soil classification Flashcards
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
