Soil Characteristics

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Soil Characteristics
Produced 11/30/2006 by Gardner Watkins

• If you ever have the honor to talk to an
  agronomist, never say dirt! They take it very
  seriously and actually take it as a personal
  affront to their very existence.

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Aids to size identification

• Soils possess a number of physical
  characteristics which can be used as aids to size
  identification in the field. A handful of soil
  rubbed through the fingers can yield the
  following
• SAND (and coarser) particles are visible to the
  naked eye.
• SILT particles become dusty when dry and are
  easily brushed off hands and boots.
• CLAY particles are greasy and sticky when wet and
  hard when dry, and have to be scraped or washed
  off hands and boots.

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Particle Size

• The range of particle sizes encountered in soil
  is very large from boulders with a controlling
  dimension of over 200mm down to clay particles
  less than 0.002mm.

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British Soil Classification System
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Cohesion Adhesion

• Cohesion is the attraction of one water molecule
  to another resulting from hydrogen bonding
  (water-water bond).
• Adhesion is similar to cohesion except with
  adhesion involves the attraction of a water
  molecule to a non-water molecule (water-solid
  bond).
• Water exist in spaces between soil particles
  called macropore water, which is also called
  Gravitational water.

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Wet Consistency

• Describe Plasticity ?Degree a soil can be molded
  or reworked causing permanent deformation without
  rupturing.
• Describe Stickiness ?The capacity of soil to
  adhere to other objects ?Estimated at moisture
  content that displays maximum adherence between
  thumb and fore finger?

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Plasticity

• The degree to which puddled or reworked soil can
  be permanently deformed without rupturing
• Evaluation done by forming a 4 cm long wire of
  soil at a water content where maximum plasticity
  is expressed

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Plastic Determination
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Plasticity Class - wire must support itself
Non-Plasticwill not form a 6 mm dia, 4 cm long
wire Slightly Plastic6 mm dia, 4 cm long
wire Moderately Plastic4 mm dia, 4 cm long
wire Very Plastic2 mm dia, 4 cm long wire
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Stickiness Classes

• Non-Sticky?little or no soil adheres to fingers
  after release of pressure
• Slightly Sticky?soil adheres to both fingers
  after release of pressure with little stretching
  on separation of fingers
• Moderately Sticky ?soil adheres to both fingers
  after release of pressure with some stretching on
  separation of fingers
• Very Sticky -soil adheres firmly to both fingers
  after release of pressure with stretches greatly
  on separation of fingers

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Stickiness
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2
1) Non-Sticky 2) Slightly-Sticky 3) Very Sticky
3
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Why soil characterisitics are important.

• Breaks in the water pipes were occurring at an
  average annual rate of 51 per 100 miles of line.
• The GIS Department began its investigation by
  referencing the 1975 Soil Survey of Dallas
  County.

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• Very acidic soil was found to be more prevalent
  in the southern area where the majority of the
  breaks were than the rest of the city.
• Layers denoting pH, electric resistivity, soil
  consistency, and expansion characteristics were
  developed from the Dallas County Soil Survey and
  made available so that waterlines could be
  analyzed in relation to soil conditions.

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References

• Soil Analysis Supplies Answers to Waterline
  Failures By David Jacobs, City of Garland,
  October 2004 Texas Downloaded 30 Nov 2006
  fromhttp//www.esri.com/news/arcuser/1104/soilana
  lysis.html
• Soil Characteristics Based on part of the
  GeotechniCAL reference package by Prof. John
  Atkinson, City University, London Downloaded 30
  Nov 2006 http//fbe.uwe.ac.uk/public/geocal/SoilMe
  ch/classification/soilclas.htm