structural resistance of earthbag housing

Panel Presentation: Habitat Author: Chris Croft Institution: University of Bath

Structural resistance of earthbag housing

Undergraduate student, University of Bath

Abstract

Earthbag structures have great potential for low cost and low carbon houses and shelters, yet little is known about their structural behaviour. This research project seeks to build upon the small amount of existing research by carrying out analysis and testing on wall sections. The outline of this pr

Keywords: Shelter, habitat, disaster relief, low carbon construction

1. Introduction

The ability to construct shelters with the materials available on any site, with the only prerequisites blightweight polypropylene bags, possibly some barbed wire and several extra hands is a very useful one. It is this simplicity that makes creating houses out of earthbags (more commonly referred to as sandbags), a potential option for use as disaster shelters as well as permanent housing.

Historically the military have utilised this building method fairly extensively for temporary outposts and for domestic applications such as flood defence retaining walls. In the 20Germany, Gernot Minke explored earthbag domes, or flexible rammed earth, for use as low cost, earthquake resistant houses in Guatemala. Subsequently an Iranian architect called Nader Khalili working in California has greatlytheir use as permanent and ‘modern’ houses.

Khalili founded Cal-Earth (The California Institute of Earth Art and Architecture) where several prototypes and projects

have been undertaken as shown in Figure 1. The houses can be rendered, which prdamage, fitted with windows and supplied with services.

2. Advantages and Disadvantages of Earthbag Construction

As mentioned above, the low cost and wide availability of materials are great advantages to using earthbags. Athe relatively straight-forward construction technique is highly adaptable with no pre determined limits on dimensions or the possibility of annexes. An advantage earthbag structures have over timber shelters is the inherent thermal mass, which provides insulation from extreme external temperatures and dampens high diurnal fluctuations.

One of the drawbacks of earthbag structures is the high labour demand for tamping down each course of bags (however the skills required are simple and easily taught)Secondly, as with many natural building materials, there is little or no authoritative guidance in the form of building codes or standards to provide a guide on the design or assessment of structures. Finally there may be cubarriers relating to the image of earthbag houses as suitable modern houses.

One of the many barriers in creating a form of technical guidance is the complex behaviour of the material under load. . It does not behave lineardeformable, which does not lend the comparison to more popular materials such clay fired masonry (which behaves rigidly).

EWB-UK National Research & Education Conference 2011

Structural resistance of earthbag housing C.S Croft

Undergraduate student, University of Bath

Email: [email protected]

tructures have great potential for low cost and low carbon houses and shelters, yet little is known about their structural behaviour. This research project seeks to build upon the small amount of existing research by carrying out

ll sections. The outline of this project is laid out in this paper

Shelter, habitat, disaster relief, low carbon construction

The ability to construct shelters with the materials available on any site, with the only prerequisites blightweight polypropylene bags, possibly some barbed wire and several extra hands is a very useful one. It is this simplicity that makes creating houses out of earthbags (more commonly referred to as sandbags), a potential option for

s disaster shelters as well as permanent housing.

Historically the military have utilised this building method fairly extensively for temporary outposts and for domestic applications such as flood defence retaining walls. In the 20th century their use became spread globally and in 1970s Germany, Gernot Minke explored earthbag domes, or flexible rammed earth, for use as low cost, earthquake resistant houses in Guatemala. Subsequently an Iranian architect called Nader Khalili working in California has greatlytheir use as permanent and ‘modern’ houses.

Earth (The California Institute of Earth Art and Architecture) where several prototypes and projects

have been undertaken as shown in Figure 1. The houses can be rendered, which protects the polypropylene from UV damage, fitted with windows and supplied with services.

Advantages and Disadvantages of Earthbag Construction

As mentioned above, the low cost and wide availability of materials are great advantages to using earthbags. Also,

forward construction technique is highly adaptable with no pre determined limits on dimensions or the possibility of annexes. An advantage earthbag structures have over timber shelters is the

es insulation from extreme external temperatures and dampens high diurnal

One of the drawbacks of earthbag structures is the high labour demand for tamping down each course of bags (however the skills required are simple and easily taught). Secondly, as with many natural building materials, there is little or no authoritative guidance in the form of building codes or standards to provide a guide on the design or assessment of structures. Finally there may be cultural

image of earthbag houses as

One of the many barriers in creating a form of technical guidance is the complex behaviour of the material under load. . It does not behave linear-elastically and the bags are

t lend the comparison to more popular materials such clay fired masonry (which behaves

Figure 1: Earthbag Domes at Cal Earth [1]

UK National Research & Education Conference 2011

‘Our Global Future’

4th March 2011

54

tructures have great potential for low cost and low carbon houses and shelters, yet little is known about their structural behaviour. This research project seeks to build upon the small amount of existing research by carrying out

The ability to construct shelters with the materials available on any site, with the only prerequisites being a supply of lightweight polypropylene bags, possibly some barbed wire and several extra hands is a very useful one. It is this simplicity that makes creating houses out of earthbags (more commonly referred to as sandbags), a potential option for

Historically the military have utilised this building method fairly extensively for temporary outposts and for domestic me spread globally and in 1970s

Germany, Gernot Minke explored earthbag domes, or flexible rammed earth, for use as low cost, earthquake resistant houses in Guatemala. Subsequently an Iranian architect called Nader Khalili working in California has greatly developed

Earth (The California Institute of Earth Art and Architecture) where several prototypes and projects

otects the polypropylene from UV

elastically and the bags are t lend the comparison to more popular materials such clay fired masonry (which behaves

Earthbag Domes at Cal Earth [1]

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3. Previous research and codes of practice

Australia, New Zealand, Spain and Zimbabwe are among the countries which provide national guidance for construction with earthen materials. In general they focus on adobe, pressed earth brick or rammed earth construction and do not take into account the specifics of a bagged form of earthen construction, which could be quite different due to the influence of soil-bag and bag-bag interaction.

In the last eight years or so a reasonable amount of experimental research has been undertaken on the properties of single earthbags or stacks of earthbags in compression (see Refs [2] [3] [4]). Last year a joint masters research proby Pelly and Vadgama at the University of Bath examined the compression of earthbag stacks, the behaviour of arches under vertical load and compared experimental results to theory. They also determined values for the coefficient of friction and cohesion between two bags and the tensile capacity of the bags [5] [6].

The next required step for understanding how whole earthbag structures behave is to understand how building elements such as walls and forms such as domes behave. The effects of vertical, must their performance in fires. A preliminary framework for assessment is set out in Table 1.

Table 1: An initial framework for understanding earthbag structures

Single bag Wall

Direct compression Vertical loads

Tension (bag) Longitudinal shear

Bag-bag Friction Flexure

Earthbag domes have been reported to perform adequately under stringent seismic testcircular form in plan provides a continuous path for horizontal movements to be carried with no sharp changes in geometry or strength. Also the ductile behaviour of the bags could dampen the seismic movements passively.

4. Proposed Investigation

The proposed laboratory tests are to place earthbag walls under longitudinal shear and transverse shear (flexural) loads. In conjunction with these experiments a comparative study into the accuracy of different structural models for earthbuildings will be undertaken. The laboratory experiments will test walls 10 bags high (bags filled with coarse sand (20kg per bag). The basic setup for both the longitudinal shear test and the flexural test are displayed in Figure 2.

Figure 2: Longitudinal shear test (left) and flexural load test (

Loads will be cyclically incremented until ultimate limit failure while vertical and horizontal deformations are also monitored. Particle image velocimetry (P.I.V) will be used where appropriated to track movement across a whole face, which will then provide useful data for interpreting the tendency for the bags to deform (as well as the magnitude of deformations).

Additional tests will seek to understand the benefits of making minor adjustments to the design of the walls to see if strength can be significantly improved. The effect of variables such as stabilised fill, barbed wire between courses and steel reinforcement stakes will be explored


Previous research and codes of practice

Australia, New Zealand, Spain and Zimbabwe are among the countries which provide national guidance for construction ith earthen materials. In general they focus on adobe, pressed earth brick or rammed earth construction and do not

take into account the specifics of a bagged form of earthen construction, which could be quite different due to the bag interaction.

In the last eight years or so a reasonable amount of experimental research has been undertaken on the properties of single earthbags or stacks of earthbags in compression (see Refs [2] [3] [4]). Last year a joint masters research proby Pelly and Vadgama at the University of Bath examined the compression of earthbag stacks, the behaviour of arches under vertical load and compared experimental results to theory. They also determined values for the coefficient of

ion between two bags and the tensile capacity of the bags [5] [6].

The next required step for understanding how whole earthbag structures behave is to understand how building elements such as walls and forms such as domes behave. The effects of vertical, lateral and seismic loadings must be known as must their performance in fires. A preliminary framework for assessment is set out in Table 1.

An initial framework for understanding earthbag structures

Arches/Domes Whole structures

Vertical loads Vertical loads Seismic loads

Longitudinal shear Lateral loads Fire resistance

Seismic loads -

Earthbag domes have been reported to perform adequately under stringent seismic tests [7], presumably since their circular form in plan provides a continuous path for horizontal movements to be carried with no sharp changes in geometry or strength. Also the ductile behaviour of the bags could dampen the seismic movements passively.

The proposed laboratory tests are to place earthbag walls under longitudinal shear and transverse shear (flexural) loads. In conjunction with these experiments a comparative study into the accuracy of different structural models for earth

The laboratory experiments will test walls 10 bags high (≈1.5m) with the polypropylene bags filled with coarse sand (20kg per bag). The basic setup for both the longitudinal shear test and the flexural test are

) and flexural load test (right) setup

Loads will be cyclically incremented until ultimate limit failure while vertical and horizontal deformations are also try (P.I.V) will be used where appropriated to track movement across a whole face,

which will then provide useful data for interpreting the tendency for the bags to deform (as well as the magnitude of

the benefits of making minor adjustments to the design of the walls to see if strength can be significantly improved. The effect of variables such as stabilised fill, barbed wire between courses and steel reinforcement stakes will be explored



4th March 2011

55

Australia, New Zealand, Spain and Zimbabwe are among the countries which provide national guidance for construction ith earthen materials. In general they focus on adobe, pressed earth brick or rammed earth construction and do not

take into account the specifics of a bagged form of earthen construction, which could be quite different due to the

In the last eight years or so a reasonable amount of experimental research has been undertaken on the properties of single earthbags or stacks of earthbags in compression (see Refs [2] [3] [4]). Last year a joint masters research project by Pelly and Vadgama at the University of Bath examined the compression of earthbag stacks, the behaviour of arches under vertical load and compared experimental results to theory. They also determined values for the coefficient of

The next required step for understanding how whole earthbag structures behave is to understand how building elements lateral and seismic loadings must be known as

Whole structures

Seismic loads

Fire resistance

s [7], presumably since their circular form in plan provides a continuous path for horizontal movements to be carried with no sharp changes in geometry or strength. Also the ductile behaviour of the bags could dampen the seismic movements passively.

The proposed laboratory tests are to place earthbag walls under longitudinal shear and transverse shear (flexural) loads. In conjunction with these experiments a comparative study into the accuracy of different structural models for earthbag

≈1.5m) with the polypropylene bags filled with coarse sand (20kg per bag). The basic setup for both the longitudinal shear test and the flexural test are

Loads will be cyclically incremented until ultimate limit failure while vertical and horizontal deformations are also try (P.I.V) will be used where appropriated to track movement across a whole face,

which will then provide useful data for interpreting the tendency for the bags to deform (as well as the magnitude of

the benefits of making minor adjustments to the design of the walls to see if strength can be significantly improved. The effect of variables such as stabilised fill, barbed wire between courses and


The first type of analysis to be carried out will be a continuous rigid limit state analysis for both load cases. This is the simplest model which ignores the deformability and nondiscreet element analysis package will then be used to model the walls for both nonbehaviour.

5. Our global future - A step towards design and assessment of earthbag houses

It is through the innovative use of readily available materials that arecreate sustainable homes for ourselves and for the generations to come. However we need to provide these solutions in conditions which are challenging and for those least fortunate.

Once the analysis of the walls has been carried out, a broader study of earthbag structures will correlate their behaviour to that shown in the different models. The arches and compression stacks tested in Pelly and Vadgama’s research will be added to sample structures for preliminary assessment for accurate modelling.

It is through accurate modelling that the design and assessment of earthbag structures can begin to be undertaken more competently. This is hopefully a step in a process to allow further use of earthbag structuand to do so with confidence.

6. References

[1] Cal-Earth Inc. / Geltaftan. (2010, February 11).

Earth: http://calearth.org/galleries/eco

[2] Lohani, T., Matsushima, K., Aqil, U., Mohri, Y., & Tatsuoka, F. (2006). Evaluating the strength and deformation

characteristics of a soil bag pile from full

[3] Tantono, S. (2007). The mechanical behavior of a

Institute of Applied Mechanics.

[4] Xu, Y., Huang, J., Du, Y., & Sun, D. (2008). (26), 279-289.

[5] Pelly, R. (2010). Plastic limit analysis of earthbag structures.

Architecture and Civil Engineering.

[6] Vadgama, N. (2010). A Material and Structural Analysis of Earthbag Housing.

Bath, Department of Architecture and Civil Engineering.

[7] Khalili, N. and Vittore, P. (1998). Earth Architecture and Ceramics: The Sandbag/Superadobe/Superblock

Construction System. International Conference of Building Officials


pe of analysis to be carried out will be a continuous rigid limit state analysis for both load cases. This is the simplest model which ignores the deformability and non-linear behaviour of the bags but provides a quick result. A

ackage will then be used to model the walls for both non-linear rigid and non

A step towards design and assessment of earthbag houses

It is through the innovative use of readily available materials that are in renewable supply locally that we will be able to create sustainable homes for ourselves and for the generations to come. However we need to provide these solutions in conditions which are challenging and for those least fortunate.

the walls has been carried out, a broader study of earthbag structures will correlate their behaviour to that shown in the different models. The arches and compression stacks tested in Pelly and Vadgama’s research will be

eliminary assessment for accurate modelling.

It is through accurate modelling that the design and assessment of earthbag structures can begin to be undertaken more competently. This is hopefully a step in a process to allow further use of earthbag structures in increasingly diverse ways

Earth Inc. / Geltaftan. (2010, February 11). Cal Earth photo gallery. Retrieved November 20, 2010, from Cal

Earth: http://calearth.org/galleries/eco-dome.html

hima, K., Aqil, U., Mohri, Y., & Tatsuoka, F. (2006). Evaluating the strength and deformation

characteristics of a soil bag pile from full-scale laboratory test. Geosynthetics International ,13

The mechanical behavior of a soilbag under vertical compression. Graz University of Technology,

Xu, Y., Huang, J., Du, Y., & Sun, D. (2008). Earth reinforcement using soilbags. Geotextiles and Geomembranes

analysis of earthbag structures. Dissertation (M.Eng.). University of Bath, Department of

A Material and Structural Analysis of Earthbag Housing. Dissertation (M.Eng.). University of

of Architecture and Civil Engineering.

Earth Architecture and Ceramics: The Sandbag/Superadobe/Superblock

International Conference of Building Officials, Cal-Earth Institute, Hesperia, CA, USA.



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56

pe of analysis to be carried out will be a continuous rigid limit state analysis for both load cases. This is the linear behaviour of the bags but provides a quick result. A

linear rigid and non-linear deformable

in renewable supply locally that we will be able to create sustainable homes for ourselves and for the generations to come. However we need to provide these solutions in

the walls has been carried out, a broader study of earthbag structures will correlate their behaviour to that shown in the different models. The arches and compression stacks tested in Pelly and Vadgama’s research will be

It is through accurate modelling that the design and assessment of earthbag structures can begin to be undertaken more res in increasingly diverse ways

. Retrieved November 20, 2010, from Cal

hima, K., Aqil, U., Mohri, Y., & Tatsuoka, F. (2006). Evaluating the strength and deformation

Geosynthetics International ,13 (6), 246-264.

Graz University of Technology,

Geotextiles and Geomembranes

University of Bath, Department of

Dissertation (M.Eng.). University of

Earth Architecture and Ceramics: The Sandbag/Superadobe/Superblock

Earth Institute, Hesperia, CA, USA.

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