Introduction to Soil and Geotechnical Engineering Flashcards

A set of vocabulary flashcards covering the fundamental concepts of soil engineering, formation, classification systems, and index properties.

Soil (Civil Engineering Definition)

The loose, unconsolidated inorganic material on the earth’s crust produced by the disintegration of rocks, overlying hard rock, with or without organic matter.

Soil Mechanics

The study of the engineering behavior of soil when used as either a construction or foundation material.

Three-Phase System

A complex soil system consisting of three distinct components: solid particles, liquid (water), and gas (air).

Weathering

The process of disintegration and decomposition of rocks and minerals into smaller grains.

Physical (Mechanical) Weathering

A process that reduces particle size without changing the chemical composition, primarily resulting in coarse-grained soils like sand and gravel.

Chemical Weathering

A process that alters the mineral nature of the original parent rock, forming new compounds and primarily producing fine-grained soils and clay minerals.

Residual Soils

Soils found at the same location where they were formed, often characterized by angular to subangular particles and similar mineralogy to the parent rock.

Transported Soils

Soils moved from their origin by natural agencies such as water (Alluvial), wind (Aeolian), glaciers (Glacial), or lake/sea beds (Lacustrine/Marine).

"O" Horizon

The soil layer primarily composed of organic matter ($> 20\%$ by mass).

"A" Horizon (Topsoil)

The uppermost mineral layer which is heavily weathered and contains high organic content.

"B" Horizon (Subsoil)

The zone of accumulation for materials leached from the layers above.

"C" Horizon

The parent material from which horizons A and B formed, showing very little weathering.

"R" Horizon

The underlying hard bedrock beneath the soil horizons.

Soil index properties

Basic characteristics, such as grain shape/size for coarse soils or Atterberg limits for fine soils, used to predict behavior and classify soil.

Sieve Analysis

A methodology used for coarse soil fractions larger than $0.075\,\text{mm}$ by shaking soil through graded mesh.

Hydrometer Analysis

A methodology used for fine soil fractions that measures the settlement rate of particles in a suspension.

Fines (Silt/Clay)

Soil particles that pass through the No. 200 sieve ($0.075\,\text{mm}$).

Consistency

The relative ease with which soil (specifically clay) can be deformed.

Liquid Limit (LL)

The minimum moisture content at which soil tends to flow as a liquid.

Plastic Limit (PL)

The moisture content where soil transitions from plastic to semi-solid and begins to crumble when rolled.

Shrinkage Limit (SL)

The maximum moisture content where further drying of the soil causes no volume reduction.

Plasticity Index (PI)

The range of water content where soil acts as a plastic material, calculated as $PI = LL - PL$.

Unified Soil Classification System (USCS)

A classification system where soil is considered fine-grained if $50\%$ or more passes the No. 200 sieve.

AASHTO Soil Classification System

A system used for highway projects where soil is fine-grained if more than $35\%$ passes the No. 200 sieve.

Group Index (GI)

A calculated number in the AASHTO system used to assess soil quality for highway subgrades; higher values indicate poorer performance.

Dilatancy (Shaking Test)

A field test where silts react rapidly to shaking (water appearing on the surface), while clays react slowly or not at all.

Thread/Toughness Test

A manual test where high plasticity clays can be rolled into very thin, tough threads.

Smear Test

A field identification method where high plasticity clays produce a slick, waxy smear, and silts produce a dull, rough smear.