Analysis of historic rammed earth construction
PhD Thesis Paul Jaquin January 2008
Rammed earth is an ancient construction technique which has recently become
popular for sustainable building. Soil is compacted in removable formwork to
make a homogeneous wall.
A lack of experimental evidence and a poor fundamental understanding means
that current design guidelines are highly conservative and inappropriate for
the analysis of historic rammed earth buildings.
This thesis shows that rammed earth can be viewed in a geotechnical engineering
framework and that doing so helps to explain many aspects of the material behaviour.
Rammed earth walls were built and tested in the laboratory then modelled using
techniques available to practising engineers. Unsaturated soil mechanics was
considered useful in explaining much of the behaviour of rammed earth. This
was investigated through a series of uniaxial compression tests and the results
are explained using unsaturated soil mechanics.
Visits to Spain and India were made to investigate rammed earth in the field.
Historic construction techniques, modes of failure and repair strategies were
studied. The unsaturated nature of rammed earth is used to explain modes of
failure and to suggest the most appropriate repair strategies.
Introduction and Literature Review
This section presents a review of literature relating to rammed earth construction.
It is argued that while some research has been carried out, and guidelines exist
for the construction of new rammed earth buildings, there is a lack of understanding
of many of the concepts which underpin earth building, and this means that many
basic questions about the nature of rammed earth remain unanswered. While these
questions have been posed, and it has been argued that rammed earth be treated
in a geotechnical engineering framework, it is shown that work to date has not
Classical testing and modelling
The design guidelines outlined in Section 1.6 are unsatisfactory for use with
historic rammed earth. This is because they are based heavily on masonry or
concrete guidelines and have been adapted for use in modern rammed earth. The
lack of definitive testing and these adapted guidelines mean that large factors
of safety must be used. When investigating a historic building possibility close
to collapse, such safety factors cannot be used. Therefore improved modelling
strategies must be developed. This chapter uses simple physical modelling to
inform numerical modelling. Physical modelling involved the construction of
five walls in the laboratory. These walls were differently shaped and loaded
in different ways because construction of the next wall was informed by the
behaviour of the previous wall. The tests were intentionally simple and only
limited instrumentation was used. These walls improved our understanding of
the construction technique and provided insights into the types of failure which
occur when loading rammed earth. The layered nature of rammed earth is highlighted.
Simple numerical models, available to practising engineers were used to represent
rammed earth behaviour. Finite elements models of some of the physical walls
were developed. The layered nature, highlighted in physical modelling was investigated
first. A layered rammed earth model was developed based on the Mohr-Coulomb
yield criteria, with the layers being assigned different properties to the body
of the rammed earth. A second approach looked at the compaction of rammed earth
using an elastoplastic hardening approach also making use of the Mohr-Coulomb
yield criteria. In both cases a parametric study of Mohr-Coulomb parameters
was carried out.
The first part of this chapter discusses soil from a geotechnical engineering
perspective. A range of constitutive models are then described. The construction
and testing of walls in the laboratory is then explained, and this leads to
the development of the numerical modelling based on the constitutive models.
Rammed earth test wall. Line load applied over centre.
Finite element model of a rammed earth wall. Red
areas have failed.
Jaquin, P.A., Analysis of Historic Rammed Earth Construction.
9th Young Geotechnical Engineers Symposium, Belfast, September 2006
of Historic Rammed Earth Construction
Advanced testing and modelling
Classical soil mechanics is well suited to a wide range of geotechnical engineering
problems. The use of simple formulae and experience based safety factors leads
to efficient design of geotechnical structures and can be used to predict the
behaviour of a wide range of soil types under different loading conditions.
However there are situations where classical soil mechanics cannot accurately
predict the behaviour of a body of soil (as described by Jennings and Burland
1962). This usually occurs when the soil becomes unsaturated, that is there
is a mixture of air and water within the pores of the soil, and the pore water
within the soil is not continuous.
This chapter first outlines the concepts of tensile strength of water and of
surface tension. The notion of suction is outlined by explaining the phenomenon
of capillary rise which is then linked to the relative humidity of the surrounding
air. Suction in soil mechanics is then explained and the concept of equilibrium
pore radius defined. The idea of a liquid bridge is outlined and the attractive
force across the liquid described. The volume of water held within a soil due
to suction is then described through the idea of a Soil Water Characteristic
The differences between the behaviour of saturated and unsaturated soils;
and ideas for the conceptualisation of unsaturated soils are described, highlighting
the double structure theory and evidence of liquid bridges. Constitutive models
which distinguish between the behaviour of saturated and unsaturated soils are
The origins of strength in rammed earth are discussed. Rammed earth practitioners
disagree on the reasons for strength in the construction material (for example
King 1997; Norton 1997 and Houben and Avrami 2000), and attempts are being made
in the field of unsaturated soil mechanics to quantify the magnitudes of the
Electrostatic actions such as van der Waals forces and Double Layer attraction
are combined as DLVO theory, and it is shown that it is suction rather than
DLVO forces which provide additional strength to highlight unsaturated soils
such as rammed earth. Cementing is briefly introduced to later explain why there
is an optimum cement content for stabilised rammed earth building.
A short series of unconfined compression tests were carried out, where suction
was measured to establish a link between sample strength and suction. Tensiometers
were introduced as a way of measuring suction. The testing procedure, and the
way in which issues in the experimentation were resolved are described.
As a result of the experimentation is it possible to describe the relationship
between a number of the measured parameters such as water content and strength.
A change in suction on loading; and the increased strength and brittleness of
drier samples was observed. The results are then explained within a double structure
framework and it is argued that this concept may be of use in explaining the
behaviour of earthen structures.
The nature of water in rammed earth is then discussed. It is argued that the
concepts outlined previously may also be used to explain the infiltration to
and evaporation from rammed earth structures. Finally further work is suggested
and implications for modern rammed earth buildings are highlighted. The work
in this chapter allows a much fuller understanding of the failure of and repair
to rammed earth structures which are discussed in Chapters 5 and 6.
Testing a rammed earth cylinder in uniaxial compression
A failed rammed earth cylinder sample
Jaquin, P. A., Augarde C.E and Legrande, L. Unsaturated characteristics
of rammed earth. First European Conference on Unsaturated Soils,
Durham, July 2008
characteristics of rammed earth
Typologies of rammed earth construction
This chapter investigates different types of historic rammed earth construction,
looking at techniques and material used in construction and the resulting rammed
earth walls. A comprehension of both the methods of construction and the composition
of historic walls is vital for the understanding of failure and repair of rammed
earth. However, until recently typological rammed earth descriptions have ‘raised
little interest when compared to ornamental and spatial studies’ (Graciani García
and Tabales Rodríguez 2003).
This chapter looks at descriptions of rammed earth in Seville, Spain proposed
by Graciani García and Tabales Rodríguez (2003) and aims to extend and improve
their framework based on field visits discussed in Appendices B, C and D.
18th century rammed earth barn in the Tapial
con Lunetos style. Villafeliche, Spain
Jaquin, P.A., Augarde, C. E. and Gerrard, C.M. Historic Rammed Earth
Structures in Spain. International Symposium on Earthen Structures,
Bangalore, August 2007
Rammed Earth Structures in Spain
Failures in rammed earth structures
Rammed earth, being constructed from soil, is perceived by many to be a very
delicate material, requiring a sympathetic climate and frequent maintenance
to preserve its appearance and structural integrity.
This chapter aims to determine the ways in which rammed earth structures fail.
This will improve the ability of engineers to assess whether rammed earth is
able to remain in a viable state over a long period of time, and if there are
any limiting factors to the survival of a rammed earth structure.
There have been many specific case studies regarding the repair of historic
earthen architecture, often looking at the failure mechanisms before proposing
and implementing repair strategies. A number of authors have presented general
failure mechanisms for earthen architecture, but few take account of the geotechnical
nature of earth building, and none take account of its unsaturated nature outlined
in Chapter 3.
This chapter combines those failure mechanisms reported by previous authors
with those identified during field visits by the author described in Appendixes
B, C and D. These failure mechanisms are explained, and in a number of cases
the previously ignored unsaturated nature of the material is explored. A number
of case study structures are then discussed, charting combinations of the different
failure mechanisms which combine to precipitate major problems in the structure.
Finally, conclusions are drawn as to the most common and most problematic failure
mechanisms, drawing out pertinent advice on the determination of problems in
rammed earth structures.
Jaquin, P. A. Study of historic rammed earth structures in Spain and
India. The Structural Engineer,
of historic rammed earth structures in Spain and India
Crack between rammed earth infill and brick columns..
Decay of render due to quicklime popping. Baños
de la Encina, Spain
Rammed earth repair
Chapter 5 introduced failures which may beset historic rammed earth buildings.
This chapter looks at repair methods which could be adopted following such failures.
It is important that the cause of any damage be determined before repair is
carried out. In many instances, if the structural integrity of the building
is not at risk, then stopping the cause of the damage may be all that is required
to ensure the safety of the building. Warren (1993) notes that property owners
may rush to repair damage for aesthetic reasons when it may not be necessary.
The principles of repair are discussed and it is argued that western ideals
of historic building conservation may be at odds with other repair philosophies.
Although no specific document relating to the repair of historic rammed earth
buildings exists, a small number of authors have discussed repair strategies
for earth buildings and their applicability to historic rammed earth buildings
This chapter presents methods for dealing with ground movement, highlighting
those which have been suggested for historic earth buildings. As many solutions
are independent of building type, this section is intentionally brief.
Issues with structural elements were highlighted in Section 5.4, and while
many of these impact on rammed earth structures, the elements themselves are
not rammed earth, and their repair requires further specialist knowledge (for
example for the repair of timber roof members). Where the structural member
issues were integral to rammed earth (for example the joint between rammed earth
blocks) it was considered that this issue would be brought about by a further
problem, (for example ground movement) and strategies for the alleviation of
these problems are presented. Both soft crack stitching and hard wall tying
techniques are given.
In Chapter 5 it was argued that excess water in a rammed earth wall is undesirable,
so ways to reduce the amount of water entering a structure and methods for increasing
evaporation are presented here. Where erosion has occurred a range of techniques
to replace missing material are given. Finally the techniques presented are
evaluated and those considered most effective are recommended.
Stitched crack in rammed earth, Basgo, Ladakh
Historic rammed earth distribution
Rammed earth is a construction technique where soil is taken from the ground
and compacted to form structures. Removable formwork is installed, and the soil
compacted within it. The technique is widespread but the distribution of rammed
earth across the world and its development over time has not previously been
fully documented. Many sources quote the same examples of the Potala Palace
in Lhasa, parts of the Great Wall of China, and the Alhambra in Granada. The
distribution of rammed earth is however more complex than usually portrayed,
appearing to spread over the world in a number of temporal waves, each precipitated
by a different set of needs.
In this appendix, a strict definition of the rammed earth technique is first
presented, identifying it by name in different languages. It will be argued
that the rammed earth technique appears to have developed independently in China
and around the Mediterranean. The technique then spread with the movement of
peoples to different parts of the world. Rammed earth has continually been reinvented
as a building material. At times it has been used as a quick technique for the
building of fortifications, a cheap way a man can build his own home, and a
sustainable construction technique using only what is available on site.
Jaquin, P.A. Augarde, C.E. Gerrard, C.M. Historic rammed earth distribution.
International Journal of Architectural Heritage
A field visit to northern Spain was carried out in October 2007, with assistance
from the Institution of Structural Engineers Rowen Travel Award. Dr Charles
Augarde and Dr Chris Gerrard were present for the first three days, and for
the following week I was accompanied on a number of days by Mr Nick Watson.
A large number of sites were visited, not all of which were found to be rammed
earth, and the four sites described in this appendix relate to those mentioned
in the body of thesis.
Seventeen locations in southern Spain were visited in January 2006. Over a
two week period I travelled from Murcia in western Spain to Seville in southern
Spain. The seventeen locations have been further split into individual sites
which range from whole castle complexes through individual to individual walls
or parts of city walls.
A short field trip to northern India was undertaken prior to a conference in
the region in late October and early November 2006. A number of historic sites
were visited, of which three rammed earth ones (shown in Figure D.1 and Figure
D.2) are described in this appendix.
If you would like a copy of all or part of the thesis, please contact
This thesis has resulted in a number of publications, see
this page for details.