INTRODUCTION - Geotechnical Earthquake Engineering - page 2

In many cases, the tasks listed above may be required by the building code or other reg-
ulatory specifications (Chap. 14). For example, the Uniform Building Code (1997) states
(code provision submitted by the author, adopted in May 1994):

The potential for soil liquefaction and soil strength loss during earthquakes shall be evalu-
ated during the geotechnical investigation. The geotechnical report shall assess potential con-
sequences of any liquefaction and soil strength loss, including estimation of differential
settlement, lateral movement or reduction in foundation soil-bearing capacity, and discuss mit-
igating measures. Such measures shall be given consideration in the design of the building and
may include, but are not limited to, ground stabilization, selection of appropriate foundation
type and depths, selection of appropriate structural systems to accommodate anticipated dis-
placement or any combination of these measures.

The intent of this building code requirement is to obtain an estimate of the foundation
displacement caused by the earthquake-induced soil movement. In terms of accuracy of the
calculations used to determine the earthquake-induced soil movement, Tokimatsu and Seed
(1984) conclude:

It should be recognized that, even under static loading conditions, the error associated with
the estimation of settlement is on the order of 25 to 50%. It is therefore reasonable to expect
less accuracy in predicting settlements for the more complicated conditions associated with
earthquake loading.…In the application of the methods, it is essential to check that the final
results are reasonable in light of available experience.

1.2 ENGINEERING GEOLOGY

An engineering geologist is an individual who applies geologic data, principles, and interpre-
tation so that geologic factors affecting the planning, design, construction, and maintenance of
civil engineering works are properly recognized and utilized ( Geologist and Geophysicist Act
1986). In some areas of the United States, there may be minimal involvement of engineering
geologists except for projects involving such items as rock slopes or earthquake fault studies.
In other areas of the country, such as California, the geotechnical investigations are usually per-
formed jointly by the geotechnical engineer and the engineering geologist. The majority of
geotechnical reports include both engineering and geologic aspects of the project, and the
report is signed by both the geotechnical engineer and the engineering geologist.
The primary duty of the engineering geologist is to determine the location of faults,
investigate the faults in terms of being either active or inactive, and evaluate the historical
records of earthquakes and their impact on the site. These studies by the engineering geol-
ogist will help to define the design earthquake parameters, such as the peak ground accel-
eration and magnitude of the anticipated earthquake. The primary duty of the geotechnical
engineer is to determine the response of soil and rock materials for the design earthquake
and to provide recommendations for the seismic design of the structure.

1.3 GEOTECHNICAL ENGINEERING TERMS

Like most fields, geotechnical engineering has its own unique terms and definitions.
Appendix A presents a glossary, which has been divided into five different parts, as follows: