Table Of ContentFurther titles in this series:
1. G. SANGLERAT, THE PENETROMETER AND SOIL EXPLORATION
2. Q. ZARUBA AND V, MENCL, LANDSLIDES AND THEIR CONTROL
3. E. E. WAHLSTROM, TUNNELING IN ROCK
4. R. SILVESTER, COASTAL ENGINEERING, I and II
5. R. N. YOUNG AND B. P. WARKENTIN, SOIL PROPERTIES AND BEHAVIOUR
6. E. E. WAHLSTROM, DAMS, DAM FOUNDATIONS, AND RESERVOIR SITES
7. W. F. CHEN, LIMIT ANALYSIS AND SOIL PLASTICITY
8.L. N. PERSEN, ROCK DYNAMICS AND GEOPHYSICAL EXPLORATION.
Introduction to Stress Waves in Rocks
9. M. D. GIDIGASU, LATERITE SOIL ENGINEERING
10. Q. ZARUBA AND V. MENCL, ENGINEERING GEOLOGY
W.H.K. GUPTA AND B. K. RASTOGI, DAMS AND EARTHQUAKES
12. F. H. CHEN, FOUNDATIONS ON EXPANSIVE SOILS
13. L. HOBST AND J. ZAJIC, ANCHORING IN ROCK
14. B. VOIGT (Editor), ROCKSLIDES AND AVALANCHES, 1 and 2
15. C. LOMNITZ AND E. ROSENBLUETH, SEISMIC RISK AND ENGINEERING
DECISIONS
16. C. A. BAAR, APPLIED SALT-ROCK MECHANICS, 1. The In-Situ Behavior of Salt
Rocks
17. A. P. S. SELVADURAI, ELASTIC ANALYSIS OF SOIL-FOUNDATION INTERAC-
TION
18. /. FEDA, STRESS IN SUBSOIL AND METHODS OF FINAL SETTLEMENT
CALCULATION
19. A. KEZDI, STABILIZED EARTH ROADS
20. E. W. BRAND AND R. P. BRENNER (Editors), SOFT-CLAY ENGINEERING
2\.A. MYSLIVEC AND Z. KYSELA, THE BEARING CAPACITY OF BUILDING
FOUNDATIONS
22. R. N. CHOWDHURY, SLOPE ANALYSIS
23. P. BRUUN, STABILITY OF TIDAL INLETS. Theory and Engineering
24. Z. BAZANT, METHODS OF FOUNDATION ENGINEERING
25. A. KEZDI, SOIL PHYSICS. Selected Topics
26. H. L. JESSBERGER (Editor), GROUND FREEZING
27. D. STEPHENSON, ROCKFILL IN HYDRAULIC ENGINEERING
28. P. E. FRIVIK, N. JANBU, R. SAETERSDAL AND L. I. FINBORUD (Editors),
GROUND FREEZING 1980
29. P. PETER, CANAL AND RIVER LEVEES
30. /. FEDA, MECHANICS OF PARTICULATE MATERIALS. The Principles
31. Q. ZARUBA AND V. MENCL, LANDSLIDES AND THEIR CONTROL. Second
completely revised edition
32. /. W. FARMER (Editor), STRATA MECHANICS
33. L. HOBSTAND J. ZAJIC, ANCHORING IN ROCK AND SOIL. Second completely
revised edition
Developments in Geotechnical Engineering 33
ANCHORING
IN ROCK AND SOIL
second completely revised edition
by
Dr. Ing. LEOS HOBST
Research Institute oj Civil Engineering, Brno ( VU1S)
and
Ing. JOSEF ZAJIC CSc
Engineering Geology, Prague (Stavebni geologie)
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
Amsterdam Oxford New York 1983
Published in co-edition with
SNTL Publishers of Technical Literature, Prague
Distribution of this book is being handled by the following publishers:
for the USA and Canada
ELSEVIER SCIENCE PUBLISHING COMPANY, INC.
52 Vanderbilt Avenue
New York, New York 10017
for the East European Countries, China, Northern Korea, Cuba, Vietnam and Mongolia
SNTL Publishers of Technical Literature, Prague
for all remaining areas
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
Molenwerf 1, P. O. Box 211
1000 AE Amsterdam, The Netherlands
Library of Congress Cataloging in Publication Data
Hobst, Leos.·
Anchoring in rock and soil.
(Developments in geotechnical engineering ; 33)
Translation of; Kotvenido hornin.
Rev. ed. of: Anchoring in rock. 1977·
Bibliography: p.
Includes index.
1. Anchorage (Structural engineering) 2. Rock bolts·
I. Zajic, Josef. II. Title. III. Series.
TA772.H613 1982 62fcM5 82-871*8
ISBN' 0-1^-99689-3 MCR2
ISBN 0-444-99689-3 (Vol. 33)
ISBN 0-444-41662-5 (Series)
With 525 illustrations and 28 tables
Translation by Ing. Prokop Maxa,
Translation Editor Mark Cowan
© 1983 Dr. Ing. Leo§ Hobst and Ing. Josef Zajic CSc
Printed in Czechoslovakia
PREFACE TO THE SECOND ENGLISH EDITION
There is a growing tendency in the construction industry to exploit the
ground as a means of taking up the tensile forces produced by structures,
and to consolidate the damaged parts of rock masses or establish an effective
support for them by introducing prestressing. Rock and soil consolidation
is most effectively realized by means of prestressed reinforcements which
are placed into boreholes in the ground and which connect the structure,
or the superficial parts of the rock or soil, with the deeper mass. This efficient
construction method is usually referred to as anchoring into rock and soil,
or the tie-back method.
The authors have played a part in the application of the anchoring method
in Czechoslovakia from the very beginning, and decided more than ten years
ago to attempt to evaluate and explain its problems, and to present their
knowledge and experience in the first Czech edition of this book. The latter
was much appreciated by its technical readership and in the years 1975 —1977
a supplemented second Czech edition was published together with an English
translation for Elsevier who subsequently expressed interest in a completely
revised edition.
We cannot suppress a feeling of satisfaction that our efforts in summarizing
the current knowledge on anchoring both from our own country and from
abroad, were justified, thereby establishing a basis for the wider utilization
of this knowledge. We are conscious of the fact that the success of our book
has not been due to its literary merits, since the information it contains has
been gathered from the minds of technical academic gentlemen. Success
is due rather to the lack of published material summarizing the principles
of anchoring, the advantages of its application in civil engineering, and the
suitability of the individual anchoring techniques for various ground types
and different anchored structures.
The complexity of anchoring problems has been growing rapidly during
the last decade and much new knowledge has been gained, although it has
remained scattered throughout the literature. For this reason the book has
had to be radically changed, and some chapters have been completely rewritten
for this new edition. We have endeavoured to improve the text wherever
this was desirable.
It is our pleasant duty to extend our sincere thanks and gratitude on this
occasion to our reviewers from all over the world for their stimulating
comments on the previous edition, to all the experts and companies mentioned
in the text for the use of their valuable specialized material, and of course
to all our collaborators at the Research Institute of Civil Engineering and
the national enterprise Stavebni geologie. Above all we thank Ing. Prokop
Maxa for the translation of the book. Last but not least we thank our wives
for their untiring support throughout our work.
L. Hobst —J. Zajic
Brno-Praha, June 1982
XIV
RELATION OF SI UNITS TO EARLIER USED UNITS
Length m (metre) = 1.09 yard = 3.28 feet = 39.37 inches
cm (centimetre) = 0.39 inch
mm (millimetre) = 0.47 line = 0.04 inch
Area m2 (square metre) = 1.196 square yard = 10.76 square
feet = 1,550 square inches
cm2 (square centimetre) = 0.155 square inch = 0.00107 square
foot
mm2 (square millimetre) = 0.00155 square inch
Volume m3 (cubic metre) = 1.308 cubic yard = 35.314 cubic feet
cm3 (cubic centimetre) = 0.06 cubic inch
Mass kg (kilogram) = 2.20 pounds = 35.274 ounces
g (gram) 0.0353 ounces
t (ton) = 2,204.6 pounds = 0.984 U.K. ton =
1.102 U.S. ton = 2.2 kips
t/m3 (ton/cubic metre) = 103 kg/m3 = 62.427 pounds/cubic
feet
Force N (newton) = 0.1 kp (kilopond) = 3.527 ounces =
0.22 pound
kN (kilonewton) = 100 kp (kilopond) == 220.5 pounds
MN (meganewton) = 100 Mp (megapond) = 98.4 U.K.
tonnes = 110.2 U.S. tonnes =
220 kips
Pressure Pa (pascal) 1 N/m2 = 10"5 bar = 0.1 kp/m2 =
(stress) 10"5 kp/cm2 = 0.0001 Mp/m2 =
10"5 atm = 0.000 142 pound/square
inch (psi)
MPa (megapascal) 1 MN/m2 = 1 N/mm2 = 10 bar =
10 kp/cm2 = 0.1 kp/mm2 =
100 Mp/m2 = 10 atm =
141. 935 pounds/square inch (psi) =
20.44 kips/square foot (ksf)
Static Nm (newtonmetre) 1 joule (J) = 0.1 kpm = 0.72 lbft
moment
(work) kNm (kilonewtonmetre) = 0.1 Mpm = 723.2 pounds feet (lbft)
Chapter 1
INTRODUCTION
1.1 TREATMENT OF THE SUBJECT
The problems associated with anchoring into the ground are extensive
and new ones arise all the time. We would like in this work to present
a comprehensive summary of the development, principles, current state
of technology and methods of application of anchoring. In order to facilitate
the approach to these problems and ensure the reliability of information,
particularly for those construction experts whose familiarity with the anchor-
ing method is limited, we have divided the subject into three principal parts
and 29 chapters.
The chapters of the first, introductory, part A deal with the main principles
of the anchoring method and its static analysis. Chapter 9 discusses the
geotechnical properties of rocks and soils and their evaluation from the
point of view of their capacity to take the tensile forces exerted by anchors.
Chapter 10 explains the results of research concerning the behaviour of
different types of the ground under the load of anchoring forces; it also
includes the formulae derived for making approximate determinations of the
anchor fixing depth both for individual anchors and grouped anchors, given
the tensile forces and the required safety margins against failure.
The second part of the book part B deals with anchoring technology. Mate-
rials for the preparation of anchors, the main technological procedures for the
fixing of anchors by different methods in different media, and the in-
formation needed for the design of the anchor root are described. Other
chapters of part B deal with the methods of fixing anchors to the surface
of the structure, the methods of drilling and checking the anchoring bore-
holes, and procedures and equipment used in the prestressing and testing
of anchors together with long term monitoring of their function under
various conditions.
The third and largest part of the publication, C, presents theoretical data
for anchorage design applied to various types of structures, and introduces
some typical examples of both underground and surface constructions. The
last chapter deals with the economics of anchoring by referring to several
examples.
3
1.2 PRINCIPLES OF ANCHORING INTO THE GROUND
Anchoring in rock or soil is a construction process in which prestressed
components (termed anchors in this case) are embedded in the ground.
The anchors are inserted into boreholes drilled in advance, and are fixed
at the distal end. After fixing, the anchors are usually prestressed and their
exposed upper ends are fixed to heads. The structure to which the anchor
heads are attached, is either one which is dependent for its stability on the
anchors, or it is merely a plate, slab, bar, grid or another structural element
which distributes the stress induced by the anchor heads onto the wider
surface of the rock or soil (Fig. 1-1).
Anchoring in the ground fulfils three basic functions:
— It establishes forces which act on the structure in a direction towards
the point of contact with the rock or soil (Fig. 1-2).
— It establishes a stress acting on the ground, or at least a reinforcement
of the rock medium through which the anchor passes if non-prestressed
anchorage is used (Fig. 1-3).
— It establishes prestressing of the anchored structure itself, when the
anchors pass through this structure.
These functions are mutually complementary, or one or more of them
may be inoperative, being inapplicable to the type of structure and anchoring
method of a particular situation.
Anchoring is always accompanied by the prestressing of the rock. In this
process the ground is consolidated, strengthened, and its mechanical
characteristics improved. This effect of anchoring is fully exploited when
the walls of underground excavations, the rock faces of cuttings, the steep
slopes of cuttings threatened by slumping, are secured; anchoring is utilized
for the pre-consolidation of the underlying ground mass, or for controlling
the deformation expected after completion of the construction, etc. Some-
times, particularly when the faces of underground excavations are secured,
the prestressing is substituted by a simple reinforcement with the use of
anchors, without pre-induced stress; a partial stress in the rock then appears
only when its superficial zones are loosened. This method is, however,
technically and economically less expedient.
The prestress introduced into a structure by the anchors may incorporate
the otherwise occurring tensile stresses of the structure; such stresses appear,
for example, within the masonry of gravity dams on the upstream face under
hydrostatic load, etc. The establishment and utilization of a prestress by this
means in masonry is not usually the main reason for the application of
anchorage. Nevertheless these considerations must be analysed in every
situation of an anchored structure, if not to exploit its contribution to
prestressing, then at least to prevent possible damage and failure proper
^
-ι
1
S
g
n
utis
distrib— sill
d-3
oas,
lb
on sla
b) —
ucture, cture, 2
ed strd stru
Fig. 1-1. Fixing of anchor heads a) on the surface of the anchorstructural elements, 1 — anchore4 — grid, 5 — anchors
Fig. 1-2. Schematic representation of the Fig. 1-3. Schematic drawing of the
principle of anchoring a dam into bedrock stabilization of a rock face with
/ — anchor head, 2 — tendon, 3 — anchor prestressed anchors
root, 4 — anchored structure 1 — anchor roots, 2 — anchor heads,
3 — prestressed rock
by siting of the anchors on the structure and correct location of the load
centre of the anchoring forces.
The most efficient, most widely used technique is a system of anchorage
in which forces are set up acting to lock together the structure with the rock.
(see Fig. 1-2.) With such an arrangement the rock is exploited to greater effect
and takes on the function of a proper construction material. The prestressed
anchors create forces of known direction and magnitude which contribute
to the stability of the superficial structure and tie together the entire complex
consisting of the structure and the co-operating rock medium. The rock
in which the structure is anchored takes the burden of the tensile and shear
forces which arise from the structure and its load (or from natural changes
in the superficial relief) more efficiently and to greater depths than occurs
in the case of structures which are not anchored. On the other hand, a com-
pressive force acting towards the plane of contact with the rock also appears
in the structure, this force depending on the weight of the structure, or the
pressure of a supporting brace or strut as the case may be. The structural
complex created in this way is qualitatively superior, and exhibits mechanical
characteristics which make it more capable of fulfilling its function at a lower
capital cost.
Anchorage, as a means of locking together the structure with the ground mass,
makes it possible to choose with comparative ease on the basis of the static
