Monitoring – Establishing Control
Hi all,
Long time reader first time poster. Any help will be greatly appreciated.
I am being asked more and more to undertake structural movement monitoring for domestic basement construction. I was wondering if anyone can shine some light on their recommended processes for establishing and maintaining a reliable control network.
I have tried a number of techniques and each has brought differing results. I’ve found that working to sub-millimetre accuracy doesn’t allow for the use of nails as my permanent/primary control due to the inaccuracies in holding a mini prism. I will always set-up with a resection and never over a station for this reason. Generally my set-up results for a resection using targets will be 0.5mm or less in E, N & H, and usually 1″ or less in orientation.
However, whilst retro targets are ideal, I am concerned that they do not provide the longevity of a permanent control network. I know monitoring works are only ever temporary (at least in my applications), but I am concerned that if by chance all of my targets were to be picked off, it’d be game over. I’ve tried to use reflectorless points (paint marks on buildings for example) but centring over these is not accurate enough for my liking due to the lack of cross hair/defined point. It is common for me to (cheekily I know) stick retros on peoples property without their permission – usually low down on garden walls and in discreet places. I will also use items such as the base of bollards and lamp posts and actually it is extremely rare that people remove these/notice them.
I guess my question is: do you guys utilise both primary and secondary control networks for small scale domestic monitoring surveys? Or do you entirely rely upon targets in reliable positions and on the basis of good geometry and consistency?
Really appreciate your time.
Chris
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