The Brew Cabin

Posted: **Sun Sep 26, 2004 4:18 pm**

Part of the project I decided to undertake (hindsight and all that) is changing the path to the front door from concrete 3x2 flags (900x600 if you are that way inclined) to marshalls driveline 50 blocks. I lifted the flags and removed the soft building sand they had been laid on down to what appeared to be compacted ballast (sharp sand small stones/pebbles) I didnâ€™t dig into this so as not to disturb it. Having already set the edge blocks on concrete haunches because the new path is to be wider I wackered about 100mill of crushed stone ( Â¾ inch down the builders merchant called it) over the area. This has compacted really well and canâ€™t be scuffed up by rubbing the soles of your boots over it BUT what it does do is flex. What do I mean by flex I hear you say! Well, itâ€™s like this. Place your foot flat on the floor and exert downward pressure,the crushed stone gives slightly in an area bigger than your foot but returns to its original position once you relieve the pressure. This is not all over but nor is it just the odd place.

Iâ€™ve tried giving it a wackering it will never forget and have dug down in a couple of places about a foot and have found granite chippings, I donâ€™t know how deep these are but it didnâ€™t appear to be anything trivial, covered with soft clay and then the ballast layer I originally exposed.

The old flags had been down since the house was built nine years ago with no problems of movement.(back to hindsight again)

I donâ€™t want to dig it all out if this can be avoided. Partly due to the crushed stone being pick axe material now and the neighbours will think Iâ€™m either mad, trying to piss them of with the wacker, or probably both.

Please help as soon as you can.

p.s GREAT SITE

Posted: **Mon Sep 27, 2004 11:50 am**

I'm not sure why it's flexing, as you seem to have a damned good layer of sub-base material over a capping layer of ballast and/or granite chippings. They sub-grade (the soft clay you mention) must be really plastic to allow so much flexion. The 'modern' method of overcoming this problem is to use a geo-membrane between the sub-grade and the capping or sub-base layers, but it's too late for that, now.

The way that most pavements work is that each successive layer 'improves' the one beneath it. So, you capping layer flexes less than the clay, and the sub-base flexes less than the capping....ideally, once you've got the block paving in place, although there will still be some flexion, it will be so minimal you really will have to get down on on your hand and knees to detect it.

The great thing about an elemental form of paving, such as blocks, is that, if there continues to be a problem, you can lift them up, sort out the problem, and re-lay them withoput anyone knowing. So: I'd say carry on, lay the blocks and see how it goes. I'd guess that there a 80% chance that you'll never have any more problem, and only a 1 in 5 chance of the flexion becoming a real problem that requires you to lift the lot, dig down to at least tghe capping level, and then install a geo-membrane, but let's try the simple option first - lay them blocks!

Posted: **Mon Sep 27, 2004 12:16 pm**

Tony
Thanks so much for the speed you placed your reply.
Your advice is what I was tempted to do but just wanted approval from the fountain of all Knowledge.

ps the neighbours say thankyou as well!!

Posted: **Mon Sep 27, 2004 5:16 pm**

Tell the neighbours I drink Boddies!

The Brew Cabin

Block paving sub-base - Crushed stone flexes