Earth construction has recently attracted great interest as post-Peak building method for the First World. (By post-Peak methods, I mean methods of producing useful products which are suitable for a declining or collapsing economy whose resource base is drying up.) The reasons for this interest have to do with looming resource constraints, in particular, the resources required for construction methods which have become standard over the last hundred years in the developed world. However, the principles of proper earth building design and construction must be thoroughly understood and properly implemented in order to avoid loss of life due to failure and collapse of buildings. There is a strong need for validation of techniques, practices and principles of structurally sound earth building. This validation must be accomplished via experimentation and mathematical modeling and analysis.
This validation is also of special interest in the Third World (also known as the developing world), where, according to at least one source, approximately one fifth of the world's population lives in adobe and rammed earth structures, and where, according to another source, more than 90 percent of the population in moderate to severe seismic zones is living and working in non-engineered earth buildings. A body of work now exists which documents the behavior of earth buildings when subjected to various loading events, including seismic and wind events. This development of this body of work has been spearheaded by engineering professionals, universities and governmental agencies both in the developing world and in the First World nations of the Global South.
This work reveals some surprising facts, both with regard to safe earth construction best practices and with regard to the flow of useful information in the developing world. As far as the flow of useful information, two things can be observed. First, there is a much greater proportion of public-minded engineering and technical professionals in the developing world compared to professionals in the First World. This is seen in the willingness of researchers to openly and freely disseminate their published work via the Web without charging rent on “intellectual property.” In the First World, on the other hand, rent-seeking vultures have restricted the free flow of potentially life-saving technical information in many cases. (Many of the publications from First World sources on the topic of earth construction are behind paywalls. One refreshing exception in the United States is the Getty Institute.) This is one reason why the Third World may be better poised for post-Peak adaptation than the First World. Secondly, the universities and professionals of the Third World are every bit as capable and competent as those in the First World, and in fact they may be far more creative.
In the literature which I have discovered, there are two categories of discussion regarding performance of earthen structures: the performance of non-engineered structures and the performance, experimental testing and analysis of engineered earthen structures. These discussions reveal the following observations:
Almost all of the literature states that typical non-engineered earthen structures perform very poorly when subjected to severe and sudden wind loads or seismic events. This applies both to rammed earth (also known as tapia, taipal or pise de terre), cob and adobe structures. Rammed earth constructions and other earth structures can be highly susceptible to damage from earthquakes and other ground motion.
The mechanism of disintegration of earth walls for various types of earth construction have been studied via shake table and compression tests. Among other things, these tests have documented the anisotropy of multi-layer rammed earth walls. A material that is anisotropic has physical properties that vary at different locations and in different directions in the material rather than being uniform throughout the material. This is important if there is a concern that a wall made of anisotropic material might have material properties that are not constant throughout the wall.
Techniques for stabilization and reinforcement of earth structures have been studied. One study focused on two particular approaches: internal reinforcement via chicken wire or bamboo, and external reinforcement with bamboo or wooden members. Internal reinforcement did not work nearly as well as external reinforcement, which spread earthquake stresses over a large wall area, dissipating earthquake energy without causing major cracking.
Proper reinforcement of earthen walls is key to surviving earthquakes and other environmental events. Unreinforced earthen structures suffered a number of typical failure modes. In addition, walls or wall elements that are reinforced internally with biodegradable materials like straw have been known to fail due to degrading of the reinforcement by insects and rot.
As a result of laboratory tests, mathematical modeling and observations of actual earth structures in the aftermath of actual earthquakes, a number of governmental agencies and NGO's have published earth construction design guides. Many of these design guides agree on key points. In addition, there are countries in the developing world and the Global South which have formulated or are formulating earth building codes. New Zealand is one such case. Their New Zealand Earth Building Standards can serve as a repository of best practices and a starting place for model codes for earth building in other countries. Unfortunately, access to the New Zealand standards is not free.
In addition to design guides for building professionals and code-enforcing officials, certain governments and NGO's have developed earth construction manuals for non-professional, unskilled builders who would be typical in rural or poor urban populations. Among the governmental agencies disseminating this design information is SENA (Servicio Nacional de Aprendizaje, www.sena.edu.co), a national public entity of Colombia in South America, which publishes literature for public education and vocational training throughout South America. In addition, the Indian Institute of Technology at Kanpur has published the IAEE Guidelines for Earthquake Resistant Non-Engineered Construction, which is available in PDF form free of charge at the IIT Kanpur National Information Centre of Earthquake Engineering website. A 2011 draft update of these guidelines is also available from the International Institute of Seismology and Earthquake Engineering in Japan. Such guidelines embody low-cost, effective approaches for building safe earthen structures.
Researchers have studied the challenge of reinforcing and retrofitting existing earthen structures which have historical significance. Recommended retrofit practices are emerging. Many of these retrofit practices involve addition of bamboo reinforcement to the exterior surfaces of earth walls, both outside and inside an earthen structure, in order to spread forces and stresses so that they don't result in concentrated failure at one point.
Many more facts could be gleaned from the available literature, but unfortunately, I am out of time. However, a list of references and cited works is included at the end of this post. Enjoy!
Additional References And Resources:
“Seismic Behavior and Rehabilitation Alternatives for Adobe and Rammed Earth Buildings,” Luis. E. Yamin, Camilo A. Phillips, Juan C. Reyes, Daniel M. Ruiz, 13th World Conference on Earthquake Engineering, 2004.
“Modern and historic earth buildings: Observations of the 4th September 2010 Darfield Earthquake,” H.W. Morris, 9th Pacific Conference on Earthquake Engineering – Building and Earthquake-Resilient Society, April 2011.
“Non-Engineered Construction In Developing Countries – An Approach Toward Earthquake Risk Reduction,” Anand S. Arya, 12WCEE 2000, Ministry of Urban Development, Government of India.
“Review of Non-Engineered Houses in Latin America with Reference to Building Practices and Self-Construction Projects,” Aikaterini Papanikolaou, Fabio Taucer, European Commission Joint Research Centre, 2004.
“Seismic Performance of Mud Brick Structures,” Joseph Hardwick and Jonathan Little, University of Bristol, EWB-UK National Research Conference 2010 and Engineers Without Borders UK, 2010.
“Low-Cost and Low-Tech Reinforcement Systems for Improved Earthquake Resistance of Mud Brick Buildings,” Dominic M. Dowling and Bijan Samali, The Getty Institute.
“Assessing the Anisotropy of Rammed Earth,” Quoc-Bao Bui, Jean-Claude Morel, 11th International Conference on Non-Conventional Materials and Technologies, 2009.
“Planning and Engineering Guidelines for the Seismic Retrofitting of Historic Adobe Structures,” E. Leroy Tolles, Edna E. Kimbro, William S. Ginell, The Getty Institute, 2002.
“An Improved Means of Reinforcing Adobe Walls – External Vertical Reinforcement,” Dominic Dowling, Bijan Samali, Jianchun Li, SismoAdobe 2005, Lima, Peru.
“Earthquake Resistant Rammed-Earth (Taipal) Buildings,” J. Vargas, Catholic University of Peru.