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Engineering characterization of earthen construction materials
Charles AugardeSchool of Engineering
Durham University
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Introduction
This is an introduction to some of the research work taking place at Durham in earthen construction materialsMy background: local authority civil engineer for six years in Manchester ... got a bit bored ... did an MSc and a PhD and ended up as an academic at Durham (there since 2001).
Most of my research is in computational mechanics
Got into earthen things about six years ago.
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EBUK relevant research areas
1.1. Characterization Characterization of earthen construction of earthen construction materials at the material level materials at the material level
What is new?What is new? We come from the geotechnical We come from the geotechnical
engineering POVengineering POV With respect, not all past characterization With respect, not all past characterization
work has been rigorouswork has been rigorous
2.2. Historic rammed earth structuresHistoric rammed earth structures, their history, , their history, conservation and the lessons they teach us for conservation and the lessons they teach us for modern buildmodern build
What is new?What is new? Crossover with archaeologistsCrossover with archaeologists We bring structural knowledge and seek We bring structural knowledge and seek
help for new buildhelp for new build
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EBUK relevant research areas
1.1. Characterization Characterization of earthen construction of earthen construction materials at the material level materials at the material level
What is new?What is new? We come from the geotechnical We come from the geotechnical
engineering POVengineering POV With respect, not all past characterization With respect, not all past characterization
work has been rigorouswork has been rigorous
2.2. Historic rammed earth structures, their history, Historic rammed earth structures, their history, conservation and the lessons they teach us for conservation and the lessons they teach us for modern buildmodern build
What is new?What is new? Crossover with archaeologistsCrossover with archaeologists We bring structural knowledge and seek We bring structural knowledge and seek
help for new buildhelp for new build
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1. Characterization
What is the source of strength in What is the source of strength in these materials (generally these materials (generally compacted earthen materials are compacted earthen materials are our primary interest)our primary interest)
How do the materials “work” on an How do the materials “work” on an engineering levelengineering level
Why is this important? Wider Why is this important? Wider acceptance and use flows from acceptance and use flows from better understanding via things better understanding via things like design codeslike design codes
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Sources of strength
The sandcastle problemThe sandcastle problem
Suction is one sourceSuction is one source
We can measure suctionWe can measure suction
TensiometersTensiometers
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Suction is the key to many interesting geotechnical engineering problems
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(Figure above after Wheeler et al., 2003)
Meniscus water
Air
Bulk water
“Pendular” and “funicular” regimes
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Unsaturated soils testing lab
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Long track record in this at Durham led by David Toll
Requires environmental control
Complex kit – e.g. double –wall triaxial cells
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Measuring suction
Tensiometers – high capacity (up Tensiometers – high capacity (up to 1.5MPa of suction)to 1.5MPa of suction)
Filter paper method (for higher Filter paper method (for higher suctions: drier mixes)suctions: drier mixes)
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1 – Pressure transducer;
2 – Water reservoir;
3 – Ceramic disc with high air entry value.
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Some results
Mix from Aykley Heads, Durham RE wall Mix from Aykley Heads, Durham RE wall (Rivergreen Developments)(Rivergreen Developments)
Details are in a soon-to-appear Géotechnique Details are in a soon-to-appear Géotechnique paperpaper
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RE testing
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Tests done at constant water content, unconfined
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Getting drier
These results show how
suction varies during testing
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Other work in the lab
Work done via PhD, MSc and Undergraduate Work done via PhD, MSc and Undergraduate projects at Durhamprojects at Durham
Modes of wetting and drying in compacted Modes of wetting and drying in compacted earth materials, suction changes are earth materials, suction changes are hysteretichystereticStabilisers from “wastes” – Basic Oxygen Stabilisers from “wastes” – Basic Oxygen Slag (BOS)Slag (BOS)Strength between lifts in rammed earthStrength between lifts in rammed earthThe use of geogridsThe use of geogridsNew tests for compacted earth materialsNew tests for compacted earth materials
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Other work
0
200
400
600
800
1000
1200
6.0% 6.5% 7.0% 7.5% 8.0% 8.5%
Water Content
Su
ctio
n (
kPa
)
514 0% 514 3% 514 6% 514 0% drying 514 3% drying 514 6% drying
More stabiliser = higher suction
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Other work in the lab
Inter-lift strength in rammed earthInter-lift strength in rammed earth Reinforcement with geo gridsReinforcement with geo grids
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Tests for compacted earth materials
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What’s happening right now?
Q: how does the Q: how does the way you build way you build createcreate the the microstructure? microstructure?
Ingredients: earth, Ingredients: earth, water, time, water, time, compaction compaction procedure, ...procedure, ...
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EU FP7 bid, Feb 08
Durham (Me), Nottingham (Matthew Hall), CRATerre (Hugo Houben), EPSCI Paris (Henri Van Damme), Technische Universität Berlin (Klaus Rückert), University of Natural Resources and Applied Life Sciences, Vienna (Wei Wu)
+ industrial partners: Earth Structures (Europe) Ltd (UK), Pitance PLC, (France), Natur und Lehm GMBH (Austria)
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2. Historic rammed earth
Collaboration between Collaboration between Engineering and ArchaeologyEngineering and Archaeology
Paul Jaquin Paul Jaquin What can we learn from old What can we learn from old
structures?structures? What are robust methods of What are robust methods of
conserving historic RE?conserving historic RE?
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Historic rammed earth
Paper just out on historical background, based on part of Paul’s thesis
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Acknowledgements
Dr Paul JaquinDr Paul Jaquin, Ex-PhD student, Now appearing at , Ex-PhD student, Now appearing at RambollWhitbybird Civil Engineering consultants, RambollWhitbybird Civil Engineering consultants, EdinburghEdinburgh
Dr Chris GerrardDr Chris Gerrard, Dept of Archaeology, Durham University, Dept of Archaeology, Durham University
StudentsStudents
MSc: MSc: Cindy McChleryCindy McChlery
MEng: MEng: Tom Horncastle, Tom Howard, Steven PerkinsTom Horncastle, Tom Howard, Steven Perkins
PhD: PhD: Chris BeckettChris BeckettThank you for listening. Please pay us a visit.
Papers available from me or at www.dur.ac.uk/charles.augarde
www.dur.ac.uk/earthen.construction (under construction as they say ...)