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CEEARTH RETAININGSTRUCTURESPart 1Fundamentals and Basic Design & AnalysisNational University of SingaporeDepartment of Civil and Environmental EngineeringSemester 1 2015/S. H. GohGoh Siang Huat 12 Kent Ridge Road / Centre for Protective TechnologyTelephone : 6516 8663 Email : gohsianghuat@nu...

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National University of Singapore Department of Civil and Environmental Engineering

CE5108 EARTH RETAINING STRUCTURES Part 1 Fundamentals and Basic Design & Analysis Semester 1 2015/16 S. H. Goh Introduction - 1

Goh Siang Huat 12 Kent Ridge Road / Centre for Protective Technology Telephone : 6516 8663 Email : [email protected] Advisable to call or email before coming!

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Module Overview  Part 1 (S.H. Goh)  Fundamentals, Earth Pressure Theories, Design Philosophies (including EC7), Rigid Structures, Flexible Walls (Cantilever + Single-Prop)  Part 2 (Prof Harry Tan)  Deep Excavations, Multi-propped Walls, Finite Element Modeling and Analysis Introduction - 3

Course Outline (Part 1 by GSH) Fundamentals and Basic Design  Introduction Brief historical review, broad overview of different types of retaining structures

 Earth pressure theories Different earth pressure theories and their mathematical derivations, relationship between soil movement and earth pressure, selection and acquisition of soil parameters, influence of groundwater seepage

 Rigid retaining structures Limit equilibrium analysis of gravity retaining walls, limit state design approach, design to EC7 requirements for different limit states

 Flexible retaining structures Limit equilibrium analysis of cantilever and single-propped sheet pile walls, design to EC7 requirements, influence of soil arching effects Introduction - 4

Broad Learning Outcomes  Appreciate and understand the significance of the different types of earth pressures and their application in the analysis of retaining walls.  Able to apply mathematical and soil mechanics concepts to derive basic earth pressure equations  Able to analyze simple retaining structures, such as rigid gravity structures, cantilever walls and singly-propped wall using common earth pressure theories with limit equilibrium approach  Understand and appreciate the key features of basic design philosophies for earth retaining structures  Able to analyse and design rigid gravity structures, cantilever walls and singly-propped walls based on EC7 code requirements Introduction - 5

Broad Learning Outcomes  Understand and appreciate common stability issues associated with earth retaining structures, and how to calculate 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 you should at least be equipped with the fundamentals to enable you to understand and absorb new information and knowledge on your own.

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CA and Exam Components  Continuous assessment for Part 1 (GSH) 1 quiz (10%) + selected assignments (10%) 17 Sept 2015

 Continuous assessment for Part 2 (Prof Harry Tan) 1 project + ?? (20%)  Final Exam (60%)

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Why Study Earth Retaining Structures

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Why study earth retaining structures? Why are earth retaining structures important? What are they used for?

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Key Function of Earth Retaining Structures Earth retaining structures or systems are used to hold back earth and maintain a difference in the elevation of the ground surface.

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Difference in Earth Elevations How does such difference in earth elevations come about? 1. Excavation

soil removed

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Difference in Earth Elevations How does such difference in earth elevations come about? 2. Artificial Raising of the Earth (Backfilling)

soil added

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Examples of Excavation Works What kind of civil engineering works require excavation? 1. Construction of building basements

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Examples of Excavation Works What kind of civil engineering works require excavation? 1. Construction of building basements

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Examples of Excavation Works What kind of civil engineering works require excavation? 2. Trench construction for installation of pipes, underground cables

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Examples of Excavation Works What kind of civil engineering works require excavation? 3. Road cuts in hilly or mountainous areas

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Examples of Excavation Works What kind of civil engineering works require excavation? 4. Cut and cover construction of subway tunnels

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Examples of Backfilling Works What kind of civil engineering works require artificial raising of the earth? 1. Construction of bridge embankment

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Examples of Backfilling Works What kind of civil engineering works require artificial raising of the earth? 1. Construction of bridge embankment

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Examples of Backfilling Works What kind of civil engineering works require artificial raising of the earth? 1. Construction of bridge embankment

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Examples of Backfilling Works What kind of civil engineering works require backfilling or building of embankment? 2. Waterfront bulkhead for flood prevention / erosion control

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Examples of Backfilling Works What kind of civil engineering works require backfilling or building of embankment? 3. Cofferdam construction to extend land into river / canal

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Examples of Backfilling Works What kind of civil engineering works require backfilling or building of embankment? 4. Construction of river-crossing bridge embankment

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Stability Issue related to Excavation/Backfilling Irrespective of whether it is excavation (earth removal) or earth backfilling, can the soil stand by itself as shown below?

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1. Introduction Types of Retaining Structures

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Types of Retaining Structure Gravity

Embedded / Flexible

Reinforced Earth

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Types of Retaining Structure Gravity

Embedded / Flexible

Reinforced Earth

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Gravity Retaining Walls • Probably the oldest type of retaining structure. • Used in fortifications, roads/pavements, bridges, underground shafts (graves). • Constructed using stone masonry in the past (e.g. during Greco-roman times). • These days, concrete walls with steel reinforcement are commonly used (e.g. counterfort cantilever walls). Introduction - 28

Gravity Retaining Walls Ancient Greek Theatre – about 300 B.C.

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Gravity Retaining Walls Longji Terraced Rice Fields in China – circa 1300.

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Gravity Retaining Walls Citadelle Besancon in France – circa 1700.

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Gravity Retaining Walls With advances in building materials (e.g. concrete, steel), cantilever wall backfill

cantilever wall

backfill

backfill counterfort

reinforcement plain concrete

Gravity wall Introduction - 32

Cantilever wall

Counterfort wall

Gravity Retaining Walls Counterfort Cantilever Retaining Wall

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Gravity Retaining Walls Counterfort Cantilever Retaining Wall

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Gravity Retaining Walls Concrete Blocks Retaining Wall

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Gravity Retaining Walls Concrete Blocks Retaining Wall

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Gravity Retaining Walls Stone Blocks Retaining Wall

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Gravity Retaining Walls Crib Walls

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Gravity Retaining Walls Crib Walls

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Gravity Retaining Walls Crib Walls

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Gravity Retaining Walls

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Gravity Retaining Walls Gabion Walls

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Gravity Retaining Walls Gabion Walls

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Gravity Retaining Walls Gabion Walls

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Gravity Retaining Walls

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Types of Retaining Structure Gravity

Embedded / Flexible

Reinforced Earth

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Embedded / 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. • Romans also built roads, aqueducts, bridges supported by timber piles ± 100 A.D. • However, it is not clear when piles were first used for their lateral capacity as a retaining wall. Introduction - 47

Embedded / Flexible Wall • Nevertheless, timber piling as a retaining wall continued as an important earth retention method until the early 20th century.

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Embedded / Flexible Walls These days, the following type of embedded flexible walls are commonly used:  Sheet Piles  Soldier Piles with Lagging  Secant Piles  Contiguous Bored Piles  Diaphragm Wall Introduction - 49

Embedded / Flexible Walls These days, the following type of embedded flexible walls are commonly used:  Sheet Piles  Soldier Piles with Lagging  Secant Piles  Contiguous Bored Piles  Diaphragm Wall Introduction - 50

Embedded / Flexible Walls Sheet Piles

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Embedded / Flexible Wall • Steel sheet piling became popular after World War I. It was first patented ~1900.

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Embedded / Flexible Walls Sheet Pile Walls • Sheet pile walls are constructed by driving prefabricated sections into the ground. These are usually steel sections, although in olden days, wood sections were also used. • Soil conditions may allow for the steel sections to be vibrated into ground instead of it being hammer driven. • The full wall is formed by connecting the joints of adjacent sheet pile sections in sequential installation.

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Embedded / Flexible Walls These days, the following type of embedded flexible walls are commonly used:  Sheet Piles  Soldier Piles with Lagging  Secant Piles / Contiguous Bored Piles  Diaphragm Wall Introduction - 54

Embedded / Flexible Walls These days, the following type of embedded flexible walls are commonly used:  Sheet Piles  Soldier Piles with Lagging  Secant Piles  Contiguous Bored Piles  Diaphragm Wall Introduction - 55

Embedded / Flexible Wall Soldier Piles with Timber Lagging

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Embedded / Flexible Wall Soldier Piles with Timber Lagging The method consists of : 1. Drilling regularly spaced boreholes in which metal beams are sunk 2. Installing cladding (wood, shotcrete, steel plates) between the beams as the excavation progresses The stability of the retaining wall is temporarily provided by struts or anchors except in shallow excavations where the wall may be self-supporting. Introduction - 57

Embedded / Flexible Wall • Driving of steel sections appears to have started ~1880. • Soldier pile walls were successfully used in New York, London, Berlin since the late 19th century. • In fact, the system of shoring using soldier pile and lagging is also known as the ______ Berlin method.

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Embedded / Flexible Wall Soldier Piles with Timber Lagging + Ground Anchors

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Embedded / Flexible Wall Soldier Piles with Timber Lagging + Ground Anchors

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Embedded / Flexible Walls These days, the following type of embedded flexible walls are commonly used:  Sheet Piles  Soldier Piles with Lagging  Secant Piles  Contiguous Bored Piles  Diaphragm Wall Introduction - 61

Embedded / Flexible Wall Secant Piles

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Embedded / Flexible Wall Secant Piles • First use of secant walls is recorded in the 1920s in Europe. • Secant pile walls are formed by constructing intersecting reinforced concrete piles. • The secant piles are reinforced with either steel rebar or with steel beams and are constructed by either drilling under mud or augering. • Primary piles are installed first with secondary piles constructed in between primary piles once the latter gain sufficient strength.

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Embedded / Flexible Wall Secant Piles

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Embedded / Flexible Wall Secant Piles

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Embedded / Flexible Walls These days, the following type of embedded flexible walls are commonly used:  Sheet Piles  Soldier Piles with Lagging  Secant Piles  Contiguous Bored Piles  Diaphragm Wall Introduction - 66

Embedded / Flexible Wall Contiguous Bored Piles • 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 watertight retaining wall. pile dia + 150 mm

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Embedded / Flexible Wall Contiguous Bored Piles

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Embedded / Flexible Wall Contiguous Bored Piles

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Embedded / Flexible Wall Contiguous Bored Piles

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Embedded / Flexible Wall Contiguous Bored Piles with steel struts support

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Embedded / Flexible Walls These days, the following type of embedded flexible walls are commonly used:  Sheet Piles  Soldier Piles with Lagging  Secant Piles  Contiguous Bored Piles  Diaphragm Wall Introduction - 72

Embedded / Flexible Wall Diaphragm Wall (with installation of ground anchors)

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Embedded / Flexible Walls Diaphragm Walls • Generally constructed in a series of discrete panels typically ranging in length from 3m to 7m. • Depths of diaphragm walls vary depending on the application and the specified requirements, but typically they can range from a few meters to tens of meters. • 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 barriers . Introduction - 74

Embedded / Flexible Walls Diaphragm Walls

reinforcement cage

bentonite slurry to support the trench

Introduction - 75

concrete

panel (3 – 7 m)

panel (3 – 7 m)

Few metres to tens of metres

Embedded / Flexible Walls Diaphragm Walls Trench excavation using the clamshell grab and stabilization using bentonite slurry

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Embedded / Flexible Walls Diaphragm Walls Lowering of the reinforcement cage into the trench panel and casting of the concrete (which displaces the bentonite slurry) Reinforcement cage

concrete

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Embedded / Flexible Walls Diaphragm Walls clamshell cutters / grab

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Embedded / Flexible Walls Diaphragm Walls Reinforcement cage

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Embedded / Flexible Walls Diaphragm wall supported by steel struts during excavation

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Embedded / Flexible Walls Diaphragm 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 walls. • Use of slurry to maintain stability in an otherwise unstable 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 1948. • The first structural slurry walls were constructed in Italy 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. Introduction - 81

Common Flexible Wall Systems Completed diaphragm walls

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Embedded / Flexible Wall

Completed diaphragm walls (for a shaft excavation)

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Types of Retaining Structure Gravity

Embedded / Flexible

Reinforced Earth

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Reinforced Earth Wall The primary components of a Reinforced Earth wall consist of alternating layers of granular backfill, and linear metallic, high-adherence soil reinforcing strips or ladders (geogrid) to which a modular precast concrete facing is attached. Its strength and stability are derived from the frictional interaction between the granular backfill and the reinforcements, resulting in a permanent and predictable bond that creates a unique composite construction material.

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Reinforced Earth Wall Mechanically Stabilized Earth Laying of Reinforcement Strips

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Reinforced Earth Wall Mechanically Stabilized Earth • An MSE wall consists of soil, reinforcement, and facing to retain earth and support overlying structures. • Although the basic principles of MSE has been used throughout history, MSE was developed in its current 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. • However, the term “Reinforced Earth” is a trade name of the Reinforced Earth Company in the US, hence it is not usually used there. • Elsewhere Reinforced Earth is the generally accepted Introduction - 87 term.

Reinforced Earth Wall Completed reinforced earth walls for bridge embankment

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Types of Retaining Structure • Brief introduction to the common types of walls used for earth retention. • Other methods of earth retention are possible: name some examples. • Different types of walls are applicable for different ground conditions and construction requirements. • Walls must be properly designed and constructed to support / retain the soil behind them. • If walls are not properly designed and constructed, they may FAIL. Introduction - 89

When Walls Fail

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When Walls Fail

West Side Highway, NY (May, 2005) Introduction - 91

When Walls Fail

Koln, Germany (March 2009) Introduction - 92

When Walls Fail

Nicoll Highway, Singapore (Apr 2004) Introduction - 93

How to minimize risks of failure  Rational Analysis  Fundamental soil mechanics  Lateral earth pressure theories  Appropriate wall type and design  Adequate resistance against different modes of failure

 Safe Design  Factor of Safety, Limit States, Eurocode Introduction - 94

Reading Materials  Beyond the Lecture Notes/Slides  Soil mechanics books Craig’s Soil Mechanics 8th Edition or other soil mechanics textbooks from the library Chapters on shear strengths, earth pressures and retaining wall designs.

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 Notes and related materials from the internet

Ending Thought Unfortunately, soils are made by ...