Does anybody have a suggestion on what to set for monitoring a slope that is potentially moving. I'm thinking hubs, but concerned with durability. rebars?
thanks
I would set either hubs or rebars at regular intervals, possibly a grid, and locate them on a regular basis. Once you have your intial location, you can stake them out, and get real-time differences between the original location and the current location.
I'm not concerned about the procedure, I already have spreadsheets that I've setup on previous montioring jobs to generate my reports. I would just like suggestions on what type of material to set in the ground. The difference here is the previous jobs were for settlement monitoring (vertical only), not for slope monitoring (3D)
On a slope monitoring job I was involved with, we set bars & caps, first for durability and second for visibility.
I would think that you should use different items.
Place a concrete block, drive a short rod/stake and drive a longer rod/stake and take readings on any structures.
Are you thinking of durability over months, years, or decades?
Do you have frost heave to worry about?
What are the chances of someone messing with your points in this area? I.e., do they need to be hidden below the surface so no one "cleans up" and removes hubs?
Would they get driven over if below ground and thus change the elevation?
Will rebars add confusion by being mistaken for property corners?
I'd avoid hubs like the plague (at least there I work) because I would be afraid of "noise" from freeze/thaw heave corrupting the data.
> I'd avoid hubs like the plague (at least there I work) because I would be afraid of "noise" from freeze/thaw heave corrupting the data.
rebar's deformations will catch frost heave as well.
galvanized ground rods could be a good candidate
see my answers below in red
> Are you thinking of durability over months, years, or decades? months
> Do you have frost heave to worry about? yes (Pennsylvania)
> What are the chances of someone messing with your points in this area? I.e., do they need to be hidden below the surface so no one "cleans up" and removes hubs? little chance
> Would they get driven over if below ground and thus change the elevation? its a steep slope, no vehicle would be driving on it
> Will rebars add confusion by being mistaken for property corners? no
A simple and affordable method that appears to work okay:
Medium size rocks (~ 0.3m x0.3m x 0.1m) placed on a grid. Hilti nail drilled into each rock at its highest point. Leveling observation(s) on each nail.
I think that a consideration should be the length of the rod (or whatever you use). If you are concerned about shallow surface movement, then you would want short rods. If the concern is deep, then you want longer rods.
Perhaps even some monitoring of the surface and deep. For the deep perhaps dig a hole and set a piece of 12" pipe to serve as a well and then a rod at the bottom. You might be able to get some idea of stability at different depths.
How dense a grid are you thinking?
How large is the area?
How do geologists commonly make these measurements?
> Does anybody have a suggestion on what to set for monitoring a slope that is potentially moving. I'm thinking hubs, but concerned with durability. rebars?
I think that if you are asking the question you ought to go with the upgrade. Come on, rebar aren't that expensive. Shoot the lock off that wallet.
I did this using a Leica HDS-3000 3D laser scanner. It is very easy, fast and accurate. Reports are based on point cloud information and excel spreadsheets. I know, its probably not an affordable solution, buy I thought it might help.
Dave's suggestion is a good one. Need to find out what the requirements and intent of the project is. If just the surface it could only be done with marks that are only effected by that surface, if needing to find what or if anything is moving below the surface it requires monitoring each layer of material. A deep movement will effect all above it and there will be shear forces in any stable layer below that movement, all above that shear plate will need stabilization.
jud
Is the slope comprised of soil, rocks, stone, what? Is there grass/weeds? Do you want only surface movement or are you interested in differential movement of surface vs. certain depths?
I've done quite a few monitoring jobs for different reasons. For slope monitoring, rebar genrally works good. You need to talk to the engineer to see what they are looking for, and what their specifications are. Keep the engineer in the loop on what your using and what your methods are.
