GEOL 446 Environmental Geology

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GEOL 446Environmental Geology
PART I FOUNDATIONS OF ENVIRONMENTAL GROLOGY
Chapter 1 philosophy and Fundamental Concepts
Chapter 2 Earth Material and Processes
Chapter 3Soils and Environment
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3. Soils and the Environment

• Soil is one of the most important earth materials
  we encounter each day, but the definition of soil
  is difficult.
• Soil Scientists (and most ordinary people)
• fine-grained, well-weathered earth material that
  is able to support plant growth
• focus on the physical and chemical properties
• Engineers
• any earth material that can be removed without
  blasting
• focus on particle size and the amount of organic
  material
• engineering applications

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3. Soils and the Environment

• Environmental Geologists
• must understand soil from many perspectives
• characteristics affect agriculture, engineering,
  hydrology, natural hazards and other aspects of
  land use
• soil development and soil character is crucial
  to good land use planning.

• Read Table 3.1 (Soil Taxonomy)
• Understand the meaning of soil types, but do not
  memorize
• all of them.
• Read Table 3.2 (Unified Soil Classification)
• Learn the definition of each constituent that
  makes up soil.

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Soil Development

• Soil is an important part of the geologic cycle
  and soil characteristics are influenced by parent
  material, climate, topography, weathering, and
  the amount of time a particular soil has had to
  develop.

As soil develops, weathering creates distinct
layers in soil. We call these layers soil
horizons, and each soil horizon has distinctive
characteristics. Every soil has a soil profile, a
list of the horizons that describe a particular
soil.
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Soil Horizons
Materials in a Soil System Vertical and
horizontal movements create a soil profile made
up of distinct layers parallel to the surface,
which are called soil horizons.
Organic top layer (O) Zone of leaching (A and
E) Zone of accumulation (B) Rock (weathered
unweathered) (C and R)
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Soil Development

• A soils profile depends on its age and its
  conditions of formation. Soil profile is the
  primary criteria for soil classification.
• Soils can be compared in terms of their relative
  development. Weakly developed soil profiles are
  generally younger and may have fewer horizons
  well-developed soils are generally older and have
  more horizons.
• Chronosequences
• Relative development of a series of soils allows
  their arrangement in a soil chronosequence. A
  soil chronosequence gives information about the
  history of the landscape. The relative
  development of the soils in a chronosequence
  tells the investigator about the climate and
  depositional history of the area.

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Soil Texture

• Texture relative proportion of sand, silt and
  clay.
• Texture classes
• Coarse
• sands, loamy sand and sandy loams with less than
  18 clay, and more than 65 sand.
• Medium
• sandy loams, loams, sandy clay loams, silt loams
  with less than 35 clay and less than 65 sand
  the sand fractions may be as high as 82 if a
  minimum of 18 clay is present.
• Fine
• clays, silty clays, sandy clays, clay loams and
  silty clay loams with more than 35 clay.

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Soil Classification

• Soils are often referred to as being sandy or
  clayey, or silty. Different countries use
  different standards to define sand particle and
  silt particle sizes.
• Particle sizes
• Gravel, Cobbles, and Boulders
• particles greater than 2 mm diameter
• Coarse and medium sand
• particles from 2 mm to 0.2 mm diameter
• Fine and very fine sand
• particles from 0.2 mm to 0.074 mm diameter
• Silt
• particles from 0.074 mm to 0.004 mm diameter
• Clay
• particles less than 0.004 mm diameter

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Soil Classification
WELL SORTED
WELL GRADED
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Unified Soil Classification System
GW well-graded gravel GP poorly graded
gravel GM silty gravel GC clayey gravel SW
well-graded sand SP poorly graded sand SM
silty sand SC clayey sand ML silt MH
micaceous silt OL organic silt CL silty
clay CH high plastic clay OH organic clay PT
peat and muck
Clean (lt5 fines) Dirty (gt12 fines)
Clean (lt5 fines) Dirty (gt12 fines)
Non-plastic Plastic
gt50 larger than 0.074 mm
FINE-GRAINED COARSE-GRAINED
Clays Silts Sands Gravels
gt50 smaller than 0.074 mm
Mostly Organics
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Water in Soils

• Types of water
• Water on Earth is known by different terms,
  depending on where it is and where it came from.
  
• Meteoric water water in circulation.
• Connate water "fossil" water, often saline.
• Juvenile water water from the interior of the
  earth.
• Surface water water in rivers, lakes, oceans,
  etc
• Subsurface water groundwater, connate water,
  soil, capillary water.
• Groundwater in the zone of saturation, may be
  fresh or saline.

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Water in Soils

• Moisture Content of soil is calculated as
  follows
• W weight, so that
• (Wwet - Wdry)/Wdry x 100 H2O content ()
• Moisture content affects the engineering
  properties and stability of soils. A soil that is
  stable in dry conditions may become unstable to
  support the structures built on it when saturated
  with water.

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Engineering Properties of Soils

• Plasticity
• related to the water content
• Liquid Limit (LL)
• water content above which the soil behaves like
  a liquid
• Plastic Limit (PL)
• water content below which the soil is no longer
  plastic
• Plasticity Index (PI), PI LL - PL
• range of water contents that make the soil
  behave as a
• plastic material
• Low PI (5 ) small change in water content, soil
  changes from solid to liquid
• High PI (gt 35) potential to expand and contract
  on wetting and drying

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Engineering Properties of Soils

• Expansive Soils
• high content of swelling clay (montmorillonite)
• soils swell when water is incorporated between
  clay plates
• shrinking occurs when soil is dried
• damage to building and road foundations
• Study Table 3.3 in textbook to understand more
  about soil descriptions and their significant
  properties.
• Study the Universal Soil Loss Equation (erosion)
  
• A RKLSCP

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Universal Soil Loss Equation

• A RKLSCP
• A long-term average annual soil loss for the
  site
• R long-term rainfall runoff erosion factor
• K soil erodibility index
• L hillslope/length factor
• S hillslope/gradient factor
• C soil cover factor (crop/vegetation and mgmt.
  factor)
• P erosion-control practice factor
• Used to predict the impact of sediment loss on
  local streams and other resources and to develop
  management strategies for minimizing impact.

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Water in Soils
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Water in Soils
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• Key Terms to Review
• weathering
• soil horizons
• soil profile development
• soil chronosequence
• soil fertility
• unified soil classification
• soil strength
• soil sensitivity
• liquefaction

• compressibility
• erodibility
• permeability
• corrosion potential
• shrink-swell potential
• expansive soils
• soil pollution
• desertification
• water table
• soil plasticity index