Soil Liquifaction

Wow! But why wouldn't a soils test pick this up beforehand?

I agree. I wondered how they managed to build it in the first place. They may have taken precautions when it was first built, and then, having no problems....

Very cool video!

I used to live in northern California. There are structures built all over the place on soils that are subject to liquification. The obvious cases are the mudslides that occur with the introduction of water, which may not be considered true liquification. There is also a lot of sandy soil, on which structures are built, that is subject to liquification, but only in the event of an earthquake. It happens.

True the mudslides in places like Malibu usually aren't a typical soil liquifaction case, but rather a loss of strength in a underlying weak clay layer that didn't get identified (or in the case of Malibu, they have been indentified many times over and people forget during the 7 to 10 year intermediate periods between the El Nino driven heavy Rains). Liquification occurs when vibrations cause non-cohesive or weakly cohesive soils to form a slurry, usually fine grained sands below groundwater that are common in valley floors. Seismic liquifacation is a common concern in California and all major projects (anything larger or more significant than a residential house) will have general liquifaction studies done as part of the geotechnical investigation. Many areas of the Central valley off the Sierras have layers of liquifiable soils

To include the Marina Green District of San Francisco right outside the gates of the Presidio. The '89 quake demonstrated the folly of building upon fill in the San Francisco Bay.

http://en.wikipedia.org/wiki/Marina_Green

Some houses sank up to the second floor. A huge mess.

http://en.wikipedia.org/wiki/1989_Loma_Prieta_earthquake

I lived in Novato, CA, stationed at the Presidio from 1895 - 1989. I remember houses built in the Fairfax area just outside San Rafeal precariously perched on the hillsides. I left (PCS'ed) just a few months prior to the quake.

GA. You provide a clear explanation.

The longer version is this... Clay particles are like playing cards and has two major states it can form in.

Throw the deck of cards on the ground and this is the way to picture the first one, they bond face to face. Any type of liquefaction for this type would be typical of any other soil (ie earthquakes or excess water pressure).

The second is like a card house bonding edge to face. This is the more typical structure for marine clay. The salt content fills in the gaps (thereby holding up the house). Should the geography change such that it is no longer in contact will the salt water, the fresh water runoff begins to displace the salt (removing the supports for the house). Actual quick clay can contain up to 80% water in those "voids". The liquefaction in this case is the card house falling down!

Actually, the end face form of clay particle is the strongest form that is where the negative charges on one can bond to the positive on the others as the ends will be oppositely charge to that of the face of a clay mineral particle, this is the floccultates structure. face to face is the very weak structure as the clay particles float on each other due to electrical repulsion of the like charges on the faces. A strongly charged relative to hydrated radius ions, like Calcium, cause clays to take this formation and be very strong. Weakly charged relative to hydrated radius ions like sodium have the opposite effect and force dispersion of the clays, face to face contact. However, in marine situations you get a case where the concentration get so high in salts that the sodium and related ions can not maintain a large hydrated radius relative to charge due to limited available water to coordinate, thus in this case the very high concentrations of salt force the clays to behave like they are exposed to ions of a smaller hydrated radius to charge. Add realtively salt free water and the sodium shifts from causing flocculation to causing dispersion, and as the sodium is replaced from the cation exchange sites it the clays begin to move back towards flocculation. Strong mechanical stress can also cause short term dispersion of the clay particles, such as the high localized pressures due to heavy compactive equipment re-working the materials. Soil liquifaction per se is not due to flocculation of clay minerals, which is not actually a form of soil liquifaction, but rather a form of materials weakness, and that is actually due to clay particle dispersion. Liquifaction occurs in soils materials that rely on mechanical contacts for strength rather than electrochemical bonds, e.g. non-cohesive soils. Soils liquifaction is the formation of a slurry where the particles lose surface to surface mechanical contacts, i.e. soil friction, which leads to a quick sand condition forming.

Desalinated clays? Manaus is 800 miles inland on the Amazon River. I suspect that the shallow fresh ground water from the river would have modified the clay cation exchange sometime in the past million plus years the river has been migrating and building the flood plains Manaus lies on.

Again (see post #12)

You may very well be right with regards to it not being quick clay. I just assumed when I read the American Geophysical Union statement that "it appears to be quick clay."

From the encyclopedia Britannica Online "The effects of the pororoca have been seen over 600 miles inland." (Translation is that the Atlantic salt water has been seen over 600 miles inland in the Amazon). Who knows what happened in the eons it took to form these deposits? Again... I'm not saying it is quick clay, but it is possible and I'd really would like to see some follow up articles on this.

but Manaus is 800 miles inland. this however, doesn't mean that the soils could still be a weakened clay. Mechanical dispersion can still occur from working the soils in the past, or other dispersants may be present from other sources that cause dispersion as the salt concentrations declines.

One thing about geologists to keep in mind, they tend not to follow any strict definitions for soils classifications, sometimes they use engineering definitions, sometimes they use soils science definitions, sometimes they just use descriptive terms that dont fall in either. It is preferable to employ either USDA (soils science) or USCS (engineering) terminology as these will be standardized to soils. Soil scientist would require that a clay be comprised of predominantly clay minerology, engineers require that the fine fraction mechanically behave predominantly like clay mineral properties and the fine fraction is dominant. At any rate both would not allow for the fine fraction to be less than 50% of the soil.

Thanks for all the input. You definitely have a point regarding soil classification/nomenclature (the difference between agencies often cause me headaches). This is causing me to break out some books and dig a little more (i.e. I'm learning loads here).

I just ran across this article from the Swedish Geotechnical Institute.

http://www.swedgeo.se/upload/publikationer/rapporter/pdf/sgi-r65.pdf

I briefly scanned this and two interesting things we didn't cover in our "ad nauseam" class discussion was that, if I'm reading this correctly, this type of clay can also be formed by organic matter instead of salts during flocculation (which are later removed, which form more void spaces... ). Also, in regards to the desalinisation formation, it must be soft water, hard water runoff leaching marine clay won't form quick clay.

How is it that an event of this magnitude isn't/wasn't all over the news??

Well stated RCE and GA. I think I was trying to say something similar in reply #20. I do not think the organic loading would be a significant factor, but I do think the mineral silt and sand lenses would be large factor compounded by the rain forest climate, and human construction along the river banks. The backhoe would be a good mechanism to cause a sudden release of water by intercepting a lens.

Amazing.

Given that this kind of "quick clay" event has known causes, it should be possible to determine, from a core sample, that a particular area is at risk, even if it is not possible to tell when a liquefaction "event" will occur.

Hopefully, then, it should be possible to chemically amend the soil - say, by injection, to prevent such an event. But injection of what? Clay is a silicate, so perhaps injecting water glass solution and a carbonate to solidify it would cement the soil into a coherent whole?

Gee whiz,

I'm starting to question my footing here on CR4.

Doogleass, (what no hyphen) is exactly right, pore water preasure. This event would occur more often if we didnt pave everything around buildings, so other than drain wicks, pave it.

Ok, I would like to amend my post above, paving in this instance may have allowed a build up of pore water presure, because evaporation could not take place. Back to drains.

I didn't map it until just now (it's over 700 miles inland). I would however point out that the Amazon does flow backwards, I don't know if the salt content would make it back that far though.

You may very well be right with regards to it not being quick clay. I just assumed when I read the American Geophysical Union statement that "it appears to be quick clay."

I'd be interested in any follow up articles, but am coming up with nada which is odd for an occurrence such as this.

it is very simple. MOVE

I was unaware of the geographical location of Manaus and did the google earth look at its situation. I should have looked before my first post. I would now doubt salt deposits are the cause of the slide. The climate of Manaus is described as tropical rainforest. The Amazon is a slow moving river by the time it reaches Manaus. As the Amazon Basin is loaded with Alluvial deposits, you would expect these deposits to be primarily clay and silt with some sand. The clay should have many silt and sand lenses. When I reviewed the film, the slide appears to be rotational and complex. One rotational slide allows the cell of clay behind it to slide, then another cell, and so on. The tropical rainfall would be very high and the removal of stable organic growth would be a contributing factor. Each large block of clay is allowed to move in a rotational manner along the face of the silt or sand lens acting like ball bearings. The backhoe digging likely contributed by removing just enough of the stability of the clay (intercepted a silt sand lens) to create the first slide starting a chain reaction.

The whole area appears to be susceptible to quick clay and the silt and sand lenses would exacerbate the problem.

It is an amazing video and I wonder why the photographer didn't run like hell. He was either very brave or not aware of the danger.

Friends,

This reminds me of an article I read a long time ago regarding a very low slope land slide that moved an entire farm and its buildings by about a half mile (the barn and farm house were relatively intact). My memory is the article was in Scientific American, during the 1960's, with a location in the Ontario Province of Canada, and a slope of less than 4%. In that article they reported that the aftermath of the slide was a soil composition that was no longer subject to the same liquifaction and slippage.

--John M.