Steep Rock Slopes
Steep Rock Slopes
(OP)
Hello,
I need an input in how to analyze steep rock slopes. I particularly are interested in software that can assist me in the analysis,
thanks
Voi
I need an input in how to analyze steep rock slopes. I particularly are interested in software that can assist me in the analysis,
thanks
Voi
RE: Steep Rock Slopes
Rocscience has a program called swedge. Essentially you enter the major rock joints (dip and dip direction) and it will tell you the factor of safety of the resulting wedge.
If you want to get fancier, you could try flac, or flac-3d by Itasca. Itasca also has software that would help with analyzing land-slides (probably not of much interest for your application of rock slopes).
You could also use a general FEM program.
RE: Steep Rock Slopes
Thank you for responding to my thread. I have a case where we are excavating four basements down ( 25 m below ground). The area is urban and the terrain is all rock. I know SLOPE/W implements the Generalized Hoek-Brown but it is very expensive. So I am looking for any other ideas or recommendation of analyzing this slope next to the deep excavation.
voi
RE: Steep Rock Slopes
RE: Steep Rock Slopes
RE: Steep Rock Slopes
RE: Steep Rock Slopes
RE: Steep Rock Slopes
RE: Steep Rock Slopes
RE: Steep Rock Slopes
Yours: "I need an input in how to analyze steep rock slopes. I particularly are interested in software that can assist me in the analysis,
thanks"
Then when someone pipes up to help you, his "tip" is criticized. One hell of a way to expect any other members will come forth.
RE: Steep Rock Slopes
For a 25m HARD rock slope, the primary mode of failure would be structural ie along fractures, joints, or other discontinuities in the rock. If the excavation is truly in hard rock, then the strength is on the order of 100MPa which would stand at any angle for a 25m height ignoring the jointing. The weak link is therefore sliding along joints. To analyze this, you first need geologic data. I assume a site reconnaissance and investigation has been completed. If so, the report should include mention of the orientation and character of joints (nearby outcrops have hopefully been mapped). The joints should be analyzed relative to the orientation of the excavation. A simple stereonet analysis would be a good start. You can then do a kinematic analysis of potential wedges and planar failures using hand calcs or SWEDGE as swiver mentioned. The slope should be designed based on a criteria that limits the potential for daylighting wedges and potential planar failures.
If the slope will be unsupported, then you have additional considerations including sizing benches based on the geotechnical limitations as described above, and the size of the equipment you'll be using to drill and blast. If you want a steep slope without benches, then you'll likely have to do a cable bolt design. This involves an additional level of complexity that I won't comment on for now.
I caution that use of the Hoek-Brown method of rock mass strength estimation has no applicability for short slopes in high strength rock. Unless the slope will be in weak/highly altered rock, use of this method for this case is meaningless. Beware of consultant reports that suggest the contrary.
Although, spending money on the SLOPEW software isn't a magic box that is going to get you the right answer after spending a few bucks, I appreciate miningman's encouragement to do it right.
RE: Steep Rock Slopes
RE: Steep Rock Slopes
RE: Steep Rock Slopes
Will the drilling data include a televiewer so you can map the rock structure? What method will give you the strike and dip of foliation, discontinuities, bedding, etc.?
I mean fundamentally, you need to assign intact rock strength, temper that strength by the shear strength of the discontinuities and the presence of water pressure. At the macro scale there will be some overall rock mass property, which you could use for horizontal earth pressures. There may (will) also be some liklihood of stress concentration associated with a random wedge that the basement wall will have to shoulder. That will be a bit differnt then you may calculate using Rankine-type earth pressures.
I don't know about FEM solutions, other than to know they exist. Good luck getting hyperbolic modulus parameters though!
At least you don't have to worry about rock fall containment!
f-d
ípapß gordo ainÆt no madre flaca!
RE: Steep Rock Slopes
In other words if you do a uniax test on a core of solid rock, then you'd get a very high strength on the order of 100MPa. However, because of the effect of joints (not necessarily daylighted) it is impossible to mobilise strengths of this magnitude. Hence, the rock mass concept. Using the HB method, the intact rock strength is downgraded empirically using GSI which is an index of rock quality. There are other factors as well. The method was developed for analysis of high stress environments primarily in mining where excavations are large and deep. It is not the only method of rock mass shear strength estimation by the way.
For a 25m excavation, stresses are relatively low in comparison with typical rock mass strengths. Another way of saying this is that rock mass failure for a 25m slope is very unlikely to happen unless the rock is altered and very soft. At 25m, the max normal stress is about 0.5MPa - a pittance in comparison with typical rock strength! Sliding along joints (discontinuities, foliation, bedding, faults, etc.) is therefore the mode of failure that is important.
A good start would be to map the joints, measure the orientations, test the shear strength, and do a stereonet analysis.
RE: Steep Rock Slopes
RE: Steep Rock Slopes
RE: Steep Rock Slopes
The end game's the same - to get the rock mass properties.
f-d
ípapß gordo ainÆt no madre flaca!