Types and classification Flashcards
Soil Categories types (how are they defined)
Reference to size, then if size too small plasticity
Soil Categories types (how are they defined)
Reference to size, then if size too small plasticity
Clay
Clay
Silt
0.05-0.002mm - small particles of disintegrated rock - little or no plasticity, little strength when dried. Exhibits dilatancy, if shaken water moves to surface, then when motion stops goes back in.
Effect of organics on soils
detrimental effect on strength and compressibility properties of the material
Indications from colour
descriptor, but can indicat chem, biol. or physical processes. Black-org matter, red/grey - Fe, in well drained Fe is rusty brown colour. In saturated soils O2 is depleted and Fe is reduced - blue/grey
Particle shapes and sizes
angular, sub ang, sub roundd, rndd
More angular particles possess better engineering properties, i.e. higher shear strength.
Soil structure (particle arrangement)
Loose (high voids), dense (close pack, minimal void).
Coarse and silts, mass great compared surface area, thus gravity has greater effect. Clays: high surface to mass ratio are more affected by electro forces than gravity
Special Soil definition and categories
behaviour that is unusual and capable of causing problems. i.e. Collapsible soil
Define Collapsible soil
Category of soil deposits experience high decrease in volume when exposed to water. (in arid regions)
-Can be solved by flooding and using mech processes prior to construction, prevent water from reaching
Define Liquefaction
Occurs when saturated cohesionless sand deposits exist in loose condition. Vibration or shock waves cause grains to quickly move into a denser arrangement but pore water interferes and particle to particle contact is prevented.
- Cause temporary loss of shear strength (i.e. becomes viscous liquid)
- Drainage to remove saturation, or densification-compaction can solve this issue.
Index properties
indicate type and condition of the soil, provide relationship to structural properties: -strength/compressibility, -tendency for swelling/permeability.
Coarse: particle properties, compaction are most signif (others: size, size distrib, part. shape, presence of fines, density)
Fine:consistency (firm/soft), plasticity are important. (others: water content, presence/type of clays)
Particle size distrib test
Sieving: weight on each sieve converted to percentage of total sample. On semi-log paper.
Results:
-Well-graded: smooth slope accross, all sizes present
-Uniform: narrow vertical slope (little size variability)
-Gap-graded (absense of size, horizontal line in slope)
Sedimentation test (hydrometer) for silts and clays. Use hydrometer to measure density over time (deposition occurs, fines in suspension longer) Well graded is poorly sorted.
Clay
-
Silt
0.05-0.002mm - small particles of disintegrated rock - little or no plasticity, little strength when dried. Exhibits dilatancy, if shaken water moves to surface, then when motion stops goes back in.
Effect of organics on soils
detrimental effect on strength and compressibility properties of the material
Indications from colour
descriptor, but can indicat chem, biol. or physical processes. Black-org matter, red/grey - Fe, in well drained Fe is rusty brown colour. In saturated soils O2 is depleted and Fe is reduced - blue/grey
Particle shapes and sizes
angular, sub ang, sub roundd, rndd
More angular particles possess better engineering properties, i.e. higher shear strength.
Soil structure (particle arrangement)
Loose (high voids), dense (close pack, minimal void).
Coarse and silts, mass great compared surface area, thus gravity has greater effect. Clays: high surface to mass ratio are more affected by electro forces than gravity
Special Soil definition and categories
behaviour that is unusual and capable of causing problems. i.e. Collapsible soil
Define Collapsible soil
Category of soil deposits experience high decrease in volume when exposed to water. (in arid regions)
-Can be solved by flooding and using mech processes prior to construction, prevent water from reaching
Define Liquefaction
Occurs when saturated cohesionless sand deposits exist in loose condition. Vibration or shock waves cause grains to quickly move into a denser arrangement but pore water interferes and particle to particle contact is prevented.
- Cause temporary loss of shear strength (i.e. becomes viscous liquid)
- Drainage to remove saturation, or densification-compaction can solve this issue.
Index properties
indicate type and condition of the soil, provide relationship to structural properties: -strength/compressibility, -tendency for swelling/permeability.
Coarse: particle properties, compaction are most signif (others: size, size distrib, part. shape, presence of fines, density)
Fine:consistency (firm/soft), plasticity are important. (others: water content, presence/type of clays)
Classification tests
Particle size distribution (sieving)
Particle size distrib test
Sieving: weight on each sieve converted to percentage of total sample. On semi-log paper.
Results:
-Well-graded: smooth slope accross, all sizes present
-Uniform: narrow vertical slope (little size variability)
-Gap-graded (absense of size, horizontal line in slope)
Well graded is poorly sorted.
Sieving semilog calculations
D10: 10% passing size
D60/D10: uniformity quotient (Cu)
-wellgraded = Cu >10
-uniform = Cu
Define clay characteristics
from alteration of rock minerals, crystalline sheet like minerals
- develop cohesion (between sheets and H2O; surface net negative charge, edges +/-, retains water longer due to charge (can remove by vaporising))
- develop plasticity
- mineral type not size that defines a clay (non clays of
Clay structure
settling produces flocculated structure (edge to face arrangement of plates). Increased floculation in saltwater than freshwater.
- High void ration
- low density
- high water content
- Thixotropic : strength increases with age, especially after remolding.(engineering becomes safer over time)
Generally define smectite
clays that swell or shink as changes in soil water occurs. (Montmorillonite, high net - charge, high capacity for ion exchange) Very high pressure forces from swelling!
Define dispersive clays
Defloculate in still water and erode if exposed to low-velocity water (non-dispersives need high velocity to erode).
Water content and consistency/plasticity of clays
high water content = liquid properties
lesser water = plastic properties
minimal water = semisolid then solid.
- liquid limit is water content division between liquid and plastic
- plastic limit is water content division between plastic and semisolid
- shrinkage limit (vol. does not decrease w/ decrease H2O) is water content division between semisolid and solid.
Liquididity index.
Li = w% - PL%/LL%-PL% = w%-PL%/PI% w= natural water content of soil
