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Earthbag Testing Research Summary

Engineering tests of earthbag structures have begun, mostly at the university level. The understanding of earthbag construction is improving as engineers are laying the groundwork for understanding the physics of these flexible walls with multiple contact planes between varying size rounded bags and soil fill. They have already established that soil in bags can have greater strength than soil alone, and that barbed wire and plaster layers contribute significantly to preventing wall failure.

It is important to note that bags of sand are not earthbags. Standard 14"-15" thick earthbag walls made with fill containing clay that is well tamped and dried, create stronger structures. Adobe, which incorporates clay has been a standard building material for millenia and earthbag is a technology that is also primarily based on the strength of the clay that acts as a binder.

Additional testing in the future can explore the difference between solid poly bags and tubes, and the strengths of walls created with HDPE raschel mesh and other plastic meshes. But currently, the most pressing need is to develop correct dimensional and reinforcement recommendations for the strongest types of bag walls (of solid poly) in hazardous locations.

The large amount of labor by engineers, students, and assistants to create multiple well-tamped test structures of appropriate materials is greatly appreciated. Earthbag builders can volunteer to help create these if testers contact Kelly at kellyhartATgreenhomebuilding.com to post contact information and approximate dates on this website.

Most of the summary commentary on the list of tests below was kindly provided by Patti Stouter.

STRUCTURAL TESTS
LABORATORY TEST REPORTS ON COMPONENTS

2006 Dunbar & Wipplinger (West Point): Prism Testing of Polypropylene Earthbags Compression of 3 bag stacks; Materials: Small solid poly bags 1350 cm² (209 in²) side when filled); rubble, sand, and unspecified ‘dirt’ fill; hand leveled, not moistened or tamped or cured (note: gravel bags single)

2008 Daigle (Queens U): Earthbag Housing: Structural Behavior and Applicability in Developing Countries Compression of 3, 6, & 9 bag stacks and fabric tension; Materials: solid poly 43 x 76 cm (17” x 30”) and 50 x 90 cm (20” x 36”) bags; gravel & two sands with low silt as fill and no clay; tamped with 2x4; dried one month (note: gravel bags single)

2010 Vadgama (Bath U): A Material and Structural Analysis of Earthbag Housing. The behavior of earthbags under uniaxial compression, the effect of material fill level, stack height, addition of stabilizer and bag material on the compressive strength were explored.
LABORATORY TEST REPORTS ON ASSEMBLIES
2009 Pelly (Bath U): Plastic Limit Analysis of Earthbag Structures Unplastered earthbag compression of stacks and 23 cm (9") thick arches that span 1.8 m (6’), shear of single bags and tension of bag fabric; Materials: small solid poly bags end size 18 x 23 x 10 cm (9” x 7” x 4”) well tamped; sand fill or sand with 4% cement (no clay); barbed wire in control; also Ring 2.0 software for prediction

2010 Vadgama (Bath U): A Material and Structural Analysis of Earthbag Housing. The behavior of earthbags under uniaxial compression, the effect of material fill level, stack height, addition of stabilizer and bag material on the compressive strength were explored.

2011 Ross (U Florida Engineers Without Borders): Wind Testing of Earthbag Wall Abstract Out-of-plane displacement of 2.1 m ht x 3.6 m (7’-6” ht x 12’) unplastered, braced wall; tamped silty sand (no clay); solid poly bags 35 cm (14”) thick wall
2011 (Peninsula University of Technology): evaluation of triple channel bag wall built with sand fill
Lateral loading of c-shaped wall with cement stucco 3.6 m (12’) long with 76 cm (2’-6”) returns; Materials: 43 x 92 cm (17” x 36”) 3 channel solid poly bags form 33cm (13”) thick walls; sand fill (no clay); no rebar or barbed wire; reinforced concrete ring beam; earthen plaster
2011 Croft (Bath U Engineers without Borders): Structural Resistance of Earthbag Housing 6 versions of 3’- 6” (1.07 m) ht. x 3’-7” (1.1 m) walls tested for shear and for flexure, barbed wire and rebar tensile strength, cement stucco with chicken wire flexure and compression tests; Materials: Small solid poly bags form 23 cm (9”) thick walls; sand fill or sand with 5% cement; barbed wire, vertical rebar, and cement stucco with chicken wire alternates.
2011 Si Hong Liu, et al (Advanced Materials Research) Cyclic Simple Shear Tests on Base Isolation Using Soilbags Soilbags have been understood to have the effect of vibration reduction and can be used as a kind of base isolation in building foundations. In this paper, a series of cyclic simple shear tests were carried out on soilbags filled with three kinds of soils under different vertical stresses to investigate the damping and stiffness characters of the soilbags. The results show that soilbags have a relatively high damping ratio and variable horizontal stiffness so that they can be used as base isolation materials.
2013 Awais Malik Structural Analysis of Earthbag Systems First Earthbag Shake Table Tests Create a Computer Model. Awais Malik dedicated 6 weeks to sew small bags, twist custom barbed wire, and plaster the corners of 1/6 scale models of 3 kinds of corners. Despite difficulties with outputs he was able to use the results of the shake test to create a computer simulation accurate to within 1.5%. Engineers use computer programs that simulate the violent stresses earthquakes cause to buildings, to learn without destruction. Mr. Malik's testing showed that 2 narrow corner buttresses or one massive thickened corner pier reduce earthbag wall motion under vibration by 26% and 33% respectively.
TESTS ON ENTIRE BUILDINGS

1998 Khalili & Vottore: Earth Architecture and Ceramics: The Sandbag/Superadobe/ Superblock Construction System An article outlining the chronology and results of testing done on Nader Khalili's superadobe system of building. Simulated static and dynamic load tests of domes and vaults. No test report available.

2010, Pakistan Straw Bale and Appropriate Building (PAKSBAB) Seismic Performance of Innovative Straw Bale Wall Systems The objective of this research project was to determine the capacity of clay plastered, load bearing, straw bale wall assemblies under in-plane cyclic loading, and the performance of a small full-scale straw bale house using shake table simulation. The straw bales were resting on a soil cement encased gravel bag foundation.
COMPUTER MODELING OF BUILDINGS
2009 Sargentis et al (conference paper):Earth Building: Models, Technical Aspects, Tests and Environmental Evaluation Preliminary structural evaluation of 4 m (interior) dome; Nastran NX with FEMAP v9.3 postprocessor
OBSERVATIONS, TESTING DESCRIPTIONS & INFORMAL EXPERIMENTS

2003 Hart: An Amazing Experiment If anyone had any doubts about the strength and integrity of this system of building, this experiment should help allay those concerns. Earthbag building of this sort can be STRONG!

2010 Stouter: Friction and Tensile Strength of EB Components Friction of two bag stacks with barbed wire, and tension pullout of barbed wire; Materials: solid poly bags, tamped subsoils with clay, cured & tamped subsoil for pullout test

2011 Stouter: Shear Strength of Earthbag Wall with Weak Cohesive Fill Shear strength of plastered 4' x 4'/ 1.2 x 1.2 m bag wall (15" / 38 cm thick) of weak cohesive soil with barbed wire; Materials: solid poly bags, tamped subsoils of silt and clay, lime and earthen plaster
THERMAL PERFORMANCE TESTS
OBSERVATIONS, TESTING DESCRIPTIONS & INFORMAL EXPERIMENTS

2011 Stouter: Experiments with Light Clay Insulation R-value and density of light clays made with 8 different materials

COMPUTER MODELING OF BUILDINGS
2009 Sargentis et al (conference): Earth Building: Models, Technical Aspects, Tests and Environmental Evaluation Thermal evaluation of 4 m (interior) dome with ECOTECT software
2011 Nijs & Schiettecatte (U Ghent): De bouwfysische…/ The construction and physical performance of earthbag dome houses in different climatic zones. Thermal evaluation of 4 m interior dome of earth fill with clay and earthen plaster in 6 different climates with mitigating measures; used Capsol 4.0 software. Available online early July, 2011.
 
BACKGROUND INFORMATION
Understanding of the strengths and limitations of earthbag is deepening, as is the difference between earthbag and now-accepted construction like adobe. Earthbag builders want to see appropriate performance-based standards develop for earthbag buildings of different types like those sited below that have been developed for adobe, CEB, and rammed earth.
EARTHEN BUILDING STANDARDS FOR ADOBE, RAMMED EARTH, CEB
1998 New Zealand Standards: Earth Buildings not Requiring Specific Design NZS 4299
2001 Minke: Construction Manual for Earthquake Resistant Houses Built of Earth (BASIN)
2004 International Association for Earthquake Engineering, National Information Center for Earthquake
Engineering: Guidelines for Earthquake Resistant Non-Engineered Construction
undated Neumann et al: The Peruvian Building Code for Earthen Buildings
2010 ASTM: Standard Guide for Design of Earthen Wall Building Systems E2392/E2392M-10
EARTHEN BUILDING TESTING
2006 New Zealand Society for Earthquake Engineering: Assessment and Improvement of the Structural Performance of Buildings in Earthquakes
2006 Morris: New Zealand: Aseismic Performance-Based Standards, Earth Construction, Research, and Opportunities
undated Shahzada (U of Engineering & Tech, Peshawar): Improvement of Masonry Structures Against Seismic Force
undated Torrealva et al (Catholic U of Peru): Earthquake Resistant Design Criteria and Testing of Adobe Buildings...
undated Dowling & Samali (U Technology Sydney): Low-Cost and Low-Tech Reinforcement Systems for Improved Earthquake Resistance of Mud Brick Buildings
2008 Mizuhashi et al (conference): Analytical Study on Geotextile-Reinforced Soil Retaining Walls…
2009 Brignola et al (U Genoa): Identification of Shear Parameters of Masonry Panels Through the In-Situ Diagonal Compression Test
2010 Walker & Morris: Development of New Performance Based Standards for Earth Building
2010 Torrealva, Newman, Blondet (Peru: Pontificia Universidad): Earthquake Resistant Design Criteria and Testing of Adobe Buildings
GEO-SYNTHETIC TESTING (SOIL BAGS OR GEO-CELLS FOR SITE STRUCTURES, RETAINING WALLS)
undated Kim et al (Hongik U): A Fundamental Approach … Using Seeded Sandbags
2006 Aqil et al: Application of stacked soil bags to repair and maintenance works of small earth dams
2006 Lohani et al: Evaluating the strength and deformation characteristic of a soil bag pile… Geosynthetic International, 13(6), 246-264.
2006 Matsuoka & Liu: A new earth reinforcement method using soilbags. London: Taylor & Francis. Included soil bags as damping layers to reduce vibration transmitted from traffic
2007 Krahn et al: Large scale interface shear testing of sandbag dyke materials. Geosynthetic International, 14(2), 119-126
2007 Singh (Auburn University) Construction Technique and Strength of Connected Regolith Bag Structures. Discussion of arch forces in 9' high unreinforced vault. Materials: custom solid poly rectangular bags sewn together with 24" thick wall base, 12" thick upper walls, vermiculite fill.
2008 Mizuhashi, et al: Analytical Study on Geotextile-Reinforced Soil Retaining Walls Damaged During the 2004 Mid Nigata Prefecture Japan Earthquake.
2008 Matsushima et al: Shear strength and deformation characteristics of geosynthetic soil bags stacked horizontal and inclined Geosynthetics International, 15 (2)119-135 Shear of 3 bag stacks level and inclined; pre-compacted bags; fill of fine sand & sandy gravel
2008 Tantono & Bauer (conference): Numerical Simulation of a Soilbag under Vertical Compression
2008 Xu et al: Earth reinforcement using soilbags. Geotextiles and Geomembranes, 26 (3), pp.279-289.
2009 Leshchinsky et al: Equivalent Seismic Coefficient in Geocell Retention Systems, (Geotextiles and Geomembrances, Volume 27:1, February 2009) 9- 18
2011 Ansari et al: Numerical analysis of soilbags under compression and cyclic shear. Computers and Geotechnics 38(5) July 2011, Pages 659-668
THERMAL PERFORMANCE OF EARTH BUILDINGS

2003 D. M Ogoli: Predicting indoor temperatures in closed buildings with high thermal mass. Energy and Buildings, 35(9):851–862, 2003, ISSN 0378-7788.

The above list of earthbag testing includes links to many public domain reports. If you are doing structural research in earthbag construction and would like to be in touch with authors of the papers that are not public domain, email Owen Geiger (strawhousesATyahoo.com) or Patti Stouter (simple_earthATyahoo.com) and ask them to forward your email to the author in question.

 

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