I'm having a hard time seeing these homeowners letting me drive mag nails in their concrete porches as these are newer 300k+ homes, even though that would be ideal. Perhaps I can do something like the yellow paint stick mark.
I will be using a digital Trimble Dini level and invar rod for this job.
Kjac must be wishing he hadn't started all this. I was about to post asking what he was actually expecting to do when his post above appeared.
Now we know the details - I had a similar job in 2008. 94 homes of similar value on a new expensive estate, mainly occupied by executives. The point about affecting appearance and resale value was a major factor. We agreed that any marks could be made to disappear when required. For each monitor position we drilled in and set a small (6mm) bolt socket such that the end of the socket was below the wall surface. We had several brackets made from 5mm. aluminium, about 4" x 4" x 2" wide. These were drilled for a tight fit on a 6mm. bolt near the top of one of the legs and then reamed out to an exact fit. The hole was also countersunk to ensure the plate really would centre on the bolt.
Each was given an identity number, so that when in use the same plate ALWAYS went on the same monitor point. When bolted on they are not tightened up, but have just enough slack to enable the plate to "self-level" under the weight of the stave. On the flat leg at the bottom you need a stop of some sort to ensure the stave always sits in the same place (in case they don't hang quite vertically). We were using old Wild invar staves, which had an interchangeable base - flat or pointed, so we glued a washer to the flat such that the bottom of the stave sat in it. The outer washer was for those points where an obstruction on the building stopped the inner washer being used. After each survey the plate is removed. We used a number of plates (8) so that those for each set-up could be bolted on without having to move plates around too much during the readings.
Monitored for three years (whilst a number of the houses were underpinned and seven were "repaired" - which means one wall at a time was taken down and rebuilt, but the builder could claim that none had to be knocked down since there were always three walls standing). Run closures were generally better than 0.5mm. We had an off site datum, about 500 yards away on a solid point.
Recommendation to the house owners, once the work was finished, was that if they wanted to hide the sockets then plug them with paper and screed over the top back to wall level (about 3mm). Then, if it was ever necessary to go back and check the sockets could be found again using a metal detector, cleaned out and re-used.
John makes another good point wind is definitely not your friend with the DiNi.
Nor the low sun...if the scope is pointing towards the sun low in the sky, it needs to be shielded. Holding a field book over it or even a styrofoam coffee cup with the bottom cut out really helps.
John Hamilton, post: 413415, member: 640 wrote: Nor the low sun...if the scope is pointing towards the sun low in the sky, it needs to be shielded. Holding a field book over it or even a styrofoam coffee cup with the bottom cut out really helps.
Or a hard hat
John Hamilton, post: 413415, member: 640 wrote: Nor the low sun...if the scope is pointing towards the sun low in the sky, it needs to be shielded.
Same with the Leica. Uneven illumination -- part of the rod shaded, part in the sun -- poses similar problems. Often twisting the rod some will allow a shot that can't be gotten with the rod directly facing the instrument. Sometimes it's taken us several minutes of trying different twist angles to get a reading. It can be pretty frustrating.
Yea, the ideal day for leveling is totally overcast, dreary, no wind.
John Hamilton, post: 413427, member: 640 wrote: Yea, the ideal day for leveling is totally overcast, dreary, no wind.
Was that the weather or the surveyor you were describing!
In really difficult conditions I've found that manual instruments perform better than digital ones - several times I've been on a job where the guy doing the checking has had a digital level and I've always finished quicker. Might be more work in the office, but when the weather is bad I know where I'd rather be spending time. I like the idea of the styrofoam cup - drink coffee, take reading. Repeat as required - certainly keep you awake.
Just describing the famous typical England weather!
Yes, I agree that there are times I wish I had an old school level when the Dini decides it doesn't want to read the rod.
Jim Frame, post: 413426, member: 10 wrote: part of the rod shaded, part in the sun -- poses similar problems
I've seen people use portable lighting to overcome this. At one time Leica may even have offered a dedicated rod illuminator. Or I may just be getting senile...
KJac, post: 413384, member: 8328 wrote: I'm having a hard time seeing these homeowners letting me drive mag nails in their concrete porches as these are newer 300k+ homes, even though that would be ideal. Perhaps I can do something like the yellow paint stick mark.
I will be using a digital Trimble Dini level and invar rod for this job.
Driving a mag nail in a porch isn't discreet. There are inconspicuous marks that can be sorted out case by case. But a potentially multi yr monitoring, with potential litigation, there are solutions.
Once again I bring up the issue of WHAT you are monitoring. I don't think a porch slab is stable to begin with. I would only consider something like a bolt or nail drilled into a vertical wall as representative of the stability of the structure, not some concrete slab porch that only has a stone base underneath.
The benchmark in the photo below may be a bit extreme (it is on the side of a Canadian Base Network Pillar), the nice rounded tip is a definite point to level to.
KJac, post: 413196, member: 8328 wrote: I'm going to be doing some settlement monitoring for a road construction project with a 0.005' tolerance. The areas to be monitored happen to be in the backyards of some understandably irate homeowners. I'm trying to think up the best way to set a point that is both temporary (leaves no trace when we leave) and stable. So far all I can think to do is make a heavy pencil mark on the concrete porches in their backyards and then note the measurements to that point from several nearby reference marks in case the pencil mark is erased. I don't trust 18" rebar not to sink in this soft ground on it's own and I really don't want to drive a longer rod to refusal when I don't know for sure what's buried below. If I have to, I'll setup the total station to shoot and locate the marks, but we're trying to streamline the process wherever possible. Anyone have a better idea?
Everybody here seems to understand the reasoning for the monitoring...I'm still trying to figure it out....What part of the road construction is supposedly causing or could cause the houses to settle?
Blasting?
Vibration compaction?
Pile driving?
Subsurface drainage disturbance?
Dewatering, pile driving, surchargeing, tunneling, rammed aggregate piers. Depending on how close to the construction it could be a lot of things or just something written into the specs to appease the property owners.
I realize there are many things that could cause settlement...I was wondering what specifically triggered this work.
Could it simply be the value of the homes and potential liability, or something more obvious like blasting, pile driving, and dewatering?
Jim Frame said: Ô
part of the rod shaded, part in the sun -- poses similar problems
Lee D, post: 413455, member: 7971 wrote: I've seen people use portable lighting to overcome this.
Wouldn't an umbrella be a cheaper, faster, lo-tech solution?
Sure... if there's enough ambient light under the umbrella for the gun to be able to read the rod.
Bill93, post: 413493, member: 87 wrote: Wouldn't an umbrella be a cheaper, faster, lo-tech solution
To date I've not had to scrub a run due to bad lighting, just futz and cuss for a couple of minutes on occasion. The rodman is already carrying an invar rod, a turning pin and a hammer. Adding an umbrella as well may be a bit much for the odd recalcitrant shot.
