What does the disk look like beneath the setting?

[+27E_20]

Just a curious newby here wondering what the whole BM disk looks like. I've seen how they monument the steel rods, but I'd like to know how the disk process works (rock outcroppings, culverts, sides of buildings, etc.) Hey one more thing- why do they consider the culvert setting "questionable or unknown stability"?

 

Thanks guys.

[ArtMan]

There are many flavors. Have a look at the website of Berntsen International, which is the leading supplier. They'll even customize one for you.

 

-ArtMan-

Edited August 6, 2007 by ArtMan

[+Trucker Lee]

Ground movement, particularly in clay areas, and the need to reset or replace culverts occasionally are reasons for considering them questionable.

[+Ernmark]

Hey one more thing- why do they consider the culvert setting "questionable or unknown stability"?

Here's a good example of what can happen after 40 years:

 

KW2131

 

I've seen some of the smaller ones acually heave to odd angles thanks to freezing/thawing..

[mloser]

Here are three pics of a disk from 1942.

The top is as you would see it in the concrete monument.

Then a pic from the side. The writing on the disk bottom is mine.

And finally the bottom. This is the first disk I found destroyed and it is currently in my possession. While disks varied over the years, they seem to have been generally like this one, with a stem of some sort and tabs that could be bent out to hold the stem into concrete. Disks from the 1960s had hollow stems and no tabs on them as you can see in this pic.

The disk on the right has a complete stem, which is hollow, with a crimped bottom. The disk on the left had the same stem but it has been bent and broken off.

 

In the 1930s and 1940s a lot of disk were set in precast concrete posts, 6 x 6 inches at the top and slightly larger at the base. The first disk above is an example of that. The tabs on the stem were bent out to hold it in the concrete more strongly. Disks set manually could also have the tabs pulled out.

 

Disks set in rocks and boulders were simply set in holes drilled in the rock and cemented in place. I am not sure what the cement was made of but am sure one of our resident surveyors can set that point straight. In olden times the holes were drilled with a hand held star drill and hammer. At some point power tools were employed when available.

 

As for why certain mountings are listed as questionable stability, Trucker Lee got it right--ground movement. A culvert is more susceptible to shift from frost heave and other things that might cause the ground to shift, since they are not large structures. Settings in bridges often have their stability as "Probably hold position/elevation well", and ones in rock outcrops, which I suppose are attached deeply to the earth, are listed as "Most reliable and expected to hold position/elevation well". It is all a matter of how likely the mounting is to shift.

Edited August 6, 2007 by mloser

[+Kewaneh & Shark]

Here is a past thread that asks the question too.

 

Bottom of marker disk?

 

Hope this helps.

 

- Kewaneh

[Z15]

Culverts are the least reliable place to set a mark. Have you ever driven over a bump or sag is the road? Chances are a culvert is at fault. Also, culvert often are just floating on a sand base, made of 10 ft sections of pipe tarred together, no footings etc and will move with the frost and the weight of the traffic over time. The headwall is built on the end section of pipe and often they will separate and become free of the main culvert.

 

I worked for the state DOT and seen many a culvert that was moving. One BM was 1 ft off in elevation, 1 ft higher because the end of the culvert was tipped up from 30 yrs of traffic pounding over it.

 

Another thing about culverts along roads, they are often replaced so a mark may not last long. We once had a US-2 project along Lake Michigan in which NOS NOAA set a lot of marks in culverts. Almost every culvert (over a period of 10 yrs) was replaced or extended in length as the road was upgraded. We had to reset every mark.

Edited August 6, 2007 by Z15

[CoyoteTrust]

So do you folks think this is the stem of a mark that is no longer there? I thought maybe it was, especially because of the rounded shape of the lighter stone around it. I looked for some pry marks around this spot but didn't notice anything out of the ordinary.

 

 

HERE is MF0844 on the geocaching web. I was riding my mountain bike on the old towpath-turned bike trail, but I didn't have mark descriptions with me (only plotted in the GPSr). The pic I took of the object was probably more than 3 1/2 feet higher than the 'road' in the description, but nature and man may have eroded/levelled this old towpath to its current elevation. Most other descriptors seemed accurate as I remember them, but, like I said, I had no datasheets with me at the site.

 

PS: Note the imprinted letters on the 'stem' in the pic.

Edited August 8, 2007 by CoyoteTrust

[mloser]

That is a PK nail, used by surveyors to mark points they use (The name PK refers to the stamping "P-K" on the top of the nail, but I think any surveyor's nail is called a PK nail now. I have a MAG nail in my desk that I got from a surveyor here at work. It is, I think, magnetic, for finding with metal detectors).

 

Without seeing the actual location I can't be sure if that was where a disk was located, but your pic seems to show a somewhat roundish area that is about disk sized that may have been. It almost looks like the nail was set in concrete in the old stem hole, and perhaps it was even set at the same level as the original disk. If that is the case it wasn't submitted to the NGS as being reset--the only recoveries are Power Squadron Not Founds in 1997 and 2002.

[+Ernmark]

..here's a few examples of missing disks w/ in-place stems

solid stem disk from the 30's (remember this one, mloser [L 4])?

 

an old USGS disk - JV1999

[Z15]

fyi

 

P K stands for the maker, Parker-Kalon

 

They are primarily masonry nails but often the favorite of surveyors for decades to the point that PK started to put a dot in the center.

 

MAG mail is another brand that came on the scene in the last 10 yrs as PK nails were not very magnetic and MAG are. We used both, whatever we could buy when we needed them and price. PK's you could usually find at big hardware stores.

 

As for the nail in the photo, someone may not have found the BM and put a nail in there for their use. This nail may be useless to anyone other then the person who set it.

Edited August 8, 2007 by Z15