I have to laugh when people keep asking me if earthbag building is strong. Earthbags (sand bags) have centuries of use by militaries worldwide, because they’re bomb, blast and bullet resistant. Millions of sand bags are used each year for flood control to stop raging rivers. As well, earthbag building is earthquake and hurricane resistant.
Massive earthbag retaining walls like the one in the photo above are now fairly common. The US Department of Transportation uses so many polypropylene sand bags for retaining walls along highways that they did an accelerated aging test to help determine the lifespan. The study showed polypropylene bags protected from sunlight may last over 500 years, and there is no effect from moisture. See my Earthbag Building ebook and DVD for details and complete step-by-step building information.
Image source: Flexmse.com