Earth buildings are, by their nature, more fragile than those built of other construction materials.
Their comparatively low strength and relatively poor resistance to water damage mean that it is often difficult to perform satisfactory and lasting repairs.
This book has outlined the fundamental science and engineering behind the behaviour of earthen construction materials present in earth buildings.
The nature of historic earthen building materials is such that, provided external dangers are removed (flowing water, for example), a structure can stand for a long period of time. The huge number of very old structures around the world is testament to this.
As shown in Chapter 2, where erosion is minimised and evaporation is allowed, a historic earth structure can last for centuries.
Many earth buildings were constructed as vernacular, but are now considered to be of great cultural value. The repair of such structures is subject to much debate and consideration before any work begins. It must first be decided whether the structure is to become a working building or a cultural monument, because such decisions determine the nature of any repair strategy
proposed. Often the most prudent decision may be not to intervene.
Understanding of the conservation and repair of earth buildings has long been the preserve of master masons and expert practitioners, but a scientific understanding of their fundamental behaviour is now developing. Earth buildings are still a long way behind those constructed of more conventional building materials, but it is hoped that a body of knowledge, published case histories and experimentation will allow earth to be treated as an engineering material. The treatment of the building material as a highly unsaturated soil represents a step change in understanding for earthen architecture, and it is hoped that a much greater understanding will be gained from this approach.
We hope that this book will help earthen architecture professionals to recognise historic earth structures, to describe them, and to place them in their historical context. Where individual failures can be identified, it is possible to
distinguish and target them. Recommendations for repair have been given, and because the unsaturated nature of rammed earth is now acknowledged, it is hoped that repair strategies will now be much improved.
6 CONCLUDING REMARKS
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INDEX 83
INDEX �
Page numbers initalics refer to illustrations and tables
A
abrasion-caused damage 51–52 additives 3, 4
construction technique 10–11 moulds used 10
particle size distribution 5, 10 straw in 10,50
adsorbed water 36 Africa 17–19
agriculture, and earth building 13, 14, 26 air dried earth blocks 9–12
air entry value 31, 32
Aït Ben Haddaou, Morocco 10, 11, 18,63, 65, 68, 76
Alcalá de Guadaira, Spain 48
Alhambra Palace, Granada, Spain 20 Alcazaba 20, 59
Ambel, Zaragoza, Spain 42, 43, 45, 49, 50, 54–55, 58, 61, 62
angle of repose 43, 46 arches 11
Arizona, adobe construction 21 Asia 14–17
central 15 eastern 14, 15 Asslim, Morocco
building materials 4, 5, 56, 70
kasbahs 18, 45, 64, 66
Australasia 25
Australia 6, 7, 25,50, 63
B
�
Bactria-Margiana Archaeological Complex 15 Balkh (Bactria), Afghanistan 15
bamboo-and-earth matting [on head of wall] 65
Bangalore, India 11, 12, 46
barrel vaults 11 base of walls
prevention of water damage at 67–68 water damage at 46, 49
Basgo castle, India 42, 46, 60
bending cracking 38, 39
besser blocks 9 Bhutan 17,49
Biar Castle, Spain 66
breeze blocks 9 buttresses 62,63
C
�
Cahuachi, Peru 23
calcium silicon hydrate (CSH) 34 bridges 35,36
Cameroon 19
capillary action 44, 45, 47,48, 49 Carmona, Spain 51
Casa Grande National Monument, New Mexico, USA 21, 67
cast-type structures 45 Catalhöyük, Turkey 14
cement-based renders 11, 49, 70
cement-stabilised compressed earth blocks 11,12
Chan Chan, Trujillo, Peru 24
chemical consolidation of earthen walls 70 China 16,52, 73,74
churches 7, 22 cinder blocks 9 city walls 16–17, 26 clay 5, 10, 27
particle sizes 5, 27
clay bridges 33 cob
buildings 8, 9, 15, 44, 69
construction technique 8–9 particle size distribution 5, 8 Cointeraux, François 21
adobe 9–11
C (cont’d) compaction 32–33 compactive effort 32
compressed earth blocks 11 cement-stabilised 11, 12
concrete facing 74, 75
concrete reconstruction 75–76
concrete ring beam at head of wall 66 conservation principles 53
conservation strategies 53–76
analysis and repair strategy 54–56 crack repair 57–60
face repair 69–70
foundation improvement 56–57 wall-lean mitigation 60–64 wall repair 71–75
water-damage repair 64–68
whole building reconstruction 75–76 contact angle, in unsaturated soils 29 Cordoba, Spain, city walls 20, 26, 51
corner battens [to mitigate wall lean] 62 crack filling 58–59
with cement mortar 58,59
column method 58, 59
with earth mortar 58 with stone(s) 58, 59
crack monitoring 57, 58
crack stitching 59–60 cracking
causes 38–40, 57 remediation of 57–60 Cumbria, UK 8, 73
D
damage to earth buildings 37–52 abrasion-caused 51–52
organic matter and 50–51 render-associated 48–49 structural 37–42
water and 43–48 Daroca, Spain 46
decorative patterns 11, 24, 26 Devon, UK, cob buildings 44, 69
differential settlement, damage caused by 37,38
Djenné, Mali 19, 70 dome structures 11, 19 Drâa Valley, Morocco 10, 18
E earth
as alternative construction material 3, 77 mixing with water and additives 4, 56
earth bricks
laying in construction 11 manufacture of 10, 11 used in wall repairs 72 earth-building techniques 3, 13
replacement by alternative techniques 23, 26 spread across world 13
earth renders 69, 70
earthen construction principles 3–4 types 3, 13
monolithic walls 5–9, 13 unit construction 9–11, 13 earthquakes 25, 37
Eden Project, UK 9
effective stress 28–29 Egypt 17
Elche, Spain 75
erosion 46, 51, 52
Euphrates and Tigris river valleys 14, 26 Europe 20–21
extension cracking 38, 39 F
film set, reconstruction for 76
fired bricks 9
formwork [for rammed earth walls] 5–7, 41 in wall repair 71, 72,74
forts 15, 16, 21 foundation failure
damage caused by 37 remediation of 57
friction between particles 43
frictional strength of soils 28 funicular water 36
G
Ghana 18–19
grass on earth walls 50, 51
Great Wall of China 16 ground improvement 56, 57
ground movement, damage caused by 37,38
INDEX 85
H
Hannibal 17–18
Haus Rath, Weilburg, Germany 21
history of earth building 13–26 Africa 17–19
ICOMOS charters 53
India 11, 12, 16,17, 42, 46, 60
Indus valley 15
ingredients, earth building 3, 27 Isfahan, Iran 8, 11, 14,15
J
�
Jaén, Spain 73
Jharkot, Nepal 39
Jiaohe, China 52
Jiayuguan Fort, China 16
Jomsom, Nepal 3, 6
K
Kagbeni, Nepal 45, 50
kasbahs 18
Kelvin equation 30–31 L
Leh Palace, Ladakh, India 16,17
lichen on earth walls 50 lime render 69
lime-stabilised earth structures 34
limewashing of earthen structures 69–70 lintels 7, 42
liquid bridges between particles 29, 35 M
Mali 19, 70
Margaret River, Australia 6, 63
Mari, Syria 63, 67, 73
Marrakech, Morocco city walls 18, 26, 47
El Badi Palace 18,39, 42
masonry-facing to walls 73–74 Merv, Turkmenistan 15
Mexico 21
mixing techniques 4 monolithic earth walls 5–9
cob 8–9
rammed earth 5–7
Morocco 4, 5, 10, 11, 18,39, 42, 45, 47, 49, 63, 64, 65, 66, 68, 70, 76
mosques 14, 19
Muktinath, Nepal 59, 65, 68
N
Nasrid wall, Granada, Spain 74
Nepal 3, 6, 16,39, 45, 50, 59, 65, 68
optimum water content (OWC) 32 laboratory determination of 32 relationship to dry density 33
Ordu-Baliq (Khar Balgas), Mongolia 15 organic matter 50–51
Ouarzazate, Morocco 49
P
�
Palma del Rio, Spain 48, 51, 74
Panjakent, Tajikistan 15 Paro, Bhutan 49
particle size distribution 5 pendular water 36
perpendicular walls, movement between 41 Perth, Australia 7, 50
Peru, adobe construction 23–24 Phoenician settlements 17, 20 pigeon infestation 51, 52
Pompallier House, Russell, New Zealand 25 pore radius, relationship to relative humidity 31 Proctor compaction test 32
propping of walls 63,64
pyramids 17, 23, 24, 26
Q
quicklime 34 R
rainfall, impact on wall surface 44
rammed earth, Chinese characters for 16 rammed earth walls
construction technique 5–7, 18 development over time 13
‘lifts’ [of formwork] 7, 41 particle size distribution 5 relative humidity 30–31
relationship to pore radius 31 suction affected by 31, 34, 43 render 11, 48
damage to earth walls caused by 49 head of wall 65
reasons for failure 48
wall face repair 69–70 residual air content 32 residual saturation 32
retaining structures, earth walls as 47 river valley civilisations 14
roof drains [for flat roofs] 68 roof elements, failure of 40
roofing on/over earth structures 66–67 rotating drum mixer 4
runnels 45, 46
S
sagging 38
salt precipitation 48
San Antonio Valley, Monterey County, USA 22
San Antonio Valley, Monterey County, USA 22