Exam Review - Engineering Geoscience

A collection of key terms and concepts related to Engineering Geoscience.

Weathering

The physical disintegration and chemical decomposition of rock into fragments.

Erosion

The detachment and transport of rock fragments by the action of water, wind, or gravity.

Mechanical Weathering

The breakdown of rocks into smaller fragments without changing their chemical composition.

Chemical Weathering

The breakdown of rocks and minerals into new chemical combinations that are stable under conditions at or near the Earth's surface.

Leaching

The process by which soluble material in the soil is washed into a lower layer or dissolved and carried away by water.

Porosity

The measure of void spaces in a material, expressed as a fraction of the volume.

Hydraulic Conductivity

The ease with which a fluid (usually water) can move through pore spaces or fractures in soil or rock.

Soil Profile

A vertical section of soil that depicts all of its horizons.

Active Layer

The near-surface layer of permafrost that thaws in the summer and freezes in the winter.

Gelifluction

Mass movement linked to the thawing of the active layer in permafrost.

Aquifer

A saturated body of rock or soil that transmits significant quantities of groundwater.

Granite

A common type of intrusive igneous rock that is granular and phaneritic in texture.

Permafrost

Ground (soil or rock, including underwater sediments) that remains at a temperature of 0°C or lower for at least two consecutive years.

Calcite

A naturally occurring mineral form of calcium carbonate, particularly susceptible to dissolution.

Hydrolysis

A reaction involving the interaction of a substance with water, where hydrogen ions replace other positive ions.

Glacial Drift

General term for all sediments of glacial origin.

Cohesion

The inherent shear strength of soils primarily due to the attraction forces between individual clay particles.

Organic Matter

Material composed of organic compounds that comes from the remains of living organisms.

Rock Quality Designation (RQD)

An index based on the cumulative length of core pieces longer than 10cm in a run divided by the total length of the core run.

Soil Hazards

Conditions that can lead to engineering problems such as settlement, expansive clay, liquefaction, and subsidence.

Frost Action

(congelifraction, the most effective agent) - Disintegration of a rock due to the pressure exerted by the freezing of water contained in pores, cracks and or along bedding planes. - When the liquid turns into water: 9% volume increase. - Contributes to talus slopes.

Hoodoos

sedimentary rock structure protected by a thin layer of harder rock. - Weathered material removed by rain.

Unloading

elastic expansion of rocks when lithostatic pressure is reduced as a result of erosion, retreat of glaciers or deep excavation (can create fractures and pop-ups)

Exfoliation

the process by which scales of rock (thickness between cm and severed m) are successively stripped from the surface of a large rock mass

Chemical Weathering

the process that breaks down rocks through chemical reactions, often involving water, acids, and gases, leading to changes in the mineral composition.

Karst

topography formed by rock dissolution and characterized by sinkholes, caves and underground drainage

Hydration

absorption of water into the crystal lattice of a mineral - Ex: the transformation of anhydrite into gypsum

Mechanical weathering results in

sharp angular topography

Chemical weathering results in

rounded softened contours.

Joint patterns often control

the extent and style of weathering

Soil hazards

settlement, expansive clay, liquefaction, subsidence.

Earth’s external processes:

Weathering - Erosion - Formation of soil

Earth materials can be subdivided into:

Rocks - Soils - Fluids

O-Horizon

The top layer of soil, rich in organic material and nutrients, where decomposition of plant and animal matter occurs.

A-Horizon

Mineral and humus, dark, high biological activity - Topsoil

B-Horizon

Substances leached out from above layers accumulate

C-Horizon

partially altered parent material(residual: weathered bedrock, transported: unconsolidated material

E-Horizon

mostly mineral particles, light grey, substances are leached away

R-Horizon

unweathered bedrockthat provides the material for other soil layers and does not undergo soil formation processes.

Outcrop

a section of bedrock or soil that is visible at the Earth's surface, often serving as an important feature in geological mapping and study.

dry density (formula)

p = Ms / Vt , where p is the dry density, Ms is the mass of solids, and Vt is the total volume.

parent material

rock from which the soiled developed

residual soils (sed)

soils that form from the weathering of parent rock in place, without transportation by external forces.

Transported soil

soils that are moved from their original location by agents such as wind, water, or ice.

Alluvial soils

soils that are formed by the deposition of sediment carried by rivers and streams.

Lacustrine soils

soils that are formed from the sediment deposited in lake beds.

Marine soils

soils transported and deposited in deltas, seas or oceans.

Glacial soils

soils that are formed by the movement and deposition of materials from glaciers.

Till

unsorted material deposited directly by glacial ice and showing no stratification can be debris left behind by melting glaciers

Eolian soils

soils that are formed from wind-blown sediment, typically consisting of silt or fine sand.

Colluvial soils (colluvium)

soils transported downhill by gravity, either slowly (creep) or catastrophically (mass movement)

Factors that control soil development

Climate, organisms, relief, parent material, and time (CORPT)

Pedocal

(white) a type of soil characterized by a high concentration of calcium carbonate, typically found in dry grasslands (semi-arid - arid)

Pedalfer

(sandy light coloured) a type of soil characterized by a high concentration of iron and aluminum oxides, typically found in humid regions.

Remoulding

inherent shear strength of soils mostly due to the attracting forces between individual clay particles

Sensitivity

strength in undisturbed conditions. strength in remoulded conditions.

symbol Grain size: sand

S

symbol Grain size: Gravel

G

symbol Grain size: silt

M

symbol Grain size: clay

C

symbol Grain size: organic soil

O

symbol Grain size: peat

Pt

Liquefaction

a phenomenon in which the strength of soil is reduced by vibrations, shaking, and loading. - Occurs in saturated sandy soils in which the space between particles is filled with water

Sinkhole

circular area of subsidence caused by collapse into subterranean void

Compaction

reduction in the volume of soil under load caused by realignment of soil particles into a denser packing, but without drainage of water from the soil.

Consolidation

reduction in the volume of soil as water flows out of the sample.

Deflation

wind erosion mechanism by which dry fine-grained particles are preferentially lifted and removed in a desert environment.

Water cycle

- Evaporation and precipitation - Runoff and infiltration - Evapotranspiration

Divide (basin)

the imaginary boundary between drainage basins

Dissolved load

chemicals in solution

Suspended load

fine particles prevented from settling to the bottom of the stream by water movement

Bed load:

large particles moving downstream by rolling, sliding and/or bouncing on the bed.

Competence

the largest particle a stream can carry

Alluvial fan

hemi-conical landform formed by stream sediments deposited on a valley floor adjacent to a mountain range

Turbidites:

continental sediments deposited on the edge of the continental shelf by rivers and waves.

Wind ocean waves

created by friction between wind and water surface. Depends on: - Wind velocity - Length of time that the wind has blown - Fetch: distance wind can travel over water

Shoaling

increase in wave height due to increase in seafloor depth. - Wavelength decreases: energy is concentrated in a shorter length - Amplitude increases: when height/wavelength = 1/7, the wave breaks

Longshore current:

the flow of water parallel to shore induced by refracted waves striking the coast at an oblique angle

Rip current:

rapid Seward flow of water created at the edge of longshore current cells

Groins:

walls build perpendicular to the beach to trap sand from the longshore current

Jetties:

larger structures build perpendicular to the beach to allow boats to get in and out of a harbour

Breakwaters

walls built parallel to the beach breaking up the longshore current.

Formation of Glaciers:

Snow accumulates - Air is present between snowflakes in snowpack - Hexagonal snowflake crystals become smaller, thicker and more spherical - Air is forced out - Snow recrystallizes into denser mass of small grains (firn) - When snow thickness > 50m, firn fuses into a solid mass of interlocking ice crystals (glacier ice)

Zone of accumulation

zone at and above the snow line, where a glacier forms

Zone of ablation:

zone of net loss of mass, due to melting, and calving.

Plucking:

: the process by which upstream melt water invades cracks, refreezes downstream and levers out rock fragments.

Glacial drift

general term encompassing all sediments of glacial origin (clay, silt, sand, gravel, boulders)

Till:

: unstratified and unsorted material directly deposited by the melting ice

Eskers:

long, narrow and sinuous till ridges deposited by a sub-glacial stream and left behind when the glacier melted.

Moraines:

lawyers of till found on the sides and/or at the front of glaciers

Drumlins

smooth, elongated oval hills

Erratic block:

a single, large block of rock transported over long distances by glaciers.

Measuring rock strength

UCS test: - Apply an uniaxial compressive stress. - Intact rocks contain small imperfections where stress concentrates and initiates tensile crack growth. - Tensile cracks grow along grain boundaries. - Cracks start to interact and merge. - Failure occurs by the accumulation of damage.

in situ

in its original position in the field

Discontinuities

the weakest link in the rock mass fabric.

Rock Quality Designation (RQD)

index based on the cumulative length of core pieces longer than 10cm in a run divided by the total length of the core run.

Rock Mass Rating (RMR):

1. Strength of intact rock material (UCS) 2. RQD 3. Joint Spacing 4. Joint condition (surface roughness, separation) 5. Groundwater conditions 6. Others (infilling, weathering, orientation)

Mass movement:

collective name for a variety of processes for the downslope movement of earth materials under the direct influence of gravity and the resulting landform. Causes: - Slope characteristics: loss of lateral support by rapid water level change. - Friction coefficient: static friction coefficient: constant proportional to the force restricting the movement of a stationary object on a relatively smooth, hard surface. - Excess pore water: effective stress is the force required to keep the soil rigid. - Deforestation - Vibrations: earthquakes.