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Georat

What's The Probability?

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What's been your experience in finding a benchmark that was placed before the construction of a shopping mall? Today I went out looking for Benchmark KR1111, only to find myself standing on top of the coordinates in the southwest corner of a shopping mall's asphalt parking lot with no benchmark in sight. So for your surveyors, contractors, subs, and experienced benchmarkers, what has been your experience on how carfully contractors and their subs preserve the locaion of existing benchmrks and what's the probability of finding one that was placed before the construction of any new structure or complex?

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You cant go by the coordinates for ones like L 323, they are only approximate for true benchmarks like this one. Look for the several objects, such as fences, in the description. If you cant find any of the reference objects within a quarter mile or so up or down the road, then its likely that everything was wiped out when they built the mall. Unless you can find and positively identify at least one of the reference objects, its not possible to make a determination about the benchmark, because you cant be sure where it is or was. Many have survived construction and are just below the surface, but many others have been lost this way.

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1. Probability near zero. In 100 'benchmarks' I haven't seen one yet that appeared to enjoy a preserved location.

 

2. The disk KR1111 is a vertical control mark and its coordinates are not going to be accurate. The clue to this situation is the line under the coordinates where it says that the "location is SCALED". So, like survey tech says, if it is a SCALED one, the only way to find it is with the verbal instructions and the landmarks mentioned.

 

3. With a mark that hasn't been seen since 1969 and is in the suburbs, but with rural landmarks in the description, the probability of its existence (and findability) is even closer to zero. The old survivors seem to be where change is slow, either way out in the country, or in the downtown area.

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To answer the question of how well the contractors and their subs preserve the location of the existing benchmarks: They protect them as well as they are told to.

 

Early on in any construction project, a surveyor maps the existing conditions of the proposed site. That map of those conditions then goes to the civil engineer so the project can be designed. If, on those design plans, a benchmark (NGS or other) is identified and noted 'to be protected', it will usually be protected and remain in place to be found again.

 

If it is identified and noted 'to be removed and replaced', that is what happens to it. It is removed prior to, or during construction, and then replaced in some fashion at, or near the end of the project by a surveyor. The exact mark may not be replaced, or it may not be replaced in the exact location, which is why it's important to actually view the benchmarks and view their inscriptions to verify that you truly found the mark you were looking for.

 

If the mark does not get identified prior to construction on the plans, it's as good as gone if it's in the way. The guy on the bulldozer isn't being paid to tip-toe around small, shiny objects. His job is to clear the site, and his dozer doesn't know the difference between a rock or a benchmark or a spotted owl. Whatever it is, it's in the way of progress... move it.

 

Sometimes if they are on smaller sites or on private property, a surveyor or engineer may never be called in and the owner may not know that it's there. The owner just want the property cleared, ...and there goes the benchmark.

 

Along with surveyors, civil engineers and most grading and building contractors know the value of a benchmark. I was on a job a few years ago where the grading supervisor called me to look at something that he thought might be important. It was a USC&GS cap set in a concrete post, that his earthmover driver had seen. We were able to mark it and let the crews know it was there and protect it. Most times the engineers and contractors will go out of their way to protect them. That can't always happen, but it would in a perfect world.

 

Keep on Caching!

- Kewaneh

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