Transcript Soil Texture - Drinking Water Testing Environmental

Soil Texture
Presented by:
Mr. Brian Oram, PG, PASEO
Wilkes University
GeoEnvironmental Sciences and
Environmental Engineering Department
Wilkes - Barre, PA 18766
570-408-4619
http://www.water-research.net
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Your Hands will Get “Dirty”
Quick Review
Major Components of Soil
Pore Space (50%)
 This may contain air and/or
water
Soil Space (50%)
• Organic Matter
• Mineral Matter
Master Soil Horizons
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O Horizon- leaf litter / humus
A Horizon- organic accumulation
in mineral soil
E Horizon- leached horizon
(elluviation)
B Horizon- zone of illuviation
C Horizon – unconsolidated parent
material
R Horizon – Lithic material
(Rock)
R
Not All the Master Horizons Will Be Present in All Profiles
Mineral Soil
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Is never saturated with water for more than a few
days and contains less than 20 % (by weight) organic
carbon
Is saturated with water for longer periods or
artifically drained and excluding live roots, has an
organic-carbon content of:
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Less than 18 % if the mineral fraction contains 60% or
more clay;
Less than 12 %, if the mineral fraction contains no clays; or
Less than 12 + (clay percentage multiplied by 0.1) %, if the
mineral fraction contains less than 60%.
Soil material containing more than the above organic carbon is an organic soil.
Describing Soil Morphology
for Mineral Soil
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Soil Texture and Coarse Fragment Content
Soil Structure
Soil Color
Consistency
Redoximorphic Features
Boundaries
Soil Texture
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Describes the mineral content of the soil - Which is
typically less than 50% of the soil volume.
Soil texture is based on a weight ratio of the 3 soil
separates (sand, silt, and clay).
Material > 2mm are coarse fragments or “rock
fragments” and used as a modifier to the soil texture
term. Modifier used only when the fragments
represent more than 15 % of the soil volume.
Material < 2mm represent the three (3) soil separates.
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Sand - 2.0 - 0.05 mm - GRITTY Feel !
Silt - 0.05 - 0.002 mm – Talc – Floury Feel !
Clay - < 0.002 mm – Tends to be Sticky when Wet !
Particle Size Classification Systems
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USDA System – Soil description for agricultural, land-based
wastewater disposal, and most environmental applications.
(i.e., loam)
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AASHTO: American Association of State Highways and
Transportation Projects – potential use as road base (i.e., A-1)
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Unified Soil Classification System (ASTM D2487-92)
Engineering Applications (i.e., SM)
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Wentworth (phi #)- Geological and Geotechnical Studies
Using screen or sieve size using the phi number. (phi #, sieve
no., or mm)
Each system has unique (“jargon” or terminology)
The Systems Do Not Group the
Soil Separates the Same
USDA Particle-Size Distribution
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This is the Particle System we will use in the course.
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System is divided into: fine-earth fraction and rock fragments.
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Fine-earth fraction: Finer than 2 mm: This is the information used to describe
the soil and is the Soil Textural Class, such as sandy loam. Classification based
on weight of 3 soil separates.
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Rock fragments: 2 mm in diameter or larger. These are commonly described
as part of the coarse fragment content.
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The rock fragment modifier is based on a volumetric fraction of the soil and is
used as a soil modifier. Therefore – Gravels made up 30 % of the volume for
a sandy loam the full description would be gravelly sandy loam.
Fine-earth fraction
The Three Soil Separates
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Sand - 2.0 - 0.05 mm
Silt – 50 – 2 um
Clay - < 2 um
USDA and NRCS
Textural Classes (12)
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Sand (S)
Loamy Sand (LS)
Sandy Loam (SL)
Loam (L)
Silt Loam (SIL)
Silt (SI)
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Sandy Clay Loam
(SCL)
Silty Clay Loam
(SICL)
Clay Loam
(CL)
Sandy Clay
(SCL)
Silty Clay
(SIC)
Clay ( C)
40 % Sand
40 % Silt
20 % Clay
Sand + Silt + Clay
= 100%
Texture = LOAM
The 21 Subclasses
in Soil Texture
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There are 12 soil texture classes.
When a sand modifier is added there can be 21
total subclasses, but 22 subclasses if very
coarse sandy loam is included.
Fraction
Size (mm)
Very coarse sand.....................................2.0 to 1.0
Coarse sand.............................................1.0 to 0.5
Medium sand.........................................0.5 to 0.25
Fine sand..............................................0.25 to 0.10
Very fine sand......................................0.10 to 0.05
Soil Texture Subclasses
SANDS (5)
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Very Coarse Sand
(VCOS)
Coarse Sand (COS)
Sand (S)
Fine Sand (FS)
Very Fine Sand (VFS)
LOAMY SANDS (4)
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Loamy Coarse Sand
(LCOS)
Loamy Sand (LS)
Loamy Fine Sand (LFS)
Loamy Very Fine Sand
(LVFS)
Soil Texture Subclasses
SANDY LOAMS (4)
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Coarse Sandy Loam
(COSL)
Sandy Loam (SL)
Fine Sandy Loam (FSL)
Very Fine Sandy Loam|
(VFSL)
LOAMS (3)
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Loam (L)
Silt Loam (SIL)
Silt (SI)
Soil Texture Subclasses
CLAY LOAMS (3)
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Sandy Clay Loam
(SCL)
Clay Loam (CL)
Silty Clay Loam (SICL)
CLAYS (3)
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Sandy Clay (SC)
Silty Clay (SIC)
Clay ( C )
Using Rock Fragment Modifiers
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Divided into Spherical (cubelike) and Flat Units
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Less than 15 percent: No adjective or modifier terms are used.
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15 to 35 percent: The dominant kind of rock fragment is used as an adjective
ie. "gravelly loam”.
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35 to 60 percent: An adjective term with the word "very" is used ie. "very
gravelly loam“.
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More than 60 percent: An adjective term with the word “extremely" is used
i.e., "extremely gravelly loam."
NOTE:
> 90 %, less than 10 % soil separates it may be advisable to use the rock fragment
modifier – such as gravel.
Estimating Rock Fabric Content
How Do We
Determine Texture ?
Determination of Texture
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Field Procedure
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The “Feel” Method
Estimating Sand and Clay Content
Field Test Kit – “Volume Method”
Laboratory Procedure
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Hydrometer
Sieve
Pipette
What Texture is This Material ?
Field Determination of
Texture- The Feel Method
Method 1: The Feel Method
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Key Features or Characteristic that We Use
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Cast Formation and Stability
Feel – Grittiness, Floury, and Sticky
Ribbon Length
Evaluate Samples that are Moist, but note
characteristics when the material is dry and wet.
See “Feel of Textural Classes” in Appendix C
of the Course Documentation.
Go to this Handout
in Appendix C of the
Course Manual.
Feel Method of
Determination of Texture
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Soil must be moist, not saturated; moist
enough to mold like putty when you try to
form a ball in your hand.
Question 1: Does soil form a ball or cast?
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No - the texture is SAND
Question 2: Does the soil form a stable cast,
but does not form a ribbon
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No – the texture is loamy sand
Thank You – Dr. David Lindo (NCSU)
Soil does not form a cast:
Textural class is SAND
Feel Method of
Determination of Texture (continued)
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Question 3: Does soil form a weak ribbon less
than 2.5 cm?
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Yes - the possible textures are sandy loam, silt
loam, or loam
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Does the soil feel gritty? ------- Sandy Loam
Does the soil feels very smooth with some grittiness? -----Silt loam
Does not feel gritty or smooth? ----- Loam
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The length of the ribbon will depend on
clay content and mineralogy.
Making a ribbon
Thank You – Dr. David Lindo (NCSU)
Feel Method of
Determination of Texture (continued)
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Question 4: Does soil form a ribbon from 2.5
to 5 cm?
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Yes - the possible textures are sandy clay loam,
silty clay loam, or clay loam
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Does the soil feel gritty? ------- Sandy Clay Loam
Does the soil feels very smooth with some grittiness? -----Silty Clay Loam
Does not feel gritty or smooth? ----- Clay Loam
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Feel Method of
Determination of Texture (continued)
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Question 4: Does soil form a ribbon > 5 cm?
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Yes - the possible textures are sandy clay,
silty clay, or clay
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Does the soil feel gritty? ------- Sandy Clay
Does the soil feels very smooth with some grittiness? -----Silty Clay
Does not feel gritty or smooth? ----- Clay
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Thank You – Dr. David Lindo (NCSU)
Forms a cast of moist soil material.
Textural class is LOAMY SAND
Method 2: Estimating Sand and
Clay Content
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Collect a soil sample and remove the
observable the coarse fragments, organic
material (roots, etc), and other materials
If sample is dry, moisten the sample. Do not
over wet or completely saturate the sample.
Knead sample between your thumb and finger
and remove any other coarse fragments or nonsoil aggregates.
Crush all the soil aggregates.
Method 2: Estimating Sand and
Clay Content
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Question 1: Does the soil have more than
50 % sand?
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Yes- Therefore, the sand texture is dominant and
the likely soil textures are sandy clay loam, sandy
clay, sandy loam, loamy sand, and sand. material
(roots, etc), and other materials.
No – Therefore, the sand does not dominate and
the likely soil textures are loam, silt loam, silt, clay
loam, silty clay loam, silty clay, and clay.
< 50 %
> 50 %
Method 2: Estimating Sand and
Clay Content
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Question 2: What is the range in clay content and is
the sand content > 20 %?
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The key is ribbon length and sand percentage.
Ribbon < 1 inch long – texture does not include the word
clay. (sand, loamy sand, sandy loam, loam, silt loam, and
silt)
Ribbon 1 to 2.5 inch (clay is 27 to 40 %), the soil texture
includes the word clay. (sandy clay loam, clay loam, and
silty clay loam)
Ribbon > 2.5 inch (clay > 40%), clay is the dominant name
in the soil texture. (sandy clay, silty clay, and clay)
Ribbon > 2.5 inches
Ribbon 1 to 2.5 inches
Ribbon < 1 inch
Method 2: Estimating Sand and
Clay Content
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Combine Your Observations
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Sand content < 50 %
Ribbons 1.5 inch
Material has more of a floury feel and no real
gritty feel. Sand content is likely under 20 %
When near saturated the material is sl. sticky.
Therefore, the field evaluation would suggest that the soil has a
clay modifier. It is likely that the soil is a silty clay loam.
Method 3 – Volume Method
Used to Estimate Soil Texture
Based on a Non-Volume and
Not on a Weight Bases
This does not account for differences
in material density, but settling
rates on particle size.
Method 4 – Hydrometer Method
The Bouyoucos hydrometer method of mechanical analysis used in routine work,
where quick measurements are necessary and extreme accuracy is not required.
The method is based on the fact that water containing material in suspension has greater
density than pure water. The more material in suspension, the greater the density.
The Bouyoucos hydrometer measures the density of the suspension. The higher the
hydrometer floats, the greater the density of the suspension.
Requirements:
1) Hydrometer- reading in grams
2) Electronic Balance
3) Dry Soil – 40 to 60 grams
4) Dispersing Agent
5) Use of an Oxidizing Agent (H202)
6) 1000 ml volumetric cylinder
7) Readings at 40 seconds and 3 hours
8) Temperature Correction
Method 5 -Sieve Analysis
Particle-Size Distribution
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Particle size distribution describes the abundance (by
weight) of the various size particles that constitute the
mineral portion of soil materials.
The distribution of the size based on mm, pH #, or
sieze size is used for more detailed geological,
engineering, and geotechnical applications.
Distribution of Particles for (Sand) can be used to
estimate the permeability using the Hazen equations.
Laboratory Method
Method 6 – Pipette Method
•The pipet method utilizes Stoke's Law by the extraction of subsamples of the
soil suspension at a given depth after a predetermined settling time for each size
fraction of interest.
•As time passes, larger particles pass by the sampling depth, and smaller and
smaller size fractions can be sampled.
•After extracting the sample, it is dried weighed, and a calculation can be done to
determine the percentage of the total soil in suspension present in each sample.
• The pipet method is very accurate, but also time consuming. Pretreatment of
the sample may include the use of dispersing chemicals or oxidizing agents.
V = (2gr²)(d1-d2)/9µ (Stokes Law)
Where,
V = velocity of fall (cm sec-¹), g = acceleration of gravity (cm sec-²),
r = "equivalent" radius of particle (cm), dl = density of particle (g cm -³),
d2 = density of medium (g cm-³), and µ = viscosity of medium (dyne sec cm-²).
Time for Review ?
Review
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The three soil separates are ?
sand, silt, and clay
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Mineral Particles Greater than 2 mm are?
Coarse Fragments or Rock Fragments
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Are all soil and textural classifications the
same?
NO the classification systems are not the same !
Soil Texture
Presented by:
Mr. Brian Oram, PG, PASEO
Wilkes University
GeoEnvironmental Sciences and
Environmental Engineering Department
Wilkes - Barre, PA 18766
570-408-4619
http://www.water-research.net