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Solution Procedure

The principle of calculation of rock slope stability for polygonal slip surface is shown in the following figures.

Rock Slope Scheme

The stability analysis is conducted in a sequential manner for all blocks ranging from the uppermost block to the lowest block. The stability of each block is assessed to the required factor of safety and forces acting on the next (lower) block are calculated. The lowest calculated value of stability from all blocks is given as the final stability of the rock slope.

Di is the vector representing the resultant of all the disturbing forces acting on the block i given by:

where:

Wi

-

weight of the block

Pi

-

external forces (loads) acting on the block

Ei

-

earthquake forces on the block

Ui

-

force due to water on external slip surface

Vi

-

force due to water on internal slip surface

Hi

-

force due to water above the terrain

Bi

-

anchor force on the block

Forces acting on block

where:

D

-

resultant of all external forces acting on the block

CI

-

cohesion on internal slip surface

CE

-

cohesion on external slip surface

I

-

interaction force

K

-

reaction force on external slip surface

To assess the stability of the block i the resultant force R is determined. It consists of resultant of external forces D and forces acting on the block from the previous block:

If the tensile has occurred on the external slip surface, the stability of the block against slip on the internal slip surface is assessed.

where:

Ti

-

resisting force

φi

-

angle of the internal friction on the internal slip surface

RN,i

-

normal component of R

RT,i

-

tangential component of R

CIi

-

cohesion on internal slip surface

If the external slip surface is loaded by compression, the factor of safety FS, for which the equilibrium of forces acting on the block is fulfilled, is determined. The force R, cohesion on internal and external slip surface must be in equlibrium with the reaction K and interaction force I. The inclination of forces K and I is given by φM.

The resulting value of SF, when the equilibrium on the block is fulfilled, is compared with the required factor of safety.

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