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

Chapter 5 INTERPRETATION OF SOIL PROPERTIES
5.1 INTRODUCTION
5 INTERPRETATION OF SOIL PROPERTIES
The results of the field and laboratory testing program must be compiled into a simplified
representation of the subsurface conditions that includes the geo-stratigraphy and interpreted
engineering parameters. Natural geo-materials are particularly difficult to quantify because they
exhibit complex behavior and involve the actions and interactions of literally infinite numbers of
particles that comprise the soil and/or rock mass. In contrast to the more "well-behaved" civil
engineering materials, soils are affected by their initial stress state, direction of loading, composition,
drainage conditions, and loading rate. Thus, the properties of soil and rock properties must be
evaluated through a program of limited testing and sampling. In certain cases, the soil properties
may be altered or changed using ground modification techniques.
All interpretations of geotechnical data will involve a degree of uncertainty because of the differing
origins, inherent variability, and innumerable complexities associated with natural materials. The
interpretations of soil parameters and properties will rely on a combination of direct assessment by
laboratory testing of recovered undisturbed samples and in-situ field data that are evaluated by
theoretical, analytical, statistical, and empirical relationships.
The application of empirical correlations and theoretical relationships should be done carefully, with
due calibration and verification with the companion sets of laboratory tests, to ensure that proper
site characterization is achieved. Notably, many interrelationships between engineering properties
and field tests have developed separately from individual sources, with different underlying
assumptions, reference basis, and specific intended backgrounds, often for a specific soil.
5.1.1 Reporting of Test Results
Reporting of test results (field and laboratory) are presented in two basic forms.
a. Factual Report
b. Interpretative Report
Factual Reports is a compilation of all the location plan of boreholes and test pits, borelogs, test pit
logs, test results (field and laboratory) and photographs of site investigation activities without
detailed interpretation of the test results. This report is basically presented by the S.I Contractor for
their Client.
Interpretative reports include the Factual Report as well as an interpretation of the test results by a
geotechnical engineer/ expert to be used by the designers. This report can also be prepared by the
S.I contractor by employing the services of a geotechnical engineer or it is prepared separately by
the Client employing a geotechnical engineer depending on the nature of the site investigation
contract. The interpretative report presents the interpretation of soil properties from in-situ tests
and laboratory test for the analysis and design of foundations, embankments, slopes, and earthretaining
structures in soils. Correlation of properties to laboratory index tests and typical ranges of
values are also provided to check the reasonableness of field and laboratory test results. Reference is
made to relevant established documents and standards in order to familiarize with appropriate and
more detailed directions on the procedures and methodologies, as well as examples of data
processing and evaluation.
March 2009 5-1