Page 159 - Geotechnical Engineering Soil and Foundation Principles and Practice

Particle Size and Gradation
154 Geotechnical Engineering

Table 7.3 Sieve number Weight percent retained Weight percent finer
Mechanical analysis (particle diameter in mm) on each sieve
data and
Sieve analysis:
determinations of
No. 4 (4.76) 0 100
weight percents finer
No. 10 (2.0) 4 100 – 4 ¼ 96
than sizes indicated No. 20 (0.84) 4 96 – 4 ¼ 92
No. 40 (0.42) 3 92 – 3 ¼ 89
No. 60 (0.25) 7 89 – 7 ¼ 82
No. 100 (0.147) 4 82 – 4 ¼ 78
No. 200 (0.075) 13 78 – 13 ¼ 65
Sedimentation analysis:
(0.025) Hydrometer reading ¼ 52
(0.010) ‘‘ 31
(0.005) ‘‘ 21
(0.001) ‘‘ 8

1/2
is defined as (D 75 /D 25 ) . A more complicated calculation also may be made to
obtain a statistical standard deviation.

7.5.3 Example of Mechanical Analysis

Measurement of soil particle sizes is called a ‘‘mechanical analysis.’’ Data from a
mechanical analysis are shown in Table 7.3.

The percent 0.002 mm clay is estimated from eq. (7.4), which gives
D 002 ¼ 0.4 8 þ 0.6 21 ¼ 16 percent finer than 0.002 mm. The various size
grades are as follows:
Size grade Calculated percent by weight
Gravel (retained on No. 10 sieve) 4
Sand (retained on No. 200 minus % gravel) (100 – 65) – 4¼ 31
Silt (coarser than 0.002 mm minus % gravel and sand) (100 – 16) – 4 – 31¼ 49
Clay (finer than 0.002 mm) 16
Colloidal clay (finer than 0.001 mm) (8)
Total
100

7.5.4 Granular vs. Fine-Grained Soils

Concrete mixes are designed based on a concept that largest particles are
touching, and progressively finer particles fill in the voids. The same concept
applies to soils, and a broad range of particle sizes is considered to be ‘‘well

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