Finite Element Programming in Non-linear Geomechanics and Transient Flow by Nobuo Morita;

Author:Nobuo Morita; [Morita, Nobuo]
Language: eng
Format: epub
ISBN: 9780323911139
Publisher: Elsevier Ltd.
Published: 2021-06-15T00:00:00+00:00

Figure 12.4 Modified Lade from Russell Ewy (Castlegate sandstone).

Figure 12.5 Modified Lade from van Eekelen (Castlegate sandstone).

Figure 12.6 Lade (Castlegate sandstone).

Figure 12.7 Failure envelope―Mohr (Castlegate sandstone).

Figure 12.8 Failure envelope―Drucker–Prager (Castlegate sandstone).

Figure 12.9 Failure envelope―Mogi (Castlegate sandstone).

12.2.2 Rozbark sandstone and sensitivity analysis

Rozbark sandstone is a very hard sandstone with 2.835% porosity. The mineral contents are: quartz=65.5%, orthoclase=2.8%, biotite=2.6%, heavy minerals=0.7%, opaque minerals=1.1%, dolomite=17.6%, illite=3.6%, and kaolinite=3.9%. The cementing mineral is the dolomite. Figs. 12.10–12.15 show the results of true polyaxial tests. The failure curves with Mohr–Coulomb, Drucker–Prager, Mogi, and Lade are compatible. Since the parameters affecting the failure are the maximum, minimum, and medium stresses in this sequence, the error sensitivity analysis is performed adding 25 psi for the maximum stress and subtracting 25 psi from the minimum stress. The highest sensitivity is shown by Mohr–Coulomb, and the lowest sensitivity is shown by Ewy’s Lade model. Drucker–Prager, Mogi, and Standard Lade models give similar sensitivity. The problem is that the Ewy’s Lade model fits any experimental data regardless of the errors included. Hence, although the fitting looks good, the model is not sensitive enough for the standard failure applications.

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