The Brew Cabin

Posted: **Sat Dec 15, 2007 9:46 am**

The roundabout near where I work (J9, M27) is being widened to accommodate a fourth lane, being intrested in this sort of thing has lead me to having a good look when driving or walking past. However, what they are doing doesn't make sense IAW what I was expecting.

They have dug down 6' where the new lane is going, shifted any pipes/cabling (gas, street lighting, traffic control) either further into the roundabout where possible or buried below this 6' dig and covered with 6" of what looks like lean mix.

Now this is the bit that really does make sense, they have now backfilled 4' (so far) of the 6' with layers of compacted crusher run. Why dig so far down? If you are going dig this far down and build up why use crusher run not Type 1? As it has natural restraint on both sides why dig half that depth and fill with concrete.

Am I being a bit naive or am I just total missing something, either way it is great to watch. Shame I can't see it from the window of my office!!!

Mike

Posted: **Sat Dec 15, 2007 10:09 am**

6' down does indeed sound deep for road construction - but it depends what the sub-soil etc was like I guess.

Posted: **Sat Dec 15, 2007 5:17 pm**

up here where they are widening the m1 (due to complete in 1 year), they have a concrete crushingplant going all the time. All the sub base is crushings, no type one in sight yet! lots of crushed glass also.
talking to my aggregate suppliers, there are supposedly new taxes coming in on type one due to its environmental impact to extract it, and process it. basically, they want you to recycle old, not dig out new. time will tell though. another government way of making money.

Posted: **Mon Dec 17, 2007 11:09 am**

To answer Mikey's question, to go down 6 feet to formation level would only take place if the ground was particularly suspect. There may be running sand or cowbelly-clay that can't be built over.

As for the crushed glass, I mentioned its use as a bedding sand in the News feature written following my visit to Civils a month or so ago. The progressive taxation of primary aggs is "persuading" us to use recycled wherever possible, and that's no bad thing, as far as I can see.

Posted: **Mon Dec 17, 2007 7:51 pm**

Thanks gents, I must admit the spoil they are removing does look a bit clay'ie, so maybe thats the cause. I guess the contractor will be a bit upset if he is on fixed price. The tarmac laying machine and a much more substantially roller arrived today. The curbs got concreted in over the weekend covered in hessian to protect them fro frost, I shall continue to watch with interest!

Posted: **Thu Dec 20, 2007 12:20 am**

SEEMS THE CONTRACTOR IS DOIN HIS BIT... BET HE GETS NO THANKS THO

Posted: **Thu Dec 20, 2007 5:12 am**

we had 10 tonnes of crushed concrete today and the guy asked us what size,you can have 75 mm stuff no fines or the type 1 35mm to fines,i must say its as good as crushed limestone and wacks down well
cheers LLL

The Brew Cabin

Major civil engineering works - Amature trying to understand