CEG4011 Test 1

granular soils

No “glue” bonding particles

Gravity dominates

More spherical

Good foundation material (buildings, roads, backfill): strong, low settlements, well-drained, particles require point-to-point friction to resist applied stress

cohesive soils

Electrostatic forces (coulombic): bonds particles together

Pancake like particle shape

Water can’t get out → good for dams, landfills

Long term settlements

Differential settlements (shrink- swell)

Undesirable foundation material: bad when saturated, lower strength, compressible

Good for building dams, levees: low permeability, stops water flow

angular particles are better for

construction. More friction between particles

Friction gives soil more shear strength to support loads

rounded particles are better for

drainage

igneous

Good construction material (hard and dense)

Coarse grained - magma cools slowly

Ex; Granite, syenites, diorites, gabros

Fine grained - magma cools rapidly

Ex: Basalt, rhyolites, andesites

metamorphic

Change in texture, structure and mineral and chemical composition of sedimentary and igneous rocks (heat, pressure and shear)

Can be hard and strong

May contain weak layers/planes

Granite “morphs” gneiss

Shale “morphs” slate

sedimentary

Great majority of rocks found on the Earth surface

Transported mineral and rock particles and remains or organism

Wind, water and ice

Deposited in layers

Strength varies

soil deposits: residual vs. transported

remain where formed with parent rock vs. transported from their place of origin and deposited elsewhere

colluvial

landslides (gravity)

alluvial

moving water (rivers, waterfall). Usually has higher moisture content and not something geotechs like to work with

lacustrine

sediments deposited in lakes

marine

sediments deposited in seas/oceans

glacial

action of glaciers

aeolian

wind (dunes: sand, loess: silt)silt

soil classification

Cohesionless: gravel, sand, silt

Silt is fine-grained. Not good material (frost action)

Cohesive: clay

Organic: peat

silt vs. clay

Silt: hand tap moist silt, water will come to the top

Clay: hand tap moist clay, no change

Cohesion ➔ bind particles

G (grain)

gravel

S (grain)

sand

M (grain)

silt

C (grain)

clay

Wa

weight of air

Ww

weight of water

Ws

weight of solid

WT

total weight

roe

density

w

moisture content

VT

total volume

Vs

volume of solid

Vv

volume of voids

Vw

volume of water

Va

volume of air

S

degree of saturation

e

void ratio

n

porosity

𝜸 = 𝜸_m

moist unit weight

𝜸_sat

saturated unit weight

𝜸_d

dry unit weight

𝜸_s

unit weight of solids

𝜸’

effective unit weight

C_u

coefficient of uniformity

C_c

coefficient of curvature

LL

lower limit

PL

plastic limit

PI

plasticity index

lecture 3: atterberg limits (cohesive: clay)

Electrostatic force

Particles → pancake shape

Highly negative charge on face

Positive charge on edges

High surface area to mass ratio

Particles can repulse each other

Ion concentration

Interparticle spacing

Other factors

Particles can attract each other

Tendency for hydrogen bonding

Van der Waals force

Other types of chemical and organic bonds

Hydrogen bonding: hydrogen atoms in water molecules shared with oxygen atoms on the surface of the clay

Partially hydrated cations in pore water

Attracted to the surface of the clay particle

Double Water Layer of Clays

Small particles have net negative charge (-)

Water is dipolar: positive (+) and negative (-) charge

well-graded distribution

wide range of soil present

uniform distribution

same size of soil

gap-graded distribution

mixing of two different soils

D60

grain size corresponding to 60% passing

D30

grain size corresponding to 30% passing

D10

grain size corresponding to 10% passing (effective diameter)

4 states: Function of water content

Liquid → plastic → Semi-solid → solid

Plasticity Index PI = LL – PL

Measure plastic range of soil

The larger the PI, the worse the soil (PI > 25 = shrink-swell clay)

Liquid Limit (LL)

w(%) at which soil changes from liquid to plastic

Plastic Limit (PL)

w(%) at which soil changes from plastic to semi-solid

Shrinkage Limit (SL)

w(%) at which soil changes from semi-solid to solid. Not used too often. Need mercury to run test

moisture content definition

the ratio of the mass of water to the mass of dry soil and tells us how wet the soil is

degree of saturation

percentage of the soil's void space that is filled with water

difference between moisture content and degree of saturation

While moisture content can vary widely, the degree of saturation cannot exceed 100%, because water can't fill more than all the available voids.