ABSTRACT
Superadobe is a patented system at the service of humanity. Superadobe buildings use the structural principles of single and double curvature compression shells that have made arches, domes and also rectangular shapes. Individuals are enabled to build their own homes without the use of heavy equipment, with materials native to the country of use. Flood control, erosion control, stabilization of waters’ edges, hillside slopes and embankments, landscapes and infrastructures are applications in which superadobe system has shown great potential.
INTRODUCTION
Approximately one third of the people of the world live in houses built with earth, and tens of thousands of towns and villages have been raised practically from the ground they are standing on. Today, world consciousness about the use of natural resources and the new perception of building codes as the steward not only of individual’s safety, but of the planet’s equilibrium, are leading us into the new millennium of sustainable living.
A Superadobe structure is made by filling long or short sandbags with earth from the building site and stacking or coiling them in to layers with barbed wares in between to serve as mortar and reinforcement. Bags and wire alone are adequate for short term use, such as in disaster relief; for a permanent home, cement or lime is added to the earth, the walls are coated with plaster, and the exterior gets a waterproof coating. Many Superadobe buildings use the structural principles of single and double curvature compression shells that have made arches and domes last for centuries, but Superadobe can also form rectangular shapes.
History
The technique’s current pioneer is Nader Khalili who originally developed the Superadobe system in 1984 in response to NASA call for housing designs for future human settlements on the Moons & Mars. His proposal was to use moon dust to fill the plastic Superadobe tubes and Velcro together the layers. In 1995 fifteen refugee shelters were built in Iran, Nader Khalili and the Uniteted Nations Development Programme (UNDP) and the United Nations High Commissioner for Refugees (UNHCR) in response to refugees from the Persian Gulf War. According to Khalili the cluster of 15 domes that was built could have been repeated by thousands. The government dismantled the camp a few years later. Since then, Super adobe method has been put to use in Canada, Mexico, Brazil, Belize, Costa Rica, Chile, Iran, India, Siberia, Mali and Thailand ,as well as in the U.S.
STEPS OF CONSTRUCTION
1) Collect the tools
2) Prepare the earth mix which is stabilized with cement or lime, or asphalt emulsion.
3) Add enough water to ball together when squeezed, yet not leave the hand wet. If no cement or lime is available, use raw earth for a temporary shelter. (Experimental - try snow in bags and compact.)
4) Place the door away from wind and water.
5) Dig the foundation trench 30 cm (12”) deep.
6) Level and compact. (The foundation will be 2-3 completed bag rows.)
7) Place the bag in the trench, fold the end under to close, and start filling upright like a short column.
8) Always put in 2-3 cans of earth and shake to the end.
9) Use gravity's help by sloping the bag on your leg and walking backwards as it fills - do not strain. Let the bag fill as full as possible and check the position with the compass tool.
10) Twist and tuck under the bag ends to close.
11) Compact the filled bag as hard as you can using a tamper, to make a smooth, solid, uniform block. Only compacted earth becomes strong.
12) Attach continuous barbed wire - 1 wire for domes up to 4m (12 ft), 2 wires for bigger. Where breaks occur, overlap the wires by 2ft. (65 cm).
13) Continue coiling bags.
14, 15) Use compass to make the dome shape
16) Pre-cut bags for a doorway knock-out Panel. Stabilized earth must be cut after tamping at every row
17) Punch out pre-cut panels to open after a min. of 5 rows, or when the dome is completed
18) Insert pipes for windows sloped to outside for rain
19) Coil upper rows, but don’t stand on the wet bag
20) Fill and place bag above the row below and work it inwards to meet the compass circle. Tamp the bag with gentle slope to outside
21) Add an arched entry to the opening to buttress and protect the entrance
22) Plaster the exterior before bags disintegrate and
23) Waterproof with locally suitable materials to resist moisture and erosion
24) Finish with a water-resistant cement/lime plaster such as Reptile layered from bottom to top, or
25) A smooth cement or lime plasters finish
STRUCTURAL CONSIDERATIONS
Superadobe techniques enable the construction of mono lithic structural systems built entirely from earth in curved forms. The sandbag, because of its flexibility, allows the construction of 9curved surfaces. When using single- and double-curvature compression shells ie arch, vault, dome etc the majority of conventional roofing systems can be eliminated. In the case of wood construction, this can save up to 95 percent of timber, allowing not only for forest products to be more wisely utilized but also resulting in fire-safe buildings. By working with the principle of gravity, these features can be built without special formwork. The success of the tested prototypes for California’s seismic codes and the resulting permits derive from the following principles:
Single- and double-curvature compression shells transfer their stresses along the surface of the structure and not from element to element like column- and beam-type buildings. When a single element in a beam and column construction is overloaded to failure, the loss of that element will create a cascading effect on adjacent elements, causing failure of all elements in the vicinity. In many cases, this will cause the entire structure to collapse, as was witnessed in earthquakes in Northridge, California, and Kobe, Japan. Such a structure is only as strong as its weakest element. In a dome, and to a lesser degree a vault, excessive loads on their surface will first cause a puncture failure. This results in the excessive load being shed with only localized damage; the remaining stresses in the vicinity of the failure are transmitted around the failed area, and other loads continue to be held by the structure without any problem.
Dead-load and live-load stresses are transferred to the supporting ground, spreading uniformly along the perimeter of a dome or bearing wall. In a beam and column structure, the loads are concentrated and transferred to the ground via a footing under each column. This situation creates the two basic structural problems of differential settlement and frost heaving. These can cause severe localized stresses within the upper structure, resulting in cracking and other failures. For this reason, most foundations are extended to below the frost line to minimize such problems. In a monolithic bearing wall, dome or vault, differential settlement and frost heaving do not pose severe problems. The base of a dome or bearing wall distributes the load of the structure over a much larger area, and local soft spots in the supporting soil will not
create a local problem, as local depressions may be easily spanned. The effect of frost can be rendered negligible with correct design when a dome is free to float on the ground.
One of the most significant advantages of a domed or vaulted bearing wall structure is its performance in earthquakes. It is difficult to design conventional structures to withstand earthquake stresses. Their basic shape creates a severe problem, as the building weight is either uniformly spread from roof to foundation or, even worse, weights are often larger in the upper floors. With this propensity for overturning, the deeply planted footings and foundations rip apart at the very base of the structure during an earthquake, causing failures rather than preventing them. Modern earthquake design that incorporates foundation isolation does have shifting capabilities, but it is expensive.
A dome or bearing wall built on a floating foundation, the base isolated by a layer of gravel or sand, provides the ideal earthquake-resistant structure. The continuous or ring foundation can slide across the moving ground, while the upper structure, which diminishes exponentially in mass toward the apex, performs as a unified monolithic piece, eliminating local failure higher up the building.
DISADVANTAGES
UNIVERSAL APPLICATIONS
Modern computer software now allows for structural design analysis on an individual basis. The computer will also permit the utilization of the Superadobe systems in space and planetary construction based on performance programs, such as finite element analysis. The construction of infrastructures, structures and shielding elements, such as for thermal, radiation and/or impact shielding on the moon and Mars, would otherwise imply costly transportation of building materials into outer space. The utilization of in-situ, minimally processed materials, is crucial to space exploration.
Flood control; erosion control; stabilization of waters' edges, hillside slopes and embankments; and retaining walls, landscapes, and infrastructures are applications in which the Sandbag/Superadobe/Superblock system has shown great potential.
Individuals are enabled once again to build their own homes without the use of heavy equipment, with materials native to the country of use. All the skills required are simple and can be acquired by anyone who wishes to learn them. The Superadobe system can use existing contractor’s machinery, such as concrete and gunnite pumps, to mechanize the packing of the fill material into the bag forms.
CONCLUSION
Superadobe is an adobe that is stretched from history in the new century. It is like an umbilical cord connecting the traditional with the future adobe world. Individuals are enabled once again to build their own homes without the use of heavy equipment, with materials native to the country of use. Superadobe has been used internationally by UN for emergency housing prototypes and is currently in limited use on several continents and under construction in several places. While many challenges lie ahead, it is still a hopeful and exciting time to be part of this quest to create a sustainable human culture.
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