I need to place some horizontal control markers onto a steeply sloped hillside with topsoil underlain by "highly weathered granite" as described in the geotechnical report. I will have to go through 3-10 feet of topsoil before I can reach this stable layer. I was considering using the extension rod type monuments that are driven with a jackhammer and was wondering if anyone has used these for this type of soil layer. The soils report indicates that this "highly weathered granite" should be "easily rippable to moderately difficult to rip with a D9 Catipiller with a single shank ripper."
Does anyone here have enough experience with extension rod monuments type monuments (aluminum or stainless steel) to know if they are strong enough for this type of application?
If this is not acceptable does anyone have any other recommendation for this type of site? This a remote radio station, access is very difficult and I would prefer to not use concrete for this project, which wouldn't work well anyway considering the thickness of the topsoil layer.
Please advise.
I would caution you not to expect horizontal stability on steeply sloped soils.
http://tidesandcurrents.noaa.gov/publications/Setting_a_NGS_3-D_Monument.pdf
I don't have experience with your particular situation, but I do have experience with driven rod marks. It seems to me that you can pretty easily penetrate the weathered granite (which sounds like it might be similar in character to compacted decomposed granite) with the rod, but that the steeply-sloped topsoil is going to be a problem. If you have 3 to 10 feet of rod sticking up out of stable material, it's going to get bent by movement of the topsoil down the slope. The rod cap might look pretty good , but its position might change radically from the one it occupied at the time of installation.
If possible, you might want to opt for simpler monuments (something that's inexpensive to buy and install), reference them to control marks in nearby stable locations, and note on the mapping product the likelihood of monument disturbance along with the stable references.
> I need to place some horizontal control markers onto a steeply sloped hillside with topsoil underlain by "highly weathered granite" as described in the geotechnical report. I will have to go through 3-10 feet of topsoil before I can reach this stable layer. I was considering using the extension rod type monuments that are driven with a jackhammer and was wondering if anyone has used these for this type of soil layer. The soils report indicates that this "highly weathered granite" should be "easily rippable to moderately difficult to rip with a D9 Catipiller with a single shank ripper."
>
> Does anyone here have enough experience with extension rod monuments type monuments (aluminum or stainless steel) to know if they are strong enough for this type of application?
>
> If this is not acceptable does anyone have any other recommendation for this type of site? This a remote radio station, access is very difficult and I would prefer to not use concrete for this project, which wouldn't work well anyway considering the thickness of the topsoil layer.
>
> Please advise.
If a D9 has moderate dificulty ripping the granite I seriously doubt that you will penetrate it with the rod. My guess would be that you will get the 1'/60sec refusal as soon as you hit the granite and like the others said, it will not be very stable on the steep slope.
Thanks for all your input. I do realize that the slope will be a problem. I hope to find some outcrops in the area to be able to set points that wont be affected by the soil movement. We'll see what I find.
