Engineering Rock Mechanics

Questions and answers: rock mechanics interactions and rock engineering systems 24 1

Plot the 20 parameters using C-E axes, and hence determine

for the natural slope system which three parameters are the most

interactive, which three are the most dominant, and which three are

the most subordinate.

A14.9 The parameters are plotted in C-E space below. Note that,
although the maximum possible (C, E) parameter co-ordinates in this
example are (19 x 4, 19 x 4) = (76,76), it has not been necessary to extend
the axes beyond (60,60).

5. Freeze and thaw


6. Previous instability


7. Intact rock strength


8. Mechanical properties


9. Rock mass strength


10. Hydraulic conditions


11. Slope orientation


12. Slope dimensions


13. In situ stress


14. Potential instability

• interactive

0 10 20 30 40 50 60

cause

The most interactive parameters are those with the highest C + E val-

ues. The three most interactive parameters are: P6, Previous Instability,

with C + E = 64; P20, Potential Instability, with C + E = 60; and P3,

Faults, with C + E = 55. Parameters with higher C + E values plot

further away from the origin along the direction of the main diagonal

from (0,O) to (60,60).

Dominant parameters have positive C- E values because their C value

is greater than their E value, i.e. they have a greater effect on the system

than the system has on them. The three most dominant parameters are:

P3, Faults, with C - E = 49; P2, Folds, with C - E = 30; and P1, Geology,

with C - E = 19. Dominant parameters, having a positive C - E value,

will plot to the right of the main diagonal.

Subordinate parameters have negative C - E values because their

E value is greater than their C value, i.e. they are affected more by

the system than the system affects them. The three most subordinate

parameters are: P20, Potential Instability, with C - E = -60 (this para-

meter was introduced originally as the purpose of the study); P15, Rock

Mass Strength, with C - E = -31; and P6, Previous Instability, with

C - E = -20. Subordinate parameters, having a negative C - E value,

will plot to the left of the main diagonal.