Slope Stability Test Help 1

[DylanZC]

I am a student at the University of Calgary looking for a bit of advice on what kind of tests I could do for an undergraduate thesis project.

I am looking at slope stability issues in the Calgary area, and am wondering if anyone might have some simple stability tests that I might be able to perform.

My only current ideas are to look at the unconsolidated material and run basic Atterberg limit tests on the soils and possible determine the angle of repose of the material.
I am also trying to get access to piezometers in the city so I can maybe look at the pore pressure and determine the safety factor, and any borehole data, but getting this information from the city is proving difficult.

If someone knows of any other tests that I could potentially use in a study of this nature it would be greatly appreciated.

Thanks,
D

 

[oldestguy]

If you can get out and do some field work, in-place shear tests might be looked at. For instance vane shear tests tell a lot if you can get down there via some form of boring, say a post hold digger. I used to run rough shear tests at distant places, sometimes at a slope failure or nearly so (getting there by air travel) with a spring scale with hook, going up to 100 pounds. My shearing plane was a 1 foot square board with cleats and a pulling ring. I would load up a bucket with site soil of different amounts, set it on the board and pull it sideways manually. Measure the pull and develop a chart of shear strength angel of friction if that was appropriate. With not much gear to carry out there, at least a rough idea of conditions can be done.

If you can get to a place where a back-hoe is available, much higher loads vertical and horizontal can be achieved with a calibrated hydraulic ram and a proving ring (calibrated). The hand powered hydraulic ram came from a 20 ton auto repair shop body shop. The vertical load comes from a back-hoe bucket as the resisting vertical load pushed up by a screw jack against the proving ring. Rest the bucket on a strut to keep it in one place and serves only as a good heavy resistance to upward push on it. You don't wnt the bucket to move while you do your tests and give the operator a break up there.

The shearing plane was developed with a steel box,open on bottom (made from angles with legs going out from all sides. Inside is a loosely set double 3/4" thick plywood, roughened on bottom. A steel plate sits on that for the downward force from the loaded proving ring. You use the hydraulic ram to push the box sideways with the other end resting against an earth bank. Dial gauges can be used to measure movements if you wish.

The back-hoe can dig down to where you want to test.

 

[DylanZC]

Thanks, that was really informative and I will definitely keep that in mind for the future, and thanks for reminding me of the shearing plane test, I had forgotten about that one.

This project is a little smaller in scale though, and will be taking place predominately on public lands so I wont have permits to do large scale excavations, and most of the slopes are in areas that can only be accessed on foot.

I am more looking for small scale tests, (lab or field tests) that I could do, with very limited funding. This is more of a preliminary site investigation, than a field survey that would be done by a geotechnical firm. I am hoping to get some bore-hole logs of certain areas from the city, and peizometer data/access to test pore pressure.

This is not an extremely official project/report, so it does not require the kind of data acquisition that a masters project may require. Small scale/simple tests would likely be the most beneficial to what I am trying accomplish.

Thanks again though.

 

[moe333]

Something I did for my undergraduate project you may want to consider:

Find a local slope where there has been a failure. It doesn't have to be a large slide. Usually you can find one in a local road cut. Try to obtain an undisturbed block sample of the failed material using a pick and shovel...I took mine from the head scarp of the slide. Also take some bulk disturbed samples, and maybe hand auger as deep as possible to estimate the sol profile. Carve and trim a sample and run triaxial or direct shear tests to estimate the shear strength. If you cannot obtain an undisturbed sample, you may need to remold to the estimated in-place moisture/density. This is not going to be a rigorous/defensible evaluation but you can learn a lot from the exercise.

Run index/classification tests, moisture, gradation, Atterbergs, hydrometer, etc.

Perform a back analysis based on the geometry of the slide and groundwater to estimate various combinations of c and phi.

Compare the results of stability analyses using the shear strength tests, and shear strength correlations from index/classifications tests with shear strengths from the back analysis and see if you can come up with any conclusions.

You can also look at unsaturated shear strengths.