Civil Engineering Reference
In-Depth Information
If C
u
<
4.0 then the soil is uniformly graded.
If C
u
>
4.0 then the soil is either well graded or gap and a glance at the grading curve should be suf-
ficient for the reader to decide which is the correct description.
Example 1.2:
Particle size distribution
The results of a sieve analysis on a soil sample were:
Sieve size (mm)
Mass retained (g)
10
0.0
6.3
5.5
2
25.7
1
23.1
0.6
22.0
0.3
17.3
0.15
12.7
0.063
6.9
2.3 g passed through the 63
μ
m sieve.
Plot the particle size distribution curve and determine the uniformity coefficient of
the soil.
Solution:
The aim is to determine the percentage of soil (by mass) passing through each sieve.
To do this the percentage retained on each sieve is determined and subtracted from
the percentage passing through the previous sieve. This gives the percentage passing
through the current sieve.
Calculations may be set out as follows:
Sieve size
(mm)
Mass retained
(g)
Percentage retained
(%)
Percentage passing
(%)
10
0.0
0
100
6.3
5.5
5
95
2
25.7
22
73
1
23.1
20
53
0.6
22.0
19
34
0.3
17.3
15
19
0.15
12.7
11
8
0.063
6.9
6
2
Pass 0.063
2.3
2
Total mass
115.5
e.g. sieve size 2 mm:
25 7
115 5
.
Percentage retained
=
×
100
=
22
%
.
Percentage passing
= − =
95 22
73%
