Soil and Rock Mechanics Unit 2

This set of vocabulary flashcards covers introductory concepts in geotechnical engineering, including rock types, weathering, soil transportation, weight-volume relationships, and Atterberg consistency limits.

Geotechnical Engineering

A major specialty area within civil engineering that focuses on how soil and rock support and affect the performance of structures built on or below the earth’s surface.

Igneous Rocks

One of the three major groups of rocks, characterized by having cooled from a molten state.

Sedimentary Rocks

Rocks deposited from a fluid medium, such as products of weathering of other rocks in water.

Metamorphic Rocks

Rocks formed from pre-existing rocks by the action of heat and pressure.

Weathering

The process of breaking down rocks by mechanical and chemical processes into smaller pieces.

Mechanical Weathering

Physical disintegration or degradation of rock pieces without a change in composition, resulting in size reduction.

Chemical Weathering

Decomposition whereby one mineral species is changed into another through various chemical processes, often involving water to provide oxygen and ion mobility.

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 sea.

Aeolian Soils

Soils transported and deposited by wind.

Colluvial Soils

Soils formed by the movement of soil from its original place by gravity, such as during landslides.

Void Ratio ($e$)

The ratio of the volume of voids to the volume of solids, expressed as $e = \frac{V_v}{V_s}$.

Porosity ($n$)

The ratio of the volume of voids to the total volume, expressed as $n = \frac{V_v}{V}$, and related to void ratio by $n = \frac{e}{1+e}$.

Degree of Saturation ($S$)

The ratio of the volume of water to the volume of voids, expressed as $S = \frac{V_w}{V_v}$.

Moisture Content ($w$)

Also referred to as water content, it is the ratio of the weight of water to the weight of solids in a given volume of soil: $w = \frac{W_w}{W_s}$.

Bulk Unit Weight ($\text{γ}$)

The weight of soil per unit volume, expressed as $\text{γ} = \frac{W}{V}$.

Dry Unit Weight ($\text{γ}_d$)

The weight of soil solids per unit volume, expressed as $\text{γ}_d = \frac{W_s}{V} = \frac{\text{γ}}{1+w}$.

Gravel

A textural class of soil where particle sizes are greater than $4.75 \text{ mm}$.

Sand

A textural class of soil where particle sizes range from $0.075 \text{ mm}$ to $4.75 \text{ mm}$.

Silt

A textural class of soil where particle sizes range from $0.005 \text{ mm}$ to $0.075 \text{ mm}$.

Clay

A textural class of soil where particle sizes are less than $0.005 \text{ mm}$.

Sieve Analysis

A mechanical analysis method used for coarse-grained soils with particle sizes greater than $0.075 \text{ mm}$ in diameter.

Hydrometer Test

A mechanical analysis for fine-grained soils with particles smaller than $0.075 \text{ mm}$, based on Stoke’s Law where velocity is proportional to diameter.

Plasticity

A property describing the response of a soil to changes in moisture content, typically involving a decrease in strength and swelling as water content increases.

Liquid Limit ($LL$)

The moisture content at which soil ceases to be liquid and starts to behave like a plastic material.

Plastic Limit ($PL$)

The moisture content at which soil ceases to be plastic and becomes a semi-plastic solid.

Shrinkage Limit ($SL$)

The moisture content at which drying-shrinkage at constant stress ceases.

Plasticity Index ($PI$)

The difference between the liquid limit and the plastic limit: $PI = LL - PL$.

Liquidity Index ($LI$)

An index relating the natural moisture content ($m$) to the consistency limits: $LI = \frac{m - PL}{PI}$.

Cohesion

The attraction of one water molecule to another resulting from hydrogen bonding, often referred to as a water-water bond.

Adhesion

The attraction of a water molecule to a non-water molecule, characterized as a water-solid bond.

Stickiness

The capacity of soil to adhere to other objects, categorized in degrees such as Non-Sticky, Slightly Sticky, Moderately Sticky, and Very Sticky.