Civil Engineering Reference
In-Depth Information
Table 2.4
Quality classes for soil samples for laboratory testing (after BSI 2007)
Soil properties/quality class
12345
Unchanged soil properties
particle size
••••
water content
•
•
•
density, density index, permeability
•
•
compressibility, shear strength
•
Properties that can be determined
e f l s
•••••
boundaries of strata - broad
••••
boundaries of strata - fine
•
•
Atterberg limits, particle density, organic content
••••
water content
•
•
•
density, density index, porosity, permeability
•
•
compressibility, shear strength
•
Sampling category to be used
A
B
C
quality and C being the worst). These relate to the techniques used in the
field for obtaining the samples. For example, drive sampling, in which a
tube or a split-tube sampler having a sharp edge at its lower end is forced
into the ground either by a static thrust (by pushing), by dynamic impact
or by percussion are mostly category A or B sampling methods. Rotary
core sampling methods, in which a tube with a cutter at its lower end is
rotated into the ground, are usually category B. Auger sampling with hand
or mechanical augers are usually category C sampling methods.
Although samples are often described as disturbed or 'undisturbed', there
is no such thing as a truly undisturbed sample as the very act of retrieving
the sample from the ground disturbs it, the stress conditions are changed
for example. Hence the term 'undisturbed' is often written in parentheses
to indicate this fact. The quality of the sampling technique also dictates
how disturbed the sample is. For example a 'bagged' sample as described
above is highly disturbed.
Table 2.5
Particle size ranges
Component
Size range (mm)
Clay
0.002
Silt (fine, medium and coarse)
0.002-0.006, 0.006-0.02, 0.02-0.06
Sand (fine, medium and coarse)
0.06-0.2, 0.2-0.6, 0.6-2.0
Gravel (fine, medium and coarse)
2.0-6.0, 6.0-20.0, 20.0-60.0
Cobbles
60.0-200.0
Boulders
200.0
