Civil Engineering Reference
In-Depth Information
Amplification
due to soil
conditions
Figure 7.18
Amplification of basic spectrum: Design acceleration response at
ground surface (Gioncu, 2006, after Midorikawa et al, 2000)
7.4.3
Soil Type
The site classification scheme is based on the following parameters:
- Type of deposit (i.e. different types of rocks and soils);
- Average shear wave velocity;
- Depth of layers.
There are different types of soil classifications, but the most close to the design
requirements is due to Borcherd (1994) and Rodriguez-Marek et al (2000). The
classification of soil conditions contains five soil classes:
- Class A refers to hard rock, igneous rocks, conglomerates, sandstones,
characterized by sheare wave velocity greater than 1500 m/sec and natural
period smaller than 0.1 sec;
- Class B considers gravelly soil and soft to firm rock, characterized by shear
wave velocity greater than 750 m/sec, natural period smaller than 0.2 sec and
soil depth of minimum 10 m;
- Class C refers to stiff clays and sandy soils and clays, medium stiff to hard
clays and silt clays, with shear wave velocity greater than 350 m/sec, natural
period smaller than 0.4 to 0.8 sec, and soil depth between 6 and 60 m;
- Class D considers soft clay soils, with shear velocity greater than 200 m/sec
and soil depth between 60 to 200 m;
- Class E refers to special soft soils (liquefiable soils, highly organic clays,
very high plasticity clays and soft soils), for which special geotechnical
investigations are recommended.
A similar classification, but with some differences in required velocities, is
presented in EUROCODE 8 (Sabetta and Bommer, 2002).
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