Slope Stability Assessment in the field
Slope Stability Assessment in the field
(OP)
I am a new graduate with a site assignent and looking for some tips on slope stability assessments in the field. Other than geological build-up, stratification, slope materials and surface water conditions, what else would you check for stability assessment in the field? Any instability signs that I can look for?
Any help is much appreciated.
Regards,
Geo66
Any help is much appreciated.
Regards,
Geo66
RE: Slope Stability Assessment in the field
You can look for tension cracks and slip scarps along the top of the slope.
Tree trunks, fence posts etc can also indicate past or ongoing movement.
Try looking at the slope from a distance as well as close up.
If you are expecting movement during your site assignment maybe you could knock some stakes in at various points on the slope and measure their angle two or three times a day with your clinometer. Also you could install a number of marker pins over the slope and get them surveyed in. then survey them again two or three times a day to measure any vartical or lateral movement.
Hope this helps
RE: Slope Stability Assessment in the field
Stego1 provides some good advice for a recent slope failure or one that is currently moving. But, how do you begin to figure out if a slope has moved in the past, say hundreds or even thousands of years ago when much of the evidence has eroded or disappeared with time?
With all due respect to Stego1, be careful with using tree trunks and/or fence posts. All slopes, i.e. both natural and man-made, are affected by a natural process known as creep. Creep is a near-surface phenomenon, and it isn't technically viewed as a slope failure.
RE: Slope Stability Assessment in the field
It is a tough question you ask, and to answer it confidently you really need to know the history of the area. You need to familiarise yourself with the way the ground behaves in that area when it does fail. Sand, Clay, Limestone, Granite will all fail in different ways you need to look for early indications.
I don't mean any disrespect (as I found myself in a similar position when I started) but sometimes you need a bit more experience to make those calls. Try spending time with other engineers or geologists who know that area and know what to look for.
Good luck with it.
There is no such thing as gravity!!!!
The Earth Just Sucks
RE: Slope Stability Assessment in the field
RE: Slope Stability Assessment in the field
By the way, how can you tell if tension cracks are serious in nature or not?
Thanks again.
RE: Slope Stability Assessment in the field
Regarding trees etc, I agree that creep can affect these in the long term however they are still worth thinking about in the context of the slope you are looking at. The best thing to do is have a look and then think about what everything is (or might be) telling you.
As mentioned above, there is no substitute for a more experienced colleague who can pass on their knowledge. Buy them a beer or two seems to work quite well!
RE: Slope Stability Assessment in the field
RE: Slope Stability Assessment in the field
RE: Slope Stability Assessment in the field
As a graduate, you need to be exposed to as many senior guys as possible as we all have our different ways and manners in the field. Do not be scared to ask questions, even if they seem stupid, sometimes that question may have been overlooked by your geotechnical team and most importantly - use your common sense, something that is lacking nowadays.
RE: Slope Stability Assessment in the field
RE: Slope Stability Assessment in the field
do you know JinPing-I hydropower station in Sichuan,China?
RE: Slope Stability Assessment in the field
Important to this whole process is also the overall objective of the slope assessment. Are you building a reservior and want to know whether innundation will trigger slides, are you doing an excavation at the toe to build a road, are you constructing a building at the top, etc.?
If you have the information in (my) paragraph 1, I'd go to the field and look for hummocky topograpy, I'd look for tension cracks, I'd look for bent trees (notwithstanding the earlier comments) and I'd bring a hand auger to confirm desktop soil review. I'd also look at other slopes in the area and document slope grades in similar geologic settings using a clinometer (angle measuring device). If you have a 24 degree slope but other (seemingly) stable slopes are present at 31 degrees, that's good information to document. What this means depends on the geologic setting, however, as a steeper slope may be stable when it crosses bedding as opposed to when it's parellel to bedding.
Slope stability can be a challenge. But a fun one!
f-d
¡papá gordo ain't no madre flaca!
RE: Slope Stability Assessment in the field
Also, do not get into the all too familiar habit of simply looking at the subject property. If the site is on a large slide, the ground at the site may show no evidence of movement. However, if you step back and start looking at a much larger area, the signs begin to reveal themselves.
RE: Slope Stability Assessment in the field
http://www
Worst case scenario is that you have some ancient slippage plane to worry about. The maps would be a good guide, but if it's a bad area, they could recommend boreholes. Anyway, there's lots of information on the web about the subject. I would go with your local engineering office, though. Free and gobs of info. Good luck.
RE: Slope Stability Assessment in the field
RE: Slope Stability Assessment in the field
Do a thorough search of resources that might be available for your area -- geologic maps, agency archives, City or County hazard mapping... Some cities, for example Seattle, have GIS databases of historic landslides. There's nothing quite so embarassing as missing a landslide feature that has been mapped in the published literature.
Topo maps and aerial photo stereo pairs are good resources, but again interpretation requires a trained eye. Some areas have started to do LIDAR mapping, which is much more detailed and very useful for evaluating potential landslide areas. You might want to check and see if any LIDAR imaging is available for your area.
Best of luck in your study.
RE: Slope Stability Assessment in the field
I know the presenters and they are very knowledgeable.
http://www.ohiovalleylandslides.com/