Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 2 GEOTECHNICAL DESIGN PROCESS
2.2.2 Decide on Appropriate Geotechnical Investigation
The objectives and various general details on the type of geotechnical investigation works are
described in Part 2, Volume 6 : Soil Investigation which include both field and laboratory works.
Suffice here to mention that the composition and amount of geotechnical investigation proposed
shall be able to provide sufficient data on the ground, groundwater conditions at the proposed site
and proper description of the essential soil properties for geotechnical design and construction. It
shall also be planned to take into account the construction and performance requirements of the
proposed structure.
Very often geotechnical engineer is required to determine the type of soil investigation works in
relation to the envisage analysis required in the design works, i.e. the long-term (drained with
effective stress analysis) or short-term analysis (undrained total stress analysis) conditions.
2.2.3 Interpret Geotechnical Investigation Result to Obtain Representative
Parameters/Properties
The evaluation and interpretation of geotechnical investigation work shall include a review of the
field and laboratory results to derive at the reasonable and representative parameters and
properties. This normally involves tabulation and graphical presentation of field and laboratory
results such as the range and distribution of values of the required soil parameters (including
ground water condition), subsurface strata profile which differentiate and group the various
formations and properties. Any irregularities or adverse field and laboratory results shall be pointed
out, commented upon, and if necessary to propose further geotechnical investigation for
verification. Reader should refer to Part 2 Volume 6 for more detail and comprehensive information
on this topic.
In spite of the many advances in geotechnical engineering theory, there are still many uncertainties
in the analysis and design due mainly to the highly variable, heterogeneous and anisotropic nature
of soil material. Designer normally use various investigation and testing techniques to determine the
soil conditions, however even the most thorough investigation program encounters only a small
portion of the soils and relies heavily on the interpolation and extrapolation. The most practical
approach to solve geotechnical design issues is to combine the sources of information gathered
through soil investigation and testing program, established theory developed to predict the behavior
of soils and experience obtained from previous projects coupled with sound engineering judgment.
These approaches are depicted in Figure 2.3
March 2009 2-5