CE 111 – Geotechnical Engineering 1 (Soil Mechanics) Chapter 1: Soil Formation and Mineralogy

60 practice flashcards covering soil formation, weathering, soils, organic soils, environmental terms, and mineralogy as per CE 111 lecture notes.

What is geotechnical engineering?

A field focusing on the engineering aspects of soils and rocks for design of foundations, earth structures, and related civil projects.

What does soil mechanics study?

The application of forces and equilibrium to soils and rocks, and how soil masses behave under loads.

What is foundation engineering?

Use of soil mechanics to design foundations and earth-supported structures, ensuring safety and stability.

How is soil defined in engineering terms?

The uncemented aggregate of mineral grains and decayed organic matter with pore water and air in voids.

What are the components of soil?

Mineral grains and decayed organic matter, plus liquid (water) and gas (air) in the void spaces.

What are the soil size fractions from largest to smallest?

Gravel, sand, silt, and clay.

Which soil size fractions provide high permeability and strength primarily by friction?

Coarser grains such as sand and gravel.

Which soil size fraction provides cohesion and strongly influences compressibility and plasticity?

Clay.

What is pore water?

Water occupying the void spaces in soil.

What is pore air?

The air filling the remaining void spaces in soil.

What is effective stress?

The stress carried by soil grains, equal to total stress minus pore water pressure.

What is weathering?

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

What are the two main categories of weathering?

Mechanical (physical) weathering and chemical weathering.

Name three mechanical weathering processes.

Wind abrasion/attrition; flow of rivers/glaciers/waves; gravity-induced breakage.

What is exfoliation in weathering?

Peeling or flaking of outer rock layers due to pressure release or temperature change.

What is frost wedging?

Water in cracks freezes and expands, widening cracks and breaking rock.

What is frost heave?

Upward displacement of soil due to freezing water expanding and lifting the surface.

What is oxidation and its effect on minerals?

Reaction of minerals with oxygen, often producing rust and making minerals less resistant to weathering.

What is carbonation in weathering?

Reaction of minerals with carbonic acid (formed from water and CO2) that dissolves minerals.

What is hydrolysis in weathering?

Chemical reaction with water that changes mineral composition and size, reducing weather resistance.

What is hydration in weathering?

Absorption of water into mineral structures, causing expansion.

What is dehydration in weathering?

Removal of water from minerals, altering structure (e.g., limonite to hematite).

How do temperature and moisture affect chemical weathering?

Chemical weathering generally occurs more rapidly in hot, humid climates.

What is biological weathering?

Weathering caused by plants, animals, and microbes.

How do plant roots contribute to weathering?

Roots exert physical pressure and can release organic acids that dissolve minerals.

How do microbes contribute to weathering?

Microbial activity alters rock chemistry, accelerating weathering processes.

What is lichen and its role in weathering?

A fungus-algae symbiosis that releases chemicals to break down rock, aiding weathering.

How do burrowing animals influence weathering?

Move rock fragments to the surface, exposing them to more intense weathering.

Can weathering processes act together?

Yes; physical, chemical, and biological weathering can all act in concert.

What are residual soils?

Soils formed in place from weathered parent rock, with finer grains increasing toward the surface and coarser grains at depth.

What are transported soils?

Soils formed away from their source due to transport by wind, water, ice, or gravity.

Name the categories of transported soils.

Glacial, Alluvial, Lacustrine, Marine, Aeolian, Colluvial.

What are glacial soils?

Soils formed by transportation and deposition of materials by glaciers.

What are alluvial soils?

Soils transported and deposited by running water.

What are lacustrine soils?

Soils formed by deposition in quiet lake environments.

What are marine soils?

Soils formed by deposition in the seas.

What are aeolian soils?

Soils transported and deposited by wind.

What are colluvial soils?

Soils moved downslope by gravity, such as during landslides.

What are organic soils and where are they found?

Soils rich in organic matter found in low-lying areas where the water table is near or above the surface.

What are characteristics of organic soils?

Natural moisture contents 200–300%, highly compressible, significant secondary consolidation settlement.

What is Boulder clay?

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

What is Calcareous soil?

Soil that contains calcium carbonate.

What is Conglomerate?

Cemented sand and gravel.

What is Dispersive clay?

A clay that erodes easily under low-velocity water.

What is Fat clay?

Highly plastic clay.

What is Hardpan?

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

What is Loam?

Mixture of sand, silt, and clay used as topsoil.

What is Loess?

Uniform, wind-blown deposits of silt-sized material.

What is Laterite?

Red-colored residual soil in tropical regions.

What is Reactive clay?

Expansive clay that swells when in contact with water.

What is Varved clay?

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

What is mineralogy of soil solids about?

The study of inorganic minerals in the pedosphere and the depth of weathering.

Approximately how many named minerals have been identified on Earth?

About 4,500 to 5,000.

What is a mineral?

Naturally occurring inorganic crystal with a definable chemical composition and a regular atomic arrangement.

What is the difference between rock fragments and minerals?

Rock fragments are mixtures of minerals; minerals are discrete crystalline substances with a fixed composition.

What are primary minerals?

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

What are secondary minerals?

Minerals formed by chemical weathering or by precipitation from dissolved components.

Are minerals metallic or non-metallic?

Minerals can be metallic (with a metallic luster and metals in composition) or non-metallic (luster is non-metallic).

What are crystal systems?

Classification of crystals by their atomic lattice; examples include cubic, trigonal, tetragonal, orthorhombic, hexagonal, monoclinic, and triclinic.

What characterizes the Cubic (Isometric) crystal system?

Three axes of equal length intersecting at right angles.

What characterizes the Trigonal (Rhombohedral) crystal system?

Three axes of equal length with none perpendicular, but crystal faces have equal size and shape.

What characterizes the Tetragonal crystal system?

Three axes, all at right angles; two axes are equal in length and the third is different.

What characterizes the Orthorhombic crystal system?

Three axes of unequal length, all at right angles to each other.

What characterizes the Hexagonal crystal system?

Four axes, three in a plane at 120 degrees, with a fourth axis of different length perpendicular to the plane.

What characterizes the Monoclinic crystal system?

Three axes of unequal length, with two perpendicular and the third inclined.

What characterizes the Triclinic crystal system?

Three axes all of unequal length with none perpendicular to another.

What is tenacity in mineral properties?

How mineral particles hold together and resist fracture under stress.

What does brittle mean in mineral tenacity?

A material that breaks or fractures suddenly with little deformation.

What does sectile mean in mineral tenacity?

A material that can be cut smoothly with a knife.

What does malleable mean in mineral tenacity?

A material that can be deformed or hammered into shapes without cracking.

What does ductile mean in mineral tenacity?

A material that can be stretched into wires without breaking.

What does flexible but inelastic mean in mineral tenacity?

A material that can bend but does not return to original shape after stress (permanent deformation).

What does flexible and elastic mean in mineral tenacity?

A material can bend and return to original shape after stress (elastic deformation).

What is hardness in minerals?

The resistance of a mineral surface to scratching, measured by Mohs scale.

What is fracture in minerals?

The way a mineral breaks: conchoidal, fibrous, hackly, or uneven.

What is cleavage in minerals?

The tendency of a mineral to split along parallel atomic planes.

What is streak in minerals?

Color of a mineral’s powder when scratched on a streak plate.

What is luster in minerals?

The appearance of a mineral’s surface in reflected light; can be metallic or non-metallic.

What are non-metallic lusters and their types?

Vitreous, resinous, pearly, greasy, silky, and adamantine lusters.

What is density in minerals?

Mass per unit volume of a mineral.

What is color in minerals?

Visible color resulting from light absorption and reflection by the mineral.