Soils and soil hazards Flashcards
Soil scientist purpose
interested in soils ability to support plant life
Layers of soil from pedologists view
Humus-just below surface= organics
A horizon - Zone of leaching
-rich in clay and insoluble minerals, leached of all soluble minerals
B horizon- zone of accumulation
-contains little organic matter, and abundant minerals dissolved from A horizon and re-precipitated
-fragments of weathered rock become more abundant and larger near base of B horizon
C horizon-slightly weathered parent materia;
-fractured and weathered but relatively intact bedrock
Geologist view on soil
interested in transport, deposition and reflection of geological processes
residual soil - evolve in place from weathering
transported soil- accumulate after being eroded
Engineer view on soil
interested in engineering properties
soil=anything that can be excavated with a shovel
Layers of soil from engineers view
Topsoil -incudes humus(organic matter), holds moisture adn prevents erosion
Subsoil - small rock material, often high concentrations of clay
Bedrock - where the above soil created(weathered from) or deposited onto
Expansive(swelling) soil
-high proportion of swelling clay
-generally occurs in upper part of soil profile, where repeated cycles of wetting/drying
-leads to structural damage
-tunnel buildngs can expose rocks to atmosphere and result in swelling
Soft soils
Soil with low strength and high compressibility
loading can induce signifigant settlement/failure
preloading necessary to reduce post-construction settlement and improve strength(load bearing capacity)
Examples: fine grained(silts/clays), organic(peat)
disadvantage - increased construction time
Collapsible soil
soils deposited with very open structures between soil grains (ex. wind deposited silts)
addition of water reduces volume
Hydrocompaction -tendecy for loose, uncompacted soil to compact under load when wetted
Collapsing soil-loose/weakly cemented soil subject to large settlement under load/ as a result of deteriorating of the cementing agent in presence of water
-similar to soft soil but have much larger void
Quick Clays
fine grained soil deposited in marine conditions where large amount of sodium(clay adapted to this)
if seawater replaced with fresh, clay dissolves(chemical alterations)
resulting material extremely sensitive, causing dramatic landslides
