Subsidence under tarmac - Should I re-surface tarmac with a history of subsidence?

[Paul Butterworth]

I have a tarmacked drive which is shared with a neighbour. The drive length is about 15 metres straight to my garage and dropping maybe a metre. There is a branch off to the neighbours’ garage and another to my front door. The whole area is about 180 square yards. The area has been subject to subsidence – both houses and garages have been underpinned c25 years ago. The drive is original about 32 years old. Unsurprisingly, it is littered with irregular cracks that seem to originate in the underlying concrete. In front of the neighbour’s garage there is clear evidence of subsidence in the drive, where it has dropped, probably, by a foot and recently a hole has appeared in the tarmac, adjacent to a soakaway, showing a 2 inch separation of the concrete joint and a hole underneath c18� deep and, at least, 3 foot wide.
One contractor proposes to cut out the centre of the subsided area (about 6 feet square - but more if necessary when he digs it out) and fill it, fill and seal the cracks then put on a new tack/wearing course.
A second contractor says this wouldn’t be satisfactory and proposes to dig the whole lot up and start again laying a sub-base of crushed concrete.

My questions are:
Is simply re-surfacing a false economy as presumably, the cracks – and there are a lot of them – will re-emerge?

Given the subsidence problem and the possibility of further movement under the drive, is tarmac a sensible approach anyway or should I go for blocks?

[84-1093879891]

I tend to favour the second contractor. Cracks will probably be reflected through to the new surfacing, and if you've holes appearing due to failing soakaways, subsidence for whatever reason, and god knows what other problems, using the 'sticking plaster' approach proposed by the first contractor seems like a false economy to me.

If this were mine, I'd be much happier to have the lot dug-up, the subsidence and drainage problems resolved, and a new sub-base installed before carrying out re-surfacing of any description.

If there is an on-going concern about movement or subsidence, then an elemental form of paving, such as block paving or flags, is a safer bet than a monolithic surface such as bitmac or PIC. Then, if there was to be any further movement, at least you can repair the damage invisibly and at minimal cost.

[99-1093880115]

I have a similar sort of problem - re shared tarmaced driveway with neighbour...and a subsidence problem.
The subsidence was thought to have been caused by a group of Leylandi trees, which have now been removed....there is a possibility that the driveway just sunk on its own though. The driveway was made 20 years ago - and the drop is about 8 inches straight down from the sewer man-hole cover. A 2 foot by 6 inches hole has appeared next to the sewer man-hole cover...and the drop through the hole is about 18 inches.

I'd like to know if it's better to knock out the top layer of bricks from the sewer to level the driveway...or build it up to the level of the sewer ie how it was in the beginning.

Thanks

[84-1089053830]

I'd be more concerned as to why the worst of the subsidence seems to be localised around that manhole. I know that <spit> Leylandii are a menace because their shallow, fibrous roots parch the ground and can, in some cases, cause subsidence, but 8 inches??

I'd be having a look down that MH to see if there's a broken pipe somewhere that's allowing the backfill and/or sub-grade to trickle into the pipeline and so cause all the problems.

When it comes to re-surfacing, the rule is to make the drainage fitting suit the surfacing, not make the surfacing suit the fittings. The levels and falls of the surfacing are the important thing - you can adjust the level of MH covers, Stop Tap boxes and gully tops to suit without impeding the actual drainage of the pavement.

[99-1093880115]

I assumed that the worst of the subsidence was round the sewer man hole....because that's made up of bricks similar to a chimney stack.
Therefore less likely to drop...as opposed to the tarmac already in place, with less substance...which has dropped.

Thanks for the confirmation I could just knock a layer out of the sewer brickwork.....I thought there might be some daft regulations saying that the sewer had to be a certain height

[99-1093880115]

An update on the subsidence problem - I had a tarmac company round this morning to give me a quote for 'fixing' the driveway and re-tarmacing it.
Unfortunately, because they weren't able to guarantee the job because of the subsidence...they wouldn't be able to do it.

I pointed out that the subsidence was thought to have been caused by the Leylandi trees, which have now been removed - but he still said he wasn't touching the job.

I'm dissapointed because I had hoped it was just a case of getting a few quotes and choosing a company/ driveway surface....I hadn't realised that it would be difficult to get someone to undertake the work.

[84-1093879891]

I'm surprised they didn't want to quote, even with the subsidence problem. Have you asked any other companies?

[99-1093880115]

No - I chose a local company as I just wanted a rough price...and didn't want to get someone from 20 odd miles away when I might not go the re-tarmacing route.

I noted your comments on my thread re rough cost estimates that tarmacing a small area was probably more expensive than block-paving....and block-paving does look a lot nicer.

It didn't occur to me that people might not attempt the job.

[84-1093879891]

Get a few prices for block paving then, and see if they baulk at the subsidence problem. To my way of thinking, the prep work that's needed for block paving should expose whatever is the cause of the subsidence and rectify it as part of the works, so, overall it could be a better option.

[condor]

Have been given a quote of £250 to re-tarmac the drive and for it to be built up with type 1 fill. They'll be a slope and no guarantees on the work done.

Seems really cheap to me.

[condor]

Thanks for the confirmation I could just knock a layer out of the sewer brickwork.....I thought there might be some daft regulations saying that the sewer had to be a certain height

This wasn't an option in the end because there was a concrete head on top of the bricks.
Thought I'd mention it in case other people have a concrete topping.

[Tony McC]

You don't get owt for 250 quid - back in the mid 1990s it used to cost me more than that to send out a blacktop gang for a day, and that was before paving for any materials!

It can only be a rip-off.

[condor]

It certainly sounds too cheap and a bit dodgy.

But I couldn't really see how I could be ripped off - they do the job and get paid....or they don't .
I can live with the idea that the materials are surplus to requirements for another job they're doing down the road...and rather than waste it - we'll be doing each other a favour. Don't forget that reputable local company wouldn't even give me a quote.

I suppose it could all break up after they've laid it and left...perhaps with the winter frosts or heat of the summer.
I don't know....but isn't the relatively small sum of £250 worth taking a chance?
or am I being incredibly naeive? and this is the oldest con in the game?

[steve r]

My nephew had a "contractor" knock on his door about 6 months ago offering to fill in the potholes in his drive for £60 each.
They were doing a job up the road etc.
He thought it would improve things until the job could be done properly.
When he returned home from work the following day the whole drive had been coated with a skim of tarmac.
Later that evening the "contractor" returned and said that to do a proper job the whole drive had to be resurfaced.
That'll be £6000 please!
To cut a long story short the police are now involved as threats have been made against his children.

caveat emptor

(Tony how do you get the italic thing to work?)

[condor]

Thanks steve r

The person who did the quote isn't a traveller - but I have those stories in the back of my mind.
Have involved the next door neighbours (they're tenants)...but the landlord is quite a tough nut
The joint work for both mine and the neighbours was quoted as £500 (£250 each).....and I 'll feel a lot more comfortable if the bruiser next door is involved