A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
3. How to identify sand and clay from the results of Cone Penetration
Testing? (SI2)
Cone Penetration Testing measures the pressure at the end of cone (end
resistance), friction on sleeve and pore water pressure. Friction ratio is
defined as the ratio of friction/end resistance.
For clay, typical CPT results exhibit low end resistance, high friction ratio
and high pore water pressure.
For sand, typical CPT results exhibit high end resistance, low friction ratio
and low pore water pressure.
4. What is the application of Continuous Piezocone Penetration Test?
(SI2)
Continuous piezocone penetration test basically consists of standard cone
penetration test and a measurement of pore water pressure. Three main
parameters, namely sleeve friction, tip resistance and pore water pressure
measurement are measured under this test.
Pore water pressure generated in the soils during penetration of the cone
is measured. An electrical transducer located inside the piezocone behind
saturated filter is used for the measurement. By analyzing the results of
pore pressure with depth, the stratigraphy of fine-gained soils with different
layers is obtained readily.
5. What is the difference between trial pit, trial trench and inspection
pit? (SI3)
A trial pit is used for obtaining information on the subsurface soil conditions.
It allows logging of the various soils types and soil sampling. Typical size of
trial pits has minimum base plan area of 1.5m 2 . Trial trench serves the
same purpose of trial pit except that they differ in size and dimension. For
instance, the length of a trial trench is normally larger than its width by a
certain factor (e.g. 5) to cater for its “trench” shape.
An inspection pit is a pit used for identifying and positioning of underground
utilities and structure.
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