where
    

W_t: Combination of the total vertical dead load and the reduced vertical live load

C: Basic seismic coefficient

(Note: This value shall be determined from Fig.1 for the seismic zones shown in Fig.2 using the structural period and the types of subsoil.)

I: Importance factor (See table 1)

K: Structure type factor (See table 2)

The types of subsoil
The types of subsoil are considered in selection of C — firm and soft. For the purpose of this code a structure shall be considered as being on a soft subsoil if it is located on soil deposits exceeding the following depths.

For a cohesive soil with an average undrained shear strength not exceeding. 5kg per sq.cm. (50 kPa) :  6m

Any site where the overlying soils are either cohesive with an average undrained shear strength not exceeding 1kg per sq.ca. (100 kPa) or a very dense granular material : 9m

For a cohesive soil with an average undrained shear strength not exceeding 2kg per sq.cm. (200 kPa) : l2m

For a very dense cemented granular soil : 20mn

These provisions should apply regardless of whether there are piles extending to a deeper hard layer.

Depths shall be measured from the level at which the ground provides effective lateral restraint to the building.