The Brew Cabin

assuming I was escavating for a driveway and was going to make a compacted sub-base of 150mm, is it ok for the edgding to sit on top of a potion of the sub-base of should it be the entrire depth (seems excessive to me)

Assuming its allowed are thier any significant 'gotchas' to be aware of in the set out phase of the project, for instance should I do a 75mm layer then set out the paving area and do a second layer etc.

any advice appreciated

For a residential driveway, the depth of the edge block bedding isn't exceptionally critical, and you can get away with a 50mm bed of concrete, sitting on top of the sub-base, if you wish. I prefer at least 75mm, so you could spread, level and compact the sub-base, then just scratch off 25-30mm or so where the edge blocks are to go and place your bedding concrete there. The haunching is very important, however, and needs to be at least 100mm wide to give it any real strength.

I can't follow your second paragraph - where does this 75mm layer come in to it? Are you talking about laying the sub-base in 2 layers, each 75mm deep? If so, then you're doubling the work to no real benefit as a decent vib plate will easily consolidate 150mm thickness in one go (that's several passes, not one single pass), but, if you want to do 2 layers @ 75mm, then there's nowt wrong with it.

Guess the second bit didnt make sense, I was trying to work out the best way to tackle things, but I think you mean escavate, then do the base, then scrape away the edging and get the formwork in place then do the haunch/edging pavers, then at this point remove the formwork and fill in the gap and recompact the base ? or is the small amount not a problem ?

note this drive is about 200 sqm so I dont particularly want to stuff it up, rather spend the extra time getting it right.

thanks

The sequence of events should be summat like...

1 - excavate and dispose
2 - lay sub-base and compact
3 - scratch out sub-base as required to accommodate edgings
4 - lay edging and haunch
5 - lay bedding, compact and screed
6 - lay rest of paving and finish

Formwork isn't essential for this type of work, but you can use it if you want.

Does that make sense?

yep your reply makes sense but maybe I can better illustrate my problem with a picture. Basically part of the problem stems from the fact that the house is being constructed on a slab that has ended up about 300mm above the current level of the ground. So rather than escavating I guess I am talking about building up in a fair bit of the drive.

I am trying to work out whether I need to almost create a retaining wall of concrete (300-400mm depth) until I top up the surrounding area with excess soil to raise it to the desired level.




or whether there is some other weay to approach it, my thinking was if the concrete sides dont go down deep enough the sub-base will just spil out the sides .

Any ideas on how to tackle this appreciated as that much concreate would definately dent the budget.



(Edited by lightning at 2:57 pm on July 30, 2003)


(Edited by lightning at 12:56 am on July 31, 2003)

The usual way to build up levels is to use the sub-base layer (or a capping layer beneath it) and allow sufficient spread so that kerbs and the paving are adequately supported, something like....



...and then, when you're ready. you can backfill over the spread of the sub-base and at the back of the kerb with your topsoil.

Thanks very much for the speedy reply, and on a side note, I am always impressed by your ability t pull out the perfect picture for any situation, it really helps a lot when your trying to understand things.

Next question...

How do I convert tonnes for cubic metres, i.e. I want to order the sub-base material and they suppy in cubic metres. For instance if I used your calculator and came out with 60 tonnes how many cubic metres would that be ?

Depends on the type of rock used as the sub-base material, but, for a sandstone or limestone, reckon on 2 tonnes per cubic metre.

There is a table of comparative densities at the bottom of the Aggregates page

Hit another issue, around the perimeter of two sides of the house (a rear corner) the builders have installed some drainage (it appears on the plans as a 'silt pit' if that means anything). Basically they dug a trench put some agi pipe in it and there is an inspection chamber at both ends. My problem is it looks like they have filled it with rocks(larger than crushed rock but not too huge) which I assume is for drainage, if I want to pave over it do I need to run some sort of grate the length of it, or should I be looking to connect some sort of pit up to the agi pipe. I have read through the drainage pages but cant quite match up what I am seeing with whats on the site (perhaps a fin drain is all I need with the pavers sloping away from the house?)

Agi pipe? Is this what we'd call a perforated pipe? And is it the pipe that's been backfilled with "rocks" or the ICs?

Assuming it is the pipe, then the best thing to do is to cover the trench with a geo-membrane, allowing at least a matre of spread to each side,if possible. Terram 1000 is probably the best 'all-purpose' geo-membrane to get hold of, and will be fine in a situation such as this.

I'm not sure as to the function of the 2 ICs - are they silt traps?

agi pipe = agricultural pipe = pipe with slots/holes in it.

Looks like I dont understand the differnce between a silt trap and an IC I was assuming they are the same thing, the two things I am talking about are silt traps and after the traps it connects back to the storm water drainage, but I am assuming they are there to prvent the house getting flooded hence my convern over paving over it, although I think they are just going to backfill dirt over it anyway (over the rocks)

I thought it must be Agi = Agricultural. We call them "Perforated' (just in case you have to deal with us Irish/Brits again!)

An IC is used on any type of drain for inspection and access. A silt trap is used only on Surface water or, more commonly, Land Drainage systems, to reduced the particulate load. Since the advent of permeable membranes, silt traps have become less essential, and are now most commonly encountered as 'settlement lagoons' on large highway schemes.

With regards to edging, how much can reasonably be expected to be laid in one days effort (and as a guide how much difference would having more people helping affect things) The perimeter of the job is approx 70m. Is this too much to bite off for one day , assuming I get a readymix delivered and have 2-3 people helping would it set too quickly?. Coupled with this if I did it in two sections(or more) do I need to do anything special to join them like starter bars etc, the shape is pretty much a horseshoe with the outer sides about 20m and the long boundary in the middle about 20m.

thanks again for the help, the actual start date is fast approacing so I am starting to get more nervous.

Also I have managed to locate a pedestrian vibrating roller that is available at a reasonable price that is meant to compact up to 250mm, assuming I use this to do the sub base, should I revert to a wacker plate for the sand and to consolidate the blocks after jointing as I assume it may be a little rough to use for the blocks (they are 65mm thick clay pavers though so maybe they would handle it)

thanks again

70m of edging kerb should be possible in a day. Before I was knackered, I would expect to lay 200-400 metres of edgings each day, with just one labourer helping me, so 70m would be done before 10am! What type of edging kerb are you using? Small unit kerbs take longer, of course, than longer units.

A Ped roller will be doing well if it compacts 250mm depth. A single drum roller is good for about 150mm of granular material, but you really need a double drum vibrating roller for anything more than that. And you'll definitely need a plate compactor for consolidating the blocks - you could use the roller for compacting the sand bed, but a plate is much better.

With clay pavers, it's a good idea to use a rubber sole on the base of the plate to prevent spalling. It's not a major problem, but, if you have to hire in, try and get one with the removable sole - take it off for consolidating aggregates, and fit it back when you come to hammering down the pavers.

Good luck!