Unified Soil Classification System (USCS) Flashcards

Questions and Answers

What does the 1st letter in the Unified Soil Classification System (USCS) represent?

Type of soil

Soil moisture content

Dominant grain size (correct)

Soil color

What does the 1st letter G stand for?

gravel

What does the 1st letter S stand for?

sand

What does the 1st letter M stand for?

silt Signup and view all the answers

What does the 1st letter C stand for?

clay Signup and view all the answers

What does the 1st letter O stand for?

organic-rich Signup and view all the answers

What does the 2nd letter in the USCS mean for coarse-grained soils?

how well graded the soil is Signup and view all the answers

Define graded in the context of soil.

opposite of sorting, ie. well sorted = poorly graded Signup and view all the answers

Which grain sizes are considered coarse?

G and S Signup and view all the answers

What does the 2nd letter C indicate?

clayey Signup and view all the answers

What does the 2nd letter M refer to?

silty Signup and view all the answers

What does the 2nd letter W stand for?

well-graded clean sand/gravel Signup and view all the answers

What does the 2nd letter P represent?

poorly graded clean sand/gravel Signup and view all the answers

What does the 2nd letter mean for fine-grained soils?

whether the soil has a high or low liquid limit Signup and view all the answers

Which of the following are considered fine-grained soils?

M, C, or O Signup and view all the answers

What does the 2nd letter H indicate?

high liquid limit Signup and view all the answers

What does the 2nd letter L refer to?

low liquid limit Signup and view all the answers

Define Atterberg limits.

limits where soil moisture affects physical properties of the soil Signup and view all the answers

Define shrinkage limit.

water content below which volume doesn't change Signup and view all the answers

Define plastic limit.

lowest water content where soil behaves plastically Signup and view all the answers

Define liquid limit.

lowest water content where soil begins to flow like a liquid Signup and view all the answers

Define plasticity index and equation.

field of water content where a soil acts plastic but not as a liquid yet; PI = LL - PL Signup and view all the answers

When is the plasticity index (PI) considered high and for what types of soils?

LL > 50, clays Signup and view all the answers

When is the plasticity index (PI) considered low and for what types of soils?

LL < 50, silts Signup and view all the answers

Study Notes

Unified Soil Classification System (USCS) Overview

USCS categorizes soils based on grain size, plasticity, and other characteristics.
Designations are represented using letters to indicate soil types and properties.

Soil Types by Dominant Grain Size

G: Gravel, a coarse-grained soil.
S: Sand, another type of coarse-grained soil.
M: Silt, classified as fine-grained soil.
C: Clay, also a fine-grained soil.
O: Organic-rich soils, indicating high organic material content.

Grading and Sorting

Coarse-grained soils are assessed for grading quality.
Well-graded indicates a variety of particle sizes, while poorly graded suggests uniformity.
Grading terminology applies, where well-sorted implies a narrow size range.

Characteristics of Coarse-Grained Soils

Coarse grain sizes include gravel (G) and sand (S).
The second letter can denote grading quality:
- C for clayey coarse-grained soil.
- M for silty coarse-grained soil.
- W for well-graded clean sand/gravel.
- P for poorly graded clean sand/gravel.

Fine-Grained Soil Analysis

Fine-grained soils include silt (M), clay (C), and organic-rich (O).
Evaluated based on liquid limits:
- The second letter indicates if the soil has a high (H) or low (L) liquid limit.

Atterberg Limits

Define plasticity and behavior of soils under varying moisture:
- Shrinkage Limit: Moisture level below which soil volume remains unchanged.
- Plastic Limit: Minimum moisture for soil to exhibit plastic behavior.
- Liquid Limit: Minimum moisture at which soil flows like a liquid.
Plasticity Index (PI): Represents the moisture range where soil behaves plastically but not as a liquid.
- Formula: PI = Liquid Limit (LL) - Plastic Limit (PL).

PI Variations and Soil Types

High PI (>50) correlates with clay soils characterized by significant plasticity.
Low PI (<50) associated with silts, indicating lower plasticity levels.

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Description

Test your knowledge of the Unified Soil Classification System (USCS) with these flashcards. Each card presents a letter and its corresponding meaning related to soil properties. Perfect for students and professionals in geology and civil engineering.