1 / 30

Soil Structure

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.

ayoka
Download Presentation

Soil Structure

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Soil Structure Presented by: Mr. Brian Oram, PG, PASEOWilkes UniversityGeoEnvironmental Sciences and Environmental Engineering DepartmentWilkes - Barre, PA 18766570-408-4619 http://www.water-research.net

  2. Quick Review

  3. Sand + Silt + Clay = 100% 20 % Sand 30 % Silt 50 % Clay Texture = Clay

  4. Mineral Soil • Is never saturated with water for more than a few days and contains less than 20 % (by weight) organic carbon • If saturated with water for longer periods or artificially drained and excluding live roots, has an organic-carbon content of: • 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.

  5. Why Is Understanding Soil Structure Important ?

  6. Describing Soil Morphologyfor Mineral Soil • Soil Texture and Coarse Fragment Content • Soil Structure (Type, Size and Grade) • Soil Color • Consistency • Redoximorphic Features • Boundaries

  7. What is the Soil Structure? How do we Describe Structure? What is Going On in this Photo?

  8. Soil Structure • “Structure is the naturally occurring arrangement of soil particles into aggregates (peds) that result from pedogenic processes. • The grouping or arrangement of individual soil particles into a larger grouping. The soil peds are a cluster or grouping of sand, silt, clay, organic material, biological slimes, and fungal masses. • Three general groups • Natural Soil Structural Units (pedogenic structure) • Structureless • Artificial Earthy Fragments or Clods

  9. DescribingSoil Structure • Type – shape of the structure • Size – relative size of the structure • Grade – how well the structure is 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??)

  10. Soil Structure • Type • Size • Grade

  11. Soil Structural Types • Granular • Blocky • Angular Blocky • Subangular Blocky • Platy • Wedge • Prismatic • Columnar • Massive • Single Grain

  12. Granular Small Polyhedrons or SpheroidsBounded by Curved or Irregular Surfaces Symbol for Structure (gr) Photo – Thank you Dr. Lindo - NCSU

  13. BlockySubangular 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)

  14. Platy – Flat and Tabular- Units Structure has a horizontal dimension that is longer or greater than the vertical dimension. The plates tend to parallel the surface. Typical Symbol (pl or PL) Photo on the Right – Thank you Dr. Lindo - NCSU

  15. 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- with Expanding clays. Photo – Thank you Dr. Lindo - NCSU

  16. Prismatic Structure Symbol pr or PR Photo 1 Photo 2 Typically associated with fragipan and other similar horizons. These are prismlike Structural units where the length and width is significantly Less 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. X Y Z Photo on the Left – Thank you Dr. Lindo - NCSU A soil with a prismatic structure may also have secondary structural units – Photo 2 has a platy secondary structure.

  17. ColumnarSymbol 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. Y X Z Photo on the Right – Thank you Dr. Lindo - NCSU

  18. Structureless (0) • Single Grain (non-coherent) • Massive (coherent mass) • Massive - Rock Controlled Fabric- May be a saprolite.

  19. Single GrainSymbol sg or SGR Lacks Structure- LooseOn rupture- more than 50 % of the mass is single Grain – example beach sand. Material is NON-Coherant.

  20. Massive Symbol m or MA Structureless material that is coherent, but is not cemented.

  21. Massive Rock Controlled Fabric Structureless 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

  22. E HorizonsCompacted Horizons and Bx Horizons Bx horizons

  23. Soil Structure • Type • Size • Grade

  24. Soil Structure Size • Very Fine (Very Thin) • Fine (Thin) • Medium • Coarse (Thick) • Very Coarse (Very Thick) Section of Size Criteria Depends on the Structural Units.

  25. Image Source:NRCS, Ver. 2.0, 2002 Soil Structure Size (Granular and Blocky)

  26. Image Source:NRCS, Ver. 2.0, 2002 Soil Structure Size (Platy and Prismatic)

  27. Soil Structure Grade • Structureless = 0 • Single Grain (non-coherent) • Massive (coherent) • Massive - Rock Controlled Fabric • Weak = 1 • Moderate = 2 • Strong = 3

  28. Description of Structure • Three class of grade (Excluding Structureless (0) ): • Weak (1)– the units are barely observable in place and when gently disturbed, the soil parts into a mixture of whole and broken units. • Moderate (2) – The units are well formed and evident in undisturbed soil. When disturbed, the soil material parts into a mixture of whole with some broken units. • Strong (3) – The units are distinct in undisturbed soil. They separate cleanly when the soil is disturbed and when removed the soil separates into whole units.

  29. DescribingSoil Structure • Grade – how well the structure is expressed in place. • Size – relative size of the structure. • Type – shape of the structure.

  30. Soil Structure Presented by: Mr. Brian Oram, PG, PASEOWilkes UniversityGeoEnvironmental Sciences and Environmental Engineering DepartmentWilkes - Barre, PA 18766570-408-4619 http://www.water-research.net Soils and Hydrogeological Work Jack Frost

More Related