Earthquake Analysis According to SL 203-97
Earthquake effects are in stability analysis represented by horizontal and vertical forces acting at the centers of gravity of individual soil blocks. Magnitude of these forces is related to the weight of soil blocks and is calculated using horizontal and vertical earthquake coefficients. Earthquake coefficients are depended on position gravity center of each block. Therefore the coefficients have individual and different values for each one of soil blocks. Horizontal earthquake force is always oriented out form the slope massif. Vertical force can be directed upwards or downwards, the orientation is defined by the sign of the force.
Horizontal earthquake force Ehs is given by formula:
and vertical earthquake force Evs is determined by:
importance coefficient for seismic design
comprehensive influence factor
meeting coefficient related to the influence of horizontal seismic effect
coefficient of horizontal seismic acceleration
coefficient of vertical seismic acceleration
weight of the soil block
dynamic distribution coefficient of block i
There are two types of dynamic distribution used for determining of αi value: inverted trapezoid and polygonal. Method for setting αi value could be seen at Figure.
Determination of dynamic distribution coefficient αi
Height H of the range of αi is given by points B and T. The bottom point B is the lowest point of terrain above the slip surface and the top point T is the highest point of terrain above the slip surface. Gi denotes gravity center points of individual blocks and Eih, Eiv are horizontal and vertical earthquake forces.