I have one site where all control nails are set into existing concrete - concrete paving, walkways, etc. Coming back to them months later and through wide variations in temperature, I consistenly set up and check in within several thousandths, pretty much just the error tolerances of equipment. Besides it being satisfying, with everything else to worry about with actual construction it makes it super simple on the mind that everything's good to go.
Then, another site, there are several control points that are best located (line of sight) in the asphalt drive aisle. Despite digging the spikes in best I can, for all the asphalt related reasons, residuals are two or three times worse than concrete points, and then of course sink and vary more through the day.
I could auger a hole, fill w/ concrete and set a bar w/ tap, but that leaves the legs. I could do the same for each of them, but seems too much. Better solution, or avoid altogether?
It's my property so no concern over owner caring what's done. In the scenario described, the whole perimeter is being regraded so a lot of grassed area is unavailable should I want to resection off of points in the lawns. I run the machines, so I know where they'd be destroyed and in those few spots, the drive aisle is best. I'd like them to last, because I'll be coming back to them for more work for a good time to come.
Do the spikes actually move that much or is most of the problem keeping a tripod stable on the asphalt? There have been numerous suggestions for the latter problem.
After standing on each leg and bearing my weight on them, the spikes get a good bit of bite, so I don't think they're slipping out sideways, like they could on a smooth floor.
I think it's just the weight of the TS on the tripod bearing down on the spikes and, over time, them sinking unevenly in the asphalt. This is the south, so the ground definitely gets hot.
Starting perfectly level, after about an hour the TS e-level could read 20" each direction, for example, so definitely moving.
Separately, I have no idea about how much asphalt expands with heat, with regards to the mag nail moving.
So I misinterpreted your words. I thought spikes were the control points and couldn't see why they would be moving so much, but you meant spikes on the legs.
Look at all the suggestions given for working on slick floors in a recent thread. Those spread out the contact suface area so there isn't so much pressure. Then the asphalt underneath won't give way so much.
I don't set points in asphalt anymore.
It is too unstable to set anything expected to stay in place because of a combination of heat, traffic count and weight and repairs.
Reference monuments, hubs and working points set under turf in the margins stay in place better and make for better instrument setup.
:gammon:
A bit of wood between the foot of the tripod and the asphalt, a sandbag over the foot, a welding umbrella. The tri ped products in the thread on working inside buildings look pretty slick.
If you are looking for roughly a 0.01' difference, try the measurement first thing in the am when there's just enough light to make sense of it all, then around 1:00 to 2:00 in the afternoon, and see what the results look like. It might make a difference depending on the length of the measurements.
How good does your control have to be for what you are doing???
Seems like it's for a project on your own property. To me 0.01 would be fine by far even if my land was a big piece which it isn't, it's tiny.
If you are concerned about the tripod sinking, just set up and throw a point off the asphalt each time and set up there.
Or resection from the 2 points to a point off the asphalt right nearby in stable ground not being disturbed that day or for a while.
And you can always put a benchmark in a tree or something to check into after your resection or traverse point to make sure the elevations were good in the asphalt still.
When I was working in Indonesia, on the island of Sumatra, just over a degree north of the equator, a road that I often drove was resurfaced with an asphalt overlay and the center-line re painted. The paint lines were straight or uniform on curves. After a few months the lines were wandering with maybe almost a foot (30 cm) deviations.
Rich., post: 379764, member: 10450 wrote: How good does your control have to be for what you are doing???
For subdivision work 0.02 in control isn't much of a concern. For construction layout of structural bolt templates it can be.
Mark Mayer, post: 379777, member: 424 wrote: For subdivision work 0.02 in control isn't much of a concern. For construction layout of structural bolt templates it can be.
0.02 within subdivision is nothing. Once it comes to retracement that precision is barely repeatable.
For Boundary and grading/improvements to a yard that would be more than acceptable to me.
Understandable it would be concern with bolt work, I just doubt he's doing steel construction with his backyard renovations.
Rich., post: 379779, member: 10450 wrote: I just doubt he's doing steel construction with his backyard renovations.
I don't know just what the OP is doing but it sounds to me like more than a DIYer building the kids a playhouse.
What is this thing called "traffic count"? Out here in the boonies, that number might well be found on one hand in many asphalt surfaces. Many county roads have numbers like 20 vpd because they don't have a lower standard number. The next one up is 40 vpd.
