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Earthquake Analysis According to NB 35047-2015

Earthquake effects are in the stability analysis represented by horizontal and vertical forces acting at the centers of gravity of individual soil blocks. The magnitude of these forces is related to the weight of soil blocks and is calculated using horizontal and vertical earthquake coefficients. Earthquake coefficients are dependant on the position of the 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 the 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. The method for setting αi value could be seen in the 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.

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