Soils Flashcards
What is engineering definition of soils?
Any solid earth material that can be removed without blasting
What is the soil scientist definition of soils?
Any solid earth material that has been altered by physical, chemical, and organic processes such that it can support rooted plant life.
What are residual soils?
Soils composed of insoluble weathered material that remains in place
What are transported soils?
Soils composed of weathered material that has been transported by water, wind, and ice
What other systems define the open soil system?
Climate, topography, parent material, time, and organic processes
What are the 6 horizons of soil?
O, A, E, B, C, R
What is the O horizon?
Mainly organic materials and is often dark brown or black
What is the A horizon?
Mixture of mineral and organic materials, and is generally light black to brown
What is leaching?
Process of dissolving, washing, or draining earth materials by percolation of groundwater or other liquids that occurs in A horizon and moves clays and other materials to B horizon
What is the E horizon?
Light colored materials as a result of leaching of clay and minerals to lower horizons
What is the zone of leaching?
Horizon A + E
What is horizon B?
Enriched horizon of clay and other earth materials leached from higher horizons
What is B horizon also known as?
Zone of accumulation
What is the C horizon?
Partially altered parent material
What is the R horizon?
Unaltered parent material
What color are well-drained soils?
Red
What color are poorly-drained soils?
Yellow
What are the engineering classifications for soil?
clay, silt, sand, particles
What size is clay?
<0.004 mm
What size is silt?
0.004-0.074 mm
What size is sand?
0.074 - 2.0 mm
What size are particles?
> 2.0 mm
What textures are sand, silt, and clay by feel?
Gritty, baking powder, cohesive
What are the four types of soil aggregates, or peds?
Granular, blocky, prismatic, and platy
What is the size range for granular aggregates and what zone is it found in?
1-10 mm; A mostly, but also B and C
What is the size range for blocky aggregates and what zone is it found in?
5-50 mm; B
What is the size range for prismatic aggregates and what zone is it found in?
10-100; B
What is the size range for platy aggregates and what zone is it found in?
1-10 mm; E mostly, but also sometimes B
What is soil fertility?
Capacity of soils to supply nutrients such as nitrogen, potassium, phosphorus
Where are soils naturally fertile?
Some flood plains and glacial deposits
Where are soils low in fertility?
Where highly leachable bedrock or loose deposits with little organic material
What are saturated soils?
All pore spaces are filled with water
What are unsaturated soils?
Some pore space is not filled with water
What is water content/moisture content?
Amount of water in the soil
Where is water flow fastest and slowest?
Fastest in pore spaces, and slowest near the edges of pores
Where is soil science taxonomy useful?
Agriculture
How is soil taxonomy divided?
Order, suborder, great groups, subgroups, families, and series
How are soil orders determined?
Number of type of present horizons, nutrient status, organic content, color, and general climatic conditions
What soil classification is used by engineers?
Unified Soil Classification System
How does the Unified Soil Classification System classify soils?
Predominant particle size or abundance of organic material
What is plasticity?
Related to the water content of the soil
What is Liquid Limit (LL)?
water content above which a soil behaves as a liquid
What is Plastic Limit (PL)?
water content below which soil no longer behaves as a plastic materal
What is the plasticity index (PI)
numerical difference between LL and PL that represents that range moisture content within which soils behaves like a plastic material
What is soil strength?
Ability of soil to resist deformation
What is cohesion?
Measure of the ability of soil particles to stick together
What is frictional force?
Function of density, size, and shape of the soil particles as well as the weight of overlying particles forcing the grains together
Where are cohesion and frictional forces most significant?
In coarse-grained soils rich in sand and gravel
What is sensitivity?
Measures changes in soil strength resulting from disturbances
What soil compositions are least sensitive?
Those composed of sand and gravel, with no clay
What is compressibility?
Measure of soil’s tendency to consolidate, or decrease in volume
What soils have high and low compressibility?
High: fine grains or organic soils; Low: coarse grained composed of gravel or sand
What is erodibility?
Ease of which soil materials can be removed via wind or water
What soils are easily eroded?
Unprotected silts, sands, and other loosely consolidated material
What soils are not easily eroded?
Cohesive soils composed of >20% clays, and naturally cemented soils
What is permeability?
Measure of ease with which water moves through the material
What has the highest and lowest permeability?
Clean gravels and sands; clays
What is corrosion?
Slow weathering or chemical decomposition that proceeds from surface into the ground
What defines a highly corrosive soil?
High ability to carry electric current
What is the ease of excavation?
What is required to remove the soil
What are three types of excavation?
Common excavation, rippable excavation, blasting or rock cutting
What is a rill?
A thin narrow channel indicating soil erosion that have the same slope as the gradient
What is a gully?
A wide non-parallel channel indicating soil erosion
What is non-till agriculture?
Agriculture method that eliminates tilling and significantly reduces soil erosion
What is contour plowing?
Plowing in conjunction with the natural contours of the land, with furrows perpendicular to the slope of the land
What are terracing slopes?
Established on steep slopes and minimizes erosion as long as it is maintained
What is sediment pollution?
Number one polluter that causes soil depletion from origin site, choking of water systems, and burying of vegetation
What are treatment options for soil pollution?
- Excavation and proper disposal
- Incineration
- Bioremediation
What are required for underground storage tanks?
- Double walled
- Leak detection
- Est. environmental program
What is desertification?
Conversion of land from productive state to that resembling a desert
What are the causes of desertification?
- Over-grazing
- Deforestation
- Adverse soil erosion
- Poor drainage of irrigated land
- Over use of water supplies
