Can anyone explain to me why Civil Engineers show proposed lot grades in a ÛÏnormalÛ subdivision to the hundredth? :-S
IÛªve yet to meet a grader operator that can grade a lot to a hundredth of a foot.
But technology is getting better, right? Can't the GPS controlled machines do everything these days with barely having a driver even? just punch the "go" button on the GPS unit and sit back and relax, watch tv, listen to the radio while the machine grades to the hundredth of a foot....
Measure to 0.001' design to 0.01' build to 0.1'?
FL/GA PLS., post: 338436, member: 379 wrote:
IÛªve yet to meet a grader operator that can grade a lot to a hundredth of a foot.
Everyone grades to the 0.01ft, but probably not the specified 0.01ft.
I too chuckle, but figured that we're supposed to know better. Also, many folks don't understand/or are to lazy to adjust the annotation commands within their CAD packages.
Steve
You never met a blade hand/grade checker team that grades to the hundredth?
Must draw the line somewhere. How about to the nearest foot? Or, hoof in my case.
Aim small, miss small ..
I've known a number of surveyors who don't really understand significant digits, and a lot more engineers. Back in the day when a guy would have to get out his sine tables and multiply out a number on a piece of paper to figure things out, they learned real quick when to stop carrying numbers.
FL/GA PLS., post: 338436, member: 379 wrote: Can anyone explain to me why Civil Engineers show proposed lot grades in a ÛÏnormalÛ subdivision to the hundredth? :-S
IÛªve yet to meet a grader operator that can grade a lot to a hundredth of a foot.
If a hun is too small, a tenth is too big. Rounding everything to the nearest three huns would be kind of a PITA, don't you think?
Not an engineer but...
They do it for the same reason that surveyors show bearings to the second on a 50' x 100' lot; because one's less prone to make a blunder if they pick a higher standard level of precision and work with it consistently (even when it looks silly) rather than evaluate every individual task and be constantly switching back and forth.
It's also so that the values can be used for further calculation, by the layout surveyor or the plan checker.
Probably for the same reason that I've seen surveyors submit sanitary sewer as-builts with invert elevations to the thousandth. If the number is on the sheet the draftsman will have the same number on the drawing. I do not excuse it, but that is probably the reason.
Andy
Yeah...I made a comment about significant digits earlier....but I tend to agree that you might publish values to one place greater in significant digits than you really have accuracy. If someone calculates a slope, or runs other math off your numbers, they don't have further pollution of the precision. If my bearings and distances are to the hundredth/and nearest arc-second, then I might publish coordinates to the thousandth so that an inverse will yield the same bearing I used.
to show a change in grade of less than 0.1'
I've known my fair share of Engineers over the years. I have yet to meet one who believed that operators could get tighter than 0.1' with dirt. If they were as dumb as some here imply we would be living in third world conditions...
It also depends on how the specs are written and if there is tolerance for acceptance. We make sure the contractor's dirt is within hundredths.
I may not work with lots as described in the original post, but 15% of the sub, CAB, CTB to HMA in one lot (one days production not to exceed 2,400sy), cannot exceed 0.04' of the approved design elevation or it must be fixed and no skin patching allowed. Within that lot (2400sy) if one elevation is +/- 0.06' from design elevation, that lot must be corrected. If they are fat on CTB and have to mill the HMA, they better have the required thickness or big sections come out at the contractor's cost.
Engineers are welcome to put anything they want on their grading plans....'Hunnerts' on grade stakes are for surveyors who have never slope-staked six miles of highway grade. 😉
I agree you can't grade to 0.01', but how about 0.07'? There might be cases where they have to note some spots close together maintaining the minimum slope. The plans are a guide that you try as hard as you can to achieve in the field.
Engineers deal with gradients and 0.01' is usually the minimum information to deal with and get reasonable accuracy. Channels, gutter lines and sewers come particularly to mind. There are numerous cases where a gutter line has to be defined at less than 1% slope. When it comes to rivers a gradient may be defined as 0.00023 or 0.023% so those significant digits do matter.
As a surveyor who just happens to be an engineer I regularly do monitoring well surveys. The specified precision for well casing elevations is 0.01'. From there measure downs to water surfaces are made, some times in wells only feet apart. The hydrogeologists need to know if the water is flowing West to East or vice versa.
If someone where to lay out paving stakes on a highway to the nearest tenth, your teeth would be rattling as you drove along that new pavement.
As for earth grading, 0.01' is definitely a requirement for a quality baseball field.
Paul in PA, PE, PLS
"Gee, I wish we had one of them hundredth grading machines!" General Turgidson's brother, Henry.