Identifying soils for engineering purposes

Sample no.

Geologic origin

Unified symbol

Group name

Density (coarse fraction)

Saturated consistency of fines

Relative moisture content

Color (when moist)

Angularity (coarse fraction)

tribution by volume

Percent boulders

Percent cobbles

Particle size dis by weight

Percent gravel

Percent sand

Percent fines

Interval (feet)

Description Criteria

Angular

Particles have sharp edges and relatively plane sides with unpolished surfaces Particles are similar to angular description, but have rounded edges

Subrounded Particles have nearly plane sides, but have well-rounded corners and edges Particles have smoothly curved sides and no edges

Subangular

Rounded

Table 2 Criteria for describing particle shape (length, width, and thickness refer to the greatest, intermediate, and least dimensions of a particle, respectively)

Flat

Elongated Flat & elongated

Particles with width/thickness > 3

Particles with length/width > 3

Particles meet criteria for both flat and elongated

Table 3 Criteria for describing moisture condition

Description Criteria

Dry Absence of moisture, dusty, dry to touch

Moist Damp, but no visible moisture Wet Visible free water, usually soil is below water table

Table 4 Criteria for describing the reaction with HCL

Weak Crumbles or breaks with handling or little finger pressure Moderate Crumbles or breaks with considerable finger pressure

Strong Will not crumble or break with finger pressure

Table 6 Criteria for describing structure

Description

Criteria

Stratified Alternating layers of varying material or color with layers at least 1/4 in (6 mm) thick; note thickness

Laminated Alternating layers of varying material or color with the layers less than 1/4 in (6 mm) thick; note thickness Fissured Breaks along definite planes of fracture with little resistance to fracturing Slickensided Fracture planes appear polished or glossy; sometimes striated

Blocky Cohesive soil that can be broken down into small angular lumps which resist further breakdown Lensed Inclusion of small pockets of different soils, such as small lenses of sand scattered through a mass of clay; note thickness

Homogeneous Same color and appearance throughout

Description Criteria

None No visible reaction Weak Some reaction, with bubbles forming slowly

Strong Violent reaction, with bubbles forming immediately

Tables 1 through 11, except 7, are Copyright ASTM. Reprinted with permission.

Table7

Criteria for describing consistency

Description

Criteria for fine Grained Saturated Soils

Penetrometer

Std. penetration

tons/ft2

test (ASTM D 1586)

or kg/cm2

blows/ft

Very soft Thumb will penetrate soil more than 1 inch < 0.1 < 2

Soft Thumb will penetrate soil about 1 inch 0.10 - 0.25 2 - 4

Firm Thumb will indent soil about 1/4 inch 0.25 - 1.00 4 - 15

Hard Thumb will not indent soil, but readily indented with thumbnail 1.00 - 2.00 15 - 30

Very hard Thumbnail will not indent soil > 2.00 > 30

Table 8 Criteria for Describing Dry Strength

Table 10 Criteria for Describing Toughness

Description Criteria

Description Criteria

None The dry specimen crumbles into powder with mere pressure of handling

Low The dry specimen crumbles into powder with some finger pressure

Medium The dry specimen crumbles into powder with considerable finger pressure

High The dry specimen cannot be broken with finger pressure. Specimen will break into pieces between thumb and hard surface

Very high The dry specimen cannot be broken between thumb and hard surface

Low Only slight pressure is required to roll the thread near the plastic limit. The thread and the lump are weak and soft.

Medium Medium pressure is required to roll the thread near the plastic limit.

High The thread and the lump have medium stiffness. Considerable pressure is required to roll the thread to near the plastic limit. The thread and the lump have very high stiffness

Table 11 Criteria for Describing Plasticity

Table 9 Criteria for Describing Dilatancy

Description Criteria

Description Criteria

None No visible change in the specimen

Slow Water appears slowly on the surface of the specimen during shaking and does not disappear or disappears slowly upon squeezing

Rapid Water appears quickly on the surface of the specimen during shaking and disappears quickly upon squeezing

Nonplastic A 1/8-in (3-mm) thread cannot be rolled at any water content

Low The thread can barely be rolled and the lump cannot be formed when drier than the plastic limit

Medium The thread is easy to roll and not much time is required to reach the plastic limit; thread cannot be rerolled after reaching the plastic limit; lump crumbles when drier than the plastic limit

High Considerable time rolling and kneading to reach the plastic limit; thread can be rerolled several times after reaching the plastic limit; lump can be formed without crumbling when drier than the plastic limit

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