A Better Monument Specification

I'm no expert, but those don't look that bad to me. I think the wider base is good. I see they included rebar in the "post". It would seem that a round post might be easier to pour into a cylindrical tube, and possibly a better design. I think round is nice to get more stability per yard (or whatever) of concrete.

I like the "deep-rod" monuments that NGS uses, the best, driven to refusal. They are more expensive I think, especially depending on how deep 'refusal' is.

The deep rods with greased sleeve would appear to have excellent vertical stability, but I've always wondered about their horizontal stability. Just seems like it would be a lot easier for roots or uneven ground settlement due to animal burrows to shift a little rod than a big chunk of concrete. Just polishing the grime off a cap on a rod to find the center dimple wiggles it enough to give the feeling of instability.

with respect to height of top relative to grade, i would recommend flush, or better yet, somewhat buried

Brad,

What is this for? Citywide benchmarks, control for a bridge, earthquake monitoring;-),

Who is it for? Depending on who it is, you may be able to convince them on the type of monument to set based on WHAT it is for.

Are these benchmarks or H&V control points? If they are labeled as BM on the disc, I would not stamp the N&E on the cap. That data can be published and researched by others if they need it. If they are going to have the N,E on them, I would label them as City of XXXX Control Point or whatever they are for.

Is there enough room for you to stamp the N, E, EL and put your number on it?

Are there any structures in the different BM areas that you could drill into and set just the cap? IE, a retaining wall on a concrete irrigation box or the like?

N, E, Elev is pretty useless without the metadata. Can you get enough on the disk so someone later can tell which datum, and whether it is true SPC or some local system?

> The deep rods with greased sleeve would appear to have excellent vertical stability, but I've always wondered about their horizontal stability. Just seems like it would be a lot easier for roots or uneven ground settlement due to animal burrows to shift a little rod than a big chunk of concrete. Just polishing the grime off a cap on a rod to find the center dimple wiggles it enough to give the feeling of instability.

Bill,
What you say does sound sensible. All I can say is, we have had pretty good luck checking first-order elevations between deep-rods. (Well, maybe not "all" I can say). They are being set at bench marks by his specks so I imagine the vertical is the primary importance. If you tie to them horizontally, I question whether a slight fluxuation of the rod will affect your results to a noticable amount. Also the NGS has pretty good and well-tested standards. They seem to be a fairly meticulous bunch of scientists that look at everything from a lot of different angles, and run their work taking everything they can possibly think of into account.

I have a little less trust in the concrete, but I suspect getting below frost line and possibly letting them cure through a winter and summer cycle might help a bit as well.

Again, I am no expert.

Tom

I agree-never a good idea to put coordinates and elevations on a disk. Remember, these are only estimates, and can and do change with better data, more ties, datum changes, etc.

I always liked this monument:

> I always liked this monument:

Geez John, I think you may be onto something.

Maybe the Egyptians were just trying to build a more stable Control Point.;-)