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Technical English - I 10th week

Soils

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

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.

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.

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

A propped retaining wall produced by means of bored piles

A steel sheet pile wall An example to earth structures: The Atatürk Dam

propped / bored pile / sheet pile wall / dam / earth structure

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

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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)

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

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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

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.

rock cycle / igneous / sedimentary / metamorphic / solidification / consolidation uncemented / pore

Soil from engineering point of view

solid

water

air

Vs

Vw

Va

Vv

VT

volume

Ws

Ww

Wa0

weight void ratio : e=Vv / Vs

porosity : n=Vv / VT volume of solid : Vs

volume of water : Vw

volume of air : Va

volume of void : Vv

total volume : VT total weight : WT

weight of water : Ww

weight of solids : Ws

dry weight : Ws=Wk

unit weight : g=WT / VT

u.w of solids : gs=Ws / Vs dry unit weight : gk=Ws / VT

degree of : S=Vw / Vv

saturation

water content : w=Ww / Ws

specific gravity : Gs=gs / gw

WT

multiphase structure of the soil and fundamental phase relationships

phase / void ratio / porosity / unit weight / solid / specific gravity / degree of saturation

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

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) Permeability 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

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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

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)

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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

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.

1) Karl von Terzaghi (1883-1963) was an Austrian civil engineer and geologist. He is known as the "father of soil mechanics".

We invite you to investigate his life and his studies more closely.

2) Watch the video about SPT (Standard Penetration Test)

http://www.vidsline.com/watch/9cUOBSF8bMg