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Posted: Sun Apr 17, 2005 6:56 am
by chips
Hi,
I have a drive sloping 9 degrees over a 10M length. I understand the requirement for intermediate restraints (IR) having FULLY read the site information!
However although one side of the sloped drive and both ends (top and bottom)will be restrained with edge blocks set correctly; the right side flanks a second drive area at a different level (approx 450mm lower). I plan to 'blend' this into the slope with a gentle drop to the lower level. Effectivley I have a drive 'L' shaped with one section at a lower level.
However if I include an IR every 3M although I will be able to tie it to the left side edge the right side 'blends' to the lower drive. This would look rather odd with a IR stopping at the start of the blended area.
I have some pics that I took but still trying to figure out how to post them!!
Any help will be greatly appreaciated
BR
Chips
Posted: Sun Apr 17, 2005 7:13 am
by chips
Posted: Mon Apr 18, 2005 1:39 pm
by Tony McC
It seems to me that the easiest option would be to extend the edge course through the paving and link the restraining courses into that.
Here's your original plan...
... and here's my suggested "fix" ...
... would this be possible?
Posted: Mon Apr 18, 2005 5:47 pm
by chips
Hi Tony,
Thanks for getting back to me - its a great help being able to ask someone these questions.
Regarding your solution I had thought of the possibility but was concerned that it would show two distinct drives with the 'blended' area even more apparent. My aim with the design I chose was that it looked one autonomous drive.
Checking around the neighbourhood with similar slopes not one has an IR and yet show no creep. As you can tell I dont want to use IRs but I also DONT want the bricks to end up in a snotty heap in the road!
Looking at my pics that I posted do you think the slope requires these? I plan to lay a subbase of 150mm type 1 well consolodated. I also plan to lay a geomembrane under the subbase. On top will be the sand which I also plan to compact prior to laying the blocks.
Two further questions:
1. On the geomembrane the manufacturer suggests laying below the sub base AND between subbase and sand. Is this just a subtle way of selling more membrane or is it reccomended!
2. I have a large area and no mates(!) so its just me to lay. (They are willing to drive the digger though!!). Do you just lay sufficient sand to complete one days activity or do you lay the complete base?
Thanks again for all your help
Russ
Posted: Mon Apr 18, 2005 9:49 pm
by Tony McC
9 degrees over 10 metres is ... is .... is ... err ... sin 9 = opposite over hypotenuse ... oh shoot! ... just over 1550mm, which is around 1 in 16. Mmmmm.
You could get away without IRs as we'd normally spaced them at 6-10m metre centres, so, taking the upper end of that range would obviate the need, and 1:16 isn't a crampon-wearing gradient.
There are ways and means of creating "invisible" IRs, depending on the block type and pattern being laid. They are very simple to create if you're using a tumbled block and/or a transverse coursed pattern.
On to your Qs...
1 - whaddya think?? It's to sell more membrane, obviously! Read the Do I really need a membrane? FAQ
2 - lay all the sub-base in one, but spread and screed only as much laying course material (sand) as you can cover with paving in around 2 hours.
Posted: Tue Apr 19, 2005 6:15 am
by chips
Thanks John!
Invisible IRs I am intrigued been throught the site including the forums and Archive and no mention. I will be laying herringbone at 45 degrees what invisible method is available for this pattern?
Can you post a pic or diagram?
SOHCAHTOA that famous Block Paving Chief!!
Thanks for your help
Russ
Posted: Tue Apr 19, 2005 6:17 am
by chips
Oh! one other piece of data the blocks I will be using are Charcon 200 X100 X 50mm
Cheers
Posted: Wed Apr 20, 2005 5:31 pm
by chips
Can anyone give me any data on these invisible intermediate rerstraints?
Thanks in advance
Chips
Posted: Wed May 04, 2005 11:34 am
by Tony McC
I've been away, hence the delayed response.
Using a 50mm deep block, the simplest way to create an invisible IR is to get hold of a handful of 60mm or 80mm block, bed them onto concrete and haunch them just enough to hold them in place without affecting the adjacent 50s, a bit like this....
...obviously, with a 45º pattern, it can be a bit tricky, and it is made even more of a challenge depending on whether the IRs are running transverse or longitudinal to the chevrons....
....with a longitudinal IR, it's just one course, but when the IR is transverse, it's better to "double up" and embed two blocks to create a more substantial IR.
Posted: Wed May 04, 2005 1:27 pm
by chips
Great Tony
When you see the solution as aleways it obvious but its nice to have the confirmation from the expert!!
The last thing I want is for the drive to end up like a rutted track.
I have been told that this 'project' should have been taken on by a proper company so I have something to prove!!!
Many thanks
Posted: Wed May 04, 2005 2:08 pm
by Tony McC
Keep us informed about how you're getting on! 
Posted: Wed May 11, 2005 1:17 pm
by chips
What a great site, so much data and support!!
Made a good start over the last weekend and I am now down to the subgrade and reduced this to 250mm below finished pavior height(which has been compacted with a vib plate). I am amazed how many skips it took!!
I plan to use a geotextile between the subgrade and the subbase as per instructions and picked on one of the links (HY-TEX). This is arriving Thursday. Discussing this with one of the other geotextile companies this was their reply-any comments?
"One aspect of compacting the subgrade could be to resist drainage & cause ponding in any deformation at the sub-base/subgrade interface. This could contribute further to the deformation. The 1:16 fall will aid drainage along this interface.
A geotextile, as I've said, will act as a filter/separator. These products will not, generally, prevent deformation caused by settlement or by trafficking e.g. channelisation rutting common with block paved installations (running/parking along the same line). So, if there is any rutting then the geotextile will just follow the deformation but keep the sub-base & subgrade from intermixing.
The weed suppression materials will be OK if they are substantial enough - aim for 100gsm or thereabouts.
Alternatively, installing a geogrid at the interface will provide reinforcement to the sub-base to resist deformation & also prevent the stone being pushed into the subgrade. Have a word with Tensar Int in Blackburn - 01254 262431 (my old company). Their grids are 50m x 4m but 1.5 to 3 times the geotextile price. You may be able to buy a roll locally from their civil engineering"
In general I have had so many different replies but sticking with the reccomendations with this web site. I figure that £50 of membrane is small potatoes which will not accentuate any rutting but may actually reduce/eliminate it
Look forward to your reply and when finished I plan to post some pics (before rutting takes place!!!!!)
Russ
Posted: Sat May 28, 2005 4:10 pm
by Tony McC
Basically, what you've quoted above is correct. A geo-textile can improve an iffy sub-grade be preventing the loss of sub-base material, but if the sub-grade is seriously weak and prone to settlement or movement, then a geo-grid would be a better choice. However, given that the loads imposed on a typical residential driveway are pretty minimal, the number of projects that would warrant the use of a geo-grid rather than a geo-textile are few and far between. In my opinion, if we encountered a serious problem with the sub-grade, I'd rather dig down and build-up with sub-base interleaved with geo-textile, but, obviously, there comes a point where no amount of digging down is going to sort the problem, and so a geo-grid would be valid.
As mentioned in the quote above, though, geo-grids ain't cheap, and they ain't easy to obtain. You can't buy, say, 50m² from Travis Bloody Perkins: they tend to come in BIG rolls of 225m² (50 x 450m² (100 x 4.5m) and so, unless you're a a civils contractor, or are pally with a civils contractor, getting the few square metres you need for a residential driveway is a major problem.
Compaction of the sub-grade prior to placement of a sub-base may cause problems with subsequent drainage, but, in the vast majority of projects, the sub-grade is either adequately free-draining or the compaction is simply a matter of tightening up the top 25mm or so of material loosened during excavation works. If there was a genuine concern regarding free drainage of the sub-grade, then this is better address before placing any sub-base material. It could be that a horiozontal drainage composite (sandwich or waffle drain) might be needed, but again, for this to be an issue on a typical residential driveway is exceptionally rare - I can think of only a couple of instances in the past decade.
It's impossible to give advice that would be suitable for every project, but, in general, most residential block paving projects do not need a geo-textile or a geo-grid, but including one (as long as it is a genuine product and not some crappy roll of polythene as has been suggested previously) can't do any harm in the long term to pavement performance.
I know it's late, but I hope it helps.
Posted: Sun May 29, 2005 1:44 pm
by chips
Thanks Tony
As I said it all helps and thanks for the site.
I put one down working on the basis that it was only fifty quid which in the scheme of things was a small cost.
I have laid the edging and in the process of putting down the bedding sand and first layer of blocks.
The problem is I work in the States a lot and coming back to work on a drive, what with the jet lag is seriously affecting my enthusiasm.
Not helped by the 'expert' driveway contractors who live in my road. Questions such as:
1. You shouldnt do it like that
2. Still got a few bumps
3. Or the best one ' Interesting approach I havent seen it done like that before'. In my line of work thats what we call the 'smiling assasin'!!!
Best regards
Russ
