Transcript Foundation Design for The United States Penitentiary

Soil Classification
Sources:
Soil Mechanics – Laboratory Manual,B.M. DAS (Chapters 9)
Class Outlines
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Soil Classification Systems
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USCS
AASHTO
USCS Classification System
USCS Classification System
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Originally developed for the United States Army
The method is standardized in ASTM D 2487 as “Unified Soil
Classification System (USCS)”
USCS is the most common soil classification system among
geotechnical engineers
A typical USCS classification would be:
SM - Silty sand with gravel
Group
Symbol
Group
Name
Naming Convention
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Fine-grained Soil
First Letter
M – Silt
C – Clay
O – Organic
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Second Letter
L – Low plastic
H – High plastic
Coarse-grained Soil
First Letter
S – Sand
G – Gravel
Second Letter
P – Poorly graded
W – Well graded
M – Silty
C - Clayey
Classification of Soils
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From sieve analysis and the grain-size distribution
curve determine the percent passing as the
following:
 > 3 inch – Cobble or Boulders
 3 inch - # 4 (76.2 – 4.75 mm) : Gravel
 # 4 - # 200 (4.75 - 0.075 mm) : Sand
 < # 200: Fines
First, Find % passing # 200
If (5%) or more of soil passes # 200 sieve, then
conduct Atterberg Limits test (LL & PL)
Cobbles or Boulders
Grain Size Distribution Curves
GRAVEL
SAND
FINES
Classification of Soils
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If the soil is fine-grained (≥ 50%
passes #200) follow the guidelines for
fine-grained soils
If the soil is coarse-grained (<50%
passes #200) follow the guidelines for
coarse-grained soils
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Find % Gravel & Sand
Calculate Cu & Cc
Calculate LL, PL and PI
Fine-grained Soils
Coarse-grained Soils
Example – Soil A
Gravel
98-62 = 36%
Sand
62-8 = 54%
Fines = 8%
Soil A: D60 = 4.2 mm , D30 = 0.6 mm, D10 = 0.09 mm
Cu = 46.67
Cc = 0.95
Example – Soil A (Cont.)
Gravel = 36%
Sand = 54%
Fines = 8%
Cu = 46.7
Cc = 0.95
LL = 42
PL = 31
PI = 42-31 = 11
GO TO
Plasticity Chart
Example – Soil A (Cont.)
LL = 42
PL = 31
PI = 42-31 = 11
ML
Example – Soil A (Cont.)
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Soil A is then classified as
SP-SM – Poorly-grades sand with silt
and gravel