Section 2 - Soils Analysis Flashcards
Porosity
Amount of pore space in soil; is related to grain size distribution + consolidation. Clay soils usu. have high porosity.
Soil Permeability
rate at which water will freely drain through a soil. Clay usu. has low permeability and may settle considerably when loaded with a foundation
Soil Strength
- a soil’s ability to resist deformation. Depends on cohesion and friction
- Cohesion –ability of grains to stick together (water)
- Friction –between grains and form density and weight of material above
- Sensitivity – refers to how easily a soil loses strength due to disturbance
Shear Strength
Force and Strength of the soil and minerals holding the block in place. Fights the Shear force that pulls the block down. Tested using a 4-bladed vane driven into soil and turned until failure (torque nec. to force failure = shear strength measure of frictional resistance and cohesion of soil)
Bulk Density
- Dry weight of undisturbed soil particles/ soil unit volume
- Includes both solids and pores and is expressed as grams/cc
- Desirable bulk densities vary depending upon soil texture
- Higher bulk density usu. = greater foundation support
Atterberg Limits - Liquid + Plastic
Measures water in a soil at a pt. where soil begins to act as a liquid or begins plastic flow; LL-PL = PI (PLASTICITY INDEX)
- Liquid Limit (LL) - moisture content at which a soil tends to flow + won’t retain shape
- Plastic Limit (PL) - moisture content at which soil deforms plastically; soil rolled into long threads until they just begin to crumble at a dia. of 3 mm. If it contains more moisture than plastic limits
(C) Clay
A clastic mineral particle of any composition that has a grain size smaller than 1/256 mm. The term is also used in reference to a broad category of hydrous silicate minerals in which the silica tetrahedrons are arranged into sheets.
- Unified Soil Classification System Symbol - C
(M) Silt
granular material of a size somewhere between sand and clay derived from soil or rock
- Unified Soil Classification System Symbol - M
(S) Sandy soil
large pore space which provides quick drainage
- Unified Soil Classification System Symbol - S
(G) Gravel
- granular rock particles ranging in size from 0.25” to 3.25”.
- -any larger rock pieces are called “cobblestones”, largest: “boulders”.
- Unified Soil Classification System Symbol - G
(O) Organic Soils/Histosols
form in continually saturated areas (marshes, bogs) where low 0 2 prevents microbial breakdown of plant materials
- Unified Soil Classification System Symbol - O
(H) High Liquid Limit
- Water content > 50%, high plasticity (v. cohesive or sticky clay)
- Unified Soil Classification System Symbol -H
(L) Low Liquid Limit
- Water content
- Low plasticity
- Unified Soil Classification System Symbol - L
(W) Well-Graded Soils
Has a good representation of all particle sizes, in proportionate quantities, from the largest to the smallest. The smaller particles fill the voids between the larger particles. This proportioning generates stability through increased grain-to-grain contact.
- Unified Soil Classification System Symbol - W
(P) Poorly Graded Soils
- Grain distribution affects consolidation and settlement
* Unified Soil Classification System Symbol - P
GRADING STANDARDS: lawn
1% MIN, 10%MAX
2-8% preferred
Grading Standards: athletic fields
1% min, 2%max
- 1% preferred
Grading Standards: Mowed Slopes
5% min, 25%max
- 10% preferred
Grading Standards: Unmowed Slopes
no min, Angle of repose (typ. 30-45 deg) max
- 25% preferred
Grading Standards: Planted Slopes
1% min, 10%max
- 5% preferred
Grading Stnd: Berms
5% min, 25%max
- 10% preferred
pH
an expression of the relative concentrations of hydrogen ions in a soil sample. A scale range form 0-14 is used. The terms “acid,” “neutral,” and
“alkaline” are used when describing the soil pH or “soil reaction.”
Acid
Used in referring to soils with a pH less than seven (7). These soils are most common in areas
with high rainfall and often are high in organic matter.
ALKALINE
Used in referring to soils with a pH greater than seven (7). These soils are most common in
areas with low rainfall.
Neutral
Used in referring to soils with a pH equal to seven (7). Most plants prefer a pH from 6.5 to 7.2 .
However, some prefer acid soils with a pH from 5.0 to 6.5 and others survive quite well with a pH from
7.5 to 8.0.
Soil Texture
Refers to the relative percentages of the primary soil particles , or separates, in a soil
mass.
Soil Structure
Refers to the arrangement of soil particles and how they are grouped together into
aggregates.
Soil Separates
The individual size groups of primary soil mineral particles of sand, silt, and clay.
Sand
The largest mineral particle of the soil separates. It is characterized by large pore space
allowing good aeration and rapid passage of water.
Silt
The intermediate-sized mineral particle of the soil separates.
Clay
The smallest mineral particle of the soil separates. It is characterized by slow drainage and
poor aeration but has the best nutrient holding capacity of all the soil separates.
Loam
Generally a fertile and easily manageable soil consisting principally of sand (±40%) and
silt.(t40%) particles with some clay (120%).
Salinity
Refers to excess salts in soils. This is common in arid areas with low rainfall because
salts are not leached out of the soil as easily as they are in areas of high rainfall. High salts can be
a result of the quality of irrigation water, fertilizers, chemical amendments, or manures high in
salt content.
