Recommendations for Prestressed Rock and Soil Anchors

106 Pages·2004·7.56 MB·English

by  Post-Tensioning Institute

Copyright © 2004
By the Post-Tensioning Institute
First Edition, 1980
Second Edition, 1986
Third Edition- First Printing, 1996
Fourth Edition - First Printing, 2004
ISBN 1-931085-29-3
Printed in the U.S.A.
All rights reserved. This book or any part thereof may not be reproduced in any
form without the written permission of the Post-Tensioning Institute.
This publication is intended for the use of professionals competent to evaluate the significance and limitations of
its contents and who will accept responsibility for the application of the materials it contains. The Post-Tensioning
Institute in publishing these recommendations makes no warranty regarding the recommendations contained
herein, including warranties of quality, workmanship or safety, express or implied, further including, but not limit
ed to, implied warranties or merchantability and fitness for a particular purpose.
THE POST-TENSIONING INSTITUTE SHALL NOT BE LIABLE FOR ANY DAMAGES, INCLUDING CONSE
QUENTIAL DAMAGES, BEYOND REFUND OF THE PURCHASE PRICE OF THESE RECOMMENDATIONS.
The incorporation by reference or quotation of material in these recommendations in any specifications, contract
documents, purchase orders, drawings or job details shall be done at the risk of those making such reference or
quotation and shall not subject the Post-Tensioning Institute to any liability, direct or indirect, and those making
such reference or quotation shall waive any claims against the Post-Tensioning institute.
Post-Tensioning Institute Prestressed Rock and Soil Anchor Committee
Chairman
Heinz Nierlich
Dywidag-Systems International USA, Inc.
Fairfield, NJ
Michael McCray
Francis J. Arland U.S. Army Corps of Engineers
Mueser Rutledge Consulting Engineers Huntington, WV
New York, NY
Theodore L. Neff
Richard J. Barrows Post-Tensioning Institute
Federal Highway Administration
Phoenix, AZ
Vancouver, WA
Matthew J. Niennann
Thomas Bird
Williams Form Engineering Corp. Schnabel Foundation Co.
Golden, CO Sterling, VA
Donald A. Bruce
Thomas D. Richards, Jr.
Geosystems, L.P.
Nicholson Construction Co.
Venetia, PA
Cuddy,PA
William R. Fiedler
U.S. Burea~:~ of Reclamation David E. Weatherby
Technical Service Center Schnabel Foundation Co.
Denver, CO Sterling, VA
Bernhard Froemel
DSI-Lang Geotech, LLC
Long Beach, CA
Reviewed and endorsed by:
ADSC Anchored Earth Retention Committee
William S. Heckman, Chairman
c/o
ADSC: The International
Association of Foundation
Drilling
P.O. Box 280379
Dallas, TX 75228
[email protected]

TABLE OF CONTENTS
1.0 SCOPE .. 1
I ••• I ••••• I I I I • I I I ••••••••••••••••••••••••••••••••••••••• •
2.0 DEFINITIONS .......................................................3
3.0 SPECIFICATIONS, RESPONSIBILITIES AND SUBMITTALS ................7
3. 1 Specifications .............................................................7
3.2 Responsibilities ............................................................7
3.3 SUBMITTALS ..............................................................9
4.0 MATERIALS . . . . . . . . . . . . . . . • . • . • . . . . . . . ............................1 1
4.1 General .......................· ..........................................1 1
4.2 Prestressing Steel .........................................................1 1
4.3 Anchorages ...............................................................1 3
4.4 Couplers .................................................................1 4
4.5 Centralizers and Spacers ....................................................1 4
4.6 Corrosion Inhibiting Compounds ..............................................1 4
4.7 Plastic Tubing .........................................................· . ....1 6
4.8 Heat Shrink Sleeves and Tapes ..............................................1 7
4.9 Grout Tubes ...................................... : .......................1 8
4.10 Grout Socks ..............................................................1 8
4.11 Grout ....................................................................1 8
5.0 CORROSION PROTECTION .........................................2 1
5.1 Design Aspects ...........................................................2 1
J
5.2 Corrosion Protection Selection Criteria .........................................2 2
5.3 Corrosion Protection Requirements ............................................2 4
5.4 Corrosion Protection Details .................................................2 9
6.0 DESIGN ................................................... ·. ......3 5
6.1 Introduction ..............................................................3 5
6.2 Feasibility of Anchors ......................................................3 5
6.3 Design Objectives .........................................................3 5
6.4 General Considerations .....................................................3 6
6.5 Site Evaluation ............................................................3 8
6.6 Anchor Capacity/Safety Factors ..............................................4 0
6.7 Bond Length Design .......................................................4 1
6.8 Free Stressing Length ......................................................4 7
6.9 Anchor Geometry ..........................................................4 7
6.10 Tendon Accessories ........................................................4 8
6.11 Cement Grout Mix Design .................................................. .49
6.12 Resin Anchors ............................................................5 0
7.0 CONSTRUCTION .......................................•..........5 1
7.1 General .................................................................5 1
7.2 Fabrication ...............................................................5 1
7.3 Storage and Handling ......................................................5 2
7 .4. Drilling ..................................................................5 2
iii
7.5 Water Pressure Testing, Pre-grouting and Re-drilling Rock Anchor Drill Holes .........5 6
7.6 Tendon Repairs ...........................................................5 7
7.7 Tendon Insertion ...........................................................5 7
7.8 Grouting .................................................................5 9
7.9 Installation of Anchorage ....................................................6 5
8.0 STRESSING, LOAD TESTING AND ACCEPTANCE ......................6 7
8.1 General ..................................................................6 7
8.2 Equipment ................................................................6 7
8.3 Testing ..................................................................7 0
8.4 Lock-Off Procedure ........................................................7 7
8.5 Initial Lift-Off Reading ......................................................7 8
8.6 Acceptance Criteria ........................................................7 9
8.7 Procedures in the Event of Failure During Testing ...............................8 1
8.8 Finishing Work for Permanent Anchors .........................................8 3
8.9 Monitoring Service Behavior .................................................8 3
9.0 REFERENCES AND BIBLIOGRAPHY ..................................8 5
9.1 Reference Standards .......................................................8 5
9.2 Selected Bibliography ......................................................8 7
SUPPLEMENTARY REQUIREMENTS FOR EPOXY-COATED STRAND TENDONS .89
S1.0 SCOPE ...........................................................8 9
S3.0 SPECIFICATIONS, RESPONSIBILITIES AND SUBMITTALS .............8 9
S4.0 MATERIALS ................•..............•......•................8 9
S4.3 Anchorages ...............................................................9 1
S6.0 DESIGN •.•......................................•................9 1
S6.6 Anchor Capacity/Safety Factors ..............................................9 1
56.7 Bond Length ..............................................................9 1
56.8 Free Stressing Length ......................................................9 1
S7.0 CONSTRUCTION ..................................................9 2
57.2 Fabrication ...............................................................9 2
S7 .3 Storage and Handling ......................................................9 2
S7.7 Tendon Insertion ...........................................................9 2
57.9 Installation of Anchorage ....................................................9 3
S8.0 STRESSING, LOAD TESTING AND ACCEPTANCE ......................9 3
58.1 General .................................................................9 3
88.2 Equipment ................................................................9 4
S8.3 Testing ..................................................................9 4
S8.4 Lock-Off Procedure ........................................................9 4
88.6 Acceptance Criteria ........................................................9 5
S8.7 Procedures in the Event of Failure (Strand Slippage) .............................9 7
S9.0 REFERENCES AND BIBLIOGRAPHY ..................................9 8
S9.2 Selected Bibliography ......................................................9 8
iv
RECOMMENDATIONS COMMENTARY
1.0 SCOPE C.l.O SCOPE
These Recommendations have been prepared to These Recommendations do not deal with the design of
provide guidance in the application of permanent anchored structures in general, but are limited to consid
and temporary prestressed rock and soil anchors erations specific to the prestressed anchors themselves.
utilizing high strength prestressing steel. They rep
The applicability of certain sections of these
resent the current state of practice and provide prac
Recommendations will depend upon the type of specifica
tical guidance for the design, installation and testing
tion used and whether the anchors are for permanent or
of grouted prestressed rock and soil anchors, but
temporary application.
are not necessarily applicable to other anchor sy::;
tems such as those, which rely only on mechanical
anchorage to the ground. These Recommendations
also do not intend to establish any requirements for
soil nails, including the ones for protection against
corrosion.
Due to the broad nature of these Recommendations,
particular sections should be clearly referenced,
when included in the specifications for a specific
project.
These Recommendations contain major technical
revisions and supersede the 1996 Edition. The
major revisions include modified requirements for:
J
• Protection against corrosion
• Grouts and grouting activities
• The use of epoxy-coated strand A condensed version of supplementary requirements for
epoxy-coated strand, as prepared by an ADSC Task
Section 3 and 9 of the 1996 Recommendations were
Group, together with most of the 1996 text on the same
combined into an enlarged Section 3. Additionally,
subject, have been moved for convenience and relative
numerous changes were made for further enhancing
emphasis into a Supplement to these Recommendations.
the understanding of the anchor technology.
A summary and the titles of the standard specifica
tions, as well as of the references cited throughout
this document can be found in Section 9.
The values stated in either Sl units or imperial units are
to be regarded as standard. Within the text, the imperi
al units are shown in brackets. The values stated in
each system are not exact equivalents, and so each
system must be used independently of the other.
These Recommendations were prepared by the PTI
Committee for Prestressed Rock and Soil Anchors
with input and review by the ADSC Anchored Earth
Retention Committee
RECOMMENDATIONS COMMENTARY
2
2.0 DEFINITIONS
Additive: Substance, which is incorporated into the Bleed: The autogenous flow of mixing water within,
dry components of a cement-based grout as deliv or its emergence from, newly placed grout; caused
ered to the site. by the settlement of the solid materials within the
grout mass and further facilitated in anchors by filter
Admixture: Substance added to the grout compo ing action of strands ("wicking").
nents during mixing to modify in a controllable fash
ion fluid grout properties (e.g., bleed, pressure filtra Bond Length: The length of the grout body that
tion, shrinkage, hydration, rheology) or set prope.r transmits the applied tensile load to the surrounding
ties (e.g., strength, permeability, durability). soil or rock. (See also the definition of Tendon Bond
Length)
Alignment Load (AL): A nominal minimum load
applied to an anchor during testing to keep the test Bondbreaker: A sleeve placed over the anchor ten
ing equipment correctly positioned. don in its free stressing length to allow elongation of
the tendon free stressing length during stressing.
Anchor: A system used to transfer tensile loads to
the ground (soil or rock), which includes the pre Cast: The amount of curvature of a length-of strand,
stressing steel, anchorage, corrosion protection, which is not restrained when placed on a flat surface.
bond breaker, spacers, centralizers and grout.
Centralizer: A device to support and position the ten
Anchor Head: The means by which the prestressing don inside the drill hole or the sheath, so that a min
force is permanently transmitted from the prestressing imum grout cover is provided.
steel to the bearing plate (wedges and wedge plate for
Coarse-Grained Soils: Soils with more than 50 per
strand tend6ns or anchor nut for bar tendons.)
cent, by weight, of material larger than the No. 200
Anchor Nut: The threaded device that transfers the sieve size.
prestressing force in a bar to a bearing plate.
Cohesive Soils: Soils that exhibit plasticity.
Anchorage: The combined system of anchor head, Atterberg limits are commonly ·used to determine
bearing plate, trumpet and corrosion protection that plasticity and better define a soil as cohesive or non
is capable of transmitting the prestressing force from cohesive.
the prestressing steel to the surface of the ground or
Consolidation Grout: Portland cement based grout
the supported structure.
that is injected into the drill hole, prior to tendon
Anchorage Cover: A cover to protect the anchorage grouting, to either reduce the permeability of the
from corrosion and physical damage. rock immediately surrounding the hole or to other
wise improve the ground conditions (e.g., improve
Apparent Free Tendon Length: The length of tendon drill hole stability).
that is apparently not bonded to the surrounding
grout or ground, as calculated from the elastic load Contractor: The person/firm, which performs the
extension data during testing. anchor construction.
Bearing Plate: A steel plate under the anchor head Corrosion Inhibiting Compound: Material used to
that distributes the prestressing force to the protect against corrosion and/or lubricate the pre
anchored structure. stressing steel.
3
Coupler: The means by which the prestressing force Free Stressing (unbonded) Length: The designed
can be transmitted from one partial-length of a pre length of the tendon that is not bonded to the sur
stressing tendon to another (mainly for bars). rounding ground or grout during stressing.
Creep Movement: The movement that occurs under Fully Bonded Anchor: Anchor in which the free
a constant load and as measured during the creep stressing length without bondbreaker is surrounded
test of an anchor. by grout, after stressing, and so is bonded to the sur
rounding structure or ground.
Creep Test: A test to determine the long-term load
carrying capacity of an anchor under a constant load. Gel Time: Time between the start of mixing of a
polyester resin with the catalyst, and the point at
Design Load: Anticipated final maximum effective
which the liquid phase changes to a viscous state.
load in the anchor after allowance for time dependent
losses or gains. (Also referred to as Working Load.) Grit: Fine-grained material impregnated onto the
outer surface of the epoxy coating, which improves
DetenslonableAnchor Head: An anchor head that is
the epoxy-coating bond to cement grout.
restressable and, in addition, permits the tendon to
be completely detensioned in a controlled way at Grout Sock: A gee-textile encasement around all or
any time during the life of the structure. part of the ground anchor length, used to control grout
loss in certain highly permeable ground conditions.
Downward Sloped Anchor: Any prestressed anchor,
which is inclined greater than 0.1 rad. (5 degrees) Holiday: A discontinuity in a coating that is not dis
below the horizontal. cernible to a person with normal or corrected vision.
Elastic Movement: The recoverable movement Horizontal Anchor: Any prestressed anchor, which is
measured during an anchor test. placed at a slope within 0.1 rad (5 degrees) of the
horizontal.
Encapsulation: A corrugated or deformed tube pro
tecting the prestressing steel against corrosion in Initial Set: A degree of stiffening of the grout mixture
the tendon bond length. less than the final set, indicating the time in hours
and minutes required for the grout to stiffen suffi
Epoxy-Coating: A product containing pigments,
ciently to resist, to an established degree, the pene
thermosetting epoxy resins, cross linking agents,
tration of a weighted test needle (Vicat, ASTM
and other additives, which is applied in the form of a
C191).
powder onto a clean, heated metallic substrate and
fuses to form a continuous barrier coating. Lift-Off: Checking the load ("lift-off load") in the ten
don at any specified time with the use of a hydraulic
Fpu: Specified minimum tensile strength of the ten
jack, by lifting the anchorhead off the bearing plate.
don as defined in the pertinent ASTM Specification.
Lock-Off Load: The prestressing force in an anchor
Final Set: A degree of stiffening of the grout mixture
immediately after transferring the load from the jack
greater than the initial set, indicating the time in hours
to the stressing anchorage.
and minutes required for the grout to stiffen suffi
ciently to resist, to an established degree, the pene Memory: The tendency of seven-wire prestressed
tration of a weighted test needle (Vicat, ASTM C191 ). strand to retain the position in which it has previous
ly been, such as on a reel or spool.
Fine-Grained Soils: Soils with at least 50 percent, by
weight, of material smaller than the No. 200 sieve size.
4