146
Appendix I
Summaries for GCO Publication No. 1/90:
Review of Design Methods for Excavation
GCO Publication No. 1/90 - Review of Design Methods for Excavations
Table I1 - Summary of Current British Standard References and Replacement Eurocodes
BS Status
Relevant Updated Code
for Citation
ID No.
Technical Clauses in Report
BS 8081: 1989 Code of Practice for Ground Anchorages
Confirmed,
BS8081:1989
P1-90:8081-2
Current,
BS EN 1997-1:2004
Partially
BS EN 1537:2013
replaced
Page
no.
58
Existing Content of Technical Guidance Document
General Comments to define Scope of Updating /
Specific Clauses in EN (s) / UK NA(s)
Scope of
Updating
A comprehensive treatment of the design of anchors is given by Hanna (1980), British Standards Institution (1989)
and Geospec 1 : Model specification for Prestressed Ground Anchors (GCO, 1989). Factors of safety for anchor
design in Hong Kong are given in Geospec 1.
1989; Informative; P1-90:8081-2; Section 6 of BS8081:1989 deals with the
fundamental principles of geotechnical design, i.e. the mechanics of how the
anchor works. Design is based on factors of safety, not limit state; although
limit state is discussed in Annex B. At present the global factor design aspects
of BS8081:1989 are valid but not used in the UK. Design in the UK is generally
required to BS EN 1997-1:2004, although the section on anchors is due of
imminent revision. BS EN 1537:2013 deals with execution of anchor
installation and supersedes some parts of BS 8081:1989. Its inclusion as a
reference may be of use to user of GCO Publication No. 1/90. It should be
noted that the factors of safety in Geospec 1 are not compatible with limit
state analysis.
Anderson et al (1983) reviewed four methods of checking of the overall stability of anchored retaining walls, viz. the 1989; Informative; P1-90:8081-3; Annex D of BS8081:1989 goes into detail of
German method (German Society for Soil Mechanics and Foundation engineering, 1980), the Ostermayer (1977)
overall stability of anchored structures and excavations. This text is
method, the French method (Bureau Securitas, 1972) and the method by Littlejohn et al (1971). They found that all considered Non-Contradictory Complementary Information (NCCI) by the UK
National Annex to BS EN 1997-1:2004.
four design methods resulted in stable systems, both at the end of construction and after backfill loading. The
determination of anchor prestress loads by the method by James & Jack (1975) was found to be based on erroneous
earth pressure assumptions (see Section 8.2.4). More consistent behaviour was found in tests designed using the
method by Littlejohn et al (1971) for overall stability, particularly on surcharge loading, indicating that a logarithmic
spiral method may be the most appropriate to use. However, Schnabel (1984) commented that the German and
French methods are wrong, as they assume the tie-back pulls on the soil without pushing on the wall. He considered
that only the Ostermayer method is correct because it considers the tie-backs as internal forces in the soil wedge
between the wall and the anchors. The method by Broms (1968) also recognizes this. A comprehensive review of
methods of analysing overall stability of anchored retaining walls is given in British Standards Institution (1989).
5
Confirmed,
Current,
Partially
replaced
BS8081:1989
P1-90:8081-3
60
Confirmed,
Current,
Partially
replaced
BS8081:1989
P1-90:8081-4
70
Clough (1972b, 1975) summarised the data from available literature on tied-back wall movements, as shown in
figure 53. Generally, the wall movements and settlements are well below one percent of the excavation depth in a
few instances values above one percent appear. The data were re-plotted in Figures 54 and 55, where the
percentage movement is plotted against the maximum ordinate of the design prestress diagram for sands and stiff
clays respectively. The maximum prestress pressure is made nondimensional by the product of unit weight and
excavation height. It can be seen that, for both sands and stiff clays, the movements decrease with increasing
prestress. The design pressure levels suggested by Terzaghi & Peck (1967) are also shown in the figures. The data
suggest that the optimum effect of prestressing in reducing movements is achieved by using pressure levels slightly
greater than those of Terzaghi & Peck (1967). Further data on movements of the crest and settlement of the ground
behind tied-back walls are given in British Standards Institution (1989).
1989; Informative; P1-90:8081-4; Table 21 of BS8081:1989 provides data on
crest and ground settlement behind tied-back walls. This information does not
appear in BS EN 1997-1:2004; it is, however, considered NCCI by the UK
National Annex.
1
P1-90:8081-1
82
British Standards Institution (1989). British Standard Code of Practice for Ground Anchorages (BS 8081:1989). British 1989; Reference; P1-90:8081-1; There are three citations to this reference, all
Standards Institution, London, 176 p.
informative. The sections of the standard referenced are all still valid as a
general reference, although design and execution requirements for the UK are
now promulgated in BS EN 1997-1:2004 and BS EN 1537:2013.
1
Reference Section of Report
Confirmed,
BS8081:1989, BS EN 1997Current,
1:2004, BS EN 1537:2013
Partially
replaced
1
Table I1
Page 1 of 1
GCO Publication No. 1/90 - Review of Design Methods for Excavations
Table I2 - Extracts of Relevant Sections or Clauses of the British Standards and Eurocodes / National Annexes
Relevant Updated Code for
Citation
ID No.
Page
no.
Technical Clauses in Report
BS 8081: 1989 Code of Practice for Ground Anchorages
BS8081:1989
P1-90:8081-2
58
BS EN 1997-1:2004
BS EN 1537:2013
BS8081:1989
P1-90:8081-3
60
BS8081:1989
P1-90:8081-4
70
Scope of
Updating
Extracts of Relevant Sections or Clauses
of the superseded British Standard(s)
All design related sections of BS8081:1989.
Additional specific design information is contained in Section 8 of BS EN 1997-1:2004, but
this is limited to limit state design methods.
Annex D of BS8081:1989.
Table 21 of BS8081:1989.
No change.
No change.
5
1
1
Extracts of Relevant Sections or Clauses
of the replacement British/European Standards
Table I2
Page 1 of 1
GCO Publication No. 1/90 - Review of Design Methods for Excavations
Table I3 - Description of Standards, Differences and Recommended Amendments
ID No.
Page
no.
Scope of
Updating
Description of Design, Specification and/or Testing Required
Quoted Standard(s)
Up-to-date Standard(s)
Effects of differences in Adopting
Up-to-date Standard(s)
Recommended Amendments
Technical Clauses in Report
BS 8081: 1989 Code of Practice for Ground Anchorages
P1-90:8081-2
58
5
Design method for ground anchors.
P1-90:8081-3
60
P1-90:8081-4
70
Reference Section of Report
P1-90:8081-1
82
Design method for ground anchors.
Up-to-date standard is restricted to limit state
analysis.
N/A
N/A
Retain existing text, but add text on BS EN 19971:2004 and BS EN 1537:2013.
Retain existing text.
Retain existing text.
1
1
Stability analysis.
Settlement analysis
N/A
N/A
1
This reference document is: Confirmed, Current,
Partially replaced.
The current document(s) is (are): BS8081:1989, BS The execution related parts of BS8081:1989 are
Retain existing reference. Add reference to BS EN
EN 1997-1:2004, BS EN 1537:2013
replaced by BS EN 1537:2013. General design
1997-1:2004 and BS EN 1537:2013.
aspects remain NCCI, with some specific additions
in BS EN 1997-1:2004.
Table I3
Page 1 of 1
GCO Publication No. 1/90 - Review of Design Methods for Excavations
Table I4 - Recommended Revisions to Existing Clauses referring to British Standards
Page
no.
BS Referenced
in Technical
Guidance
Document
Scope of
Updating
ID No.
58
BS8081:1989
5
P1-90:8081-2
60
BS8081:1989
1
P1-90:8081-3
70
BS8081:1989
1
P1-90:8081-4
82
BS8004:1986
1
P1-90:8081-1
Existing Content of
Technical Guidance Document
Recommended Content for
Updated Technical Guidance Document
(1)
Additional reference required.
Additional reference required.
A comprehensive treatment of the design of anchors is given by Hanna (1980),
British Standards Institution (1989) and Geospec 1 : Model specification for
Prestressed Ground Anchors (GCO, 1989). Factors of safety for anchor design in
Hong Kong are given in Geospec 1.
A comprehensive treatment of the design of anchors is given by Hanna
(1980), British Standards Institution (1989) and Geospec 1 : Model
specification for Prestressed Ground Anchors (GCO, 1989). Additional
useful information is contained in British Standards Institution (2004, 2013).
Factors of safety for anchor design in Hong Kong are given in Geospec 1.
Anderson et al (1983) reviewed four methods of checking of the overall stability of No Change
anchored retaining walls, viz. the German method (German Society for Soil
Mechanics and Foundation engineering, 1980), the Ostermayer (1977) method, the
French method (Bureau Securitas, 1972) and the method by Littlejohn et al (1971).
They found that all four design methods resulted in stable systems, both at the end
of construction and after backfill loading. The determination of anchor prestress
loads by the method by James & Jack (1975) was found to be based on erroneous
earth pressure assumptions (see Section 8.2.4). More consistent behaviour was
found in tests designed using the method by Littlejohn et al (1971) for overall
stability, particularly on surcharge loading, indicating that a logarithmic spiral
method may be the most appropriate to use. However, Schnabel (1984)
commented that the German and French methods are wrong, as they assume the
tie-back pulls on the soil without pushing on the wall. He considered that only the
Ostermayer method is correct because it considers the tie-backs as internal forces
in the soil wedge between the wall and the anchors. The method by Broms (1968)
also recognizes this. A comprehensive review of methods of analysing overall
stability of anchored retaining walls is given in British Standards Institution
(1989).
No Change
Clough (1972b, 1975) summarised the data from available literature on tied-back
wall movements, as shown in figure 53. Generally, the wall movements and
settlements are well below one percent of the excavation depth in a few instances
values above one percent appear. The data were re-plotted in Figures 54 and 55,
where the percentage movement is plotted against the maximum ordinate of the
design prestress diagram for sands and stiff clays respectively. The maximum
prestress pressure is made nondimensional by the product of unit weight and
excavation height. It can be seen that, for both sands and stiff clays, the
movements decrease with increasing prestress. The design pressure levels
suggested by Terzaghi & Peck (1967) are also shown in the figures. The data
suggest that the optimum effect of prestressing in reducing movements is achieved
by using pressure levels slightly greater than those of Terzaghi & Peck (1967).
Further data on movements of the crest and settlement of the ground behind tiedback walls are given in British Standards Institution (1989).
British Standards Institution (1989). British Standard Code of Practice for Ground No change.
Anchorages (BS 8081:1989). British Standards Institution, London, 176 p.
BSI (2004). Eurocode 7: Geotechnical Design – Part 1: General Rules (BS
EN 1997-1:2004). British Standards Institution, London, 168 p.
BSI (2013). Execution of special geotechnical works - Ground anchors (BS
EN 1537:2013). British Standards Institution, London, 56 p.
Table I4
Page 1 of 1