Introduction to Geotechnical Engineering - VOCABULARY Flashcards

Vocabulary flashcards covering geology, rock and soil properties, geomaterials, and geotechnical engineering concepts from the lecture notes.

Geotechnical Engineering

Civil engineering discipline focused on design and assessment involving soil and rock in engineering projects.

Geology

Science of the structure, materials, and processes of the Earth.

Geomechanics

Behaviour of soil and rock in an engineering context.

Engineering Geologist

Professional who applies geology to engineering design and assessment.

Geologist

Scientist who studies the Earth, its materials, and processes.

Geotechnical Engineer

Engineer who designs and assesses underground and soil/rock conditions for civil works.

Rock Cycle

Natural cycle describing the transformation between igneous, sedimentary, and metamorphic rocks through weathering, deposition, burial, and metamorphism.

Minerals

Naturally occurring inorganic solids with a crystalline structure and fixed chemical composition.

Rocks

Naturally occurring aggregate of one or more minerals or mixtures; rocks are formed through lithification, cementation, or crystallization.

Intact Rock

Rock material with minimal pre-existing defects; homogeneous in strength.

Rock Mass

Aggregate of rock including defects, fractures, and discontinuities that influence engineering behaviour.

Lithification

Process of turning loose sediments into solid rock via compaction and cementation.

Weathering

Breakdown of rock by mechanical, chemical, or biological processes at or near the surface.

Mechanical Weathering

Physical breakdown of rocks without chemical change (e.g., unloading, abrasion, frost wedging, thermal expansion).

Unloading/Pressure Release

Expansion and cracking of rocks as overburden is removed, forming joints parallel to the surface.

Abrasion

Wear of rock by friction from particles transported by wind, water, or ice.

Frost Wedging

Mechanical weathering where ice expands in cracks, widening them during freeze-thaw cycles.

Thermal Weathering

Rock breakdown due to expansion and contraction from temperature changes.

Wetting/Drying

Weathering in which cyclic wetting and drying causes expansion, contraction, and cracking, especially in clays.

Chemical Weathering

Rock alteration via chemical reactions with water, air, and chemicals in the environment.

Dissolution of Limestone

Chemical weathering where calcite dissolves in acidic water, creating voids and cavities.

Biological Weathering

Rock breakdown driven by biological activity (roots, organisms, lichens, fungi).

Weathering Rates

Rate at which rock/soils degrade, influenced by mineralogy, climate, topography, and time.

Erosion

Removal of weathered material from its source by wind, water, or ice.

Degradation

Lowering of the ground surface due to weathering and erosion.

Transportation

Movement of eroded material from source to deposition site by water, wind, or ice.

Mass Movement

Downslope movement of soil/rock under gravity (rockfall, landslide, debris flow).

Alluvium

Transported soil/deposit laid down by rivers and streams.

Colluvium

Transported soil deposited at the base of slopes by gravity and surface runoff.

Glacial Till

Unsorted glacial sediment deposited directly by ice.

Aeolian (Loess)

Wind-transported soils, including fine silt and sand deposits.

Volcanic Soils

Transported soils formed by volcanic processes, often layered by eruption events.

Residual Soils

Soils formed by in-place weathering of the parent rock.

Organic Soils

Soils with significant organic material that influence strength and stiffness.

Transported Soils

Soils deposited by transport processes (water, wind, ice, gravity).

Soil Phases

Three-phase system: Solid particles, Water (liquid), and Air (gas) within voids.

Phase Diagram

Diagram showing relationships between soil phases (solid, water, air) and properties.

PSD (Particle Size Distribution)

Distribution of particle sizes in a soil; describes gradation by mass across sizes.

Sieve Analysis

Laboratory method to separate coarse particles by size using progressively finer sieves.

Hydrometer Analysis

Laboratory method to determine fines content by sedimentation for fine particles.

Well-Graded

Soils with a well-distributed range of particle sizes, typically higher compaction and strength.

Poorly Graded

Soils with limited gradation, dominated by a narrow range of particle sizes.

Gap Graded

Soils with distinct size gaps in the distribution, leading to unique packing.

Cu (Uniformity Coefficient)

Index Cu = D60/D10, indicates soil gradation; higher values mean better grading.

Cc (Coefficient of Curvature)

Index Cc = (D30)²/(D10·D60); assesses the shape of the PSD curve.

Grain Size Categories

Gravel (>2 mm), Sand (0.06–2 mm), Silt (0.002–0.06 mm), Clay (<0.002 mm).

Intact Rock vs Rock Mass

Intact rock has no significant defects; rock mass includes discontinuities influencing strength and stability.

Bedding

Planar layering in sedimentary rocks, formed by depositional processes.

Cleavage

Planar splits in minerals, typical in metamorphic rocks due to foliation.

Foliation

Planar fabric in metamorphic rocks from directed pressure, giving layered appearance.

Joint

Fracture in rock with no displacement; commonly in sets with varying spacing and aperture.

Fracture

Crack in rock mass that may have displacement; includes joints and faults.

Planar Defects

Fractures or discontinuities that lie in a plane, such as joints, cleavage, bedding.

Zonal Defects

bands of defects with varying spacing, often creating shear or weak zones.

Faults

Fractures with displacement; classified by movement: strike-slip, normal, reverse (thrust).

Strike-Slip Fault

Fault with horizontal movement along the fault plane; little vertical displacement.

Normal Fault

Fault with vertical displacement; hanging wall moves down relative to footwall.

Reverse Fault

Fault with compression; hanging wall moves up relative to footwall.

Intrusive Igneous Rocks

Igneous rocks crystallized below the surface (plutonic) with coarse grains.

Extrusive Igneous Rocks

Igneous rocks erupted onto the surface (volcanic) with fine grains.

Sill

Tabular igneous intrusion that runs parallel to the surrounding rock layers.

Dyke

Discordant igneous intrusion that cuts across rock layers.

Batholith

Large plutonic igneous intrusion, exposed at the surface through uplift and erosion.

Igneous Rock Texture

Characterized by grain size: aphanitic (fine), phaneritic (coarse), porphyritic (mixed).

Igneous Rock Types

Granite, Diorite, Gabbro (plutonic); Basalt, Andesite, Rhyolite (volcanic); Pumice, Obsidian, Pyroclastics.

Sedimentary Rock Groups

Clastic (fragments), Biogenic (biological remains), Chemical (precipitated), Volcaniclastic (volcanic debris).

Sedimentary Rock Strength

Generally weaker than most igneous/metamorphic rocks; influenced by grain size, sorting, and deposited environment.

Lithification Process

Process of turning sediment into rock via compaction and cementation.

Weathering vs Lithification

Weathering breaks down rocks; lithification turns sediments into rock.

Soil Classification by Weathering

Weathering descriptors (colour, fabric, weathering grade) inform rock/soil properties.

Dry Unit Weight

Unit weight of soil solids only, excluding water in voids.

Bulk Density

Mass of soil per unit total volume (including solids and voids).

Unit Weight

Weight per unit volume of soil (total or saturated depending on water content).

Specific Gravity (Gs)

Ratio of solid density to water density; Gs = ρs/ρw.

Void Ratio (e)

Ratio of volume of voids to volume of solids in a soil mass.

Porosity (n)

Fraction of total soil volume that is voids (Vv/V).

Water Content (Wc)

Mass of water in a soil sample relative to the mass of solids (or total).

Capillary Rise

Upward movement of water in small pores due to surface tension; height varies with pore size.

Pore Pressure (u)

Pressure of pore water within the voids of a saturated soil.

Effective Stress (σ′v or σ′)

Stress carried by the soil skeleton, equal to total stress minus pore pressure (σ′ = σ − u).

Total Stress (σ)

Weight of overlying soil and any applied loads per unit area.

Water Table (WT)

Depth to the level below which the soil pores are saturated with water.

Unsaturated vs Saturated

Unsaturated: voids contain some air; Saturated: voids filled with water.

K0 (Lateral Earth Pressure Coefficient)

Ratio of horizontal to vertical effective stress at rest in soil.

Rock Types

Three main rock classes: Igneous, Sedimentary, Metamorphic.

Sedimentary Rock Weathering

Weathering affects grain size, porosity, and cementation; sedimentary rocks often weaker.

Phase Diagrams in Soils

Visual tools showing relationships among soil phases (S, W, A) and properties.

Field vs Laboratory Soil Tests

Field (e.g., soil description, visual classification); Laboratory (PSD, Atterberg limits, etc.).

Bedding Planes

Planes separating bedded layers in sedimentary rocks.

Joints vs Fractures

Joints: fractures with no displacement; fractures may include displacement (faults).

Cleavage vs Foliation

Cleavage: planar weakness in minerals; Foliation: metamorphic fabric from deformation.

Alluvial Meandering

Meandering floodplain deposits in river systems formed from deposited alluvium.

Rock Texture Types

Aphanitic (fine-grained), Phaneritic (coarse-grained), Porphyritic (mixed grain sizes).