Reinforced Earth

147 Pages·1982·8.523 MB·English

by  Ingold, T. S

REINFORCED EARTH
Reinforced Earth
T. S. I N G O LD
BSc, MSc, PhD, DIC, MICE, MIHE,
MASCE, MSoclS(France), FGS
Chief Engineer, Ground Engineering Ltd
Visiting Professor, Department
of Civil Engineering, The
Queen's University, Belfast
Thomas Telford Ltd, London, 1982
Published by Thomas Telford Ltd, Telford House, PO Box 101,
26-34 Old Street, London EC1P 1JH
ISBN: 0 7277 0089 8
© Ground Engineering Limited 1982
All rights, including translation reserved. Except for fair copying, no part
of this publication may be reproduced, stored in a retrieval system or
transmitted in any form or by any means electronic, mechanical, photo­
copying, recording or otherwise, without the prior written permission of
the Managing Editor, Publications Division, Thomas Telford Ltd, PO Box
101, 26-34 Old Street, London EC1P 1JH
Photoset, printed and bound in Great Britain by
Redwood Burn Limited, Trowbridge, Wiltshire
Publishers' Note
The writer of the foreword to this book, M. H. Vidal, the French
architect and civil engineer, is the grantee of various UK patents re­
lating to the construction of REINFORCED EARTH structures.
Additionally, and subsequent to the grant of M. Vidal's principal
patents, patents relating to the design and construction of intern­
ally mechanically stablized earth structures have been granted to a
variety of other people and organizations.
At the time of publication, REINFORCED EARTH is the trade
name of Reinforced Earth Company Limited, and the term RE­
INFORCED EARTH is the subject of a British trademark appli­
cation by that company which is M. Vidal's exclusive licensee in
Britain.
Finally, thanks are due to M. Vidal and his licensees for permis­
sion to reproduce the following figures based on his and their
published works: Figures Nos'2, 22-27, 34-39, 57-66, 69-71, 75
and 76.
Contents
Preface 1
1 MECHANISMS AND CONCEPTS 4
The work of Henri Vidal 5
The anisotropic cohesion concept 7
The enhanced confining pressure concept 20
Randomly reinforced soil (RRS) 27
The limitations of laboratory studies 32
2 APPLICATIONS 33
Ground slabs 36
Dams 38
Foundations 39
Embankments 44
Walls 49
3 RESEARCH AND DEVELOPMENT 55
French research 56
The UCLA study 66
The DoE/TRRL study 72
Recent research 80
Current design and construction systems 99
CONTENTS
Cohesive fill 109
Economics 113
Polymer reinforcement 114
4 FUTURE TRENDS 123
References 111
Index 139
Preface
Reinforced Earth is a composite construction material in which the
strength of engineering fill is enhanced by the addition of strong
inextensible tensile reinforcement in the form of strips. The basic
mechanism of Reinforced Earth involves the generation of friction-
al forces between the soil and the reinforcement. These forces are
manifested in the soil in a form analogous to an increased confining
pressure which enhances the strength of the composite. Addition­
ally the reinforcement has the ability to unify a mass of soil that
would otherwise part along a failure surface. Reinforced Earth is
potentially a very versatile material; however, the vast majority of
applications to date involve walls in various forms. These struc­
tures embody two basic components, namely engineering fill and
reinforcement as well as some form of facing which prevents
surface erosion and gives an aesthetically pleasing finish. In analys­
ing these walls consideration must be given both to internal and
external stability. The latter consideration presents no problem
since the reinforced mass forming the wall may be considered as a
gravity retaining wall whence conventional design methods can be
employed to check bearing capacity, base sliding and overall stabil­
ity. The assessment of internal stability is somewhat more compli­
cated, however; in essence this involves designing the
reinforcement against failure by either tensile fracture or pull-out
from the main body of the fill.
1
PREFACE
In the late fifties, Henri Vidal, a French architect and engineer,
investigated the frictional effects of reinforcement in soil with the
aim of improving the mechanical properties of the soil in the direc­
tion in which the soil is subject to tensile strain. As a result of these
investigations Vidal launched a new civil engineering material
known as Reinforced Earth. Subsequently patents were granted to
Henri Vidal on his invention in many countries throughout the
world.
The subsequent years witnessed intensive worldwide research
with particular emphasis on the performance of model and full-
scale walls. The first fundamental research of wall behaviour and
design methods started at the Laboratoire Central des Ponts et
Chaussees (LCPC) in 1967. Within 5 years similar research had
commenced both in the United States of America and the United
Kingdom. The end of 1976 heralded a bonanza of research with
publication of the proceedings of the international symposium
'New Horizons in Construction Materials', held at Lehigh Univer­
sity, Pennsylvania. This was rapidly followed in 1977 by the inter­
national conference The Use of Fabrics in Geotechnics', and the
Transport and Road Research Laboratory (TRRL)/Heriot-Watt
University symposium 'Reinforced Earth and other Composite
Soil'. Two international symposia took place in 1978: the American
Society of Civil Engineers (ASCE) spring convention symposium
'Earth Reinforcement', held in Pittsburgh, and the New South
Wales University/Institute of Technology symposium 'Soil Rein­
forcing and Stabilising Techniques', held in Sydney. A further in­
ternational conference, 'Soil Reinforcement', was held in Paris in
1979. In the same year session eight of the seventh European con­
ference on soil mechanics and foundation engineering was devoted
to 'Artificially Improved Soils' with a speciality session 'Reinforced
Earth' being incorporated in the sixth Panamerican conference on
soil mechanics and foundation engineering held in Peru.
The resulting deluge of information has prompted the publi­
cation of this slender volume which seeks to review developments
and applications as well as introducing design and construction
2
PREFACE
methods. Before this, however, an attempt is made to shed light on
some of the basic mechanisms involved and to illustrate the poten­
tial versatility of this phenomenon.
3
1
Mechanisms and Concepts
Walking across a dry sandy beach soon reveals that soil is an
inherently weak material. If the same beach sand is sealed in a
simple jute sack it will resist the weight of several men without
showing signs of failure. A similar observation was made by Henri
Vidal, a French architect, who found that roughly formed mounds
Figure 1 Failure in unreinforced soil
4