In Words of Wisdom an old paper from BiTech’s Geotechnical News, newly posted into the InfoMine Library, quotes from the writing of Ralph B. Peck are collected. Here are some, as background to a second paper called Desiccation Cracks Result in Preferential Flow, on crack-induced increases of clay permeability resulting from desiccation cracking.

  • Those who try to force nature into a pattern by simplifying assumptions of theory will be courting disaster.
  • The most fruitful research grows out of practical problems.
  • I doubt if guidelines, regulations, or even the best of specifications can take the place of personal interaction between designers and field forces.

Drumm, Boles, and Wilson describe a U.S. Department of Energy sponsored study of the increase of clay hydraulic conductivity with desiccation. The paper is from 1997, and so I know we are now all aware of this phenomenon. At least we should be, although I still see papers that seem to think that the infiltration though a constructed cover will be less than through a similar natural soil sequence.

To the geotechnical engineer trying to close the mine’s waste disposal facilities, it would be good to read these papers and then to walk & work the fields of the farm where I write this piece: what is written about in the papers and what is happening here will soon enough happen at the covered pile and waste rock dump. Calculations notwithstanding, nature will do its thing, and the poorly graded pile and cover will erode, the compacted clay will equilibrate with cycles of drying & wetting and freezing & thawing, the infiltration will be as the surrounding landscape, and seepage will occur along preferential flow paths at changes of soil type.

For example the clays of this Iowa farm were scraped down from eastern Canada by glaciers and no doubt compacted by great weights of ice. My wife dumped some soil into a pot yesterday and could not get the water to drain from it, so low is the permeability of this fat, black clay. But after a great rain storm the water drains away soon enough. Books on the agricultural potential of the area tell of ten thousand years of prairie grasses dying and mixing in with the soil to create the ideal growing medium. The clay hydraulic conductivity is controlled as much by its soil gradation, as by the included decaying roots and leaves, as by summer desiccation and winter freeze-thaw.

Erosion is controlled by topography and land disturbance. On the high ridges, the clay erodes away fast enough once the grass is disturbed, the land inappropriately ploughed, and the corn cut to expose the bare soil. Just over the road, the sandy ridge that once edged a glacier’s retreat is now devoid of clay and the soil that took thousands of years to form. Soon enough this will be wasteland and suitable only for the poetry of the bleaker British poets.

There are two ponds formed by un-engineered clay embankments. Both embankments are in trouble: the lower one is raveling back as the winter’s ice and spring thawing loosen the edge of an over-steep slope resulting from dredging too deep, too close to the edge. And the upper one is leaking along the contact between the natural landscape and the embankment. Where the seepage emerges, the hillside is piping and collapsing and eating back. Left to their own, they will soon enough be gone, proving only that perpetual monitoring and maintenance are required once we create a geotechnical form at odds with nature.

Please keep in mind I love the ponds, the rippling water over which our silly little wooden boats are blown by the wind, the muddy banks where the kids slip and slide and turn pink from the sun and black from the mud, and the geese that swoop down at sunset. But this is not nature: far from it. This is as unnatural as any mine, and requires as much thought and action and respect for field processes as any mine, now and in the long term, if we are to enjoy the benefits of our creations.