rises about 2.5 m over its 8 m length. A low retaining wall stands between the driveway and the first terrace and the water comes from the garden through ground under the wall. The property is at the bottom of a great big hill so that doesn't help things either.

It has been mostly dry here for the past week, so I will be interested to see how things are after a spell of rain. There has been so much ground disturbance putting the drainage in I think I should level the site up and leave it over the winter to settle.

[williams]

It's not in essex is it? I've had this several times over the years and it is a nightmare.

Here's what I'd do, dig down as much as is realistically possible, usually that means about 18" if it's the bad it will still be spongy, I'd then put in some decent 50mm crushed in layers to stabilise, then type1 it properly, haven't encountered any problems this was.

I had one once which was so wet it all turned to slop, I pulled back a load of type one and mixed in a load of cement, we are talking an equivilant of about 15/1 and then compacted then based as normal. My theory was the dry cement took the moisture out.

It's a nightmare though and as the contractor it's funny how your the one responsible for crap ground, imagine knocking on the door asking for more money! Oh no it's me who pays for that