Our ever alert researcher into all things earthen, Patti Stouter, has found that testing has confirmed that earthbags can provide excellent base isolation to lessen the impact of earthquakes and severe winds on buildings. The Advanced Materials Research group has published a paper titled Cyclic Simple Shear Tests on Base Isolation Using Soilbags.
“Soilbags have been understood to have the effect of vibration reduction and can be used as a kind of base isolation in building foundations. In this paper, a series of cyclic simple shear tests were carried out on soilbags filled with three kinds of soils under different vertical stresses to investigate the damping and stiffness characters of the soilbags. The results show that soilbags have a relatively high damping ratio and variable horizontal stiffness so that they can be used as base isolation materials.” They go on to say that the bags can even be filled with construction waste rubble and still be effective.
Studies like this will likely put earthbag technology in the forefront of building design for safety! You can read more details about their study at the above link, and can purchase the entire paper if you want.
6 thoughts on “Earthbags Provide Excellent Base Isolation”
Is this suitable for multi storey buildings ?
Multi-story earthbag buildings are possible in non-seismic areas. See my Earthbag House Plans site for some examples: http://earthbagplans.wordpress.com/
I would stick to one story structures in seismic areas.
A base isolation system of rubber can reduce the strength needed for walls by about 30% on a multistory building of conventional materials.
After sand or gravel-filled earthbags have been tested on a shake table with floor infill, we may find that in a similar way, we can safely use lower strength walls above them.
But we don’t yet know how strong earthbag walls are, under sideways forces like winds, or under shaking. We need to know more about how best to reinforce earthbags and just how much force specific size walls of the strongest or medium-strength soils can resist.
So for now, Owen’s advice is the best. We shouldn’t build multi-story buildings of earthbag in seismic areas until we know more.
A base story of earthbag might be fine to support a well-braced light weight upper story wall like wood or bamboo structure with wood or bamboo sheathing, or with some light infill like light clay or trash wattle. But the advice of an engineer about the soils under and in the walls would be a good thing.
Several engineers at universities have recently expressed an interest in testing earthbag walls built with cohesive soil. Some are waiting for large grants to be available, others might do small tests with modest amounts of money.
In the meanwhile, I am about to start a series of test walls at my new Albuquerque home. I need $500 to invest in a hydraulic arm machine to do in-plane testing. Any volunteers to help build or advise or even small donations to help with the building materials would be very welcome.
The full research paper proves that a stack of 4 bags filled with sand or silt can stop many quake vibrations from passing through to the building. They performed as well as the costly high quality rubber bearings used to greatly reduce the need to stiffen buildings around the world.
Base isolation reduces the movement of buildings in quakes. This preserves non-structural walls and prevents equipment and furniture from also causing damage.
I am trying to contact the authors and find out their first guesses for detailing. Note that these were loose types of fill. Normal earthbag fill that is moist, contains clay, and is tamped into a solid block may not have this effect.
Coarse sand or loose sandy silts without clay may be needed as a special plinth section of 4 or 5 courses, to be topped with adobe-type bags filled with strong clay soil and/ or a ring beam. We don’t know yet how well gravel can function to stop transmission of earthquake vibrations. But gravel bags form a flexible footing that should probably be a part of the total building plan.
This sandbag base isolation layer may become standard for all earthen or concrete buildings in hazardous areas. Included sections of narrower sandbags may also be used to provide damping and absorb energy between separate parts of larger masonry buildings. There’s a lot to find out, but lives will be saved!
Excellent news. Thanks for the update, Patti. This could very well become more mainstream. I look forward to hearing from the researchers and will gladly publish a follow-up blog post on the subject.
Readers need to be aware that silt will turn to mud if it gets wet, which is highly probably in a below grade application, and so silt is not the best choice. Sand may be the best choice, although it’s less stable than gravel when bags are stacked in a wall. Gravel will shift or give much like sand and so that would be my recommendation at this point. Rebar and mesh on both sides will help contain the bags. In case anyone missed it, see my blog post on Seismic Resistant Gravel Bag Foundations. http://earthbagbuilding.wordpress.com/2011/09/18/seismic-resistant-gravel-bag-foundations/
This is fantastic news. The earthbag community has been unable to fund tests, but proactive scientists and engineers understand the logic and are doing the tests. Our Testing page at EarthbagBuilding.com has an extensive list of tests conducted so far: http://www.earthbagbuilding.com/testing.htm
And I’m very glad to see that rubble can be used effectively. Most foundation courses are gravel (sometimes rubble) to prevent wicking of moisture. This test covers the PAKSBAB shake table test: http://earthbagbuilding.wordpress.com/2010/11/24/flood-and-earthquake-resistant-earthbag-foundations-in-pakistan/