A Closer Look at Prevailing Civil Engineering Practice - European ...

A Closer Look at Prevailing Civil Engineering Practice, What, Why and How
Vincent T. H. CHU
Chapter 9. Site Investigation
1. What is the difference between Dynamic Probing and Standard
Penetration test
Standard Penetration Test (SPT) is an in-situ dynamic penetration test to
provide information on the properties of soil. It may also collect a disturbed
soil sample for grain-size analysis and soil classification. SPT involves the
driving of a standard sampler through a distance of 450mm into the bottom
of a borehole using the standard weight of 63.5kg falling through 760mm.
Dynamic Probing Test as per BS1377: Part 9: 1990 involves the driving of
a metal cone into the ground through a series of 1-metre length steel rods.
These rods are driven from the surface by the hammer system on the rig
which drops 63.5 kg weight onto the rods through a fall of 760mm. The
number of blows that is required to drive the cone down each 100mm
increment is then recorded until a required depth is reached or a refusal is
achieved. Dynamic Probing has many applications. For instance, it may be
used to estimate the depths of at the interface between hard and soft strata
and to trace the outline of objects buried underground.
SPT test is used to provide valuable information on soil properties.
However, the main use of dynamic probing is to interpolate information
between boreholes/trial pits swiftly and to supplement information found
from boreholes and trial pits at a low cost. For instance, dynamic probing is
carried out close to a borehole where the underground conditions are
identified. As such, by using the dynamic probing, the result of borehole
can be extended to other areas in between two boreholes.
2. What is the difference between trial pit, trial trench and inspection
pit
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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