Summary
This review discusses rock slope stability at open pit mines. Links to books, online courses, computer codes and software are given, as well as several consulting companies with experience in rock slope stability issues. Fluid flow in jointed rock masses is also discussed.
INTRODUCTION
My introduction to rock slope stability was Bomvu Ridge in Swaziland as I sat on a view point with Professor Jennings who was smoking his pipe and contemplating a solution to the instability of the mine's sideslopes. I was there to help understand the flow of water in the rock joints and hence predict the water pressure distribution. A quick search of the internet now tells me that early man was extracting specularite from the mine as long ago as 40,000 B.C., making it the oldest mine in the world.
My most recent encounter with rock slope stability was in New Mexico last year. If you approach Chaco Canyon from the south along the route used for over a thousand years, you see the cliffs stretch from one horizon to the other. Only directly in front of you there is a break, a gash dominated by a towering mesa. Gingerly, for the site inspires awe, you round the mesa and quietly enter the still valley. Proceed a short way up to the main building; perhaps this was the palace, or the temple, or merely the granary of the vast empire that was ruled from this site for over 400 years. Regardless of its longevity and grandeur, in the early 1900s the rock slope behind the structure failed and obliterated about a third of the building. Today the rubble of the failure makes a good viewing point.
TECHNICAL BACKGROUND
Rather than trot out the usual fundamentals of rock slope stability which is well documented in books, I encourage you to go to the fascinating
site where you will find a beautifully presented story of regional-scale rock slope stability currently being investigated by the Norwegian Geotechnical Institute.
If you do, however, seek on the internet a quick primer, you cannot do much better than go to the site where once again the U.S. Army Corps of Engineers puts it well and succinctly.
I am sure there is more to the site than I know, but go there and you can download free Chapter 9 of Practical Rock Engineering by Hoek. I did and it's a gem and as good an example as any.
BOOKS
If you are not wedded to the use of the internet as a copious source of free information, and do not mind the expense of thick books, the following are some you may wish to have on your shelf on the topic of rock (and soil) slope stability-they are available from Amazon.com and all cost about a $100 each, new or used:
- Rock Slope Engineering by E. Hoek, J. Bray, and J. Barry was first published in 1981 and is still the classic.
- Rock Slope Stability by C.A. Kliche, a professor at the University of South Dakota.
- Rock Slope Stability Analysis, by Gian Paolo Giani was published in 1992.
- The Stability of Slopes, by E.N. Brodhead, was published in 1992.
- Slope Stability and Stabilization Methods, by Lee W. Abramson, Thomas S. Lee, Sunil S. Sharma, and Glen M. Boyce, was published in 2001.
- Soil Strength and Slope Stability, Stephen G. Wright, J. Michael Duncan was published early in 2005 so should be the most up-to-date on the topic.
COURSES
Giving and attending courses on rock slope stability is a profitable pastime. Here are some courses that might interest you:
COMPUTER CODES
Once you have the basic data about the slope and the rocks of which it is comprised, you may want to feed the data into a computer code to calculate the factor of safety and seek out the optimum slope geometry. Here are some sites that provide free software or which offer to sell relevant computer codes:
Geotechnical and Geoenvironmental Software Directory is run and maintained by Tom Spink who says that he updates the list at least four times a year. This is the most comprehensive site I found and you probably need go no further in your search for a suitable code. I did and here follows the results of my time on the internet.
I simply quote from the site's introduction which says it all rather nicely:
Rocscience software has been creating easy to use, reliable software since 1996. Our experienced team has expertise in a variety of disciplines, from geotechnical specialties through software marketing and sales. When you need us, we're ready to help - to provide information about our software functionality, free technical support or details on the status of your order. If you ever have any questions, be sure to email us at software@rocscience.com
An amazing site that I recommend you go to is at www.ejge.com. While at this site take time out to examine the many fascinating pages, in particular the on-line geotechnical journal and the review of slope stability computer codes.
ROCKPACK III is a package of programs useful for all phases of rock slope analysis and design where stability is controlled by the orientations and characteristics of rock mass discontinuities (joints, bedding, foliations, faults, etc).
Professor Kroeger at the Southern University Illinois has free download software.
Another source of free software is the Geoengineering Website where a pretty cartoon lady will greet you a vaguely European accent.
SLOPE/W is the leading slope stability software product for computing the factor of safety of earth and rock slopes. With SLOPE/W, you can analyze both simple and complex problems for a variety of slip surface shapes, pore-water pressure conditions, soil properties, analysis methods and loading conditions.
Andreas Gunter of the German Federal Institute for Geosciences and Natural Resources describes a suite of powerful looking codes. I could not tell if these codes are free or whether you will be charged; either way take a look and if they interest you contact Gunter.
GeoStru Software is described thus on their website which came up at about 150 in my Google search: GeoStru is an enterprise, in the southernmost part of Italy, started by a group of engineers in cooperation with geologists and topographers to create and distribute software tools for environmental, structural and geotechnical engineering in geology and topology applications. See their site and products list at http://www.geostru.com/ .
HCItasca with offices across the world including the U.S., Canada, and South Africa. They have FLAC/Slope, an advanced factor-of-safety determination for rock and soil slopes in 2D.
O. Hungr Geotechnical Research has some codes he swears by.
Zostrich Geotechnical promises help with use of their proprietary codes on a case by case basis.
MORE ANALYTICAL SOFTWARE
The following is from a previous
InfoMine page-a list of analytical software for rock slope analysis:
Geologic Modeling
Drill Hole Logging
The following all should have drillhole logging input/output routines available for their systems. They are, however, generally not in geotechnical format:
- Maptek Home of VULCAN 3D geologic modeling software
- Datamine Software Ltd. 3D geologic modeling software, stereonet plots, data log (drillhole) logs
Slope Stability
- GEO-SLOPE International Ltd. makers of SLOPE/W, a 2D slope stability program with probabilistic capabilities
- GEOSYTEM software (GEOSLOPE)software
- Interstudio S.r.l.
Circular failure analysis - Macintosh based
- Rocscience Inc. - geomechanics software and research Formerly associated with the University of Toronto and E. Hoek, this site contains the programs DIPS (stereonet analysis), UNWEDGE (wedge failure analysis) and the finite element code PHASE2.
- Geocomp Corp. GEOSLOPE (DOS version) for wall stability, slope indicator data reduction, rock wedge stability
- TAGAsoft 2Dand 3D slope irregular solid slope stability analysis, seismic analysis
- Software from EJGE A collection of soils type programs,(bearing capacity, elastic stress analysis, 2D Bishop's analysis)
- Datasurge - GEOROK A complete suite of rock mechanics programs including stereonets, wedge analysis, blasting, etc.
Underground Excavations
- Rocscience Inc. - geomechanics software and research Formerly associated with the University of Toronto and E. Hoek, this site contains the programs DIPS (stereonet analysis), UNWEDGE (wedge failure analysis) and the finite element code PHASE2.
- Datasurge - GEOROK A complete suite of rock mechanics programs including stereonets, wedge analysis, blasting, etc.
Numerical Stress/Strain Analysis
Programming Resources
CONSULTANTS
The internet and Infomine's consultants listing yields these consultants who claim expertise in rock slope stability:
- Agapito Associates, Inc. in Chicago and Golden
- Agua Tierra Land and Water Services in Washington State
- Antonio Associates in the UK
- Ashford Engineering Consultants also in the UK
- Barr Engineering Company of Minnesota, Missouri, and Michigan
- Cornforth Consultants in Portland, Oregon
- Cotton, Shires & Associates in Los Gatos and San Andreas, California
- Coffey Geotechnics in the United Kingdom serving Africa
- FracMan Technology Group, a division of Golder Associates with Dr. William Dershowitz
- HCItasca Consulting Group, Inc.
- GeoTek Solutions in Australia
- RSRead Consulting Inc. in Okotoks, Alberta
- Robertson GeoConsultants in Vancouver, B.C, with Dr. Andy Robertson
- Saguaro GeoServices in Tucson
- Snowden Group in Perth, Brisbane, Johannesburg, and Vancouver, and Surrey, U.K.
- SubTerra Engineering Ltd in the United Kingdom, and in the United States in Washington and Colorado
- Zostrich Geotechnical in the US
FLUID FLOW IN JOINTED ROCK MASSES
To establish the factor of safety of a rock slope, you need the water pressure in the rock mass. My master thesis was called Determination of the Hydraulic Potential Distribution in Jointed Rock Masses. I have a faded copy of the typed script somewhere in the attic, but who would want to read it now. There are so many excellent free publications on the internet on this topic that old documents and books and paper you have to pay for might as well not exist. On the topic of fluid flow in jointed rock masses and hence impact on rock slope stability I recommend a look at these two documents that come to your computer at no cost and no effort:
Google list three papers that are frequently quoted on the topic of fluid flow in jointed rock masses, namely
- Equivalent Continuum Model for Coupled Stress and Fluid Flow Analysis in Jointed Rock Masses by M. Oda
- The Elastic Coefficient of Double Porosity Models for Fluid Transport in Jointed Rocks by J. Bergman
- Characterizing Rock Joint Geometry with Joint System Models by W. Dershowitz.
I tried accessing these papers; I needed a password for one, I needed to send money to get the next, and the third provided text of this complexity-while nevertheless summarizing the field and topic:
Phenomenological equations (with coefficients to be determined by specified experiments) for the poroelastic behavior of a dual porosity medium are formulated, and the coefficients in these linear equations are identified. The generalization from the single-porosity case increases the number of independent coefficients for volume deformation from three to six for an isotropic applied stress. The physical interpretations are based upon considerations of different temporal and spatial scales. For very short times, both matrix and fractures behave in an undrained fashion. For very long times, the double-porosity medium behaves like an equivalent single-porosity medium. At the macroscopic spatial level, the pertinent parameters (such as the total compressibility) may be determined by appropriate field tests. At an intermediate or mesoscopic scale, pertinent parameters of the rock matrix can be determined directly through laboratory measurements on core, and the compressibility can be measured for a single fracture. All six coefficients are determined from the three poroelastic matrix coefficients and the fracture compressibility from the single assumption that the solid grain modulus of the composite is approximately the same as that of the matrix for a small fracture porosity. Under this assumption, the total compressibility and three-dimensional storage coefficient of the composite are the volume averages of the matrix and fracture contributions.
I understood all this because of my Master's thesis and a training in law, but I did not read the rest of the paper. I quote it, however, to impress future readers of my learned publications.
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