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2012/12/1
1
AN OVERVIEW OF
EXCAVATION AND LATERAL
SUPPORT (ELS) SYSTEMS
December 2012 K.W. LEUNG
Outline of the Talk
� Basic considerations
� Typical lateral support systems
� Permanent support
� Temporary support
� Statutory requirements for ELS Plan
� Experience sharing
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� Site
characteristics
� Development
proposal
� Construction
� Design
� Performance
Basic
Considerations
CIRIA C580
Typical Section
Struts
Ground surface
Excavation
levelTie-backs (as an
alternative to struts)Seepage
cut-off
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Braced Excavation
Tie-back Excavation
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Bottom-up Construction
� � � �
Top-down Construction
� �
� �
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Permanent Support
� Usually thick and massive
� Suitable for both top-down and
bottom-up construction
� Common types:
� Diaphragm wall
� Bored pile wall
� Caisson wall
Diaphragm Wall
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Bored Pile Wall
Caisson Wall
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Temporary Support
� Generally slim and flexible
� Used with bottom-up construction
� Common types:
� Channel planking
� Sheet pile wall
� Pipe pile wall
� Soldier pile and laggings
� Grouted pile wall
� Soil nailing for open cut
Channel Planking
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Sheet Pile Wall
Pipe Pile Wall
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Soldier Pile Wall
Grouted Pile Wall
Formed by
� PIP (Pakt-in-Place) piles; or
� Jet grouting; or
� Deep mixing
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(a) PIP Piling
(b) Jet Grouting
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(c) Deep Mixing
Soil Nailing for Open Cut
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Statutory Requirements
� B(A)R 8(1)(bc) requires submission of ELS
plans where consequence of failure is serious
� PN for APs, RSEs & RGEs – APP 57
� Submission is required where the excavation is:
• >4.5m deep and > 5m long
• liable to affect any road, structure, slope (>30o),
or water main (≥75mmø) within the 45o line up
from the base of the excavation to the ground
surface
Contents of ELS Plan
� Lateral support system, e.g. sheet piles
� Strutting (or tie-back) layout
� Construction sequence
� Supporting geotechnical documents
� Realistic estimates of ground movements
� Assessment of effects of excavation & dewatering on adjoining structures
� Monitoring proposal
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Common Deficiencies
• B(A)R 8(1)(bc) prescribed documentation
• Geological profile
• Groundwater
• Interaction with adjacent features/ structures
• Design calculations
• Inconsistency between plans and calculations
Non-compliance with
Approved Plans
� Support
� Excavation
� Loading situation not covered by design
� Precautionary measures
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What Happened?
What Happened?
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Observational Method
�9th Rankine Lecture by
Peck(1969) – “The
Observational Method
in Applied Soil
Mechanics”
�It has the potential for
savings in time or
money, or providing
needed assurance of
construction safety
THANK YOU!