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Technical English - II 4th week

Geotechnical Engineering

soil / branch / gravitational force / sediments / consolidated / unconsolidated / accumulation / solid particle / disintegration / profession / geo

Soil Mechanics is defined as the branch of engineering science which enables an engineer to know theoretically or experimentally the behavior of soil under the action of loads (static or dynamic), gravitational forces, water and, temperature .

Karl von Terzaghi (1883-1963) was an Austrian civil engineer and geologist. He presented to the world the new science, Soil Mechanics, that he developed mainly while working at ITU and Bogazici University (then known as Robert College) in Istanbul. That is why he is known as the "father of soil mechanics".

According to Karl Terzaghi, Soil Mechanics is the applications of Laws of Hydraulics and Mechanics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by Mechanical and Chemical Disintegration of rocks.

The profession that deals with mechanical behavior of soils and the design-analysis of foundations which transfer structural loads to the underlying soils is called as geotechnical engineering.

Geotechnical Engineering

Civil Engineer must study the properties of soil, such as its origin, grain size distribution, ability to drain water, compressibility, shear strength, and load bearing capacity. In this respect a sound understanding of soil behavior is necessary in geotechnical engineering.

Geotechnical Engineering is the sub discipline of Civil Engineering that involves applications of the principles of Soil Mechanics and Rock Mechanics to design of foundations, retaining structures and earth structures.

grain size / distribution / drain / compressibility / shear strength / bearing capacity / expulsion / relocation / failure surface / strip footing / foundation / retaining structure

Soil Mechanics What is the difference between soil and dirt?

If you can grow food in it, get paid to analyze it, or get college credit for playing with it, it’s soil; otherwise it’s dirt.

Agricultural engineer’s soil

Geotechnical engineer’s soil

Dirt

Soil is defined as the weathered and fragmented outer layer (crust) of the earth’s terrestrial surface.

The term soil, according to engineering point of view, is defined as the material by means of which and upon which engineers build their structures.

For engineering purpose soil is defined as the uncemented aggregate of mineral grains and decayed organic material (solid particle) with liquid and/or gas in the empty spaces (pores) between the solid particles.

terrestrial / weathered / fragmentation / rock cycle / igneous / sedimentary / metamorphic / solidification / compaction / consolidation / uncemented / pore

Soil from engineering point of view Remember: Concrete and steel are textbook materials; soil is not. This statement reminds us that soil is not a standard engineering material. It is a granular and multi-phase material. Each site poses a unique case since soil properties usually vary both in space and time. In general, soil is found in anisotropic state although it may rarely exhibit isotropic characteristics. It is also a nonconservative material meaning that it shows plastic (nonlinear) deformation if its elastic (linear) response limit is exceeded.

unique / isotropic / anisotropic / conservative / nonconservative / elastic response / linear / nonlinear / elastic / plastic

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Three phases of the soil are the solids, water and air. Granular nature of the soils result in formation of voids. The voids, however, may be partly or fully saturated depending on the amount of pore water present in the voids. If there is no water then the soil is said to be in dry condition. The relationships between soil phases are commonly used in soil mechanics. The unit weight, porosity, void ratio, water content, degree of saturation are major definitions of phase relationships.

solid

water

air

Vs

Vw

Va

Vv

VT

volume

Ws

Ww

Wa0

weight void ratio : e=Vv / Vs

porosity : n=Vv / VT

volume of solids : Vs

volume of water : Vw

air volume : Va

volume of voids : Vv

total volume : VT

total weight : WT

water weight : Ww

solid weight : Ws

dry weight : Ws=Wk

unit weight : g=WT / VT

solid unit weight : gs=Ws / Vs

dry unit weight : gk=Ws / VT

degree of

saturation : S=Vw / Vv

water content : w=Ww / Ws

WT

multi-phase structure of the soil and

fundamental phase relationships

Note that permanent deformation takes place as void ratio changes. This is the basic cause of plastic response of soils to the distortion of equilibrium condition. Soil is said to be in equilibrium condition if the effective stress state stays unchanged.

Fine grained soils are classified according to the plasticity they pose. The plasticity chart is used for this purpose.

fine grained / plasticity / fraction / index / No.200 sieve / inorganic / silt / rock flour / clayey / gravelly / lean clay / fat clay / cohesionless / peat / micaceous

No.200 sieve (sieve opening: 0.076 mm)

well graded / poorly graded / coefficient of uniformity / coefficient of curvature / borderline / hatched zone (see plasticity chart) / Atterberg limit / dual symbol / No.4 sieve

No.4 sieve (sieve opening: 4.75 mm)

0.076

sieve hydrometer

grain size distribution curve / particle diameter / flocculated / dispersed total stress / effective stress / pore water pressure / soil skeleton / volume change /

isotropic / induced stress / self-weight

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The failure occurs because the shear strength of the soil is exceeded.

We need to determine the soil’s shear strength and design the slope so that the shear stress imposed is not greater than the shear strength of the soil.

Strength of different materials

Steel

Tensile strength

Concrete

Compressive strength

Soil

Shear strength

Presence of pore water Complex behavior

Load

Load

Load

Strength of different construction materials

Steel

Concrete

Soil/Rock

Example of material involved in the construction of suspension bridge: I. Steel = suspension cable II. Concrete = road deck III. Soil/Rock = foundation

Embankment

Strip footing

Soils generally fail in shear

At failure, shear stress along the failure surface (mobilized shear resistance) reaches the shear strength.

Failure surface

Mobilized shear

resistance

Embankment Failure

overconsolidated / normally consolidated / strain / stress / dense / loose / residual strength / steady / critical state / deviatoric / axial / confining stress / Mohr-Coulomb Failure Criterion

stress-strain response of soils largely depends on relative density (or consolidation state) and effective confining stress.

Laboratory testing devices in Terzaghi’s laboratory Direct shear testing device designed and made by Terzaghi in his İstanbul years (early twentieth century)

Classification, shear, settlement, compressibility and several other characteristics of soils are investigated in soil mechanics laboratory.

index / compressibility / preconsolidation / specimen / direct shear / device / apparatus

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Classification tests Sieve analysis Hydrometer Consistency limits (liquid limit, plastic limit, shrinkage limit) Natural water content determination Determination of unit weight and porosity Specific gravity Shear strength tests Direct shear box Uniaxial compression Triaxial compression Miniature Vane One-dimensional compression Odeometer (consolidation for fully saturated clays) Permability tests

Falling head Constant head Flexiwall

hydrometer sieves for grain size analysis

consistency limit / uniaxial / triaxial / odeometer / falling head / constant head / flexiwall

Sieve set

Casagrande liquid limit set

Falling cone liquid limit set

Plastic limit and shrinkage limit test

Specific gravity test Soil mechanics lab oven 0.01 gr accurate balance

oven / plastic limit / liquid limit / shrinkage limit / oven / balance / accuracy

Odeometer test set-up

Direct shear box test set-up

Triaxial test set-up

test set-up / direct shear box / triaxial / test cell / membrane / cell pressure / deviator stress

It is important to perform field tests in order to find out in-situ shear resistance of soils. Although Standard Penetration Test is a mandatory one to be performed in each engineering borehole, others are especially for soils from which acquiring undisturbed samples is difficult or impossible due to their stiff and laminated or very soft nature. One should also note that undisturbed soil recovery from cohesionless soils is extremely difficult and lack of cohesion prohibits sampling without altering soil’s density.

Standard Penetration Test / Cone Penetration Test / flat / dilatometer / prebored pressuremeter / borehole / acquire / recovery / in-situ / field cohesion / cohesionless / alter / density / split spoon sampler

Disturbed soil sample in SPT split spoon sampler

Driving sequence of split spoon sampler during SPT

seating / blow count / increment / reference energy efficiency / drop hammer / split-barrel sampler (split spoon sampler) cone penetrometer / apex angle / porous filter / tip resistance / sleeve transducer / rod

Cone penetration test system

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Virtually every structure is supported by soil or rock. Those that aren’t either fly, float or fall over.

Various reasons to study the properties of soil:

1. Foundation to support structures and embankments

2. Construction material

3. Slopes and landslides

4. Earth retaining structures

5. Special problems

A floating structure

A flying structure

embankment / slope / landslide / supported

1. Foundation to support Structures and Embankments • Effects of static loading on soil mass

• Shear failure of the foundation soil

• Settlement of structures

• Stability criteria (Solution)

• There should be no shear failure of the foundation soil.

• The settlement should remain within permissible limits.

• Firm Soil -> Spread Footing (Spread Foundation)

• Soft Soil -> Pile Foundation (Vertical members transferring load of structure to ground i.e. rock)

spread foundation

piled foundation

shear failure / settlement / permissible limit / firm / soft / spread footing / pile foundation

2. Construction Material • Subgrade of highway pavement

• Land reclamation (Dubai Palm City)

• Earth dam

Soil subgrade (a) in a cut (b) on an embankment

Soil types utilized in constructing an earth dam

Construction of Dubai Palm City reclaimed island

subgrade / land reclamation / gravel / clay / core / rock facing (rip-rap) / filter / rock / toe

3. Slopes and Landslides • Major cause is the moisture variation resulting in;

• Reduction of shear strength

• Increase of moisture

• Increase in unit weight

• Excavation of trenches for buildings require braced excavation.

Landslide of a parking area at the edge of a steep slope, mainly due to increase in moisture content.

A braced excavation

moisture / variation / reduction / unit weight / excavation / trench / braced / steep

4. Earth Retaining Structures • Earth retaining structures (e.g., Retaining walls) are constructed to

retain (hold back) any material (usually earth) preventing it from sliding or eroding away.

Reinforced earth wall construction and section

reinforced earth / erode away / geogrid / backfill / drainage / walling unit / retained soil

5. Special Problems i. Effects of water (current and/or wave action) on soil mass

ii. Land Erosion

iii. Land subsidence

iv. Liquefaction

v. Effects of frost action on soil mass

scour / fineness / pier / erosion / land subsidence / frost / heave / thaw

Effects of river water on soil mass 1) Scouring Causes:

•Increased flow velocity due to obstruction •Fineness of riverbed material

Stability criteria: •The foundation of pier must be below the scour depth

Effects of frost action on soil mass 1) Reduction of Shear Strength 2) Settlement of Structure in Summer 3) Lifting up of Structure in Winter Causes: •Heaving (due to formation of ice lenses) •Increase of moisture due to thawing (MELTING)

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Ice lenses that cause frost action

Land subsidence took place as a result of excessive ground water pumping from deep aquifer layers

Soil scouring around bridge foundations

ice lenses / surface wake / excessive / pumping / aquifer

LIQUEFACTION

Liquefaction is phenomenon that usually takes place in loose to medium dense sandy soil layers under earthquake action. Although wave, traffic vibrations and sometimes static loads may also cause liquefaction, it is usually triggered by gradual accumulation of excess pore water pressure during earthquake excitation. The soil turns out to be a viscous liquid following the onset of liquefaction and grain contact is lost once accumulated excess pore water pressure gets equal to initial effective stress (i.e. effective stress prior to the earthquake; ru=ue/’v =1.0). Earthquake magnitude, grain size distribution of the soil, fine fraction, plasticity of the fines, and soil’s relative density are considered as major factors controlling liquefaction potential.

liquefaction / loose / dense / gradual / accumulation / pore water pressure / viscous liquid effective stress / grain size distribution / fine fraction / plasticity

Bearing capacity loss and excessive settlement due to liquefaction

Sand grains are carried to the ground surface by pressurized pore water as the sand layer liquefies during earthquake

Not only shallow foundations are damaged in liquefied soils

liquefied soil / shallow foundation / deep foundation / sand grain / earthquake / pressurized pore water

Examples of Geotechnical Projects: Panama Canal Location: Panama

Completion Date: 1914

Length: 47.8 miles

Cost: $375 Million

Capacity: 14,000 vessels/yr.

Type: Lock canal

Materials: Rock, clay, concrete

lock canal / rock / clay / landslide

Several landslides took place during construction of the canal.

The Culebra Cut in Panama Canal

The excavation of the cut was one of the greatest areas of uncertainty in the creation of the canal, due to the presence of unpredicted large landslides.

The Americans had lowered the summit of the cut from 59 meters to 12 metres above sea level, at the same time widening it considerably, and had excavated over 76 million cubic meters. Some 23 million m³ of this material was additional to the planned excavation, having been brought into the cut by the landslides.

excavation / cut / summit / landslide / widen

Major landslide in Culebra Cut

Examples of Geotechnical Projects: Aswan Dam

Location: Aswan, Egypt

Completion Date: 1970

Cost: $1 billion

Capacity: 169x109 m3

Type: Embankment

Materials: Rock, clay

The Aswan Dam was built on Nile River. It is a 111 m high embankment type earth dam and has a unique grout curtain underneath the clay core. It is the largest earth dam in terms of reservoir capacity.

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Construction of a grout curtain was necessary since the dam would not be able to store water due to underlying highly permeable sand and gravel layers that would cause steady state water flow beneath the core leading to piping and eventual catastrophic failure of the dam.

rock fill / clay core / grout curtain

Construction of grout curtains at the base of an earth dam site.

Examples of Geotechnical Projects: Chunnel (The Euro Tunnel) Location: Folkestone, England Sangatte, France

Completion Date: 1994

Cost: $21 billion

Length: 163,680 feet (31 miles)

Purpose: Railway

Setting: Underwater

Old way of tunnelling and modern TBM

Examples of Geotechnical Projects: Foundations of the Golden Gate Bridge

Location: San Francisco and Sausalito, California, USA

Completion Date: 1937

Cost: $27 million

Length: 8,981 feet

Type: Suspension

1. Start rock dike (Coffer)

2. Construct crib dike for the part that is in water (timber box filled w/ rock and set in place).

3. Install sheet piling.

4. Pump area dry.

5. Construct foundation on rock surface exposed below water level.

cofferdam / waling / interlocking steel sheet pile / strut / end fixing plate / puncheon / ground level

Examples of Geotechnical “Structures”: Petronas Towers Foundations

Location: Kuala Lumpur, Malaysia

Completion Date: 1998

Cost: $1.6 billion

Height: 489 m

Stories: 88

Massive bored piles were constructed and an RC mat was cast in order to avoid potential bearing capacity and settlement problems.

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A propped retaining wall produced by means of bored piles

A steel sheet pile wall

propped / bored pile / sheet pile wall / dam / earth structure / tieback anchor / deadman / raker / brace

Components of retaining systems in deep excavations

KUTLUTAŞ - DILLINGHAM

İzmir - Aydın freeway Construction

"slope stability” with anchorage

Components of Shallow Foundations

Construction Technique of Franki Piles

Franki pile is a driven cast-in-place reinforced concrete pile type where the tip of the pile is greatly enlarged in order to increase load carrying capacity of the pile tip.

Construction Technique of Driven Piles

lead / swivel / crane / hammer / drive cap / pile monkey / wire rope / batter pile / cushion / striker

plate / adapter / helmet