The water contents that correspond to

the boundaries between the states of

consistency.

Almost like a phase change but not as

abrupt, these states change gradually. A

specific testing method provides an

arbitrary value to mark as the limit in

order to establish consistent

comparisons.

We can not properly classify a soil on grain size distribution alone (sieve analysis)

USCS uses sieve analysis and AtterbergLimits

Mechanical and physical properties of soil may change with moisture

Atterberg Limits allow us to classify the plasticity and compressibility of the soil.

Atterberg limits use the portion of the soil passing the #40 sieve.

The soil samples are usually completely

disturbed and remolded. Thus the

structure/fabric of the fines are altered

(usually made weaker) and the behavior

from the field (in situ) will change some.

Atterberg Limits still provide useful

information, but how a sample was

retrieved must be always considered.

From increasing moisture content:

Shrinkage Limit- solid to semi-solid state,

increase in volume starts

Plastic Limit semi-solid to plastic state

Liquid Limit- plastic to liquid state

Increase in moisture content decrease

the strength of fines (all things being =).

(Empirical)A- line separates

inorganic clays from

inorganic silts

U-Line is approximatelythe upper limit of the

relationship of the PI to LL

for any currently know

soil Plasticity and

compressibility increase as

you move up and right on

the chart

Used for LL testing

Calibrate a 10 mm cup fall height

Place a moist soil pat into the cup with a uniform thickness of 8 mm

Use the cutting tool to cut a trench 2 mm wide at the bottom and 11 mm wide at the top through the soil pat

Count the blows required to cause a 12.5 mm (1/2) long closer in the trench

Must have at least 3 data points between 15 and 30 blows

LL is the water content at which 25 blows achieves the 12.5 mm closer, may interpolate

British Standard to determine LL

Uses a 80 g cone, 35 mm in length, with an apex angle of 30

Placed with tip just touching soil surface of a 55 mm diameter and 40 mm high soil sample.

Allowed to push into soil for 5 seconds

3 trails needed(start with low water content)

LL is the moisture content where the cone falls 20 mm into the soil in 5 seconds

Moisture content at which a thread of

soil will just crumble when rolled to a

diameter of 3.2 mm (1/8 in.)

See handout