Geotechnical Engineering 1 - Soil Formation and Mineralogy

Flashcards covering the definitions of geotechnical engineering branches, weathering processes, types of transported and residual soils, and the physical properties of common rock-forming minerals.

Geotechnical Engineering

A field focusing on the engineering aspects of soils and rocks, essential for the design of foundations, retaining structures, and earth structures.

Soil Mechanics

A core area within geotechnical engineering involving the study of forces and equilibrium as they pertain to soils and rocks, and how soil masses behave under loading.

Soil Engineering

The application of soil mechanics principles to practical, real-world engineering problems related to soil behavior and stability.

Foundation Engineering

A branch of geotechnical engineering that deals with the use of soil mechanics to design earth-supported structures like foundations for buildings, dams, and retaining walls.

Soil (Engineering Definition)

An uncemented aggregate of mineral grains and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles.

Pore Water

The liquid phase primarily occupying the spaces between soil particles, influencing engineering properties like weight, effective stress, and settlement.

Weathering

The natural process through which rocks are broken down into smaller fragments by both mechanical and chemical actions.

Mechanical Weathering

Also called physical weathering, it is the breaking down of rocks into smaller pieces without a change in mineral composition through agents like wind, water, and gravity.

Abrasion

The wearing away of rock surfaces by the impact of sand grains carried by the wind, acting like sandpaper.

Attrition

The wearing down of the sand grains themselves as they collide with each other during transport.

Exfoliation

The peeling or flaking off of outer rock layers due to expansion and contraction caused by temperature changes or the release of overlying pressure.

Frost Wedging

A process involving water freezing in cracks within rocks, widening and deepening them until pieces break off.

Chemical Weathering

The weakening and subsequent disintegration of rock by chemical reactions like oxidation, hydrolysis, and carbonation that alter the mineral composition.

Oxidation

The reaction of rock minerals with oxygen, making them less resistant to weathering and often causing an iron-rust color.

Carbonation

The process where rock minerals react with carbonic acid (formed by water and carbon dioxide) to dissolve or break down the minerals.

Hydrolysis

A chemical reaction caused by water that changes the chemical composition and size of minerals; for example, orthoclase yields kaolinite, silicic acid, and potassium.

Hydration

The absorption of water into the mineral structure, such as anhydrite forming gypsum, which results in volume expansion and rock deformation.

Dehydration

The removal of water from rock or mineral structures, such as the formation of hematite from limonite.

Biological Weathering

The disintegration of rock caused by plants (roots), animals (burrowing), and microbes (secreted acids).

Lichen

A symbiosis of fungi and algae where fungi release chemicals to break down minerals that the algae then consume, creating holes in rocks.

Residual Soils

Soils that stay in the place of their origin; characterized by fine-grained soil at the surface and grain size that increases with depth.

Glacial Soils

Transported soils formed by the movement and deposition of glaciers.

Alluvial Soils

Soils transported by running water and deposited along streams.

Lacustrine Soils

Soils formed by deposition in quiet lakes.

Marine Soils

Soils formed by deposition in the seas.

Aeolian Soils

Soils transported and deposited by wind actions.

Colluvial Soils

Soils formed by the movement from their original place by gravity, such as during landslides.

Organic Soil

Soils with natural moisture content ranging from $200\%$ to $300\%$, found in low-lying areas, and known for being highly compressible.

Boulder Clay

An unstratified mixture of clay and rock fragments of all sizes.

Calcareous Soil

A soil that contains calcium carbonate.

Conglomerate

Cemented sand and gravel.

Dispersive Clay

A clay that is easily erodible under low-velocity water.

Fat Clay

A highly plastic clay.

Hardpan

A very dense soil layer, often cemented, that is difficult to excavate.

Loam

A mixture of sand, silt, and clay used as topsoil.

Loess

Uniform silt-sized wind-blown deposits.

Laterite

A red-colored residual soil found in the tropics.

Varved Clay

Thin alternating layers of silts and fat clays of glacial origin.

Minerals

Naturally occurring inorganic crystals with a definable range of chemical composition and a regular, repeating atomic pattern.

Primary Minerals

Minerals derived directly from geological and geochemical processes in the Earth’s crust.

Secondary Minerals

By-products of chemical weathering formed through alteration of primary minerals or chemical precipitation.

Tenacity

Describes how the particles of a mineral hold together or resist separation when subjected to stress like crushing, bending, or tearing.

Malleable

A material property where it can be deformed or shaped by hammering or compressive forces into thin sheets without cracking.

Ductile

A material property where it can undergo significant plastic deformation by stretching or pulling without breaking, often into wires.

Mohs Hardness Scale

A scale from $1$ to $10$ used to measure the scratch resistance of minerals, where Talc is $1$ and Diamond is $10$.

Cleavage

The splitting of a crystal between two parallel atomic planes, named by shape or directions such as cubic, basal, or rhombohedral.

Streak

The color produced by a fine powder of a mineral when it is scratched on a streak plate.

Feldspars

A group of aluminosilicate minerals containing $Ca$, $Na$, or $K$ that make up over half of Earth's crust.

Quartz

The second most abundant mineral in Earth's crust, consisting primarily of silica or silicon dioxide ($SiO_2$).

Amphibole

Silicate minerals forming long prismatic crystals with two cleavage directions at approximately $56^{\circ}$ and $124^{\circ}$.

Mica

Hydrous potassium, aluminum silicate minerals with a layered structure and perfect cleavage into thin elastic sheets.

Calcite

The most common form of calcium carbonate ($CaCO_3$), ranked number $3$ on the Mohs hardness scale.

Pyroxene

High-temperature ferromagnesian silicate minerals with stubby prismatic crystals and cleavage angles of about $87^{\circ}$ and $93^{\circ}$.