Geoscience Reference
In-Depth Information
Soil strength parameters from
classification and testing
5.1 Errors in measurement
•
The industry trend is to minimise laboratory testing in favour of correlations from
borelogs. This is driven by commercial incentives to reduce the investigation costs
and win the project.
•
This approach can often lead to conservative, but sometimes incorrect designs.
Table 5.1
Errors in measurement.
Type of error
Comment
Inherent soil variability
Sufficient number of tests can minimise this error.
Sampling error
Correct size sample/type of sampler to account for
soil structure and sensitivity in situ testing for
granular material.
Measurement error
Not all test results from even accredited laboratories
should be used directly. Sufficient number of laboratory
tests to show up “outliers''.
Understand limitation of the tests.
Validate with correlation tests.
Appreciate significant variation correlations however.
Statistical variation
Use results knowing that results do vary (Chapter 10).
Use of values appropriate to the risk and confidence
of test results.
- Clay strength is typically 50% to 100% of value obtained from a 38mm
sample. Larger samples capture the soil structure effect (refer Table 1.13).
5.2 Clay strength from pocket penetrometer
•
The pocket penetrometer (PP) is the simplest quantitative test used as an alternative
to the tactile classification of strength (Table 2.14).
•
The approximation of PP value
=
2C
u
is commonly used. C
u
(kPa)
=
q
u
/2.
However this varies for the type of soil as shown in the table.
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