for background I’m pretty new to model building and skipped the “surveyor” step in my career path so i’m asking this question to fill in some missing fundamental knowledge.
it’s come to my attention one of our model builders is building their jobs finish model per engineer plan, then once cut sheets are provided he is rebuilding his finish grade models off cut sheets to better match the stakes in the field.
I’m trying to better understand why this is necessary? Assuming you’re within a .01’ of the design elevations shouldn’t the stakes match the design barring any blunders/busts on the engineers side of things? Wouldn’t using cut sheets theorhetically decrease model accuracy? I guess i’m missing the benefit of cut sheets and how others utilize them, or do you even utilize them?
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What’s a cut sheet? Lol. The only reason I could see for rebuilding the model as described is to compare the staked information with the proposed Finish Grade model. Why does his model need to match the stakes precisely?
Hey Grady,
In my experience the reason would probably be to account for a variety of factors that I will detail a bit for you. One reason to make changes after staking is because there may be design oversights that required field adjustments and he wants his model to reflect those changes. A common area where this typically occurs on most jobs is anytime you need to match into existing. Existing match details are typically wrong when measured in the field.
Another reason you might want to make a change is around tie slopes, if the existing surface model used in the design was inaccurate then this can adversely affect your tie locations depends on how accurate you want to be really
The final reason I will outline here is if you are tracking contract quantities for the project, then changes in the field layout will of course affect the final quantities or the As-builts, this could also be a reason for making the staked changes to your model so that it represents an As-built model. As-built models aren’t common place in the industry to date, but I expect that to change over time.
Hope that helps,
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Not how I would do things. We build per the plans. Not infield missteps. If you can’t build it per design or per revised design…maybe do something your better at. Your just making things less like the plans and building a larger bust into the finished product
Thanks shane, my understanding is the surveyor is adjusting things in the field when doing hand calcs, whats confusing to me is… Contractually we’re only obligated to build per the plans, not the stakes. Obviously the assumption is the surveyor will be calling the engineer to update him on any busts/adjustments and revise the sheets but until that happens it seems like a ton of extra work to go back and adjust the model for this purpose. Our finish grade models are only encompasing paving/curb/sidewalk in this instance.
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Yeah its hard to say without talking to the guy, I was just throwing out some possible reasons to why he might be doing it. Could be unnecessary, but there are instances where you might want to adjust your model to match what your seeing in the field. Hard to really say without more detail.
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Much appreciated thanks, it definitely helped understand some things better, though i’m curious how doing so could impart more error into the model.
Yeah I guess I would say that error tends to be relative to a number of variables. things like survey practices, control survey quality, length of time from design to construction to name a few.
If the plans say your top back of curb elevation at the connection to existing is 103.2 but in the field it is measured at 103.5 which is correct?
I would argue that you should use the 103.5 rather than 103.2 assuming you have no other issues causing the error. Documenting this in the model would probably be necessary in this instance because we have to match existing and probably need to adjust the difference over an agreed length to make sure we don’t cause drainage issues.
Just a single scenario but a common one, just because a designer draws it up doesn’t mean it will work in the field. However, you could argue that these adjustments should be done in a different file so that you keep the data sorted. Without knowing the particulars it is really hard to say whether the practice is correct or not.
You may be putting in pipe and realize that at the plan elevations there is a conflict with another utility, which would probably warrant a change. If you are running machine control on the trench you may want to update the model to help the operators.
If its me doing the survey then I am more comfortable adjusting the model to match field conditions but that is more anecdotal than anything.
- important to note my experience comes from the DOT where I had the contractual authority to make changes, but sometime changes occur from a contractor’s surveyor’s recommendation. And not all changes to the contract are handled through plan revisions, sometimes its just a letter or a handshake in my experience. If I was in charge of a project and wanted to waste material on a slope to flatten it out and use excess material, it probably wasn’t going back to design…
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