Exam 1 - Lecture 2

Front 1

What is a rock?

Back 1

An aggregation of one or more minerals

Front 2

Igneous Rock

Back 2

Cooling of magma

Granite, Basalt

Front 3

Sedimentary Rock

Back 3

Erosion, deposition and induration of sediments from other rocks and soils

Sandstone, siltstone, shale, conglomerate, limestone

Front 4

Metamorphic Rock

Back 4

Alteration of igneous or sedimentary rock by heat and pressure

Marble, Gneiss

Front 5

Unweathered Rock is...

Back 5

good material to build with

Front 6

Rock are always found with...

Back 6

discontinuities (joints, fractures)

Dominate properties and behavior of rocks

Front 7

Stability of Rock depends on:

Back 7

Type of Rock

Degree of Weathering

Joint/Fracture distribution and orientation

Presence of cavities

Stresses applied by any construction

Front 8

Weathering

Back 8

Physical and geochemical processes that break down the parent rock and alter the minerals

Front 9

Physical weathering

Back 9

physical breakdown of rock, no chemical change

- Thermal stress

- Freeze/Thaw

- Pressure Change

- Water

Front 10

Chemical Weathering

Back 10

Chemical breakdown of rock

- Acidic water

- Water reaction with rock minerals

- Oxidation

Front 11

As particles get smaller...

Back 11

- increases specific surface area

- reaction rates increase

- faster weathering

Front 12

Particle sizes

Back 12

Gravel > 4.75 mm

Sand 4.75 - 0.075 mm

Silt 0.075 mm - 2 um

Clay < 2um

Front 13

Effect of water on soil

Back 13

1. Plasticity - ability to mold soil

2. Cohesion - ability to stick together

Front 14

Gravel and Sand

Back 14

Non-plastic

Cohesionless

Front 15

Silt

Back 15

Can be plastic or non-plastic

Can be cohesionless or cohesive

Front 16

Clay

Back 16

Plastic

Cohesive

Front 17

Why do coarse-grained and fine-grained soils act differently?

Back 17

Particle forces

- Gravity force is proportional to volume

- Electrostatic force is proportional to surface area

Large D - gravtiy and friction dominant

Small D - electrostatic and cohesion dominant

Front 18

Particle shapes

Back 18

Rounded, Sub-rounded, Sub-angular, Angular

Front 19

Major Soil Groups

Back 19

Residual Soils

Transported Soils

Organic Soils

Front 20

Residual Soils

Back 20

Rock weathered in place to form soil

Front 21

Transported Soils

Back 21

Formed by rock weathering and then transferred to another place

1. Alluvial Soils (alluvium)

2. Colluvial Soils (colluvium)

3. Glacial Soils

4. Aeolian Soils

Front 22

Alluvial Soils

Back 22

Transported and deposited by running water

Front 23

Colluvial Soils

Back 23

Transported and deposited due to down-slope movement

Front 24

Glacial Soils

Back 24

Transported and deposited by glacial action (ice and water)

Front 25

Aeolian Soils

Back 25

Transported and deposited by wind

Front 26

Organic Soils

Back 26

Formed from decomposition of organic materials

Front 27

Peat

Back 27

Completely composed of decomposing plant matter

Front 28

Organics

Back 28

Soils with enough organic matter to influence properties, but organic material is not dominant

Front 29

Clays

Back 29

Have a net negative electrical charge

Can absorb cations

Front 30

Isomorphic Subsitutions

Back 30

Influences the clay type, negative charge, and Cation Exchange Capacity (CEC)

Front 31

Tetrahedral Sheet

Back 31

1 Silicon

4 Oxygens

Represented by a trapezoid

Front 32

Octagedral Sheet

Back 32

1 Cation

6 Oxygen or Hydroxyl

Represented by a rectangle

Front 33

Multiple Sheet Clays

Back 33

Tetrahedral and Octahedral sheets combine to form clay minerals

Simple sheet minerals become charged due to ionic imbalance

Charge imbalance can be due to replacement of cations in structure with different cations

Front 34

Inter-sheet boundary

Back 34

Shared atoms - strong bonding

Charge differences - weaker bonding

Front 35

Cation Exchange Capacity (CEC)

Back 35

Quantity of exchangable cations required to balance the negative charge deficiency of a clay

High CEC means good ability to immobilize heavy metal contaminated groundwater

Front 36

Clay Minerals important in Civl Engineering

Back 36

1:1 family: Kaolinities

2:1 family: Illites, smectites

Front 37

Basal Spacing

Back 37

Distance between repeating units

Front 38

Kaolinite

Back 38

1:1 Mineral (one tetra and one octa unit)

Hydrogen bonds (strong)

Low CEC

Low shrink-swell potential

Stable against chemical attack

Front 39

Illite/Smectite

Back 39

2:1 Mineral (two tetra and one octa units)

Negative charge on surface due to ion subsitution

High plasticity

Front 40

Illite

Back 40

Interlayer Cations - Potassium (K)

Potassium helps prevent swelling

CEC is higher than kaolinite

Front 41

Montmorillonite (a smectite)

Back 41

Interlayer - water + cations

Weak bonds between layers

Swelling because of presence of water

Front 42

Geochemical Environment around clay particles

Back 42

Swarm of cations and water are attracted to the negatively charged particle

Front 43

Three ingredients necessary for potentially damaging swelling

Back 43

1. Presence of montmorillonite in the soil

2. Natural water content must be around plastic limit

3. Must be a source of water for the potentially swelling clay

Front 44

Treatment of swelling clay by "Lime Treatment"

Back 44

Adding lime can reduce the swelling potential due to Ca2+ displacing Na+

Can increase strength

Front 45

"Drilling Mud"

Back 45

Bentonite

Use of swelling clay to decrease permeability

Front 46

Soil Structure/Fabric

Back 46

Geometric arrangement of the soil particles within a soil volume

Influenced by interparticle forces (electrostatic), grain geometry

Front 47

Elementary Particles

Back 47

Indivudual sand, silt, clay particles

Front 48

Particle Assemblage

Back 48

Elementary particles physically/chemically bound

Front 49

Pore Spaces

Back 49

Within and between elementary particles and assemblages

Front 50

Soil fabric largely controls

Back 50

- Permeability

- Strength

- Stiffness

- Unit weight and density of a volume of soil

Front 51

Macrostructure

Back 51

Stratigraphy

Defects control the engineering behavior of the soil

Front 52

Microstructure

Back 52

Reflects the depositional history and environment of the deposit

Front 53

How to avoid frost heaving?

Back 53

- Build foundations below the frost line

- Good drainage

- Removal of frost susceptible soils

- Use of impervious membranes, chemical additives, foam insulation