Materials Man

Higher densities, better physical properties, all civil engineering graduates know this. The specification for highway works has a method specification for general soil compaction and an end of product density for special fills. Now special fills that require density measurements are generally those behind structures, with limited space and therefore limited choice of compaction plant, you can begin to understand this, especially as the structure will not move. Where do you feel serious bumps on motorways? generally at structures. So is density measurement working?

The difficulty I approach, is returning to measuring densities on general embankment fill, the method compaction (admitted as conservative in the DMRB) seems to have served us well, where is the evidence contrary to this? the specification remains the same! and is emulated in other sectors (railways) and countries.

Where are we returning to densities? well Trunk roads in Scotland, but it appears to be a fact gathering exercise at the moment, there is no end product performance. We the contractors measure densities and report against no % requirement. If this is the thin end of the wedge when density measurement is routine, and Scotland blazes the comeback of the measured soil density, then history has been lost, and productivity will be lost, waiting for someone to make a decision. Never an easy situation where boxes are not easily ticked.

This is not the time to talk of testing errors and sand replacement densities, a UK, university taught method, almost symbolised as a method to calibrate other methods. I would just say , how many other countries use this method?

No one would dispute maximum density in soil, without producing pore pressures, provides the best properties, but measuring it layer by layer in road construction and comparing it to laboratory testing is retrograde. It also raises safety issues where testing techs have to mingle with earthmoving machines. Or as I have been told when raising this issue, stop the earthworks till the testing is complete!! Try tying up a sub-contract where testing techs stop the sub-contractor desperate to work in our fluky weather!!

Perhaps the industry is not providing / evolving experienced engineers, (perhaps because historical evidence is not taught?) such that they understand by heel and eye what good compaction is.

We live in a tick box environment, we don’t need a soil density box that we had thirty years ago.

Running up to Christmas, just had company Christmas lunch, do you notice when the loud music starts the older guys head for the door? I am part of that congregation.

Anyway I am old enough to remember digging sand replacement densities in lean mix and wondering at the mysteries of comparing them to a theoretical density. Then there used to be a minimum strength, then a minimum and a maximum, then if my memory is correct, a minimum again. Whether it was the blacktop lobby or a diminishing amount of long greenfield road jobs, the good old leanmix was no longer in favour. perhaps also by then enough roads had been built and the resultant transverse cracks were apparent. Again by memory (this site is for conversation, not for me to reel off details checked and verified, thats for you lot!) so memory, was not lean mix a not allowed roadbase on Scottish roads?

I am getting round to HD 26/06 and IAN 73/06, isn’t the IAN wonderful reading? not, but as I see it trunk roads, 80MSA stuff, brings in lean mix, OK it’s HBM now and you have to design it on 365 day results, add PFA, and test beams, cylinders, cubes and any other testable shape, for creep, compression, bending strength, indirect tensile strength and tensile strength, whow. why is it engineers (them with degrees) want to test brittle materials for everything? is it because they can? Flexible materials get of lightly, or did, another post!

where was I? Christmas lunch top up happening! Oh yes back to the past lean mix road bases are in, and the only fight back the blacktop boys have is EME2, how lucky is that that a flexible material is stiff? Trust the French, and why? Well the trunk roads in France are essentially DBFOs (design build finance and operate) so the contractors control the research. Yes, the most Social (with development) part of Europe allows the market place to sort out the roads.

Ask yourself how many “developments” in UK blacktop have come from Germany and France?

Sounds like a bit of a rant, but Talisker makes you type, see what I saying, where’s the leadership is road design? lean mix good, lean mix bad, new lean mix necessary for trunk roads but test it for everything and have design parameters for year old tested specimens.

explain that to an estimating manager!

David?