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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!