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Flashcards in soil classification Deck (14):

3 Types of soil classification systems: Wentworth scale

Used for classification of sediments and sedimentary rocks -- clastics -- see chart on hand out


3 Types of soil classification systems: engineering classifications of soils

chart eg. 80% gravel, 20% sand (sandy gravel. gravel, some sand)


3 Types of soil classification systems: U.S department of agriculture soil classification system

loam is apprx. equal portion of silt, sand and a smaller fraction of clay. (soil triangle)


3 Types of soil classification systems: Unified soil classification system

Universally accepted. See chart


Describing soils in the field. field descriptions of soils should include:

a) main sediment type: eg. Gravel, written first

b) minor components: gravel

c) Colour, adj. (lt, med, dk) or reds/browns

d) moisture content: dry, moist, wet (saturated)

e) consistency: soft, stiff, hard

f) density: coarse grained soils only eg. loose to dense

g) geological origin: fluvial, glacial till

h) foreign material: concrete, barrels, wood

i) odour: hc

j: presence of contaminants


Jar test

sand, silt, mud. measure and divide by total


Lab analysis of coarse grained soils

sieve analysis.


Hydrometer analysis

for fine grained soils.


Particle size distribution curves

graphical display of sieve and hydrometer tests


Lab analysis of fine grained soils

Classification based on grain size and plasticity. cohesive consistency due to presence of clays.


Atterberg method

used to describe the consistency of fine grained soils


Plastic limit (PL)

moisture content (%) of a soil at which it will crumble when rolled into 3.2 mm diameter threads


Liquid limit (LL)

moisture content (%) of a soil required to close a distance of 0.5" along the bottom of a grove after 25 blows


Plasticity index (PI)

PI= LL-PL see plasticity chart