Environmental Engineering Reference
In-Depth Information
which makes it possible to keep the traditional shear strength of frictional interfaces
τ = σtgφ with:
c
⎛
⎞
σ
φφ
=
⎜
+
JRC Log
⎟
[4.6]
r
10
⎜
⎟
σ
⎝
⎠
where:
φ
r
: angle of residual friction or on smooth joint;
JRC: geometric roughness coefficient (0 < JRC < 20);
c
σ : compressive strength at the face of the joint according to alteration of the
rock
(
)
*
0.1
σ<σ <σ
rock
.
c
c
c
It must be noted that this expression of φ
takes into account an interleaving
cohesion of the joint and corresponds to a peak strength. In a mass that is already
displaced or on plane smooth discontinuities, φ
tends toward φ
γ
.
4.2.2.
Toppling
Mode d,
rather frequent in cliffs with a bedding inclination toward the interior of
the slope, favors the fall of boulders by abrupt toppling (see Figure 4.4).
Figure 4.4.
Example of cliff toppling according to [HOE 81]
