seismic-resistant earthbag. Construction method Construction usually begins by digging a trench to undisturbed mineral subsoil, which is partially filled with stones and/or gravel to create a rubble trench foundation. In high seismic risk regions a reinforced concrete footing or grade beam may be recommended. Earthbag buildings can also be built on conventional concrete slabs (though this is more expensive and uses more embodied energy than a rubble trench foundation) and can have a bermed or underground "floating" foundation like an earthship as well. Several courses of gravel in doubled woven bags form a water-resistant foundation. 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. Bags on the course above are offset by —half of the wall width—similar to running bond in masonry. Bags can either be pre-filled with material and hoisted up, or bags or tubes are filled in place. The weight of the earthen fill locks the bag in place on the barbed wire below. A light tamping of the bags or tubes consolidates the moist clay-containing fill and creates interlocking bags or tubes anchored on the barbed wire. Container types Solid-weave polypropylene is most popular, available around the world to transport rice or other grains. Polypropylene is low cost and resists water damage, rot, and insects. Tubes are often available from manufacturers who sew them into bags. Mesh tubes of soft crocheted poly fibers are also used, although stiff extruded mesh or woven mesh bags can also be used. Organic/natural materials such as hemp, burlap (like "gunny sacks") can be used. Since these may rot, they should only be used with cohesive fills (containing a significant proportion of clay) that form solid masses when tamped. Terminology Earthbag is now a varied family of techniques. Each type of fill and container has different strength and reinforcement requirements. For hazardous locations, accurate terminology is needed. 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. CE is not "sandbags". Contained sand (CS) uses sand fill or any fill too dry or with poor cohesion that performs structurally like sandbags. CS must be built with solid-weave fabric bags