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Summary

Uscs chart...

Description

UNIFIED'SOIL'CLASSIFICATION'SYSTEM' Group Symbols 3

Major Divisions

Silts and clays Liquid limit less than 50

Typical Names 4

Between 5% and 12% fines is borderline and requires dual symbols

Clean gravels (little or no fines, less than 5%) Gravels with fines (appreciable amount of fines, greater than 12%) Clean sands (little or no fines, less than 5%)

Well-graded gravels, gravelsand mixtures, little or no fines

GP

Poorly graded gravels, gravelsand mixtures, little or no fines

GM

Silty gravels, poorly graded gravel-sand-silt mixtures

GC

Clayey gravels, poorly graded gravel-sand-clay mixtures

SW

Well graded sands, gravelly sands, little or no fines

SP

Poorly graded sands, gravelly sands, little or no fines

SM

Silty sands, poorly graded sand-silt mixtures

Non plastic fines

SC

Clayey sands, poorly graded sand-clay mixtures

Plastic fines

Dilatancy Toughness *

Quick to slow

Medium to high

None to very Medium slow

CL

Slight to medium

None to very Medium slow

OL

Organic silts and organic silty clays of low plasticity

Slight to medium

Slow to Slight to none medium

MH

Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts

CH

Inorganic clays of high plasticity, fat clays

OH

Organic clays of medium to high plasticity

None

None

High

None to Slight to very medium slow

Predominantly one size or a range of sizes with some Not meeting the requirements for GW intermediate sizes missing Atterberg limits below Above “A” line with Nonplastic fines “A” line or PI less PI between 4 and than 4 7 are borderline Atterberg limits above cases and require “A” line, with PI Plastic fines dual symbols greater than 7

ML

Wide range in grain sizes and 𝐶! = !" greater than 6 !!" substantial amounts of all !!" ! intermediate particle sizes 𝐶! = !!"!!" between 1 and 3 Predominantly one size or a range of sizes with some Not meeting the requirements for SW intermediate sizes missing

Inorganic silts and very fine sands, rock flour, silt or clayey fine sands with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays

Peat and other highly organic soils * Dry strength (crushing characteristics); Dilatancy (reaction to shaking); Toughness (consistency near plastic limit) Highly organic soils

6

!

None to slight

Medium to high

Laboratory Classification Criteria

Wide range in grain size and 𝐶! = !" greater than 4 !!" substantial amounts of !!" ! intermediate particle sizes 𝐶! = !!"!!" between 1 and 3

GW

Dry strength

High to very high

Field Identification Procedures 5

!

Sands with fines (appreciable amount of fines, greater than 12%)

Sands (more than half of coarse fraction is smaller than No. 4 sieve size.)

Gravels (more than half of coarse fraction is larger than No. 4 sieve size.)

2

Silts and clays Liquid limit greater than 50

Fine grained soils more than half of material is smaller than No. 200 sieve size

Coarse grained soils more than half of material is larger than No. 200 sieve size.

1

Pt

Atterberg limits below Above “A” line with “A” line or PI less PI between 4 and 7 than 4 are borderline Atterberg limits above cases and require “A” line, with PI dual symbols greater than 7

Information Required for Describing Soils 7 Give typical name: Indicate approximate percentage of sand and gravel, maximum size, angularity, surface conditions, and hardness of the coarse grains; local or geologic name and other pertinent descriptive information, and symbol in parentheses. For undisturbed soils add information on degree of stratification, degree of compactness, cementation, moisture conditions, and drainage characteristics. Example: Silty sand gravelly, about 20% hard angular gravel particles ½ in. maximum size; rounded and subangular sand grains, coarse to fine; about 15% non plastic fines with low dry strength; well compacted and moist in place; alluvial sand (SM)

Give typical name, indicate degree and character or plasticity, amount and maximum size of coarse grains, color in wet conditions, odor (if any), local or geologic name, and other pertinent descriptive information and symbol in parentheses. For undisturbed soils add information on structure, stratification, consistency in undisturbed and remolded states, moisture and drainage conditions. Example: Clayey silt, brown, slightly plastic; small percentage of fine sand; numerous vertical root holes; firm and dry in place; loess (ML)....