In The News

[ArtMan]

Washington Post columnist John Kelly today features a discussion of benchmarks prompted by a reader question about marks set by the regional transit authority, Metro. He gets some of the details wrong, and I may shoot him an email just to be a smartass (and to let him know that a bunch of geeky hobbyists spend some of their precious time actually looking for the things). But at least some of the Post's half-million or so readers will have a bit of exposure to the topic on this freezing Monday morning.

 

-ArtMan-

[evenfall]

Aww C'mon Artman,

 

Overall I would say that the article was pretty good coming from a journalist... No offense to journalists either. This is a tough subject to tackle even for a surveyor. I would say John Kelly did pretty well. He even quoted DaveD... That is pretty good I'd say.

 

And as for the part about stainless steel rebar being driven as far as 200 feet in the ground, that is true, and plausable. Today's geodetic survey marker is a brass disc attached to sections of rebar which are driven into the ground until they reach what is called refusal. Refusal is when the bar stops going into the ground. If you attach lengths of these rebar together and keep driving until it stops going into the ground any further, which means how ever far that is... 200 feet is a long way but it isn't impossible. These are a different kind of station than the old concrete monuments that many are used to seeing, But it is a very very stable station by comparison.

 

There are a lot of factors that can cause the stability that we would like to have in survey marks to be found lacking... One of the ways these rods driven to refusal do is to go well below the surface so at to avoid the factors that affect the surface. At the surface, these survey markers sort of borrow from an old trick that the pile driver crews have used for years. A sleeve is placed over the rod which is greased so that surface movement from things such as frost heave and such will not affect the stability of the station. Unfortunately the old concrete markers could be pumped and heaved right out of stability by frost. This design helps solve that.

 

The things we have learned from more stability and higher accuracy as well as GPS and real time monitoring is that the earth moves a lot more than we thought. And it moves more in the western US than the east. Earthquakes, Tectonic plate movement, other forms of geological instability and so on. Welcome to the Pacific Rim. The accuracy tells us a lot!

 

I imagine John Kelly knows his readers are adapted to about a 3 minute read per story. Overall he covered it pretty well. Really Artman, Think about it... Some people do think it is geeky and pretty boring, ( I have been so counseled, yes I have, ) I'd say the three minute taste was about right! :-)

 

Happy Holidays!

 

Rob

 

P.S. For more boring geeky stuff about survey markers, yes, I did say about survey markers click Here. Of course your IP will be logged and soon we will expose your interests to the world! Bwahahaha, Bwhahahahahahaha!!!!