Earthbag construction
Earthbag construction is an inexpensive building method using mostly local soil to create structures which are both strong and can be quickly built.
Kaki Hunter and Doni Kiffmeyer worked on a variety of projects after studying with Khalili, calling earthbag "flexible form rammed earth".
[6] A 2011 e-book by Geiger, Earthbag Building Guide: Vertical Walls Step-by-Step, provides photo illustrations of the process and discussions of new techniques for low-risk areas.
[7] Many like Akio Inoue, from Tenri University in Japan and Scott Howard of Earthen Hand have tested and built buildings.
While Gernot Minke, the German professor of earthen architecture, first developed a technique of using bags filled with pumice to build walls, architect and builder Nader Khalili helped reintroduce earthbag construction as a modern technique called superadobe for humanitarian efforts (particularly for residential buildings) as well as natural flood control.
Engineer Nabil Taha developed the first general specifications for one type of exterior pinning reinforcement appropriate for the highest seismic risk zones.
[13] Organizations building in Nepal are currently working with engineers to improve and refine reinforcement options for seismic-resistant earthbag.
Each layer usually has two strands of barbed wire on top, that attaches to the bag to prevent slippage and resists any tendency for the outward expansion of dome or rectangular walls.
Contained earth (CE) is based on the original technique, but with specific soil strengths and reinforcement chosen for hazard levels.
CE uses damp, cohesive, tamped bag fill, which bonds strongly with barbed wire and other reinforcement as the wall cures.
Contained gravel (CG) uses fill of any aggregate larger than coarse sand, usually in doubled rice bags, although strong mesh can be used.
Solid CE is hyperadobe built in some type of knit raschel mesh tube, so that the damp earthen fill solidifies between courses.
Sands, stone dust and gravels can survive prolonged flood conditions, but most require special bracing during construction as well as some form of structural skin.
Sand fill may be appropriate for several courses to provide a vibration damping building base, but becomes unstable in ordinary bags above 60–100 cm (24–39 in) in height.
Cement, lime or bitumen stabilization can allow clay soil to withstand flooding or allow sands to be used in traditional bags with a non-structural plaster skin.
United Earth Builders has tried a light straw clay in the hyperadobe mesh tubing to form a layer 200 mm (8") thick outside of a dome.
Clay or sand also have excellent heat retention characteristics and, when properly insulated from the home's exterior, can serve as thermal mass in a passive solar building design in cool climates, keeping interior temperatures stable year-round.
Earthbag using woven bags or tubes need barbed wire for any level of natural hazard since the bag-to-bag surfaces are slippery.
Earthbag of weak soil with no steel can be half the shear strength of unreinforced adobe, which is easily damaged in earthquakes.
New Zealand's code detailing and plans allow unreinforced adobe walls to survive almost 0.6 g forces (comparable to Ss values for 2% probability of excedance in 50 years), but earthbag needs stronger soil to match this strength.
[18] Current earthbag techniques of inserting rebar unattached to base and overlapping without connection may only resist 1.2 g or less, even if using very strong soil.
Base walls of CG in high risk regions may need additional buttresses at the foundation level where builders cannot afford a reinforced concrete (RC) grade beam or footing.
A narrower plastic mesh tube often used for erosion control wattle could be filled with gravel to allow a half-width RC ring beam under the wide walls.
Cover the wall to prevent damage to the bags from UV rays or moisture with cement-based stucco, or lime or earthen plaster.
Since then, local builders flocked to ongoing earthbag training opportunities, including those by Good Earth Global, which have led to official Nepal building code acceptance of this technique for residences.
International NPOs have built hundreds of contained earth or earthbag buildings in Nepal as well, more residences than larger clinics or schools.
