1. Introduction1

National University of SingaporeDepartment of Civil and Environmental Engineering

CE5108EARTH RETAINING

STRUCTURESSTRUCTURES

Part 1Fundamentals and Basic Design & Analysis

Semester 1 2013/14

Goh Siang Huat 12 Kent Ridge Road / Centre for Protective TechnologyT l h 6516 8663Telephone : 6516 8663Email : gohsianghuat@nus.edu.sgAdvisable to call or email before coming!g

OverviewOverview 1st Half (S.H. Goh)( )

Fundamentals, Earth Pressure Th i D i Phil hiTheories, Design Philosophies, Rigid Structures, Flexible Walls (C til + Si l P )(Cantilever + Single-Prop)

2nd Half (Prof Harry Tan) D E i M l i d Deep Excavations, Multi-propped

Walls, Finite Element Modeling and A l iAnalysis

Course Outline (Part 1) Fundamentals and Basic DesignFundamentals and Basic Design

Introduction IntroductionTypes of retaining structures

Earth pressure theoriesEarth pressure theories, relationship between soil movement and earth pressure, selection and acquisition of soil parameters

Rigid retaining structuresLimit equilibrium analysis limit state design approach seepageLimit equilibrium analysis, limit state design approach, seepage analysis, displacement and ground water control, design to EC7 requirements

Flexible retaining structuresCantilever and anchored sheet pile walls, pore water pressure and

l i il hi ff tseepage analysis, soil arching effects

Broad Learning Outcomes Appreciate the significance of the different types of earth

pressures and their application in the analysis of retaining llwalls.

Able to apply mathematical and soil mechanics concepts to derive basic earth pressure theories

Able to analyse simple retaining structures, such as gravity ( i id) t t til ll d i l d ll(rigid) structures, cantilever walls and singly-propped wall (using common earth pressure theories)

Understand and appreciate basic design philosophies (for Understand and appreciate basic design philosophies (for retaining structures)

Understand the key features of Eurocode 7 and able to Understand the key features of Eurocode 7, and able to apply the code requirements for design of earth retaining structures

Broad Learning Outcomes Understand and appreciate common stability issues

associated with earth retaining structures, and how to l l t f t f t f t bilit blcalculate safety factors for common stability problems

Appreciate that there is a lot more to earth retaining structures that we do not have time to cover but youstructures that we do not have time to cover, but you should at least be equipped with the fundamentals to enable you to understand and absorb new information and k l dknowledge on your own.

CA and Exam ComponentsCA and Exam Components

Continuous assessment for GSH part1 quiz (10%) + selected assignments (10%)

Continuous assessment for Prof Harry Tan’s part

18 Sept 2013 (subject to change)

Continuous assessment for Prof Harry Tan s part1 project + ?? (20%)

Final Exam (60%)

1 Introduction1. IntroductionTypes of Retaining Structuresyp g

Types of Retaining StructureTypes of Retaining StructureGravityy

Embedded / Flexible

Mechanically StabilizedMechanically StabilizedEarth (MSE)

Embedded / Flexible

Gravity Retaining WallsGravity Retaining Walls

• Probably the oldest type of retaining• Probably the oldest type of retaining structure.

• Used in fortifications, roads/pavements, bridges underground shafts (graves)bridges, underground shafts (graves).

• Constructed using stone masonry in the g ypast.C i h l i f i• Concrete with steel reinforcement quite commonly used these days.y y

Ancient Greek Theatre – about 300 B CAncient Greek Theatre – about 300 B.C.

Longji Terraced Rice Fields in China – circa 1300Longji Terraced Rice Fields in China – circa 1300.

Citadelle Besancon in France – circa 1700Citadelle Besancon in France – circa 1700.

Modern TimesModern Times

Gabion WallsGabion Walls

Stone Blocks Retaining WallStone Blocks Retaining Wall

With advances in building materials (e gWith advances in building materials (e.g. concrete, steel),

cantilever wall

backfill backfill

wallbackfill

counterfort

plain concrete

reinforcement

Gravity wall Cantilever wall Counterfort wall

Counterfort Cantilever Retaining Wall

Embedded / Flexible

Embedded / Flexible WallEmbedded / Flexible Wall• Also has historical roots.

• Earliest embedded walls made of timber piles.

• Swiss Lake Dwellers – about 6000 years ago –houses built on platform supported by timber piles.

• Greeks were using timber piles in ~400 B C• Greeks were using timber piles in ~400 B.C.

• Romans also built roads, aqueducts, bridges , q , gsupported by timber piles 100 A.D.

H it i t l h il fi t d• However, it is not clear when piles were first used for their lateral capacity as a retaining wall.

Embedded / Flexible WallEmbedded / Flexible Wall• Nevertheless, timber piling as a retaining wall

continued as an important earth retention method until the early 20th century.

Embedded / Flexible WallsEmbedded / Flexible WallsThese days, the following type of embedded y , g ypflexible walls are commonly used:

Sheet Piles

Soldier Piles with Lagging

Secant Piles / Contiguous Bored Pilesg

Diaphragm Wall Diaphragm Wall

Sheet Piles

Embedded / Flexible WallEmbedded / Flexible Wall• Steel sheet piling became popular after World p g p p

War I. It was first patented ~1900.

Sheet Piles

Embedded / Flexible WallEmbedded / Flexible Wall

• Driving of steel sections appears to have startedDriving of steel sections appears to have started ~1880.

• Soldier pile walls were successfully used in New York, London, Berlin since the late 18th century.

• In fact, the system of shoring using soldier pile and lagging is also known as the methodBerlinand lagging is also known as the ______ method.Berlin

S ldi Pil ith Ti b L iSoldier Piles with Timber Lagging

Soldier Piles with Timber Lagging + Ground AnchorsSoldier Piles with Timber Lagging + Ground Anchors

Sheet Piles

Embedded / Flexible WallEmbedded / Flexible WallSecant Piles

• Secant pile walls are formed by constructing intersectingreinforced concrete piles

• First use of secant walls is recorded in the 1920s in Europe.

reinforced concrete piles. • The secant piles are reinforced with either steel rebar or

with steel beams and are constructed by either drillingwith steel beams and are constructed by either drilling under mud or augering.

• Primary piles are installed first with secondary piles y p y pconstructed in between primary piles once the latter gain sufficient strength.

(primary pile)(secondary pile)

Secant PilesSecant Piles

Embedded / Flexible WallEmbedded / Flexible WallContiguous Bored Piles

In the U S the first se of contin o s or contig o s bored

• Closely spaced bored piles can be used to form a retaining

• In the U.S., the first use of continuous or contiguous bored pile was in 1950.Closely spaced bored piles can be used to form a retaining wall, perhaps for the construction of a deep basement or a cut and cover tunnel.

• The piles may be constructed so that they virtually touch each other (contiguous).

• The gaps between the piles can be grouted to form a• The gaps between the piles can be grouted to form a watertight retaining wall.

Contiguous Bored PilesContiguous Bored Piles

Sheet Piles

Embedded / Flexible WallsEmbedded / Flexible WallsDiaphragm Wallsp g

• Generally constructed in a series of discrete panels typically ranging in length from 3m to 7m.yp y g g g

• Depths of diaphragm walls vary depending on the application and the specified requirements but typicallyapplication and the specified requirements, but typically they can range from a few meters to tens of meters.

( ) f f• The width (thickness) of the wall can vary from 600mm to 1800mm, again depending on the application.

• Diaphragm walls can be used as (a) retention systems, (b) permanent foundation walls, and/or (c) groundwater b ibarriers .

Embedded / Flexible WallsEmbedded / Flexible Walls

Diaphragm WallsDiaphragm Walls

Few metres to tens

bentonite slurry to

reinforcement cage

to tens of

metres

support the trench

concrete

panel (3 – 7 m) panel (3 – 7 m)

Embedded / Flexible WallsEmbedded / Flexible WallsDiaphragm Walls

• Because slurries are used to provide the trench stability before the concrete is poured in, diaphragm walls are also commonly referred to as slurry wallsalso commonly referred to as slurry walls.

• Use of slurry to maintain stability in an otherwise unstable hole was born in the petroleum industry in 1914unstable hole was born in the petroleum industry in 1914.

• The first slurry trench cutoff walls for ground water control were installed in the U S in 1948control were installed in the U.S. in 1948.

• The first structural slurry walls were constructed in Italy in 1950.in 1950.

• Structural slurry walls did not appear in the U.S. until 1962.

• The original World Trade Centre ‘bath-tub’ was constructed as a diaphragm wall in the mid 1960s.

Diaphragm WallDiaphragm Wall

C l t dCompleted diaphragm walls

(for a shaft excavation)excavation)

Embedded / Flexible

Mechanically Stabilized Earth (MSE)Mechanically Stabilized Earth (MSE)Mechanically Stabilized Earth

A MSE ll i t f il i f t d f i• An MSE wall consists of soil, reinforcement, and facing to retain earth and support overlying structures.Altho gh the basic principles of MSE has been sed• Although the basic principles of MSE has been used throughout history, MSE was developed in its current form in the 1960s.form in the 1960s.

• The reinforcing elements used can vary but include steel and geosynthetics.

• Another common name for this type of wall is Reinforced Earth.H h “R i f d E h” i d f• However, the term “Reinforced Earth” is a trade name of the Reinforced Earth Company in the US, hence it is not usually used thereusually used there.

• Elsewhere Reinforced Earth is the generally accepted term.

Mechanically Stabilized Earth (MSE)Mechanically Stabilized Earth

Mechanically Stabilized Earth (MSE)

Laying of Reinforcement Strips

Mechanically Stabilized Earth (MSE)Mechanically Stabilized Earth (MSE)

Completed reinforced earth walls forCompleted reinforced earth walls for bridge embankment

Types of Retaining StructureTypes of Retaining Structure• Brief introduction to the common types of walls

used for earth retention.• Other methods of earth retention are possible:

soil nailing, ground freezing.• Different types of walls are applicable for yp pp

different ground conditions and construction requirements.q

• Walls must be properly designed and constructed to support / retain the soil behindconstructed to support / retain the soil behind them.

• If walls are not properly designed and• If walls are not properly designed and constructed, they may FAIL.

When Walls FailWhen Walls Fail

How to minimize risks of failureHow to minimize risks of failure

Rational Analysisat o a a ys s Fundamental soil mechanics L t l th th i Lateral earth pressure theories Appropriate wall type and design Adequate resistance against

diff t d f f il

pp op ate a type a d des g

Safe Designdifferent modes of failure

Safe Design Factor of Safety, Limit States, y, ,

Eurocode

Ending ThoughtEnding Thought

Unfortunately, soils are made by t d t b d thnature and not by man, and the

products of nature are alwaysproducts of nature are always complex.

Karl von Terzaghi, 1936

1. Introduction1

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