Dear reader in our last post we have learnt that IBC classify site as Class A, Class B, Class C, Class D, Class E and Class F for earthquake design. Of these except class F, all are depend on shear wave velocity. In other building code, shear wave velocity is also important to classify site depending on soil properties.
Site class A and class B are defined as rock (soil profile), class C also include soft rock and dense soil. At first we start with site class B. it is recommended in code that shear wave velocity to measure on site.
Alternatively, seismologist/ engineering geologist or geotechnical engineer can estimate shear wave velocity on competent rock having moderate weathering and fracturing.
Site class C can be determined by determining value of shear wave velocity. But the rocks that are relatively weathered and fractured highly and also softer, we can classify them as class C.
The soil profile representing site class A is hard rock. Here also shear wave velocity is recommended to measure on the site. Alternatively, a value, measured in soil having identical soil profile of same type of rock in identical formation having a same or more fracturing or weathering condition, is recommended in code.
Dear reader in next part of this topic, we will learn about determination of shear wave velocity of soil form shear wave velocity of different layers in soil profile and additional information about site classification for earthquake design.