Driveway - concrete slab heave

[felixcanis]

Have a concrete driveway - probably laid when the house was built in 1975. One slab has a number of large, deep cracks running in various directions across the concrete and some parts of this are lifting. It needs replacing, but we won't do that until we find out why the current slab has gone cracked and wonky.

We know the house drainage system goes under this section of driveway to join the main drain as there is a manhole cover in this slab. We have had a few blockages both at that point and further up the system nearer to the house. We have cleared these with rods after digging out soil and stones we found in the chambers. We don't put anything dodgy down our drains - no fat, wipes, paper hankies etc - old habit gained when living at our last house which had a septic tank. We have no idea how the soil & stones get in.

We also know there may be a problem with tree roots. We had 2 large conifers and an ash tree removed from a raised bed which is next to the slab - no idea why the previous owner thought planting trees in a small raised bed was a good idea... The conifers were cut down in Sept 2018, and the Ash in Nov 2019. Neither had stump grinding. We had hoped the small amount of heave would get better after the tree removal once the roots began to die back.

We know the 'lift' has increased since last year. What we don't know is where to start - with a driveway contractor or a drain survey?

Also - are there any gotchas in getting driveway quotations - any common ruses to get customers to do more than necessary?

Thanks
FelixC

[Arborbridge]

Also - are there any gotchas in getting driveway quotations - any common ruses to get customers to do more than necessary?

Thanks
FelixC

First find a recommended firm. I found a local one man band + helpmates who is currently re-laying my drive. The way I found him was to knock on doors of driveways which had recently be done, using the Portillo gambit "Excuse me, d'you mind my asking...?"

If you are lucky, this will bring forth a reaction pointing to Mr X being reasonable and reliable, as in mycase. I doubt whether there's much difference in cost, but I'd value a genuinely good recommendation above price.

As for getting doing more than necessary, just see what other people have done and if you like it, make up your own mind. If you've found a straight talking, reecommended, drive man who looks you in the eye with not too many words a minute, then take his advice. Befware shifty fast talkers.


Arb.

[bungeejumper]

Actually I think I'd start by getting the drain videoed. Once I'd rodded out as much rubble and stuff as possible, of course.

Tree roots will show up clearly. But is it also possible that the ground itself has heaved over the years? That wouldn't be unknown in some places. Any likely watercourses that might also be responsible?

ISTR that you're well north, but even down here in softy Wiltshire we have three artesian springs running through our garden, and the roadmenders can't keep up with what they do to the road sub-surface outside.

BJ

[tikunetih]

If you suspect tree root ingress I'd have a camera survey done - you don't want to discover you've a problem a year or two after you've fixed the drive.

But.... the concrete cracking in that drain area may simply be that, unlike the rest of the concrete drive that was (presumably) poured on undisturbed earth, this section was poured in an area that was previously dug up for the drains to be laid; so, if that excavated area wasn't back-filled properly, then over time the ground will have settled and any (un-reinforced) concrete slab sitting above it could crack under the strain. So that may be all that has occurred.

[Howard]

I have found Checkatrade to be a very good source of reliable contractors. Over recent years I've used three contractors found on their site for different projects and have found their reviewers' comments accurate. After completion, Checkatrade checked my positive reviews for each of the contractors used to ensure that I was giving an independent view.

I looked up "drainage inspection" out of interest and there were a number of local firms who scored highly.

Good luck with the project!

Howard

[bungeejumper]

Going back to the trees, conifers are invariably shallow-rooted - which doesn't mean they can't disrupt a concrete slab, but which makes it less likely that they'd perforate a drain - which, in a 1975 house, would presumably have had to be deep enough?

Ash, though, is a different beastie. Formidable roots. How big/thick at the trunk was yours?

BJ

[richlist]

Tree roots breaking into drains is a myth. They never will break into a drain UNLESS the drain is broken/ cracked in the first place. In which case the drain has been leaking and washing sand/ subsoil away leaving the drive unsupported to take the weight of a vehicle.

[bungeejumper]

Tree roots breaking into drains is a myth. They never will break into a drain UNLESS the drain is broken/ cracked in the first place.

Right on the second point, but far too big a statement on the first. Tree roots will exploit any weakness they can find, and then get straight in and make it worse. But for example, a holly tree's roots are stronger than oak, and they'll bust anything, including an intact concrete pipe.

But you knew that, surely?

BJ

[felixcanis]

Re the Ash tree - it was a fairly weedy specimen as Ash trees go - the trunk was about 12-15" across and it didn't have a full head of branches and it looked a bit poorly. The 2 conifers were Leylandii -and they were enormous - at least 25ft tall and around 24" across. Our house survey mentioned they might cause difficulties with the drains but the surveyor couldn't lift the nearest manhole as it has slipped down and one end was wedged in. My OH used a lot of brute force & got it out once we'd moved in. At that point the drain chamber was empty apart from a few fine rootlets which I removed - that was in 2017.

Fast forward to 2020 and the same chamber was full of soil and stones and needed digging out.

We used to drain problems - our farm in Moray had miles of field drains, both Wavin and clay pipes. The Wavin could block with plant rootlets which needed pulling out with the screw fixing on the rods, the older clays were installed too near the surface and often were a bit squashed by tractor traffic . We dug them out and replaced with a lower wavin coil.

We're in the Yorkshire Wolds now and live at the top of the Wolds rather than in one of the villages in the dale bottoms. Lots of chalk here. Not sure what that means for underground water and/or ground stability.

Thanks for the comments so far

FelixC

[Maroochydore]

If you replace the slab make sure the contractor uses reinforcing mesh and expansion joints if the overall area demands it. I think the ratio is 30:1 so 100mm deep slab needs a joint every 3 metres.

[jackdaww]

slightly off topic -

i use limestone chippings everywhere .

easy to put down .

covers a multitude of sins

if a mess is made eg. oil spill , easy to rake clean stones around .


2/3 inches should be sufficient .

recommended.

[Mike88]

Trees will be the problem. You don't get heave if a drain is broken; you merely get a sunken hole in the vicinity of the breakage.

[88V8]

i use limestone chippings everywhere .....recommended.

Not if you want to lie on the drive to work under the car

V8

[jackdaww]

i use limestone chippings everywhere .....recommended.

Not if you want to lie on the drive to work under the car

V8

=========================

i use an old rug ....

but so little under car work is possible now anyway .

[pochisoldi]

If you suspect tree root ingressI'd have a camera survey done- you don't want to discover you've a problem a year or two after you've fixed the drive.

Fixed that for you - especially if you are planning on any kind of "continuous" covering (i.e. concrete/tarmac rather than block paving which can be partially removed/replaced)
And while you are at it, consider whether providing a duct for cable TV/fibre to the home might make sense.

[AsleepInYorkshire]

Have a concrete driveway - probably laid when the house was built in 1975. One slab has a number of large, deep cracks running in various directions across the concrete and some parts of this are lifting. It needs replacing, but we won't do that until we find out why the current slab has gone cracked and wonky.

We know the house drainage system goes under this section of driveway to join the main drain as there is a manhole cover in this slab. We have had a few blockages both at that point and further up the system nearer to the house. We have cleared these with rods after digging out soil and stones we found in the chambers. We don't put anything dodgy down our drains - no fat, wipes, paper hankies etc - old habit gained when living at our last house which had a septic tank. We have no idea how the soil & stones get in.

We also know there may be a problem with tree roots. We had 2 large conifers and an ash tree removed from a raised bed which is next to the slab - no idea why the previous owner thought planting trees in a small raised bed was a good idea... The conifers were cut down in Sept 2018, and the Ash in Nov 2019. Neither had stump grinding. We had hoped the small amount of heave would get better after the tree removal once the roots began to die back.

We know the 'lift' has increased since last year. What we don't know is where to start - with a driveway contractor or a drain survey?

Also - are there any gotchas in getting driveway quotations - any common ruses to get customers to do more than necessary?

Thanks
FelixC

Conifers are amongst the worst trees for creating ground heave. When your trees were cut down that will have created the heave you are now witnessing.

There are essentially two forms of concrete. The first is cracked concrete. The second is concrete waiting to crack. The depth of the concrete on your drive may be a cause of the cracking. It may also be cracking if there are no movement joints to allow for expansion and contraction due to hot and cold weather.

It's possible to test your drain without going to the expense of CCTV. You will need to buy or hire a couple of drain bungs. These will block the drain at two ends. Then fill the drain with water. If the water level drops dramatically it's an indication of a broken drain. If the damage is due to roots breaking into the drain it is possible to remove the roots without digging up the drain and "relining" the drain from inside. I can't give you any idea of cost as I don't use this sort of service for small lengths of pipe. I'm assuming it will be cheaper than digging the drive up and replacing the broken drainage.

Once the drainage issue is sorted you can concentrate on replacing the concrete drive. Make sure you look into the specification closely - refer to my quote above - if you don't construct a concrete dive correctly then it will from the outset be "concrete waiting to crack".

AiY

[felixcanis]

Thanks to all who have replied.

My OH is looking forward to having a play with a couple of drain plugs (apparently a man can never have too many tools) and then we'll decide about the drains.

Once that's settled we'll get some quotes to remedy the drive - the front drive is quite large and the driveway continues down the side of the house and extends through the garden to the garage at the rear boundary. All of driveway is concrete and as we don't want the expense or upheaval of having the lot changed, I expect we'll get the broken slab replaced with concrete. Unless I can persuade my OH that the front of the house would look better with something different...

Thanks again for the input, helpful to get a collective view on things.

FelixC