soil structure
DESCRIPTION
Soil Structure. 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. Quick Review. Sand + Silt + Clay = 100%. 20 % Sand. 30 % Silt. 50 % Clay. - PowerPoint PPT PresentationTRANSCRIPT
Soil Soil Structure Structure
Presented by:Presented by:Mr. Brian Oram, PG, PASEOMr. Brian Oram, PG, PASEO
Wilkes UniversityWilkes UniversityGeoEnvironmental Sciences and GeoEnvironmental Sciences and
Environmental Engineering Environmental Engineering DepartmentDepartment
Wilkes - Barre, PA 18766Wilkes - Barre, PA 18766570-408-4619570-408-4619
http://www.water-research.nethttp://www.water-research.net
Mineral SoilMineral Soil Is never saturated with water for more than Is never saturated with water for more than
a few days and contains less than 20 % (by a few days and contains less than 20 % (by weight) organic carbonweight) organic carbon
If saturated with water for longer periods or If saturated with water for longer periods or artificially drained and excluding live roots, artificially drained and excluding live roots, has an organic-carbon content of:has an organic-carbon content of: Less than 18 % if the mineral fraction contains Less than 18 % if the mineral fraction contains
60% or more clay;60% or more clay; Less than 12 %, if the mineral fraction contains no Less than 12 %, if the mineral fraction contains no
clays; orclays; or Less than 12 + (clay percentage multiplied by 0.1) Less than 12 + (clay percentage multiplied by 0.1)
%, if the mineral fraction contains less than 60%.%, if the mineral fraction contains less than 60%.Soil material containing more than the above
organic carbon is an organic soil.
Describing Soil MorphologyDescribing Soil Morphologyfor Mineral Soilfor Mineral Soil
Soil Texture and Coarse Soil Texture and Coarse Fragment ContentFragment Content
Soil Structure (Type, Size and Grade)Soil Structure (Type, Size and Grade) Soil ColorSoil Color ConsistencyConsistency Redoximorphic FeaturesRedoximorphic Features BoundariesBoundaries
Soil StructureSoil Structure ““Structure is the naturally occurring arrangement of soil Structure is the naturally occurring arrangement of soil
particles into aggregates (peds) that result from pedogenic particles into aggregates (peds) that result from pedogenic processes.processes.
The grouping or arrangement of individual soil particles The grouping or arrangement of individual soil particles into a larger grouping. The soil peds are a cluster or into a larger grouping. The soil peds are a cluster or grouping of sand, silt, clay, organic material, biological grouping of sand, silt, clay, organic material, biological slimes, and fungal masses.slimes, and fungal masses.
Three general groupsThree general groups Natural Soil Structural Units (pedogenic structure)Natural Soil Structural Units (pedogenic structure) StructurelessStructureless Artificial Earthy Fragments or ClodsArtificial Earthy Fragments or Clods
DescribingDescribing Soil StructureSoil Structure
Type – shape of the structureType – shape of the structure Size – relative size of the structureSize – relative size of the structure Grade – how well the structure is Grade – how well the structure is
expressed in place.expressed in place.
When described in a soil profile the full description of the structure is describe in the following order – grade, size, shape.
Such as: weak medium subangular blocky (WHAT??)
Soil Structural TypesSoil Structural Types GranularGranular BlockyBlocky
Angular Blocky Angular Blocky Subangular BlockySubangular Blocky
PlatyPlaty WedgeWedge PrismaticPrismatic ColumnarColumnar MassiveMassive Single GrainSingle Grain
GranularGranular
Small Polyhedrons or SpheroidsBounded by Curved or Irregular SurfacesSymbol for Structure (gr)
Photo – Thank you Dr. Lindo - NCSU
BlockyBlockySubangular or AngularSubangular or Angular
Subangular Blocky – the three dimensions are about the same size, but polyhedrons are subrounded. Symbol (sbk)
Angular Blocky – the three dimensions are about the same size, but edges are shape and faces appear flattened. Symbol (abk)
Platy – Flat and Tabular- Units
Structure has a horizontal dimension that is longer or greater than the verticaldimension. The plates tend to parallel the surface. Typical Symbol (pl or PL)
Photo on the Right – Thank you Dr. Lindo - NCSU
Wedge Structures
Elliptical Interlocking lenses that terminate in acute angles, bounded by slickensides. This structure is Not limited to Vertic martials or Vertisols. Symbol: WEG
Soil: Has a High Clay Content- withExpanding clays.
Photo – Thank you Dr. Lindo - NCSU
Prismatic StructurePrismatic Structure Symbol pr or PR Symbol pr or PR
Typically associated with fragipan and other similar horizons. These are prismlikeStructural units where the length and width is significantlyLess than the depth. (Vertical Structures)
These structures have flat tops or caps. Water movement tends to be associated with movement along the vertical contact between units.
A soil with a prismatic structure may also have secondary structural units – Photo 2 has a platy secondary structure.
Photo 2Photo 1
Photo on the Left – Thank you Dr. Lindo - NCSU
Z
Y
X
ColumnarColumnarSymbol cpr or COLSymbol cpr or COL
Prism-like structural units where the length of the unit in the x and y direction are much less than the z direction.
The units tend to have rounded tops.XY
Photo on the Right – Thank you Dr. Lindo - NCSU
Z
Structureless (0)Structureless (0)
Single Grain (non-coherent)Single Grain (non-coherent) Massive (coherent mass)Massive (coherent mass) Massive - Rock Controlled Fabric- Massive - Rock Controlled Fabric-
May be a saprolite.May be a saprolite.
Single GrainSingle GrainSymbol sg or SGRSymbol sg or SGR
Lacks Structure- LooseOn rupture- more than 50 % of the mass is single Grain – example beach sand.
Material is NON-Coherant.
Massive Massive Symbol m or MASymbol m or MA
Structureless material that is coherent,but is not cemented.
Massive Massive Rock Controlled Rock Controlled
FabricFabricStructureless material that is coherent,but is not cemented or weakly cemented
In this case the material contains the original apperance of the bedrock material, but lacks the strength.
Possible – Cr Horizon – Saprolite
Photo on the Right – Thank you Dr. Lindo - NCSU
Soil Structure SizeSoil Structure Size Very Fine (Very Thin)Very Fine (Very Thin) Fine (Thin)Fine (Thin) MediumMedium Coarse (Thick)Coarse (Thick) Very Coarse (Very Thick)Very Coarse (Very Thick)
Section of Size Criteria Depends on Section of Size Criteria Depends on the Structural Units.the Structural Units.
Soil Structure Size Soil Structure Size (Granular and Blocky)(Granular and Blocky)
Image Source:NRCS, Ver. 2.0, 2002
Soil Structure Size Soil Structure Size (Platy and Prismatic)(Platy and Prismatic)
Image Source:NRCS, Ver. 2.0, 2002
Soil Structure GradeSoil Structure Grade Structureless = 0Structureless = 0
Single Grain (non-coherent)Single Grain (non-coherent) Massive (coherent)Massive (coherent) Massive - Rock Controlled Fabric
Weak = 1Weak = 1 Moderate = 2Moderate = 2 Strong = 3Strong = 3
Description of StructureDescription of Structure Three class of grade (Excluding Structureless (0) Three class of grade (Excluding Structureless (0)
):):1)1) Weak (1)– the units are barely observable in Weak (1)– the units are barely observable in
place and when gently disturbed, the soil parts place and when gently disturbed, the soil parts into a mixture of whole and broken units.into a mixture of whole and broken units.
2)2) Moderate (2) – The units are well formed and Moderate (2) – The units are well formed and evident in undisturbed soil. When disturbed, the evident in undisturbed soil. When disturbed, the soil material parts into a mixture of whole with soil material parts into a mixture of whole with some broken units.some broken units.
3)3) Strong (3) – The units are distinct in undisturbed Strong (3) – The units are distinct in undisturbed soil. They separate cleanly when the soil is soil. They separate cleanly when the soil is disturbed and when removed the soil separates disturbed and when removed the soil separates into whole units.into whole units.
DescribingDescribing Soil StructureSoil Structure
Grade – how well the structure is Grade – how well the structure is expressed in place.expressed in place.
Size – relative size of the structure.Size – relative size of the structure. Type – shape of the structure.Type – shape of the structure.
Soil Structure Soil Structure Presented by:Presented by:
Mr. Brian Oram, PG, PASEOMr. Brian Oram, PG, PASEOWilkes UniversityWilkes University
GeoEnvironmental Sciences and Environmental GeoEnvironmental Sciences and Environmental Engineering DepartmentEngineering DepartmentWilkes - Barre, PA 18766Wilkes - Barre, PA 18766
570-408-4619570-408-4619
http://www.water-research.nethttp://www.water-research.net
Soils and Hydrogeological Work Jack Frost