Waste Rock Behavior at High Pressures: Dimensioning High Waste Rock Dumps - Multiscale Geomechanics: From Soil to Engineering Projects - page 88

4.4.3. Oedometric test results

The oedometric behavior of the ROM and the leached waste rocks is indicated in
Figure 4.4, where a good reproduction of the various test results for the stresses
applied can be noted.

4.4.3.1. Behavior under monotonic loading

Initially, for vertical stresses lower than 0.9 MPa, waste rock presents an
overconsolidated behavior with a low void ratio decrease under the applied stresses.
For vertical stresses higher than 0.9 MPa, a significant void ratio decrease takes
place, reflecting an increase in the granular skeleton compressibility and then,
finally, a void ratio variation proportional to the logarithm of the imposed vertical
stresses is obtained, similar to the normally consolidated behavior. This behavior of
granular materials has already been pointed out by many researchers on the subject
of gravels, sands and petroleum cokes [BAR 93, BIA 71, BIA 92, COL 86,
ROB 58]. Void ratios obtained after monotonous loading are reported in Table 4.2.

4.4.3.2. Behavior under constant vertical stresses

For each test, the maximum vertical stress applied was kept constant after
monotonous loading, such as after the saturation stage, until the vertical deformation
became stable. For both conditions, it could be noted that the compressibility of the
granular skeleton continues to develop and that saturation leads to a reactivation of
the deformations stabilized in the previous load increment (Table 4.2).

Δ e Δ e (one period of 30 hours)

Maximum
vertical
stress.
σ' v (MPa)

σ' v
keep up
constant and
saturation

σ' v
keep up
constant

Material

Δ e total

Monotonic
loading

4 0.144 0.014 0.019 0.177

ROM
waste
rock

8 0.179 0.010 0.023 0.212

12 0.219 0.012 0.023 0.254

4 0.162 0.019 0.022 0.203

Leached
waste
rock

8 0.210 0.015 0.019 0.244

12 0.251 0.017 0.016 0.284

Table 4.2. Oedometric tests: void ratios variation

The effect of time on the compressibility of granular materials has also been
analyzed by several researchers. For the waste rock tested, vertical deformations