Lesson 1: Soil Formation Flashcards
it is defined as the uncemented aggregate of mineral grains and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles.
Soil
it is used as a construction material in various civil engineering projects and it supports structural
foundations.
Soil
Is a branch of science that deals with the study of the
physical properties of soil and the behavior of soil
masses subjected to various types of forces.
Soil Mechanics
Subdiscipline of civil engineering that involves natural
materials found close to the surface of the earth.
Geotechnical Engineering
This includes the application of the principles of soil mechanics and rock mechanics to the design of
foundations, retaining structures, and earth materials.
Geotechnical Engineering
The Application of principles of soil mechanics to engineering problem:
a. Highway retaining wall
b. Building basement walls
c. Bridge abutments
d. Earth dam
e. Waterfront bulkhead
Examples of Geotechnical Systems:
- Dams
- Tunnels
- Excavations
- Slope stabilization
- Earth retaining structures
- Subgrade support
- Ground improvements
- Foundation for buildings
Examples of Geotechnical Failures:
- Leaning Tower of Pisa
- Failure of Transcona Grain Elevator
Soils are formed by ____________ of rocks.
weathering
the chemical elements that constitute rocks
Minerals
the aggregation of minerals into a hard mass
Rocks
average particle diameter of the soil at the 10th percentile or 10% of the particles are smaller that this diameter size.
Effective particle size (D10)
average particle diameter of the soil
Average particle diameter (D50)
numerical measure of uniformity
Uniformity of coefficient (Cu)
measure of the shape of the particle distribution curve (coefficient of gradation/ coefficient of concavity)
Coefficient of curvature (Cc)
measure of the shape of the particle distribution curve (coefficient of gradation/ coefficient of concavity)
Coefficient of curvature (Cc)
Process of which rocks are broken into pieces by physical force
Mechanical Weathering
Process of chemical decomposition of the original rock
Chemical Weathering
Rocks can be divided into three basic types:
- Igneous rock
- Sedimentary rock
- Metamorphic rock
Rocks that are formed by the solidification of molten magma ejected from deep within the earth’s mantle.
Igneous rock
Soils that are formed by the weathered products at their place of origin. These soils retain many of the elements that comprise the parent rock.
Residual Soil
The composition of these soils depends on the environment under which they were transported and is often different from the parent rock.
Transportation soil
The five major categories of Transported Soils:
a) Colluvial/ Gravity Transported - soils from
landslides or mudflows.
b) Lacustrine - formed by deposition in quiet lakes.
c) Alluvial - transported by running water &
deposited along streams.
d) Glacial - formed by transportation and
deposition from glaciers.
e) Aeolian - transported & deposited by wind.
f) Marine - formed by deposition in the seas.
The deposits of gravel, sand, silt, and clay formed by weathering may become compacted by overburden pressure and cemented by agents like iron oxide, calcite, dolomite, and quartz. Rocks formed this way is called:
Sedimentary Rocks
Metamorphism is the process of changing the composition and texture of rocks (without melting) by heat and pressure. During metamorphism, new minerals are formed, and mineral grains are sheared to give a foliated texture. Rocks formed this way is called:
Metamorphic rocks
____________ are classified according to chemical composition and structure. Most minerals of interest to geotechnical engineers are composed of oxygen and silicon, two of the most abundant elements on earth.
Minerals
It is a common mineral in rocks and is the principal mineral of coarse-grained soils.
Quartz
A rock mineral that is hard is hard and composed of silicon dioxide (SiO2 in colored, colorless, and transparent hexagonal crystals.
Quartz
The particles of coarse-grained soil are naturally
____________.
Angular
Clay Minerals are complex aluminum silicates made of
two distinct structural units:
silica tetrahedron and alumina octahedron
Each tetrahedron consists of four ____________ atoms surrounding a ___________ atom .
oxygen, silicon
In Silicon tetrahedron, the combination of tetrahedral silica units gives ____________.
silica sheet
In Alumina Octahedron, consists of six hydroxyls surrounding the aluminum atom and the combination of the units gives an _____________.
octahedral sheet / gibbsite sheet / brucite sheet
Clay mineral that consists of repeating layers of elemental silica- gibbsite sheets in 1:1 lattice. The layers are held together by hydrogen bonding and occurs as platelet.
Kaolinite
Clay mineral that is used in paints, paper, pottery and pharmaceutical industries.
Kaolinite
Clay mineral that consists of gibbsite sheets bonded to two silica sheets - one at the top and another at the bottom, also bonded by potassium ions. It is sometimes called clay mica.
Illite
Clay mineral that has a structure similar to that of illite. There is isomorphous substitution of magnesium and iron for
aluminum in the octahedral sheets.
Montmorillonite
In this clay mineral, Potassium ions are not present as in illite and large amount of water is attracted into the space between the layer. It is also called smectite and is a highly reactive clay (expands on contact with water).
Montmorillonite
From kaolinite family with hydrated and tubular structure
Halloysite
From montmorillonite family; used as drilling mud, in slurry trench walls, stopping leaks
Bentonite
Soil particles are assumed to be rigid. During deposition, the mineral particles are arranged into structural frameworks that we call _______________.
Soil Fabric
Two common types of soil fabric which are formed during the soil deposition of fine-grained soils.
a. Flocculated structure
b. Dispersed structure
soil fabric where the particles tend to orient parallel to one another.
Flocculated structure (saltwater environment)
soil fabric where particles oriented in perpendicular manner.
Flocculated structure (freshwater environment)
soil fabric that occurs when majority of the particles orient parallel to one another.
Dispersed structures
3 major categories of Particle Shapes
- bulky particles
- flaky particles
- needle-shaped particles
particle shape mostly formed by mechanical weathering of rocks.
bulky particles
4 descriptions of bulky particles:
a) Angular
b) Sub-angular
c) Rounded
d) Sub-rounded
particle shape with very low sphericity, predominantly clay minerals.
flaky particles
particle shape that is less common than the two
other particle types. Examples are some coral deposits
and attapulgite clay.
needle-shaped particles
Soils can be identified according to its size of particles. These are the following soil types:
a. Gravel (G)
b. Sand (S)
c. Silt (M) and Clay (C)
______________ are pieces of rocks with occasional particles of
quartz, feldspar, and other minerals.
Gravel (G)
____________ mostly made of quartz and feldspar
Sand (S)
_____________ consists of very fine quartz grain, mostly flake-shape microscopic and submicroscopic particles of mica, clay mineral and others.
Silt (M) and Clay (C)
Four systems used in describing soil types based on particle size:
a. European standards
b. USCS
c. AASHTO
d. ASTM
It is the determination of size range of particles present in a soil, expressed as % of the total dry weight.
Mechanical Analysis of soil
2 methods used in Mechanical Analysis of soil:
a. Sieve Analysis
b, Hydrometer Analysis
This method analysis is used for particle sizes larger than 0.075 mm in diameter.
Sieve Analysis
This method analysis is used for particle sizes smaller
than 0.075 mm in diameter.
Hydrometer Analysis
This consists of shaking the soil sample through a set of
sieves that have progressively smaller openings.
Sieve Analysis
This is based on the principle of sedimentation of soil grains in water.
Hydrometer Analysis
4 parameters determined from the particle size distribution curve:
- Effective Size (D10)
- Uniformity Coefficient (Cu)
- Coefficient of gradation (Cc)
- Sorting Coefficient (S0)
It is a parameter used where the diameter in the particle-size
distribution curve corresponding to 10% finer. D10 is a
good measure to estimate the hydraulic conductivity and
drainage through soils.
Effective Size (D10)
another measure of uniformity and is generally encountered in geologic works,
Sorting Coefficient (S0)
a type of particle size distribution curve that represents a type of soil in which most of the soil grains are the same size.
Curve I (Poorly graded)
a type of particle size distribution curve that represents a soil in which particle sizes are distributed over a wide range.
Curve II (Well graded)
a type of particle size distribution curve where the soil might have a combination of two or more uniformly graded fractions.
Curve III (Gap graded)
