Category Archives: Site Features

Slope failures, landslides and mines

On 11 of April 2013, around 9:30 p.m. a large slide (maybe the largest) in the northeast section of the Kennecott mine occured (fig 1). The slide was preceded by slope movements that reached ~50mm per day. Two major questions could be raised, why this slide occurred and could it have been predicted before hand and remediated?

Kennecott mine

These are very difficult questions and require significant knowledge of the geology, geotechnical conditions of the area, operational practices, climatic conditions etc. In the following paragraphs some initial ideas regarding the stability of high mine slopes and some interesting references will be provided for interested individuals. The incident in Kennecott is an important lesson of how important continuous monitoring of slopes is in such mine operations.

I would like to start with a very interesting graph published by Hoek et al (2000), “Large-scale slope Design – A Review of the State of the Art”.

This chart presents slope height versus overall angle with solid markers representing unstable slopes and open markers represent stable slopes. This chart is for copper porphyry open pits. In this graph the Kennocott mine (Bingham Canyon) is also shown but not the April 2013 one.

It is very interesting to note that most of the unstable markers are located in a range between 35 and 45 degrees of slope angle. Although much information is required for detail evaluation of each point and why instability occurred, a trend can be seen. Can we assume that slopes designed bellow 32-35o would not provide stability problems?

In the next figure I would like to focus on scale effects when dealing with mine slopes in rock or even hard rock materials. In the down left side of the figure 2 a slope with 30 meters height is depicted. In the upper left one of 90m with the same spacing of joints and finaly on the right a slope of 500m again with the same spacing and trance length of discontinuities (figures adopted from Sjoberg, 1996).

What can be seen from this slope scale is that even solid lightly fractured hard rock can be seen as an accumulation of infinite rock items such as a gravel slope or sand slope, just with better interlocking. One additional question can be, “what is the effect of bridging (intact rock between discontinuities) in such large scale slopes”? Very difficult question but maybe the previous graph provides an explanation (maybe negligible?).

Is the scale effect, in relation to joint spacing, orientation and stress field producing a ductile (sand or gravel like) behavior that may control the overall stability?

In the left graph (Ross, 1949) tests on intact marble with different confining pressures are presented. On the right (Holtz, 1981) normalized stress – strain with different confining pressures for dense Sacramento sand are presented. As can be seen, both materials in low confining pressures present a brittle behavior and as confining pressure increases, the behavior becomes more ductile and strain hardening.

Strong rock and dense sand can have the same behavior in different stress scale? And if this is the case, should high slopes be treated in a different way? Neglecting cohesion and using a possible “critical state friction angle” approach in slope stability? This issue requires additional research and detailed case studies but at least we can have some perspective regarding to scale effects.


Sjoberg J., (1996). Large scale slope stability in open pit mining – a review. Technical Report 1996:10T, Lulea University of Technology

Hoek E., Rippere K. H. and Stacey P.F. (2000). Chapter 1, Slope stability in surface mining, Hustrulid, McCarter, VanZyl (eds), Society for Mining, Metallurgy and Exploration

Ros Μ. und Eichinger Α. (1949). Die Bruchgefahr fester Korper (Eidgenoss. Material prufungs versuchsanstalt, Ind., Bauw. Gewerbe. ZUrich, l72), 246 pp.

Holtz R. D., Kovacs W. D., (1981). “An Introduction to Geotechnical Engineering”, Prentice Hall.

Introducing User Participation!

As we have mentioned in the very first entry of this blog, one of our aims is to build an online community for anyone interested in geotechnical engineering. So far, however, we had only introduced a web site for that. But how can there be an online community without members? There cant’!

So, we are happy to introduce the option for you to sign-up with Geotechpedia!!logon1
You can find the “Log On or Register” option on the top right corner of the site. In order to register with us, all you need to have is an OpenID account. Since most of you probably already have a gmail or yahoo mail account, you do not need to create a new account. Just sign-in using your existing one. You do not therefore need to create yet one more username/password combination.

So what’s the point in signing up?

Well for one you can rate what you see.

The typical star rating you see in many sites, available for you to pass your judgement on what you come across in Geotechpedia as well.
Rating Items
Then, just below the ratings, there is the favorite item option…

Favorites are sort of like bookmarks, but specific to Publications, Software and Equipment Records. Since our goal is to provide you with the most information we can find, we also need to provide you with a way to keep track. So each time you come across an entry you like and want to remember, you can just click on the Mark as favorite option and you’re all set!

You can see the list of all your favorite items on your user page, which is available once you click on your username on the login panel on the top right corner:Click on your username

On your user page, you can find a list of all your favorite Publications, Software and Equipment.


Since Geotechpedia is still under heavy development, you can expect a lot more new features that will enhance your user experience. This is just to get you started. So stay tuned with this blog and will keep you informed of all the upcoming changes…

Getting social

You might have noticed that some familiar buttons have popped-up in the site. social1

Yep, these are the ones!

Since every site nowadays needs a social presence in order to be more noticable, we wouldn’t want to be left behind. In other words, we are very eager for you to introduce us to your friends!

However, you probably have noticed these as well right?

So what’s the point of having two sets of the same buttons on a page? Well it’s not actually the same set. The set of buttons on the footer of the site have to do with the social aspect of Geotechpedia in whole. If you like the site, send a kind word for us over the internet kind of thing.

The latter set of buttons, appear in the Item view of a Publication/Software/Equipment record. The purpose of this set of buttons, is to share the information about the actual record. If for example, while browsing thourgh the site you come across theExtended Nucleation of the 1999 MW 7.6 IZMIT Erthquake, and find it interesting, you might want to share it with other people.

Just head over to the right pane of the Publication and click on the share option you prefer. If you choose more than one you will make us even happier!

Happy sharing!