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safety features for wofati design in an earthquake-prone area?

 
Posts: 12
Location: La Peche, West Quebec; hardiness zone 4a
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I'm thinking of building with wofati principles in southern Yukon, which turns out to be an area where earthquakes occur more often than in the middle of the continent.

Does anyone have any thoughts about what sort of safety features could be usefully incorporated into a wofati design in an earthquake zone?

It seems ridiculous to contemplate building underground in an area where the earth itself is unstable, but having great insulation is a major bonus for the sub-Arctic and I'm reluctant to give it up.

Thank you, and Happy New Year
El
 
master pollinator
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Location: Toronto, Ontario
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Hi El.

I think it depends on what style wofati you want to build. To be clear, some of the ways in which you might want to change your design to make it safer might make it different from many wofati designs, but as with all permaculture, you need to suit the design to the specific scenario.

If you are looking to build a pole structure out of round wood or split logs, for instance, I would look at what wisdom pole structures in earthquake-prone areas have to offer. Likewise, if you are looking to make your structure out of something closer to masonry, like compressed earth block, say, I would consult a mason with experience building earthquake-resistant structures.

I might be wrong about this, but I think a design using something closer to monolithic design might be useful. What if the foundation, walls, and even supportive interior structural walls, were made of rammed earth, and effectively acted as a single piece? I think perhaps earth bag building might even have some points, though I prefer the idea of rammed earth.

I think wide load-bearing walls that don't require the integrity of the roof or surrounding structure to stay upright is the ticket. What does it matter how strong your walls are in the right position when the ground moves them out of place and ontop of you?

This is a hugely important issue to many people, and I am surprised it hasn't come up sooner.

-CK
 
Posts: 145
Location: MA
forest garden purity trees
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The best way I know is to use "stabilized earth".  This is as simple as laying horizontal layers of a suitable "geotextile" fabric ( perhaps even a woven poly landscaping fabric?).   It interrupts the shear-curve where soil avalanches.  This is how everything from earthbag structures to civil-engineered embankments stand up.  Honestly I don't know why this isn't used on every retaining wall everywhere.  It's astonishingly effective.  Also see: This video
 
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One of the first things to determine, is the type of foundational material.  Do you have deep or permafrost soils or solid rock.  Solid rock is the best foundation for earthquake resistant construction.  In softer earth, earthquake energy moves all the soil particles.  There are three types of movement in most earthquakes, depending upon depth, strength and foundation material.  P, S and Surface waves.  P waves are pressure waves and generally are the first to arrive.  They move forward and backward.  S waves are secondary waves.  They tend to move from side to side.  The last form is the least common and is the Surface Wave.  This is the Hollywood favorite as the ground moves similarly to water waves and can crack open and close.  

If you have certain types of soil, they may be subject to a process known as liquefaction.  This is a soil that is usually solid enough, but when subjected to a sudden jolt, turns to near liquid.  In 1964 several hundred feet of a cliff along the coast of Alaska failed, nearly taking a hospital with it.  It also led to massive road disruptions.  If you have any potential liquefaction soil or permafrost, I would tend to discourage an underground construction method, I would opt instead for a earth bermed structure with reinforcement.  Wood has great tensile strength and lasts underground for decades if not allowed to connect with the atmosphere.  Constructing a net of wooden poles, especially poles with wood mortise and tendon connections is extremely strong and resilient.  Connecting layers of such wood nets and covering them with cob or rammed earth would create a very high strength system.  Earth bag construction can be earthquake resistant, as noted in one of the replies, but generally, my experience has been that is only if the entire structure is placed on stone fill.  It seems the stone fill under the entire structure allows the structure to move as an integral unit, dissipating the earthquake energy.  In Alaska, with the high water table, a stone base might become a source for too much humidity inside.  The initial design for the earth bag round homes that have the above earthquake construction method were for arid/semi-arid areas without the issue of high ground water tables.  I would avoid any long, straight walls with earth bag construction.

You identify that you live in southern Yukon.  It is not clear what resources you might have available.  If you have a source of waste tires available, bolting tires together and ramming earth into them would provide an earth bermed structure that would be highly resistant to many hazards.  The walls would be strong enough to take the weight of earth bermed against them in terraces which would allow placement of a roof with a natural grass cover.  I would be cautious if the area gets too dry and would allow the grass to become readily flammable however.  It may also be prohibitive from a resource/time/cost perspective to strengthen a natural earth roof to resist earthquake forces.  It is probably better to consider using a metal sandwich roof.  A good insulation could be made of ground foam mixed with concrete.  It is light, highly insulating and non-flammable.  Just as a comment, I would strongly suggest cutting any nearby trees if wildfire is at all possible.  Also ensure no shrubs are allowed to grow under nearby trees.  Those are called "ladder fuels" in wildfire parlance.  Trim any lower branches to 8 to 10 feet above dry grasses.

As in any earth bermed or underground structure, please ensure you are above the 1,000 year flood.  Flood is a hazard no construction can resist.
 
pollinator
Posts: 1793
Location: Wisconsin, zone 4
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Mike Phillipps wrote:The best way I know is to use "stabilized earth".  This is as simple as laying horizontal layers of a suitable "geotextile" fabric ( perhaps even a woven poly landscaping fabric?).   It interrupts the shear-curve where soil avalanches.  This is how everything from earthbag structures to civil-engineered embankments stand up.  Honestly I don't know why this isn't used on every retaining wall everywhere.  It's astonishingly effective.  Also see: This video



Thanks for posting that video. I had no idea that was possible. Amazing.
 
Mike Phillipps
Posts: 145
Location: MA
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Thanks Todd, sure thing.  
-Mike
 
Mike Phillipps
Posts: 145
Location: MA
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I think Richard made lot of excellent points regarding: soil types, fire safety, not living in a flood plain, not using long straight walls especially with no tensile strength.  (Sometimes in an earthquake zone they'll put a layer of fiberglass-epoxy over an old brick wall to make it safer.)  

Wood is an easy material to use but has a lot of problems...too many really.  I agree on not trusting an earth roof; consider a metal roof instead.  Foamed/aerated concrete is an amazing material.  About the only reason I know why it's not a perfect building material is that if it gets wet it gets waterlogged and loses strength.  Using fiber-fill reinforcing seems to help with this.  If it was somehow made more waterproof or kept dry it would be amazing.  
 
Richard Henry
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Mike

Although fiberglass-epoxy is a good start, for old brick walls in an earthquake zone, cross bracing with a tensile material (often cable) is necessary.  And, as noted under liquefaction, do not consider any modified old masonry wall safe during or after a good shake.  One, there are both large pre shock quakes and large post shock quakes.  Two with liquefaction under the foundation, the structure is very likely to drop uneavenly, and no masonry wall is designed to hang out there when tilted.

Wood will last an amazing time so long as it is kept from the air.  Oxygen is what generally eats wood or allows organisms to do so.  Mortise and tenon construction is extremely strong.  I remember a badly rotted barn frame (all planks removed) as it pulled a bulldozer to a halt.  we had to get out the chain saw to get it down.

I agree that foamed concrete is great stuff.  It can be made both waterproof and highly insulated by placing urethane foam over it.  Just make sure that urethane foam is not able to be heated too much.  I nearly stayed under 50K tons of fertilizer during a barn fire when the cyanide released due to heating of insulating foam dropped down like a blanket.  Good thing I have a sense of direction, just started walking toward the door and made it out.
 
El Rowlatt
Posts: 12
Location: La Peche, West Quebec; hardiness zone 4a
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Chris, Mike, Richard -

The permafrost line is north of my area and moving pole-ward every year; I don't think that will be an issue. I will have to look into the nature of liquefying soils, though, as I can't say whether or not that's what is in my valley from looking at it.

Thank you guys very much. I'm going to return to this thread when I've digested your comments , and I appreciate the time you gave to sharing your knowledge.

El
 
Richard Henry
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Lucky you!  Southern Yukon has multiple types of potentially liquifiable soils.  One is called quick clay.  It is clay that can be placed in a smooth cylindrical container and when decanted onto a flat surface, holds up quite well until the surface is struck sharply.  If it then runs like thick mud, you have quick clay.  Silts are often subject to liquifaction.  To test for these, take a small container and get a chunk of damp soil.  Tap the container and if water wells up out of the material, it is liquifying.  Lastly, organic soils can liquify.  Essentially, if a soil readily loses internal water when subjected to sharp tapping, it is at least partially liquifiable.  The best mitigation would be to place a wider base for a foundation below frost line.  This spreads the weight of the structure and allows it to act more like a snow shoe on powder.  Good luck
 
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Hi El,
My wife and I or getting geared up to build a wofati this year.  We live 20 mins north of Whitehorse please drop me a pm If you would like to meet up and discuss design and challenges up here.

Byron
 
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