SOILS AND ENVIRONMENT

1. SOILS AND ENVIRONMENT We can save 700 lira by not doing soil testing!

2. Introduction to Soils Definition varies with viewer • Soil scientists--altered earth materials that can support rooted plant life • Engineer--earth material that can be removed without blasting • Both perspectives are important in environmental geology

3. Introduction to Soils • Land Use • Capability • Waste Disposal – site suitability • Natural hazards • Soil Profiles • Weathering • Physical • Frost wedging • Thermal changes • Exfoliation/unloading • Organic activity Talus Frost Wedging

4. Mechanical Weathering Increase in surface area by mechanical weathering

5. Exfoliation dome

6. Weathering • Chemical Weathering • Process by which rocks are decomposedby chemical alteration (acids, water, gases) • dissolution: dissociation of solids in water • Oxidation: reactions with O2 which form oxides or hydroxides • Hydrolysis: Incorporation of water into the mineral structure. Reaction between the H+ ions and OH- ions of H20 • Carbonation-reaction of CO2 with cations

7. Weathering • Biological weathering • Roots • Lichen/moss • Organisms • Weathering of a granite • Quartz: no alteration; residual mineral • Feldspar: forms clays • Mica: forms clays

8. Chemical Weathering

9. Rates of weathering • Factors: • Particle size/surface area • Rock characteristics • Climate (temperature and moisture) • Stability of individual minerals determined by the pressure and temperature conditions under which they formed • Goldich stability series

10. Goldich & Bowen Series Goldich Bowen

11. Weathering Pyrite Oxidation and Hydrolysis-- Results in Aggregate failure in Portland Cement Concrete Stadium FeS2 + H2O Fe(O,OH)n + SO2 SO2 + CaCO3 CaSO4 X 2H20 Sidewalk

12. Soils • Residual vs. Transported • Soil Horizons • Variables • Climate • Topography • Parent material • Maturity/time • Organic activity/vegetation

13. Weathering

14. Weathering

15. Soil Horizons • Result of horizontal and vertical movement of materials • Layering parallel to the surface • Usually restricted to the upper 2 meter • May not be a good system for some parts of Florida

16. Soil Profiles – Horizon Descriptions • O or A Horizons • Highly conc. organic material • Differences are in % organics • O is the organic litter horizon • A contains more mineral matter • E Horizon • Occurs below the A or O (if present) • Has had its iron-bearing components leached; • Zone of leaching= E-horizon plus A-Horizon

17. Soil Profiles – Horizon Descriptions • B Horizon— Zone of accumulation: enriched in clays, Fe-oxide, silica, carbonate or other materials leached from overlying horizons • may be several types • Bt-argillic (enriched in translocated clay minerals) • Bk-contains carbonate layer • Bh-organic matter • K Horizon • Dominated by calcium carbonate • Soils of this type are called caliche • Typical of dry areas

18. Soil Profiles – Horizon Descriptions • C horizon--partially altered parent material • R horizon--unaltered rock horizon Soil Color--may indicate how well a soil is drained • O and A may be dark due to organic matter; may be white if leached • E if present, may be white • Bk may be white, if present • Note: color is also a factor of original parent material, and Fe-rich materials may produce red soils w/ little soil profile development

19. Soil Profiles – Horizon Descriptions B horizon usually shows most color variation well-drained = well-aerated = oxidizing = reddish color of B horizon Poorly drained = wet = more reducing conditions for Fe = more of a yellowish color

20. Soil Texture • Varies with: • Sand (0.05-2 mm) • Silt (0.05 to 0.002 mm) • Clay (below 0.002 mm) Tips: • Sand can see ind. Grains w/ naked eye. Feels gritty; crunches between teeth • Silt: can see ind. Grains w/ 10X hand lens, feels like flour • Clay, cannot see ind. Grains w/o microscope, cohesive, mix w/ water and rub on back of hand. When dry won’t dust off

21. Soil Structure Descriptions of peds(soil aggregates) Indicator of Increasing age as b-horizon content increases

22. Relative Profile Development • Degree of development indicates the age of the soil • May range from hundreds to hundreds of thousands years Soil Chronosequences • Arrangement from youngest to oldest based on profile development • Good indicator of the relative stability of an area : Important for hazards assessment. (See fig 3.4 in book)

23. Soil Fertility • Fertility • Capacity of soils to supply nutrients (N, P, K) for plant growth • Some are naturally fertile (soil developed on some glacial deposits and floodplain deposits) • Can be manipulated using fertilizers and irrigation and adversely affected by interrupting natural processes like flooding • Water in Soils: can greatly affect strength, and shrink/swell potential • Saturated-- voids are filled with water, • Unsaturated--void not filled with water

24. Soil Classification - Taxonomy • Soil taxonomy (U.S.D.A.) • Basis for classification • Chemical and physical • Genetic scheme (origin implied) • Six fold hierarchy (see Table 3.1) • Order--11 orders based on: • Morphology (# and types of horizons present) • Nutrient status • Organic content • Color • General climatic conditions

25. Soil Classification • Suborder (each step down from order gets more specific) • Great Group • Subgroup • Family • Series • Problems: • Useful for agricultural purposes • May be too complex for most applications • Lacks engineering data • Benefit: Individual county reports. County soil surveys are v. useful info sources

26. Florida SoilsMap

27. Distribution of Soils • FL is State with greatest number of orders • Diverse topography • Diverse climates

28. Engineering Properties of Soils • Unified Soil Classification System • Used by engineers and the military • Classification Parameters • Coarse textures • Size • Gradation • Fine textures • Clay content (generally minus-200 mesh, 73 mm) • Organic matter

29. 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 = clayey silt OL = organic silt CL = silty clay CH = high plastic clay OH = organic clay Clean (<5 % fines) Dirty (>12 % fines) Clean (<5 % fines) Dirty (>12 % fines) Non-plastic Plastic >50 % larger than 0.074 mm FINE-GRAINED COARSE-GRAINED Clay Silts Sands Gravels >50 % smaller than 0.074 mm Mostly Organics PT = peat and muck

30. Atterberg Limits Plasticity (related to water content) • Plasticity Index= • (liquid limit - plastic limit) • Values less than 5 • may change from a solid to a liquid easily • Values greater than 35 • may expand/contract on wetting • Proctor Density --this is a laboratory test used to determine the "ultimate" dry density and "optimum" moisture content for a soil sample. It varies with moisture content

31. Strength of Soil Soil Strength is a combination of two factors • Cohesion in fine grained a consequence of electrostatic forces (clay minerals). In unsaturated coarser–grained soils grain boundary wetting and surface tension provides cohesion (sand-castle analogy) • Can be destroyed if completely dry (low PI) • Can be destroyed if completely saturated (increased pore pressure; high PI) • Frictional forces • Grain-to-grain contact • Function of density, size and shape (roundness)

32. Engineering Properties of Soils • Sensitivity--changes in soil strength due to vibration or excavation; clays more sensitive than sand or gravel. Can lead to liquifaction. • Compressibility--tendency to consolidate or decrease volume; can cause settling. Coarse-grained ( gravels, sand) tend to be less compressible than fine • Erodibility--ease of removal by wind or water. Function of cohesiveness and degree of consolidation • Permeability--measures the ease with which a liquid moves through a material (related to porosity, but not always).Clean sand and gravels are v. permeable. Decreases w/ increasing fines. Clay v. low permeability