Sandstone-making microbes, tafoni - and an extraordinary design idea

I love connections. Those unexpected and wonderful threads of stories that link and flow from one subject to another, subjects that would have seemed to have had nothing in common whatsoever. So here's one such story. The thread is earthquakes-bacteria-desertification-tafoni-sustainable design.

Shake waterlogged sand, and liquefaction occurs: the grains move apart and the friction and adhesion between them is lost, destroying the stability of the material, which then flows and compacts, expelling the water. Earthquakes are particularly good at doing this, with catastrophic consequences. The earthquake that devastated the region around Bhuj in northwestern India in 2001 was one of the most damaging in the country’s history. Twenty thousand people were killed and the havoc caused more than $3 billion of damage. Because the vibrations provoked the sand and soil into liquefying, buildings no longer had a foundation, causing them to sink, tilt, and collapse. Huge cracks in the earth appeared, and water and sand erupted in volcanic fountains as the ground collapsed back on itself. This is a common result of earthquakes: more damage is done by liquefaction than by the tremors themselves. This was the case in Anchorage in 1964, the great San Francisco event of 1906, and in the Loma Prieta earthquake in 1989, where some buildings in San Francisco sank until their third floors were at ground level, and sand volcanoes or “boils” erupted from the ground. Liquefaction was also amply demonstrated in the most powerful series of earthquakes to strike the lower 48 in recorded history—not in California, but in New Madrid, Missouri, between 1811 and 1812.

It is therefore no surprise that liquefaction is the focus of intense research by engineers, physicists, and lovers of granular materials. Is one solution to try to glue the grains together so that they can’t liquefy? In spite of the scale of the challenge, the answer is yes, and we may be able to seek help in this from a seemingly unlikely source. Currently, engineers can inject chemicals, such as epoxies, into sandy soil, but the chemicals may be toxic. The unexpected help comes from Bacillus pasteurii, a natural bacterium that lives between sand grains and in soils. Research by Professor Jason DeJong and his colleagues at the University of California at Davis and the University of Massachusetts have shown that the bacterium causes calcite, or calcium carbonate, to precipitate, which glues the grains together. Inject sand with cultures of these bacteria, feed them well, provide oxygen and a source of calcium, and they will turn loose sand into solid rock. As DeJong says, "Starting from a sand pile, you turn it back into sandstone." The remarkable scanning electron microscope images below are from Eric Seagren, Chiung-Wen Chou and co-workers at the University of Maryland who are also inducing bacillus pasteurii into lithification activities (see the full set of images here).

 

Now, desertification. An evocative word, conjuring up apocalyptic images of the spread of aridity and the destruction of habitable and agricultural lands. It is indeed happening, but often as much as the result of human activity - the massive destruction of forests and other vegetation in China, for example - as climate change. But the edge of the desert shifts, as it always has, sometimes simply because dunes inevitably move on, and sometimes because climate fluctuates. The semi-arid sahel region of North Africa has always had a complex and delicate relationship with the Sahara, suffering drought (as well as excessive rainfall) and dune encroachment; it is in may parts heavily populated and livelihoods are vulnerable to shifting sands and climate change, the current effects of which appear to result not necessarily in less rain, but in less predictable, and periodically more torrential, rain. Massive projects are underway to create immense barriers of vegetation - the "Great Green Wall" of North Africa, 7000 kilometers long and 15 kilometers wide (China has its own version).

But what has this to do with bacteria? I recently came across (initially because it quoted from my book) a compelling report on BLDGBLOG, an eclectic and fascinating collection of writing on "Architectural Conjecture, Urban Speculation, and Landscape Futures" by Geoff Manaugh in San Francisco. This particular report was on the design project that last year won first prize in the Awards for Sustainable Construction by the Holcim Foundation, based in Switzerland. The project is by Magnus Larsson, a student, and it is staggering in its imagination, creativity and scope. Titled  " DUNE: Arenaceous Anti-Desertification Architecture, An Adaptive Proposal for Sahel/Sokoto/Northern Nigeria" it proposes that “maybe there’s a way to sculpt the desert into living spaces.” The sculpture would cross the northern edge of the Sahel, supporting and complementing the Great Green Wall, and would be sculpted by bacillus pasteurii.

Larsson espouses "aggregation as a design strategy":

in one way, all design is aggregation. even the most austere minimalistic design usually produces an aggregation of elements that weren't there before. on one level, it is hard to do anything in the world without adding something to it: a trace, a movement; something.

sand is the very epitome of aggregation. a single grain of sand is almost nothing: a splinter of rock, something that once was something, but has now become a memory of that thing. but put myriad grains together and you get entire landscapes, deserts, the earth. you get fascinating forms and emergent patterns. you get possibilities, potentials, a fluid material from which to build our structures. and you get a force to do it for you: as the sand is carried by the wind, "all" we have to do is make sure we design with this in mind. work with the aggregation, not against it. allow the aeolian forces to put the sand in motion, allow saltation to do its thing, and then, when the sand has aggregated into a shape that we like, use an intelligent strategy for how to solidify it, petrify it, freeze it into a solid state that speaks of that one moment in time.

To me, of course, that is poetry.

Among the patterns and forms that inspired Larsson (and Gaudi - see previous posts) are tafoni, "a cavernous rock structure that formally ties the project back to notions of aggregation and erosion." He describes how bacillus pasteurii could be harnessed to sculpt the desert into those forms that speak of one moment in time, but endurably, sustainably, providing not only a barrier against desertification, but habitable and cultivatable envrionments:

I researched different types of construction methods involving pile systems and realised that injection piles could probably be used to get the bacteria down into the sand – a procedure that would be analogous to using an oversized 3D printer, solidifying parts of the dune as needed. The piles would be pushed through the dune surface and a first layer of bacteria spread out, solidifying an initial surface within the dune. They would then be pulled up, creating almost any conceivable (structurally sound) surface along their way, with the loose sand acting as a jig before being excavated to create the necessary voids. If we allow ourselves to dream, we could even fantasise about ways in which the wind could do a lot of this work for us: solidifying parts of the surface to force the grains of sand to align in certain patterns, certain shapes, having the wind blow out our voids, creating a structure that would change and change again over the course of a decade, a century, a millenium.

The resulting forms of Larsson's vision are staggering, both in their scale and in their aesthetics:

 

Yes, this is a vision, a design fraught with practical challenges, questions, and difficulties in the real world, not to mention ethical aspects. But "if we allow ourselves to dream" (and we must), then beautiful, visionary, creative, and challenging ideas will result, and wondrous stories will be told.

[for details of Magnus Larsson's project, see http://www.flickr.com/photos/bldgblog/sets/72157612777908074/ and http://bldgblog.blogspot.com/2009/04/sandstone.html. For the work of Jason DeJong and his colleagues, see  http://www.sil.ucdavis.edu/projects-bsi.htm and, for example, this Discovery Channel article. Images copyright Magnus Larsson, Eric Seagren et al.]

Comments

[BrianR]

Michael ... I figured you'd post about that BLDGBLOG post soon ... very cool stuff!

btw, 'Sand' has arrived at my house, but is currently on the bottom of rather large stack of to-read books ... maybe it'll somehow get on top :)

[Michael Welland]

If the book is bigger than the rest, then a slight shaking, a minor tremor or whatever, and the infamous brazil nut effect will kick in and it will end up on top.

[BrianR]

ahh yes ... kinetic sieving!