So those that know me personally (not in the “biblical”
sense that is), know that in real life, sadly, I am a geotechnical engineer… Cue
the theme song for the “Revenge of the Nerds” movie right now!
I normally like to keep my “scootering” & “work”
separate, as; generally no-one in the scootering world is really that interested
in things geotechnical… & vice versa…
THAT IS UNTIL NOW!
Have a look at this nice country lane way, it’s not too far
from where I live & I was actually riding home when I noticed a rather poor
piece of road way; so, I stopped to take a photo of the mighty Silver Surfer
& what I suspect is a geotechnical issue with the road at the same time
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| A nice rural road... |
I reckon (& I
have been terribly wrong at times!) that this is a road foundation issue.
I was pelting along (in a racing crouch) at the Silver
Surfers top speed … of not very much … when I noticed some undulations in the
road immediately ahead. As there was a truck coming in the other direction I
slowed down – I figured that coming off in front of someone is not a cool thing
to do.
That was when I “saw” the funny shapes of the undulations in
the road as I rode past. Note I looked & SAW something, rather than just
seeing a shape & ignoring it…
The undulations were actually cracking in the surface of the
road! They are following a large circular shape/pattern. They were dislocated
both vertically & horizontally - the geotechnical engineer reels his head
& says “Settlement cracking AND Tension cracking; indicating movement …”
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| See the cracking in the road loosely mirrors the drip line of the gum tree? |
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| Low lying area; drain beside the road... And a Vespa! |
To my mind seem to start at the drip line of the trees
beside the road.
I had to stop & investigate…
I noticed that the area is at the bottom of a very wide
valley
I noticed that there is a drain beside the road
I noticed that the area has a spoon drain beside it & it
is near a creek (indicating that water will be seeping into the soil in the
area)
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| The size is quite large! |
At a guess, I would say that when this road was constructed,
many many moons ago, the road builders have bridged over a swampy section of
ground with a thick layer of road base (to support the traffics loading on the
ground).
But, as with most “rules of Thumb”, the exception causes the
problem. At a guestimate, I suspect that the trees roots have pumped water out
of the ground in the area & that traffic above has “pushed” water out of
the area as well. As the area underneath the road is less able to absorb water
from rain due to the membrane of bitumen on top of it the other areas of the
ground have had a ready supply of water from the creek & swampy nature of
the soil. The drain directly beside the trees has continually kept the area
around saturated as well, which possibly assists the replenishment of water
around the general area. This leaves the relatively dry section associated with
the tree’s roots to settle in this manner.
Standard practice
displayed here (Just put 1500mm of fill down & keep the road going!) And
generally, you’d be right with that; but what has changed is that the trees
beside the road have removed the water from the soil underneath the foundation;
causing the soil in the drip line area to dry out.
Either that or the road builders stuffed up on other grounds
– the above is only my take on the issue & I have been wrong on these
situations before!
In my defence, I do recall the phrase of one of my lecturers
at Uni said: Water an interesting material; it has the bearing strength of
steel, but has absolutely no strength in tension. This means that water will
give way if it is not contained (think of the situation when you stand on a PET
drink bottle that is full with water & has a firmly attached lid, versus if
it does not have a lid – the former will support your weight, the later will
squirt water out over the ground & you will sink by the diameter of the
full bottle). If the water was contained under the road, the road would look
fine (as is evident elsewhere on this road)… or it could start chopping the
road up if the water is too close to the surface; but let’s keep it simple for
this example!
This phenomenon is referred to as differential settlement
& can be a huge issue – the leaning tower of Pisa is a case of this; if the
settlement were even across the base, the tower would have been a renaissance
example of poor foundation engineering – perhaps called the Sinking Tower of
Pisa, rather than the tourist draw card that it is!
This example of differential settlement was just one that I
noticed on this particular day; we see many other examples all around the place
(such as cracking in your house…) You will get this when your structure spans
across 2 different ground types (as above saturated & being dried by roots,
or the contact between a deep soil & a rocky outcrop) – unless you spend a
heap of cash on the engineering of the foundations that is!
The other issue is, it is dam hard to come up with a design that
works over such a large area; the lane is otherwise in good condition except
for this bit
Given that OJ has highly reactive volcanic clay soils, it is
to an extent surprising that I haven’t noticed more of these issues… I do
generally just notice the general crappy conditions of some of our byways!
As they say, when you are doing your licence – ride to
conditions! As I am not on a warp speed Japanese sports bike, this is not a necessarily
huge issue for me – the concept is still a good one. I do always think about
the cars coming in the other direction though…
When I did the rider training course when I was getting my
rider licence, the instructor told us about some defensive riding tips;
including the idea: I see; I think that; I will react by…
I see… (eg; a “T” intersection up ahead)
I think that… (eg ; a car may not see me approaching &
not give way to me)
I will react by… (eg, By slowing, setting up to brake &
“buffering” by moving to the right hand side of the lane)
Pretty good idea for anybody really; but especially we riders
and, a road section like this is a classic example of where you can put this
practice into play. I think the Keep Upright instructors would be happy to hear
that I WAS still using the technique!
As for those of us that are complaining about the state of
the roads here in Oz – Whilst you have a good point; think about the rural by ways
that the Silver Surfer was scooting on before he came to the big flat continent;
even though we get the poo’s with them, our roads are way better than what so
many others have!
So Mote It Be!
Leigh
By the way, I actually did something rather than just whinge
& contacted council about this small issue - I was told to drive to
conditions until they has resources to repair that little section of the road!
Serious Science type
footnote:
Maybe this was a bit of a diversion from my normal Vespa
ridding shenanigans; BUT, Science & Engineering are not solely the domains
of the “nerd”; these areas are as interesting as any other topic when presented
in the “right” manner.
I encourage all (especially children & teenagers) to
embrace science with the passion that we have for Football, Honda Cubs, Vespa’s
& Beer). Sir Isaac Newton, Albert Einstein & Steven Hawkins are quite rightly
cult figures, but there are many others out there as well, striving for
excellence in their own fields & trying to make the world a better place
through their research & daily work.
My particular field is Mining Geomechanics (That is: the
geotechnical engineering of big holes in the ground). It IS interesting &
rewarding area (for me at least).
If you are interested in some geoscience based blogs &
maybe some further reading that will provide you with knowledge; the American
Geophysical Union has some fantastic stuff here:
http://blogs.agu.org/
please check them out, they are informative without being snooty or nerdy (Dave
Petley’s Landslide Blog is one that I regularly read & is in my opinion top
notch).
