Archive for May, 2009

I went out drinking with a colleague last night. He works in the oil sands industry. We got to arguing about total and effective stresses in soil mechanics and tailings engineering. I illustrated the differences between total stress, effective stress, and pore pressure via our drinks, thus:

Add ice to your brandy, and you have a fluid in which the pore pressure is equal to the total stress; the ice cubes are not carrying load but are just floating or bobbing in the water, thus the effective stress is zero.

Conversely take your brandy on the rocks and the effective stress is pretty much equal to the total stress, and unless you have overdone the brandy, the pore pressure is pretty nearly zero. The ice carries the load and the brandy is nice and cold for drinking.

The point is that for both forms of brandy and ice, the effective stress law is valid. Altough if the ice is floating in the brandy, the effective stress equation may simply be irrelevant.

Of course you can think of this in terms of phase diagrams as mechanical engineers do when they plot regions for steam, water, and ice: the same stuff, just that different equations are more or less important depending on temperature and pressure.

We concurred on these concept. And we drank and chatted about total stress, effective stress, pore pressure, or common old garden stress in a fluid like brandy with a few clumps of ice where the effective stress concept and law are simply irrelevant—until that terrible time came when we had drunk too much brandy and the individual ice cubes were in particle to particle contact and the brandy bottle was empty. And the dominance of the effective stress induced sobreity panic.

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Yesterday a wise professor made a presentation that caputured an enduring fact and a recent change in tailings analysis and modeling. He did this at a meeting I happened to be in, and I repeat below from his PowerPoint presentation.

  • In 1943, Terzaghi wrote: “Soil Mechanics is the application of the laws of Mechanics and Hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles.”
  • It was difficult to do this for even the simplest problems until the development of the computer and specific codes in the past 20 years.
  • We have used the Computer Code FLAC, Fast Lagrangian Analysis of Continua, for design of the cover of the tailings pond as the code incorporates these laws of mechanics and hydraulics in a rigerous manner.

One day, maybe we will publish a paper on the results.

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Yesterday I stood outside the office smoking when a pretty lady in a nice car drove by. She stopped and backed up, rolled down the window, and asked why I was not at the dance lesson.

“I am on my way,” I protested. I recognized her from my regular West Coast Swing Dance lessons.

“Get in,” was her command. So I did.

We fell to talking work. She is the manager of environmental affairs for a British Columbia coal mining company. I asked the obvious: “How is it going?”

“We are just surviving,” was her reply. “We have closed one mine, and put the other two to less than 40 percent production.”

“And who is buying that coal,” was my obvious follow on question.

“The Koreans and maybe the Japanese, with a little going to Europe.”

“Who is your competition?” I wondered.

Here is the answer from Mineweb:

India imports of South African coal in 2009 could be considerably higher than last year’s 10 million tonnes because many buyers who formerly favored Indonesian coal are switching to currently cheaper South African coal, Indian trade importers said.

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For two years I blogged at I THINK MINING. That blog was hosted by InfoMine. I was not paid to write the blog; although I was paid to write technical and engineering-related articles for TechnoMine, which is a part of InfoMine.

Earlier this year, some managers of InfoMine became concerned that my blog postings may offend the mining industry. We could not agree, and so I stopped blogging for InfoMine. After a decent break, I now start this blog, with a similar name and similar purpose: to write about mining in all its many guises.

So come back, for in the days to come, I will continue my blogging. In the meantime take a look at the original I THINK MINING if you want the approach, the tone, and the opinions I hold. There are more of the same on the way.

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