Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
53 Cards in this Set
- Front
- Back
What is a rock? |
An aggregation of one or more minerals |
|
Igneous Rock |
Cooling of magma Granite, Basalt |
|
Sedimentary Rock |
Erosion, deposition and induration of sediments from other rocks and soils Sandstone, siltstone, shale, conglomerate, limestone |
|
Metamorphic Rock |
Alteration of igneous or sedimentary rock by heat and pressure Marble, Gneiss |
|
Unweathered Rock is... |
good material to build with |
|
Rock are always found with... |
discontinuities (joints, fractures) Dominate properties and behavior of rocks |
|
Stability of Rock depends on: |
Type of Rock Degree of Weathering Joint/Fracture distribution and orientation Presence of cavities Stresses applied by any construction |
|
Weathering |
Physical and geochemical processes that break down the parent rock and alter the minerals |
|
Physical weathering |
physical breakdown of rock, no chemical change - Thermal stress - Freeze/Thaw - Pressure Change - Water |
|
Chemical Weathering |
Chemical breakdown of rock - Acidic water - Water reaction with rock minerals - Oxidation |
|
As particles get smaller... |
- increases specific surface area - reaction rates increase - faster weathering |
|
Particle sizes |
Gravel > 4.75 mm Sand 4.75 - 0.075 mm Silt 0.075 mm - 2 um Clay < 2um |
|
Effect of water on soil |
1. Plasticity - ability to mold soil 2. Cohesion - ability to stick together |
|
Gravel and Sand |
Non-plastic Cohesionless |
|
Silt |
Can be plastic or non-plastic Can be cohesionless or cohesive |
|
Clay |
Plastic Cohesive |
|
Why do coarse-grained and fine-grained soils act differently? |
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 |
|
Particle shapes |
Rounded, Sub-rounded, Sub-angular, Angular |
|
Major Soil Groups |
Residual Soils Transported Soils Organic Soils |
|
Residual Soils |
Rock weathered in place to form soil |
|
Transported Soils |
Formed by rock weathering and then transferred to another place 1. Alluvial Soils (alluvium) 2. Colluvial Soils (colluvium) 3. Glacial Soils 4. Aeolian Soils |
|
Alluvial Soils |
Transported and deposited by running water |
|
Colluvial Soils |
Transported and deposited due to down-slope movement |
|
Glacial Soils |
Transported and deposited by glacial action (ice and water) |
|
Aeolian Soils |
Transported and deposited by wind |
|
Organic Soils |
Formed from decomposition of organic materials |
|
Peat |
Completely composed of decomposing plant matter |
|
Organics |
Soils with enough organic matter to influence properties, but organic material is not dominant |
|
Clays |
Have a net negative electrical charge Can absorb cations |
|
Isomorphic Subsitutions |
Influences the clay type, negative charge, and Cation Exchange Capacity (CEC) |
|
Tetrahedral Sheet |
1 Silicon 4 Oxygens Represented by a trapezoid |
|
Octagedral Sheet |
1 Cation 6 Oxygen or Hydroxyl Represented by a rectangle |
|
Multiple Sheet Clays |
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 |
|
Inter-sheet boundary |
Shared atoms - strong bonding Charge differences - weaker bonding |
|
Cation Exchange Capacity (CEC) |
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 |
|
Clay Minerals important in Civl Engineering |
1:1 family: Kaolinities 2:1 family: Illites, smectites |
|
Basal Spacing |
Distance between repeating units |
|
Kaolinite |
1:1 Mineral (one tetra and one octa unit) Hydrogen bonds (strong) Low CEC Low shrink-swell potential Stable against chemical attack |
|
Illite/Smectite |
2:1 Mineral (two tetra and one octa units) Negative charge on surface due to ion subsitution High plasticity |
|
Illite |
Interlayer Cations - Potassium (K) Potassium helps prevent swelling CEC is higher than kaolinite |
|
Montmorillonite (a smectite) |
Interlayer - water + cations Weak bonds between layers Swelling because of presence of water |
|
Geochemical Environment around clay particles |
Swarm of cations and water are attracted to the negatively charged particle |
|
Three ingredients necessary for potentially damaging swelling |
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 |
|
Treatment of swelling clay by "Lime Treatment" |
Adding lime can reduce the swelling potential due to Ca2+ displacing Na+ Can increase strength |
|
"Drilling Mud" |
Bentonite Use of swelling clay to decrease permeability |
|
Soil Structure/Fabric |
Geometric arrangement of the soil particles within a soil volume Influenced by interparticle forces (electrostatic), grain geometry |
|
Elementary Particles |
Indivudual sand, silt, clay particles |
|
Particle Assemblage |
Elementary particles physically/chemically bound |
|
Pore Spaces |
Within and between elementary particles and assemblages |
|
Soil fabric largely controls |
- Permeability - Strength - Stiffness - Unit weight and density of a volume of soil |
|
Macrostructure |
Stratigraphy Defects control the engineering behavior of the soil |
|
Microstructure |
Reflects the depositional history and environment of the deposit |
|
How to avoid frost heaving? |
- Build foundations below the frost line - Good drainage - Removal of frost susceptible soils - Use of impervious membranes, chemical additives, foam insulation |