Earthbag Tests in Comparison to NZ Tests

More testing info from Patti Stouter:

What’s so important about New Zealand’s earth building standards? Well, no one else has based earth building guidelines on so much testing. And recently earthquakes in New Zealand (including a magnitude 7.1) proved how well these standards keep buildings safe. Engineers visited 14 adobe and rammed earth buildings to see how well they survived. Since earthbag is a masonry technique that has similarities to adobe, their 10 page report should be of great interest to all earthen building designers.

Earth buildings that used construction techniques recommended by the standards fared well despite experiencing peak ground acceleration of 0.5 – 0.65g or more. Some historic rammed earth buildings with less reinforcement than the standards requires also survived. Earth buildings (wisely built) have been proven strong enough. But photos of the repairs needed for some buildings where construction details were weaker than the standards require can teach us a lot.

Tempted to stretch those pier spacing guidelines? Want to put just one window closer to a corner? If you’re designing for an area at risk for earthquakes, these photos may be a needed dose of reality.

Earthbags may absorb vibrations better than adobe and rammed earth. The barbed wire sunk into strong clay bags may provide more strength. But we don’t know this for sure yet. When we do know, then educated designers can use or adapt New Zealand’s earthen building guidelines to the unique strengths and needs of earthbag.

What’s the weak point of the New Zealand earth building standard? The author of a blog called The Well Run Dry pointed it out clearly in his July 1st post called ‘The Sound Foundations of Engineered Earth Construction’. Although strong earth buildings are a matter of survival in the third world, ‘Many of the publications from First World sources on the topic of earth construction are behind paywalls.’ Simpler guidelines developed for India and Colombia and Japan are available freely on the internet. But New Zealand’s guidelines help with the difficult size and construction detail decisions needed for anything beyond a minimal 2 room house. The NZS engineers have shared some test values and some construction details in several free papers on the web. But New Zealand’s three guidelines cost $100 each even in PDF form.

With unique earthbag testing results, can we craft some guidelines for earthbag that use information similar to parts of the NZ standards? I hope so. Perhaps earthbag won’t need as much reinforced concrete in bond beam and footing as the NZS recommends, at least in low and moderate seismic risk regions. But charts of bracing wall lengths needed for different wall heights and support wall spacing would help earth builders everywhere. And my goal is to make needed information freely available.

17 thoughts on “Earthbag Tests in Comparison to NZ Tests”

  1. From what I have read on the subject and my personal physics knowledge, the idea that the bags shift and relieve the stress of an earthquake makes a lot of sense to me, I study physics in Christchurch, New Zealand. Over the last year I feel I can say I have experienced my fair share of earthquakes, from the 7.1 last september that gladly did not kill anyone, to the horrific 22 February quake felt here.

    I worked with the New Zealand Earthquake Commission over the summer inspecting the damages of the houses here and from my personal experience the houses that could not hold up were, quite obviously, the ones that could not relieve the adequate stress in time ie brick, stone and adobe built houses, wood is remarkable in its flexibility, steel too, and I have yet to see the direct effects of an earthquake on a house built from Earth-bags, but I assume it could be quite good.

    The only fear I would have is if the jolt was quite significant, could it not simply dislodge a large amount of individual bags from a certain area of the house, and thereby worsening the structural integrity of the structure (whether isolated or complete failure is just a matter of the given situation), what are you thoughts Owen? I like hearing your opinions on this subject as you seem to have done your research, whether it be first hand or otherwise.

    Cheers and greetings from NZ :)

  2. Ok. I gotta read thru all the testing pages. I am planning a large rectangular garage/shop/future living space. I just feel unnervey with the bottom layers being gravel bags in an earthquake. It just seems to me all the rock-in-and-rollin we get in California would do it in at the foundation. For the small structure Im working on right now, Im not concerned. Earthbags are my preferred way of building. I cant afford the many truckloads of cement and steel that would be required normally to build a earth building foundation according to code, nor do I believe it is the best way or needed.

    • There’s a quote in my new earthbag book by a world class physicist who specializes in this type of work (building with poly tubes). He supports the theory of earthbags shifting in earthquakes to release stress rather than rigid structures that shatter.

      • That makes me feel better about it! Again though I am still kinda worried about the gravel breaking thru the bags in an earthquake. “Maybe” if I trenched, lined the trench with cut up tire treads (drill holes to allow for drainage, though I only get about 3″ a year here) and then lay gravel bags…… then maybe I would feel totally confident! I dont know……. but I do know I feel better about it all

    • I don’t recommend building with tires at all. They’re much slower to build with than earthbags. They smell awful. And there’s the risk of offgassing. Not everyone agrees about the dangers of tires offgassing, but I am definitely suspicious of claims that say there’s no risk. Why take the risk and why bother when earthbags are faster, simpler and thoroughly proven?

      • I agree with you 100% on the way it is done traditionally….. that is why I thought this new way was sooo much better. There is no pounding/ramming and the tire tread is cut off into long strips. The strips are bolted together and act as a spring in an earthquake. As for the off gassing, I have read that as long as tires are not exposed to UV rays they dont off gas…… I dont know if that is true or not, but it is what I have read on some sites…. The only question I have about earthbag foundations is that they need to be filled with gravel and there is no “glue” to hold the gravel together when the bags eventually decompose…… other then that, Im completely sold on them and am working on an earthbag under and above ground small storage area right now.

        • Polypropylene bags last for hundreds of years if kept out of sunlight. Search this site for the highway transportation study that tested poly bags. So no ‘glue’ is needed if the bags are not in sunlight. Still, I double bag foundation courses for extra strength.

  3. Are the Indian, Columbian, and Japanese standards linked somewhere here? If so, I’ve managed to miss them. I’d certainly like to have them as reference material.



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