Hello, I am building a superadobe dome here in Brazil and was wandering if I could ask you for some advice about safety issues. It is one dome only building with internal diameter about 24.6 ft wide (7.5 m) and we are using 19.7 inches (50 cm) wide poly bags. The estimated height we´ll be achieving soon for the closure of the dome is about 23 ft (7 m). The earth material is a mixture of clay, cement and sand to avoid infiltration because of the high rainfall here. We are planning to make a light dome on top, which will make us finish the dome in a wide internal ring about 6.5 ft
wide (2 m).

My concern is about people´s safety working and moving heavy material in height. I tried to install some hooks with safety ropes and people are using harnesses to move along the wall. We are using movable scaffolding inside the dome to distribute material along the rows, but it is still not working well. I am not sure how to guarantee the safety of the people working during the closure. Another concern of mine is about the structural integrity of a dome this wide, does it need temporary or permanent. anchoring or reinforcement of any kind? Do you know how can I find technical information I could use in this case? See attached photos (not shown here).
Andre

Owen:
Hello Andre, Your project looks pretty good to me. Just be careful though since you’re at about the maximum size dome for earthbags. I would have added some rebar down through the bags as the walls went up. It’s cheap ‘insurance’. If the dome is not perfectly symmetrical, then problems can develop. Be sure to read the article about the Om Dome. They had to tear down the walls because the shape was off just a little, so be careful. If you feel or see anything strange, be prepared to jump to the outside immediately.

Machinery of some sort is the most efficient way to move lots of soil high up on a wall. The next best way is probably a chain gang of sorts, where workers pass 2-gallon buckets from one person to the next. It’s safer to keep all the workers on the outside until the earthbag work is finished. You could use ladders instead of scaffolding if not enough scaffolding is available, or both. And don’t rush things. It does get quite dangerous up on the wall. That’s one reason I like a loft, because it creates a nice work platform. Next time consider embedding lots of short poles between the bags to support planks to stand on. Cut them off when finished. Good luck and please keep us posted.

Kelly:
Hi Andre, I read Owen’s advice and agree with what he suggests. One factor in determining the stability of the building is how much the wall moves or vibrates when being walked on. If it is shaking very much, then I would be more concerned than if it felt rock solid. All of the larger domes that I have made have stabilizing supports or vigas going across at loft level, and this has rigidified the structure considerably. You might want to add something like this for this reason alone, if you feel unsure about the stability. These vigas can also provide a nice platform for further work above to finish the dome.

In studying you photos, I also have a concern about the way that the large arched opening was formed. I see that you still have the supports for it in place, and this might be a good thing. Even though you are using cement stabilized fill, that top bag runs many feet almost horizontally, with practically no arch to it. This concerns me because it is easy for me to visualize that collapsing at some point, after the form is removed. Usually with long superadobe arches people make sure that the bags also arch, especially directly over the top. You can see this in the pictures at http://earthbagbuilding.com/projects/sandbagshelters.htm You might want to provide further solid reinforcement, such as with a steel frame, to help support this area of the opening.

This looks like a fun project, and will certainly be one of the largest earthbag domes that I know about. Do keep us posted on how it turns out.

Owen:
A few more thoughts. Are you using one of the recommended methods for earthbag domes?
Kelly Hart’s method
Two string-lines method
– Catenary dome: explained by Doni and Kaki in their book Earthbag Building – The Tools, Tricks and Techniques

Also, I suggest inspecting the dome about twice a day to see if any gaps develop between courses of earthbags.


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