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christoffel

Painted Triangles

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I was wondering about some odd benchmark type things that I mainly see in Arlington County, Virginia. These are usually in the sidewalk. These are small painted triangles, less than a foot each side and all sides equal length. IN the center of these triangles is a small metal disk less than the size of a dime. These disks are like large nail heads that have been hammered in the sidewalk. Often, there are some simple initials in these disks such as P&K. I was wondering if these are private survey marks, but they do appear in public sidewalks. Or is it a state or county benchmark system? I don't know if this phenomena is restricted to Arlington County. If it is a county or state benchmarking system, is there a database to reference?

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It is Common in Construction Surveying and Staking to use a nail with a washer, and possibly a piece of colored Flagging or not, nailed to a hard surface. Different companies use their own color codes with flagging to discern what kind of work is being performed with a particular staking.

 

In the Dirt, we would set or drive a Hub, which is a 2x2 of various lengths, into the ground with a sledgehammer. Sometimes, based on the need for higher accuracy, we will set a tack in the top of that hub. Set our target instrument on the top of that hub or tack if there is one and the instrument operator would take the reading of what that hub is, as to its location and elevation. Commonly this is not arbitrary. We are placing this hub so that Constructors can establish line and grade. Once we know what the location is we can define it on a Lath, a 1/2x2x 3 or usually4 foot length of wood stating what that hub is for, and how it is to be used. We will often assign an elevation to the top of the hub, and establish what work is to be performed at or near the hub, whether it is a Cut or fill, meaning the adding or removal of soil to accomplish what ever it is which is in the Plan for the job. The Instrument Op will record this information on a Cut Sheet, and a Point sheet. The point sheet will tell anyone later that a specific Point on an engineering plan was surveyed, and how to locate the point, It will correspond to a Plan View map with points notated on the job. The Cut sheet will denote what grade elevations were found at a point, and what will need to be added to or subtracted from that location to concur with a final engineering plan. It could be any number of things such as the centerline of a road, Back of sidewalk where a curb is to be placed, a Right Of way, a Building Foundation corner etc.

 

Over Asphalt and Concrete we cannot set a hub and a Lath so a Nail, or a something we call a Mag, which is a kind of nail we can easily find later with a metal detector is set in that surface, and we record all the same things to it we would a hub, and file a copy in an office file for the job, and give copies of the info to the people building on that Job. The Builders will then engineer, and take measurements from that Hub or nail to perform the work that is needed and check it against the Hub and the instructions on the Lath to affirm that the work is finished correctly. Once the point serves it's purpose it is forgotten, and no one ever thinks about it again.

 

In any case they are usually just a temporary Bench Mark or point for something, and the only people who know are the companies who are using them to do a job.

 

Added in edit here: I forgot to add, the painted triangles may be being used as an aid to help find the nailed stations over a longer period of time. One thing that may be happening is a set of point has been nailed in a side walk or road, but only so many points were set, so as not to fill the sidewalk with nails. Then a number of different kinds of work can be assigned to a given point, and the point gets re used several times until all the work is done. It saves money on survey and keeps the sidewalk a lot more tidy...

 

Beyond this, there are a number of reasons a Nail with a washer can be pounded into a sidewalk or road, and I could be wrong about why those particular ones are. But They are Survey, and the do correspond to something.

 

Rob

Edited by evenfall

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Welcome, christoffel, to this forum and to benchmarking in general from one of several Northern Virginians hereabouts.

 

Strongly urge you to read the FAQ and browse through previous postings to get a sense of what goes on here. Many of us take this benchmarking hobby fairly seriously, and some even post reports to the National Geodetic Survey, where they will be used by land surveyors and other professionals for decades to come. Others are more casual. (That disparity prompts some conflicts.)

 

The DC area is blessed by the large number of marks, but on the other hand a disproportionate number are either lost (due to construction, development and sprawl) or are unavailable - for example, the many located on the White House grounds.

 

I think the beauty of this hobby is that you can learn a great deal - about history and the "invisible" infrastructure around you - while enjoying the challenge of a treasure hunt.

 

~ArtMan

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Route surveying 101.1

 

We routinely painted triangles on our survey marks in hard surfaces for all the reasons evenfall mentioned and more. Triangles were often used to ID a horizontal control point, but some would prefer to paint a "+" instead or just a circle. For highway work, we used the triangle to show points of intersection (PI=line changes direction) , circles around a plus sign to indicate point on a straight line or the beginning and ending of a curve (PC, PT, POT, POCT). It could have been just an outlined or a painted-in triangle with a nail, rebar or anything of permanent nature with the intent being to make it easy to find the mark by subsequent persons, be they engineers. We called it "eye food".

 

Also because it was dangerous out in traffic we would often run parallel offset lines on the sidewalks or paved shoulders, even in dirt if need be. Then do our work (mapping and property tie in) from this line. It was just coordinate geometry)

 

It just a means to mark the point to be able to find it in the future, be it next week or next year.

 

Acronyms used in our survey work for highways which we often painted near the marks.

 

PC - Point of Curvature (highway curve starts here)

POC - Point on Curve (any point of the curve C/L)

POCT - Point on the Curve Tangent (point on the tangent for curve, not on curve)

PT - Point of Tangency (curved ends here)

POT - Point on Tangent (on line between a PT and a PC or 2 PI's)

PI - Point of Intersection (2 lines meet)

Edited by elcamino

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There is certainly alot of construction and infill development going on around this section of Arlington County near the Courthouse. I am not surprised that there are so many surveying marks. The sidewalks and streets around here are painted with all kinds of infrastructure signs in orange (communications), white (excavation), yellow (gas), and red (power). I managed to get some info on the colors and some of the mark abbreviations from the web. I also happen to work near the Arlington Courthouse which used to have some public USGS benchmarks, but the courthouse was razed into a parking lot. I don't think the benchmarks are still there. They used to be in the walls of the courhouse.

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christoffel -

 

The PK nails are a particular brand of masonry-type nail commonly used around here. Some of the PID descriptions around here mention PK nails as reference marks. You can walk in and buy a box of them at a local surveying supply shop just outside of Arlington.

 

The triangle is the surveyor's typical mark. Sort of a pun in a way - triangulation.

 

Occasionally I use a triangle character in a benchmark area picture to indicate the position of a benchmark disk when I post a find here. :o

 

HV1731 and HV1732 were on the courthouse walls and the walls are gone and as you say there's a parking lot where the building was. These marks are logged as Destroyed.

 

A picture of a PK nail is on Dustyjacket's Benchmark site, in the 'Unusual department'. It is a reference mark of traverse station Elmer, which mentions 2 PK nail reference marks in the description.

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Route surveying 101.1

 

We routinely painted triangles on our survey marks in hard surfaces for all the reasons evenfall mentioned and more.  Triangles were often used to ID a horizontal control point, but some would prefer to paint a "+" instead or just a circle.  For highway work, we used the triangle to show points of intersection (PI=line changes direction) , circles around a plus sign to indicate point on a straight line  or the beginning and ending of a curve (PC, PT, POT, POCT).  It could have been just an outlined or a painted-in triangle with a nail, rebar or anything of permanent nature with the intent being to make it easy to find the mark by subsequent persons, be they engineers.  We called it "eye food".

 

Also because it was dangerous out in traffic we would often run parallel offset lines on the sidewalks or paved shoulders, even in dirt if need be.  Then do our work (mapping and property tie in) from this line.  It was just coordinate geometry)

 

It just a means to mark the point to be able to find it in the future, be it next week or next year. 

 

Acronyms used in our survey work for highways which we often painted near the marks.

 

PC - Point of Curvature  (highway curve starts here)

POC - Point on Curve (any point of the curve C/L)

POCT - Point on the Curve Tangent (point on the tangent for curve, not on curve)

PT - Point of Tangency (curved ends here)

POT - Point on Tangent (on line between a PT and a PC or 2 PI's)

PI - Point of Intersection (2 lines meet)

 

Thank you for the acronyms....

 

You might consider putting the full list in the pinned topic at the top? Just for reference for us amateurs?

 

(am·a·teur

Pronunciation: 'a-m&-(")t&r, -"tur, -"tyur, -"chur, -ch&r

Function: noun

 

1 : DEVOTEE, ADMIRER

2 : one who engages in a pursuit, study, science, or sport as a pastime rather than as a profession :o

3 : one lacking in experience and competence in an art or science)

 

Thank you,

 

Shirley~

Edited by 2oldfarts (the rockhounders)

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Hi Shirley,

 

When I read your request I couldn't help to think it was an interesting thought. But I know, as well as the others here who work in the field know that a list like that is quite an undertaking, and to be honest, rarely ever complete. I fear that if I attempted a full list it would be a big job, and never done because there are always more acronyms.

 

Construction Staking, Surveying, Engineering, and the Acronyms attached to that work is a vast and varied set. Yes there are main acronyms, and I think I will have you covered for a good many of them by the time I am done, but I want you to know that there are no real hard and fast rules, There are lots of Acronyms and they are as varied as the industry is, and written as differently as the Firm that is establishing them. So more than it being right or wrong as to the method, the trick is to know how to interpret the meanings either way. There is more than one way to write the same thing in engineering code. In the end it comes down to the reader. That is tricky, but it is how it is. They may use Acronyms differently from company to company and state to state.

 

For many who may be interested in this kind of information, I can offer you this. No matter what state you live in, it is highly likely that your State, County, and many Cities have engineering information on line. Departments of Transportation and City Engineers are likely sources. Many publications are available from them for free, as a .pdf document download for use with Adobe Acrobat Reader.

 

Here in Washington State, the Department of Transportation, WSDOT, offers a number of different Publications, and many are free downloads. One I think everyone may enjoy downloading is Highway Survey Manual. It is 204 pages, about 1.8 MB and is an overview of the Survey methods and standards they use. To be sure it is just a Guideline, and not a lock step method that even their own crews use, but is still good information. Beginning on page 26 of that manual there is a 4 1/2 page list of Acronyms that they use, but as I said it is by no means exhaustive. But perhaps this information as well as other things you may have wondered about will be a wealth of understanding going forward. I would suspect that there are other states who have similar information and publications online.

 

If you are interested in downloading a copy of this, it is available Here. Clicking that link will likely begin a download from The Washington State Department of Transportation Website, so please be prepared in advance for this in case that is not what you expect to have happen.

 

I hope that helps!

 

Rob

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