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Geotechnical Engineering I: Classification of Soils | CEG 4011, Lab Reports of Civil Engineering

Material Type: Lab; Class: Geotechnical Engineering I; Subject: Civil Geotechnical Engineering; University: Florida International University; Term: Unknown 1989;

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03- Classification of Soils
*01. Determine the percentage of each of the four grain sizes.
*02. Coefficients of uniformity and curvature of granular soils.
*03. Classify two soils using the USCS.
*04. Manufacturing a “new” soil from two unacceptable soils.
*05. Use Casagrande A-chart to classify a soil via USCS.
*06. Identify a very highly plastic soil.
*07. Find the Activity number of a clay.
*08. Classify a soil comparing USCS with AASHTO.
*09. Classify a soil comparing USCS with AASHTO.
*10. Classify five soils using both USCS and AASHTO.
*11. Find the fine’s portion particle size with a hydrometer.
*12. Using a hydrometer to classify the fines portion of a soil.
*13. Compare the relative density versus the relative compaction.
**14. Find the range of relative densities Dr for a granular soil.
**15. Relative densities of quartzitic versus calcareous sands.
**16. The theoretical minimum voids ratio of uniform sand.
Symbols for the Classification of Soils
Cc Coefficient of curvature (also known as coefficient of gradation).
Cu Coefficient of uniformity.
RC Relative compaction.
Dx Diameter of the grains (at % finer by weight).
Dr Relative density of a granular soil.
e Voids ratio.
emin Minimum voids ratio.
emax Maximum voids ratio.
IP Index of plasticity (also referred to as PI, plasticity index).
K Constant of the yield value.
LL Liquid limit.
PL Plastic limit.
SL Shrinkage limit.
V Volume of the soil sample.
W Weight of the soil sample.
γd(min)Dry unit weight in loosest condition (voids ratio emax).
γd In-situ dry unit weight (voids ratio e).
γd(max)Dry unit in densest condition (voids ratio emin)
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03- Classification of Soils

*01. Determine the percentage of each of the four grain sizes.

*02. Coefficients of uniformity and curvature of granular soils.

*03. Classify two soils using the USCS.

*04. Manufacturing a “new” soil from two unacceptable soils.

*05. Use Casagrande A-chart to classify a soil via USCS.

*06. Identify a very highly plastic soil.

*07. Find the Activity number of a clay.

*08. Classify a soil comparing USCS with AASHTO.

*09. Classify a soil comparing USCS with AASHTO.

*10. Classify five soils using both USCS and AASHTO.

*11. Find the fine’s portion particle size with a hydrometer.

*12. Using a hydrometer to classify the fines portion of a soil.

*13. Compare the relative density versus the relative compaction.

**14. Find the range of relative densities Dr for a granular soil.

**15. Relative densities of quartzitic versus calcareous sands.

**16. The theoretical minimum voids ratio of uniform sand.

Symbols for the Classification of Soils

Cc → Coefficient of curvature (also known as coefficient of gradation). Cu → Coefficient of uniformity. RC→ Relative compaction. Dx → Diameter of the grains (at % finer by weight). Dr → Relative density of a granular soil. e→ Voids ratio. emin → Minimum voids ratio. emax → Maximum voids ratio. IP → Index of plasticity (also referred to as PI, plasticity index). K→ Constant of the yield value. LL→ Liquid limit. PL→ Plastic limit. SL→ Shrinkage limit. V→ Volume of the soil sample. W→ Weight of the soil sample. γd(min) Dry unit weight in loosest condition (voids ratio emax ). γd In-situ dry unit weight (voids ratio e ). γd(max) Dry unit in densest condition (voids ratio emin )

The Unified Soils Classification System:

GROUP SYMBOLS TYPICAL NAME 1 3 4 GW

Well-graded gravels & gravel- sand mixtures, little or no fines GP

Poorly-graded gravels & gravel- sand mixtures, little or no fines GM Sitly gravels, gravel-sand-siltmixtures

GC Clayey gravels, gravel-sand-claymixtures

SW

Well-graded sands & gravelly sands, little or no fines SP

Poorly-graded sands & gravelly sands, little or no fines SM Sitly sand, sand-silt mixutres

SC Clayey sands, sand-clay mixtures

GROUP SYMBOLS TYPICAL NAME 1 3 4

Dry strength (crushing characteristic s)

Dilatancy (reaction to shaking)

Toughness (consistency near PL) ML

Inorganic silts, very fine sands, rock flour, silty or clayey fine sands

None to slight

Quick to Slow None

CL

Inorganic clays of low to medium plasticity gavely clays, sandy clays, silty clays, lean clays

Medium to high

None to very slow Medium

OL Organic silts & organic silty claysof low plasticity Slight tomedium Slow Slight

MH

Inorganic silts, micaceous or diatomaceous fine sands or silts, elastic silys

Slight to medium

Slow to none

Slight to medium

CH Inorganic clays of high plasticity,fat clays very highHigh to None High

OH Organic clays of medium to highplasticity, organic silts Medium tohigh very slowNone to Slight tomedium

PT Peat & other highly organic soils

MAJOR DIVISIONS

FIELD IDENTIFICATION PROCEDURES (excluding particles larger than 75mm & basing fractions on estimated weights)

Coarse

Grained

Soils

M ore

than

half of material is

larger than

No. 200

(

μm) sieve

size

SANDS

More

than

half of Coarse

Fraction

is

smaller than

No. 4

Sieve

Size

(4.75mm)

2 5

Wide range in grain sizes & substantial amounts of all intermediate particle sizes Predominantly one size or a range of sizes with some intermediate sizes missing Nonplastic fines or fines with low plasticity (for identification procedures see ML below) Plastic fines (for indentification procedures see CL below) Wide range in grain sizes & substantial amounts of all intermediate particle sizes Predominantly one size or a range of sizes with some intermediate sizes missing

Sands

with

fines

(appreciableamount of fines)

Clean

sands

(little

or no

fines)

5

FIELD IDENTIFICATION PROCEDURES (excluding particles larger than 75mm & basing fractions on estimated weights)

Identification Procedures on fractions smaller than No. 40 sieve size

Readily identified by color, odor, spongy feel, & frequently by fibrous texture

Nonplastic fines or fines with low plasticity (for identification procedures see ML below) Plastic fines (for indentification procedures see CL below)

Silt and

Clays

Liquid

Limit Less

than

50

Silt and

Clays

Liquid

limit greater than

50

Highly Organic Soils

Fine

Grained

Soils

M ore

than

half of material is

smaller than

No. 200

(

μm) sieve

size

MAJOR DIVISIONS

2

Clean

Gravels

(little

or no

fines)

Gravels with

fines

(appreciableamount of fines)

GRAVELS

More

than

half of gravel fraction

is

larger than

No. 4

Sieve

Size

(4.75mm)

For visual classifications, 5mmmay

be

used

as

equivalent to

the

No. 4

sieve

size

The AASHTO Classification table :

General Highly Classification Organic

A- Group Classiification A-1-a^ A-1-b^ A-3^ A-2-4^ A-2-5^ A-2-6^ A-2-7^ A-4^ A-5^ A-6^ A-7-5^ A- A-7- Sieve Analysis percent passing: #10 <^50 #40 < 30 < 50 < 51 #200 < 15 < 25 < 10 < 35 < 35 < 35 < 35 > 36 > 36 > 36 > 36

Characteristics of fraction passing #40: b Liquid limit < 40 > 41 < 40 > 41 < 40 > 41 < 40 > 41 Plasticity index (^) NP a^ < 10 < 10 > 11 > 11 < 10 < 10 > 11 > 11

Usual types of Fine Peat or significant sand muck constituent materials

General as Unstable subgrade

passing No. 200 sieve)

sand

Silty or clayey gravel and sand

Granular Materials (35 % or less passing No. 200 sieve) c

A-1 A-

< 6

Silty soils Clayey soils

Fair to Poor

Stone fragments; gravel and

Excellent to good

Silty-Clay Materials (more than 35 %

Types of grain-size distribution curves:

Correlation between the symbols of USCS and AASHTO

USCS AASHTO

Most Probable Possible

GW A-1-a

GP A-1-a A-1-b

GM A-1-b, A-2-

A-2-5, A-2-

A-2-

GC A-2-6, A-2-7 A-2-4, A-

SW A-1-b A-1-a

SP A-3, A-1-b A-1-a

SM A-1-b, A-2-

A-2-5, A-2-

A-2-6, A-4, A-

SC A-2-6, A-2-7 A-2-4, A-

A-4, A-7-

ML A-4, A-5 A-6, A-7-

CL A-6, A-7-6 A-

OL A-4, A-5 A-6, A-7-5, A-7-

MH A-7-5, A-

CH A-7-6 A-7-

OH A-7-5, A-

Pt A-

*Classify–02: Coefficients of uniformity and curvature of granular soils.

(Revision: Sept.-08) Determine the uniformity coefficient Cu and the coefficient of gradation Cc for soil A.

Solution: From the grain distribution curve, D 60 = 1.4 mm, D 30 = 0.95 mm and D 10 = 0.50 mm, therefore the coefficients are,

( ) ( )( )

2 2 60 30 10 60 10

U C

D mm D

C and C

D mm D D

A uniform soil has a coefficient of uniformity Cu less than 4, whereas a well-graded soil has a uniformity coefficient greater than 4 for gravels and greater than 6 for sands. Since soil A has a low value of 2.8, and it is sand, this corresponds to a poorly-graded sand (SP). Steep curves are uniform soils (low Cu ) whereas diagonal curves are well-graded soils (high Cu ). Smooth curved soils have coefficients of curvature Cc between 1 and 3, whereas irregular curves have higher or lower values. Soils that are missing a type of soil (a gap) are called gap-graded ( Cc will be less than 1 or greater than 3 for gap-graded soils). Therefore, this soil is classified as poorly-graded sand (or SP).

*Classify-03: Classify two soils using the USCS.

(Revision: Aug.-09) Use the grain-size distribution curve shown below to classify soils A and B using the USCS. Soil B’s Atterberg limits are LL = 48% and PL = 44%?

Solution:

Classify Soil A: For soil A, the distribution is G = 2%, S = 98%, M = 0% and C = 0%.

60 10

U

D mm C D mm

= = = , therefore, soil A is a poorly graded sand (SP).

Classify Soil B: For soil B, the distribution is G = 0%, S = 61%, M = 35% and C = 4%.

60 10

U 0.

D mm C D mm

= = = , therefore, soil A is very well graded silty sand (SM).

A third method to classify soil B is the combination of the plasticity chart and the flow chart, as follows:

*Classify-04: Manufacturing a “new” soil from two unacceptable soils.

(Revision: Aug.-09)

Sieve No. Grain^ Percent Finer Size (^) Soil A Soil B 4 4.750 98 100 10 2.000 92 100 20 0.850 24 100 40 0.425 7 99 60 0.250 1 94 100 0.150 0 85 200 0.075 0 67 0.030 0 48 0.020 0 41 0.010 0 27 0.006 0 19 0.002 0 12

Hydrometer Analysis

A site has an unsuitable in-situ soil A that does not

compact properly. In lieu of removing that soil A, you

have decided to improve it by mixing it with a borrow pit

soil B to produce an improved new soil C that will

compact better.

You desire a coefficient of uniformity Cu of about 100 for

the new soil C. Determine the relative percentages of

these two uniform soils A and B so that they will result in

better graded soil C. Plot your results.

The plots of soils A and B are as shown below,

*Classify–05: Use Casagrande A-chart to classify a soil via USCS.

(Revision: Aug.-09) Laboratory tests were performed on a light-brown sandy soil; the fines had a plastic limit PL = 27 % and the liquid limit LL = 35%. Classify this soil using USCS.

Sieve No. % Passing 4 98. 40 46. 200 30.

Solution: Note that the 30.0% that passed the #200 sieve are fine-grained and the remaining 70.0% are sands and gravels, but mostly sand since there is only 2% of gravels. Since IP = PI = LL - PL = 35%–27% = 8%, the A -chart indicates that the fines portion of the soil is an inorganic silt of medium plasticity. This soil could be classified as medium plasticity silty sand (SM).

*Classify–06: Identify a very highly plastic soil.

(Revision: Aug.-09)

What type of soil would have a LL = 150% and a PI = 80%.

Solution:

Determine the value of the plasticity index PI from the A-line equation, using LL = 150%, PI = 0.73( LL – 20) = (0.73) (150 – 20) ~ 95. Checking, the plasticity index PI from the U-line equation, using LL = 150%, PI = 0.90( LL – 8) = (0.90) (150 – 8) ~ 128.

Obviously, a PI = 80% and a LL = 150% falls below the A-line, and therefore the soil is a very highly plastic silt (MH). Some research indicates that this soil could also be an organic clay.

*Classify–08: Classify a soil comparing USCS with AASHTO.

(Revision: Sept.-08) Given the grain-size chart shown below, classify this soil using both USCS and AASHTO, if LL for soil = 23.2% and PL=15.7%.

Solution:

Determining the coefficients of uniformity and curvature for this soil.

Coefficient of uniformity Æ = = = 17.

Coefficient of curvature Æ = = 0.

Based on these values the soil appears to be a well graded sandy-silt, since the coefficient of

uniformity is very high (well above 6 for sands), and also, the coefficient of curvature is

almost 1 (between 1 and 3, the soil is well graded). By method of coefficients of curvature

and uniformity of the soil, it appears to be an SW as per USCS.

Classify this soil using both USCS and AASHTO.

Soil Composition is as follows: Gravel 0.0% Sand 56.8% Silt 36.9% Clay 6.3%

Using the ‘Unified Soil Classification System’ developed by Arthur Casagrande in 1948:

1. Since less than 50% pass through the #200 Sieve, the soil is ‘Coarse Grained’: **= 100 - = 100 – 43.2 = 56.8 50

  1. The soil is not a peat.
  2. = 100 - = 100 – 100 = 0 --** Æ = 0 0.5 (We now refer to Table 3.3, lecture 12

for the soil symbol).

4. Per USCS, the percentage passing the #200 sieve is more than 12 percent, and the and Atterberg limits fall in the hatched area marked CL-ML on in Figure 3.3. So, per USCS: (Well graded) SM****.

For the AASHTO soil classification we proceed as follows:

Soil is coarse grained: Soil passing #10 Sieve: 80.0 percent Soil passing #40 Sieve: 75.0 % Soil passing #200 Sieve: 43.2 %

Using the AASHTO Formula, since more than 35% passes #200 sieve:

From where GI = 0.

Flow chart we determine that the soil is an A-4 (0.359).

For the clay in the soil from the Activity formula we obtain: = 0.079/0.063 = 1.

Based on the Plasticity index: LL - PL = 0.232 – 0.157 = 0.

The clay appears to be an Illite or Horton clay.

*Classify–10: Classify five soils using both USCS and AASHTO.

(Revision: Aug.-09) Using the grain size distribution curves shown on the next page and the LL+PI shown below, classify each soil.

Solution:

Soil # 1: LL = 19, PI = 5; the curve shows G = 0%, S = 45%, M = 40% and C = 15%. USCS Classification: sandy low plasticity silt (ML). Soil passing #10 sieve = 93%; #40 sieve = 86%; #200 sieve = 55%; AASHTO Classification: A-4 (non-plastic silty soil).

Soil # 2: LL = 24, PI = 0; the curve shows G = 4%, S = 83%, M and C = 13%. USCS Classification: well graded sand (SW). Soil passing #10 sieve = 88%; #40 sieve = 38%; #200 sieve = 13%; AASHTO Classification: A-1-b (coarse sand).

Soil # 3: LL = 30, PI = 13; the curve shows G = 0%, S = 4%, M = 22% and C = 74%. USCS Classification: low plasticity clay (CL). Soil passing #10 sieve = 100%; #40 sieve = 100%; #200 sieve = 96%; AASHTO Classification: A-6 (clayey soil).

Soil # 4: LL = 55, PI = 25; the curve shows G = 0%, S = 33%, M = 45% and C = 22%. Activity A = PI / % of clay = 25/22 = 1.13 placed almost on the A-line; USCS Classification: borderline high plasticity clay (CH) (Illite). Soil passing #10 sieve = 97%; #40 sieve = 90%; #200 sieve = 67%; AASHTO Classification: A-7-6 (high plasticity clayey soil).

Soil # 5: LL = 17, PI = 0; the curve shows G = 69%, S = 23%, M and C = 8%. Cu = D 60 / D 10 = 16 mm / 0.15 mm = 107 very well graded; Cc = ( D 30 )^2 / ( D 10 )( D 60 ) = (4.3 mm)^2 / (0.15)(16) = 8 USCS Classification: well and gap-graded sandy gravel (GW). Soil passing #10 sieve = 26%; #40 sieve = 16%; #200 sieve = 8%; AASHTO Classification: A-1-a (stone fragments and gravelly soil).

Notes: The AASHTO soil classification group index GI formula is,

GI = (^) ( F 200 (^) − (^35) ) ⎡⎣ 0.2 + 0.005 (^) ( LL − (^40) ) ⎤⎦+ 0.01( F 200 − (^15) ) (^) ( PI − (^10) )

The GI is reported to the nearest whole integer. For granular soils GI = 0. If GI < 0, set to zero.

For groups A-2-6 and A-2-7 use the partial group index PGI^ =^ 0.01(^ F 200^ −^15 )^ ( PI −^10 )

The higher the PGI integer, the lower the quality of the soil as a subgrade material; the PGI has to be less than 20 for any of the groups between A-4 and A-7 (A-8 = peat).