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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

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

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

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

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

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 ...)

charles.augarde@dur.ac.uk