Factor A

The stability graph method’s factor A, also known as the “Rock Stress Factor” was initially designed to replace the “Stress Reduction Factor” in Q (1974) [1].

Depending on which version of the “Stability Graph Method”, factor A can be calculated differently.

Anyhow, all methods share the same way of estimating the maximum Tangential Induced Stress acting on a wall.

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References

[1]

N. Barton, R. Lien, and J. Lunde. Engineering classification of rock masses for the design of tunnel support. Rock Mechanics, 6(4):189–236, 1974. doi:10.1007/BF01239496.