Engineering characterization of earthen construction materials

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Engineering characterization of earthen
construction materials

• Charles Augarde
• School of EngineeringDurham University

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Introduction
This is an introduction to some of the research
work taking place at Durham in earthen
construction materials
My 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

• Characterization of earthen construction
  materials at the material level
• What is new?
• We come from the geotechnical engineering POV
• With respect, not all past characterization work
  has been rigorous
• Historic rammed earth structures, their history,
  conservation and the lessons they teach us for
  modern build
• What is new?
• Crossover with archaeologists
• We bring structural knowledge and seek help for
  new build

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EBUK relevant research areas

• Characterization of earthen construction
  materials at the material level
• What is new?
• We come from the geotechnical engineering POV
• With respect, not all past characterization work
  has been rigorous
• Historic rammed earth structures, their history,
  conservation and the lessons they teach us for
  modern build
• What is new?
• Crossover with archaeologists
• We bring structural knowledge and seek help for
  new build

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1. Characterization

• What is the source of strength in these materials
  (generally compacted earthen materials are our
  primary interest)
• How do the materials work on an engineering
  level
• Why is this important? Wider acceptance and use
  flows from better understanding via things like
  design codes

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Sources of strength

• The sandcastle problem
• Suction is one source
• We can measure suction
• Tensiometers

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Suction is the key to many interesting
geotechnical engineering problems
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Unsaturated soils testing lab
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 to 1.5MPa of
  suction)
• Filter paper method (for higher suctions drier
  mixes)

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Some results

• Mix from Aykley Heads, Durham RE wall
  (Rivergreen Developments)
• Details are in a soon-to-appear Géotechnique paper

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RE testing
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 projects
  at Durham
• Modes of wetting and drying in compacted earth
  materials, suction changes are hysteretic
• Stabilisers from wastes Basic Oxygen Slag
  (BOS)
• Strength between lifts in rammed earth
• The use of geogrids
• New tests for compacted earth materials

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Other work
More stabiliser higher suction
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Other work in the lab

• Inter-lift strength in rammed earth
• Reinforcement with geo grids

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Tests for compacted earth materials
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Whats happening right now?

• Q how does the way you build create the
  microstructure?
• Ingredients earth, water, time, compaction
  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 Engineering and Archaeology
• Paul Jaquin
• What can we learn from old structures?
• What are robust methods of conserving historic RE?

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Historic rammed earth
Paper just out on historical background, based on
part of Pauls thesis
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Acknowledgements

• Dr Paul Jaquin, Ex-PhD student, Now appearing at
  RambollWhitbybird Civil Engineering consultants,
  Edinburgh
• Dr Chris Gerrard, Dept of Archaeology, Durham
  University
• Students
• MSc Cindy McChlery
• MEng Tom Horncastle, Tom Howard, Steven Perkins
• PhD Chris Beckett

Thank you for listening. Please pay us a
visit.Papers available from me or at
www.dur.ac.uk/charles.augarde www.dur.ac.uk/earthe
n.construction (under construction as they say
...)charles.augarde_at_dur.ac.uk