1-33 retaining wall construction

7242019 1-33 Retaining Wall Construction

httpslidepdfcomreaderfull1-33-retaining-wall-construction 15

TheStructuralEngineer42

Technical Guidance Note

Technical

October 2013

Note 33 Level 1

991290

Retaining walls can be grouped into three

categories gravity embedded and hybrid

They all perform the function of supporting

a material which is typically soil at an angle

that exceeds the angle of repose Each type

has unique properties making them ideally

suited to specific situations

Gravity retaining walls

A gravity retaining wall relies upon the

friction between it and the founding

material together with the wallrsquos self-weight

to resist sliding and overturning They can

be formed from masonry concrete or

reinforced soil and are typically used when

a shallower depth of excavation needs to be

retained They are normally between 1-3m

and are constructed to make way for level

ground such as a railway siding (Figure 1)

Retaining wall constructionIntroduction

Retaining walls have been used for thousands of years whether in the

construction of terraced fields on a steep slope or a railway cutting through

a hill side a retaining wall is used in some form or another

This Technical Guidance Note is a description to the various forms

of retaining walls that are currently used It is primarily concerned with

structures that retain soil although many of the aspects described can

be translated to retaining other materials such as grain sand and liquids

The water table will have design implications on the wall the pressure of

which can be alleviated by providing drainage and weep holes depending

on the soil conditions The aim of this note is to provide you with suffi cientfamiliarity of the various types of retaining wall so that when you encounter

them or are developing a retaining wall solution you will know what options

are available

983127 Retaining walls

983127 Applied practice

983127 Further reading

983127 Web resources

ICONLEGEND

Retaining wallsEmbedded retaining walls

Embedded retaining walls rely on being

installed into the soil to below the depth of

excavation Once the wall is in place within

the ground soil is excavated from its front

to a defined depth based on the bending

capacity of the retaining wall and the depth

of its embedment into the soil Embedded

retaining walls rely on the passive resistance

of the soil in front of them along with the

shear and bending capacity of the wall itself

to keep it in place They are most often

used for basements and other excavations

cut into previously level ground They are

suitable for very deep excavations ie in

excess of 10m andor where the site is

restricted eg adjacent site boundaries

or existing sub-structures (Figure 2)

For excavations in excess of 4-6m deep

propping to the embedded wall is usually

necessary to control wall deflections and

prevent excessive depths of embedment

Hybrid retaining walls

Hybrid retaining walls (Figure 3) combine

the features of both gravity and embedded

forms They rely on shear and bending

resistance of the wall and its base which

may or may not be fixed into position by

piles They are typically used where ground

levels need to be raised eg where there

are poor soil conditions to the extent that a

gravity retaining wall solution is not viable

Gravity retaining wallsGravity walls come in many different forms

all of which follow the principles described

in Fig 1 ie supporting lateral forces via

their resistance to sliding and overturning

They are often constructed using a backfill

method where the wall is built with the soil

it is to retain being placed against it Gravity

retaining walls can be split into three sub-

groups masonry reinforced concrete and

soil reinforcement

983123 Figure 1Concept

diagram of gravitybased retaining wall


diagram ofembedded retainingwall with pivot point


diagram of hybridretaining wall

Active

ActivePassive

Passive







wwwthestructuralengineerorg

45

Contiguous bored piled walls

Contiguous bored piled walls also referred

to as lsquocontigrsquo are dug and cast into the

ground with a small gap of 50-150mm

between each pile The presence of

this gap makes contiguous piled wallsunsuitable to retain granular soils like

sand and gravel as such soil types fall

through the gaps between the piles (Figure

10) Similarly they cannot retain water

and can only be placed in areas above

the water table or where de-watering is

being employed Where they are used

in permanent conditions a facing wall is

needed in front of contiguous piled walls

due to the gaps between each pile

Secant bored piled walls

Secant bored piled walls are a variant of

the contiguous piled wall with the majordifference being that there is no gap

between piles Instead the piles are divided

into primary and secondary (historically

referred to as female and male respectively)

The primary piles are installed first and the

bored secondary piles overlap their primary

neighbours (shown in green in Figure 11)

This creates a continuous wall that can resist

water penetration when carefully detailed

and executed Secant bored piled walls

come in three varieties that are dependent

on the characteristic compressive strength

of the primary bored pile (Table 1) Secant

bored piled walls can be installed into almost

any type of soil and can be placed where

there is a high water table

King postSoldier piled walls

King post or Soldier piled walls consist

of a series of steel posts that are either

driven into the ground or cast into place

within an excavated hole The posts are

installed 1-3m apart and the gap between

them is filled with spanning panels which

are typically precast concrete segments

(Figure 12) These are installed as the soil in

front of the retaining wall is removed They

are typically used in clay and granular soils

provided the water table is below the extent

of the excavation

Diaphragm walls

Diaphragm walls are a series of interlocking

reinforced concrete panels that have been

cast in situ by excavating a segment of

soil and replacing it with a fluid (typically

bentonite) A reinforcement cage is then

inserted and concrete is poured in via a

tremie pipe The concrete displaces the

bentonite as it is poured Diaphragm walls

can be 600-1500mm thick with each panel

being typically 22-8m wide They can retain

significantly more soil than most other wallswith a depth of 120m being possible due to

Table 1 Types of primary piles in secant bored piled wall

Secantprimarypile type

DescriptionCharacteristiccompression

strength (Nmm2)

Reinforcementpresent

Soft Bentonite cement 1-3 No

FirmConcrete with an admixture that

delays the development of strengthin the pile during drilling

10-20 No

HardFull strength concrete often with an

admixture that delays the developmentof strength in the pile during drilling

25-60Can be

installed inprimary pile

There is a risk of encountering any reinforcement in the primary pile when drilling

the secondary piles so it is preferable to avoid reinforcing primary piles

their ability to withstand very high lateral

loads They can be installed into almost any

type of soil and can resist water pressure

provided water bar seals are installed

across each segment (Figure 13)

Hybrid retaining wallsThe archetypal hybrid retaining wall is the

unpropped cantilever that is founded on pile

foundations Hybrid walls can be installed in

most soils and can retain water pressures

provided appropriate drainage and water

proofing measures are installed (Figure 14)

Criteria for retaining wall selectionThe primary criterion for the selection of

a retaining wall is the height required Of

secondary concern are space restrictions

as they will impact on the preferred

construction method and can preclude

certain types of walls As an example

a 2m high retaining wall adjacent to a

rural highway would likely be a gravity or

hybrid wall as it is not very high and space

restrictions are not likely to be a concern

A 4m deep basement construction within

a city centre however would most likely

require an embedded wall due to its height

and limited site access

Other criteria that should be considered

include stiffness of the wall to prevent

movement during its design life and

required water resistance which is

of particular relevance in basement

construction Water proofing construction

method and materials all have an impact on

cost and programme and should therefore

be taken into consideration

For further advice on selecting an

appropriate retaining wall solution see

Table 82 in the Manual for the geotechnical

design of structures to Eurocode 7

983123 Figure 13Diaphragm wall

983123 Figure 14Hybrid retaining wall





Technical

October 2013

Note 33 Level 1

991290

Eurocode 0

Web resources

The British Geotechnical Association

httpbgacityacuk

Eurocode 0

Applied practice

BS EN 1992-1-1 Eurocode 2 Design of

Concrete Structures - Part 1-1 GeneralRules for Buildings

BS EN 1992-1-1 UK National Annex to

Eurocode 2 Design of Concrete

Structures - Part 1-1 General Rules

for Buildings

BS EN 1997-1 Eurocode 7 Geotechnical

Design - Part 1-1 General Rules

BS EN 1997-1 UK National Annex to

Eurocode 7 Geotechnical Design - Part 1-1

General Rules

BS EN 15362010 - Execution of special

geotechnical work ndash bored piles


geotechnical work ndash diaphragm walls


geotechnical work ndash sheet pile walls

Glossary andfurther reading

Angle of repose -The deepest angle

of slope relative to a horizontal surface agranular material such as soil is

resting upon

Bentonite - A form of absorbent clay that

is used during the construction of some

forms of retaining wall

Caisson - A water-tight retaining sub-

structure typically used for the construction

of marine engineering works such as piers

Tremie pipe - Method of placing concrete

within a liquid or highly viscous material that

relies on the delivery pipe remaining in thefreshly placed concrete so that it displaces

the liquid

Unsupported height - The extent of a

retaining wall that has no propping

Water table - The depth at which ground

water is located

Technical Lecture SeriesConferences amp Seminars Annual Institution Events Special Interest Series A series of lectures organised in partnership by

the Institution and other leading organisations

Registration is required in advance by visiting the events section of the Institution website wwwistructeorg and following the

instructions provided Registration will close Friday 11 October Space is limited and latecomers will only be admitted to the

eventsistructeorg

Pai Lin Li Lecture

Institution members wishing to spend 4 ndash 6

weeks outside their own country studying

unrivalled opportunity to sample the technical

economic social and political conditions in

another country and to examine how these

various factors affect the practise of structural

engineering

winners John Orr and Katie Symons who will

Form an adventure in concrete

and brick

Form active design can facilitate architecturally

construction

John Orr

PhD MEng(Hons)

John Orr is a lecturer in

sustainable construction at

the University of Bath UK He

degrees from the same institution in 2009 and 2012

respectively His research interests include the design

of concrete structures using fabric formwork and

the shear behaviour and computational modelling of

concrete

International perspectives on Life Cycle

Assessment of structural materialsparticularly timber lessons to be learned

from Australasia

Australia and New Zealand in 2013 examining the

materials particularly with respect to embodied

materials particularly timber is also explored

Katie Symons MEng MA

(Cantab) MIStructE MICE CEng

Katie Symons has a keen

interest in the sustainability of

the built environment especially

the embodied energy andcarbon of buildings She presented her research

undertaken during a secondment to the University of

Society conference in Sydney in July 2012 She

has had journal papers published on the subject of

evaluating embodied energy and carbon

Thursday 17 October

Registration from 1730

Lecture at 1800

International HQ

Further ReadingThe Institution of Structural Engineers

(2013) Manual for the geotechnical design

of structures to Eurocode 7 London The

Institution of Structural Engineers

The Institution of Civil Engineers (2012) ICE

manual of geotechnical engineering London

Thomas Telford

The Institution of Structural Engineers

(2004) Design and construction of deep

basements including cut and cover structures

London The Institution of Structural Engineers

CIRIA (2000) Publication C516 Modular

gravity retaining walls design guidance

London CIRIA

CIRIA (2003) Publication C580 EmbeddedRetaining Walls London CIRIA








45














































of the excavation

Diaphragm walls















strength (Nmm2)





10-20 No



25-60Can be
















































Technical

October 2013

Note 33 Level 1

991290

Eurocode 0

Web resources


httpbgacityacuk

Eurocode 0

Applied practice






for Buildings





General Rules










resting upon










the liquid




water is located





eventsistructeorg

Pai Lin Li Lecture







engineering



and brick


construction

John Orr

PhD MEng(Hons)








concrete



from Australasia














Thursday 17 October


Lecture at 1800

International HQ







Thomas Telford







London CIRIA






Technical

October 2013

Note 33 Level 1

991290

Eurocode 0

Web resources


httpbgacityacuk

Eurocode 0

Applied practice






for Buildings





General Rules










resting upon










the liquid




water is located





eventsistructeorg

Pai Lin Li Lecture







engineering



and brick


construction

John Orr

PhD MEng(Hons)








concrete



from Australasia














Thursday 17 October


Lecture at 1800

International HQ







Thomas Telford







London CIRIA


1-33 retaining wall construction

Documents