Volume 30, Issue 6 (November 2007)
Influence of Membrane and Filter Paper on Plane-Strain Testing of Soft Sedimentary Rock
It is recognized that the intermediate principal stress plays an important role in the strength and the stress-dilatancy relation of soft sedimentary rock. However, few plane-strain/true triaxial experiments on soft rock have been referenced in literature due to the relatively high strength of geomaterials. With a conventional plane-strain apparatus, equipped with a prefixed plane-strain confining frame, it is difficult to obtain real isotropic consolidation before shearing. On the other hand, it has been found that the influence of the membrane/covering material on a high-strength specimen cannot be ignored. In this study, therefore, an innovative plane-strain test system for soft rock, that can overcome the shortcomings of the conventional type of apparatus, and issues related to specimen preparation are introduced. The results of drained compression tests and drained creep tests, along with theoretical simulations, are reported. The influence of the membrane and the filter paper are illustrated by a simple finite element method. A combination of experimental and theoretical approaches is employed to facilitate the understanding of the mechanical behavior of soft rock.