soil mechanics chapter 1 (1)

Course : Soil MechanicYear : 2014Lecturer :Erol ADOLU

CONTENT

1. FORMATION OF SOIL

2. BASIC PHYSICAL PROPERTIES OF SOIL

3. CLASSIFICATION OF SOILS3. CLASSIFICATION OF SOILS

4. GROUNDWATER

5. SOIL PERMEABILITY

6. WATER FLOW IN SOIL

7. COMPACTION OF SOIL

8. STRESSES IN A SOIL MASS DUE TO APPLIED LOADING

SESSION 1SESSION 1

FORMATION OF SOILS

CRUST

The crust is theoutermost solid shellof the Earth. The crustof the Earth iscomposed of a greatof the Earth iscomposed of a greatvariety of igneous,metamorphic, andsedimentary rocks.

IGNEOUS ROCKS

Igneous rocks; formed by cooling from hot moltenmaterial within or on the surface of the Earth crust e.g.Granite, basalt, dolarite, etc.

Sedimentary Rocks

Sedimentary rocks; formed in layers from sedimentssettling in bodies of water such as seas or lakes, e.g.Limestone, sandsrone, mudsrone conglomorate, shale.

Metamorphic Rocks

Metamorphic rocks; formed by alteration of existingrocks due toa) Extreme heat e.g. Matble, quartziteb) Extreme pressure e.g. slate, schist

DEFINITION OF SOIL

To the civil engineer, soil is uncemented or weaklycemented accumulation of mineral particlesformed by the weathering of rocks, the void spacebetween the particles containing water and/orbetween the particles containing water and/orair.

The processes that conver solid rocks into soilstake place at or near the Earths surface.

Bina Nusantara

GEOTECHNICAL ENGINEERING

Geotechnical engineering is the branch of civilengineering concerned with the engineeringbehavior of earth materials.

Geotechnical engineering includes investigatingexisting subsurface conditions and materials;existing subsurface conditions and materials;assessing risks posed by site conditions; designingearthworks and structure foundations; andmonitoring site conditions, earthwork andfoundation construction.

SOIL MECHANIC

Soil mechanics is the application of the laws ofmechanics and hydraulics to engineering problemsdealing with sediments and other unconsolidatedaccumulations of solid particles regardless ofwhether or not they contain an admixture of organicaccumulations of solid particles regardless ofwhether or not they contain an admixture of organicconstituents.

SOIL FORMATION

Weathering is the process of the breaking down rocks. Weathering embraces a numberof natural surface processes which result from the single or combined actions of suchagencies as wind, rain, frost, temperature change and gravity.

There are two different types of weathering. Physical weathering and chemicalweathering.

Physical weathering involves break down of rocks and soils through direct contactwith atmospheric conditions such as heat, water, ice and pressure.

STAGE 1 STAGE 2 STAGE 3

STAGE 4

SOIL FORMATION

Chemical weathering involves the direct effect of atmospheric chemicals orbiologically produced chemicals in the breakdown of rocks, soils and minerals.

CO2 + Raining> Chemical weathering

Dimensions of soil particles changes from 100 mm to 0.000001 mm

0.002 mm> clay chemical weathering

STAGE 1 STAGE 2 STAGE 3

STAGE 4

SOIL PROFILE

SOIL TYPESSOIL TYPES

RESIDUAL SOILS

Soils that have remained at their parent site are termed as residual soilresidual soil

SOIL TYPESSOIL TYPES

TRANSPORTED SOILS

Soils that have been transported by rivers, transported by rivers, winds, glaciers, and gravity.

SHAPE OF SOIL PARTICLE

STRUCTURE OF SOIL PARTICLE

LOOSE SAND DENSE SAND

BASIC PHYSICAL PROPERTIES OF SOIL The basic physical properties of a soil are those required to define its

physical state. For the purposes of engineering analysis and design, it is necessary to quantify the three constituent phases (solid, liquid, and gas) and to be able to express relationships betweeen them in numerical terms.

BASIC PHYSICAL PROPERTIES OF SOIL In a typical soil, the solid, liquid and gaz are naturally intermixed, so

that relative proportions are difficult to realize. It is therefore convenient to consider a soil model in which three phases are separated into distinct amounts.

Mass

PHASE DIAGRAM

Air

Water

Soil

Mw

Ms

M

BASIC PHYSICAL PROPERTIES OF SOIL The amount of volume in soil not occupied by solids is termed the voids

volume (Vv).

In a perfectly dry soil, there is no water and the void space is entirely air. In a saturated soil the void space is full of water

Mass

PHASE DIAGRAM

Air

Water

Soil

VOID RATIO; e : The ratio of void volume (Vv) to soil volume (Vs)

0 < e <

POROSITY ; n : The ratio of void volume (Vv) to total volume (V)

0 n 1

s

v

VV

e=

VV

n v=

RELATIONSHIP BETWEEN VOID RATIO AND POROSITY

or

Vn =

n

ne

=

1 ee

n+

=

1

WATER CONTENT; : The ratio of the amount of water (Ww)to the soil (Ws) and expressed as a percentage

0% < <

DEGREE OF SATURATION ; S : The ratio of water volume air (Vw) to void volume (Vv) and expressed as a percentage

w

s

Mx100%

M =

volume (Vv) and expressed as a percentage

0% S 100%%100xVVS

v

w=

BULK (NATURAL) DENSITY: The ratio of total mass to total volume

DRY DENSITY; : The ratio of mass of solids to total volume

total s wn

total s W a

M M MV V V V

+ = =+ +

M M = =

SATURATED DENSITY

s sdry

total s a

M MV V V

= =+

total s wsat

total s v

M M MV V V

+ = =+

GRAIN (PARTICLE) DENSITY:

DRY DENSITY; : The ratio of mass of solids to total volume

sS

s

MV

=

M M = =

SATURATED DENSITY

s sdry

total s a

M MV V V

= =+

total s wsat

total s v

M M MV V V

+ = =+

GRAIN (PARTICLE) DENSITY:

SPECIFIC GRAVITY; GS : The ratio of unit weight of soil to unit weight of water

sS

s

MV

=

water

RELATIVE DENSITY; Dr :

Bina Nusantara

w

sGS

=

%100minmax

max xee

eeDr o

=

Granular soils are qualitatively described according to their

relative densities as shown below

The use of relative density has been restricted to granular soils

because of the difficulty of determining emax in clayey soils.

Liquidity Index in fine-grained soils is of similar use as Dr in

granular soils.

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Solids

Water

AirIf given e, assume Vs =1

1

e

1+eMw

MsMs=s

Mw=w s

Solids

Water

AirIf given n, assume Vtotal =1

Ms

Mw

Mw+Ms

n

1-n

1Mw=(1-n) w s

Ms=(1-n)s

RELATIONSHIP OF SOIL PARAMETERS

nn s s

total

M (1 n) (1 n) wV

= = +

dry s(1 n) =

sat s w(1 n) n = +

Bina Nusantara

sat s w(1 n) n = +

SESSION 2SESSION 2

Determination of Basic Physical Properties

Soil Sampling Disturbed

In situ structure not retained

Water content, classification, compaction

Undisturbed

32

Undisturbed In situ structure almost retained

Shear strength, consolidation, permeability

Disturbances Shearing and compression In situ stress release Drying Vibrations

Cylindrical Sample Method (The cone cutter method):

This method is suitable for fine grained soils free of stones and consists of driving a steel cylinder with a hardened cutting edge into the ground using a specially designed steel rammer and a wood head.


Since volume of the tube is known

and the contained mass of soil can

be found by weighing and the bulk

density easily be determined.Small

samples can be taken form either to

determine water content.

The sand replacement method

This method is suitable for granular soils and involves the use of a sand pouring cylinder as shown in the Figure.


The sand replacement method

Firstly, sample hole is dug about 100 mm in diameter and not more than 150 mm in depth and the soil removed carefully and weighed. The volume of the hole is than determined by pouring sand into it from the pouring cylinder. The sand pouring cylinder is weighed before and


cylinder. The sand pouring cylinder is weighed before and after this operation, and the mass of sand filling the hole determined. Since the density of sand is known, the volume of the hole can be determined and hence bulk density of in situ soil.

hole sandn hole

hole sand

M MVV

= =

Rubber Baloon Method

This method is similar to Sand Replacement Method. Only difference is that Vhole is determined by pumping a rubber balloon.


balloon.

hole sandn hole

hole sand

M MVV

= =

Immersion in Water Method

This method is suitable for cohesive and stabilized soils where an irregular shaped intact lump of soil has been obtained. The lump sample is weighed (Mn) and after cooling with wax weighed again (Mn+p). The volume of waxed soil sample is found by lowering it into a container


waxed soil sample is found by lowering it into a container of water

hole sandn hole

hole sand

M MVV

= =

Immersion in Water Method

This method is suitable for cohesive and stabilized soils where an irregular shaped intact lump of soil has been obtained. The lump sample is weighed (Mn) and after cooling with wax weighed again (Mn+p). The volume of waxed soil sample is found by lowering it into a container


waxed soil sample is found by lowering it into a container of water

soil

n p n

pparaffin

soil 2 1 p

nn

M M MMV

V V V VMV

+ = =

=

=

Determination of water content

A sample of soil is placed in a container that is weighed before (M2). Mass of the sample and the container is determined(M1). The soil sample is placed in an oven and dried between 105 C and 110 C to a constant mass. After drying, the container is removed from the oven and allowed to cool. The mass is determined again (M3).


1 c w s

2 c

3 c s

w 1 3

s 3 2

M M M MM MM M M

M M Mw

M M M

= + +

=

= +

= =

Determination of particle density

A soil sample is dried in an oven. Then, the weight of soil used for determination of particle density is recorded (Mdry). A Pynometer filled with water is weighed (M1) and then the suspension of water and soil filled in a pynometer is weighed again (M2).


is weighed again (M2).

s=Mdry/[Mdry-(M2-M1)] /water

Determination of emax

A mould filled with soil in the loosest state by pouring gently. Then, the mass of soil in the mould is recorded. From the volume of mould and the mass of soil dry(min) is evaluated.


dry(min)=s/(1+emax)

Determination of emin

The mould is filled with the soil by compacting or vibrating in three layers of equal thickness.

dry(max)=Msoil/Vmould=s/(1+emin)


soil mechanics chapter 1 (1)

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