Complex load response of a dry, highly porous tuff

Results from an experimental study to define the mechanical properties of a highly porous (42% porosity) tuff are described in this paper. The property requirements were defined by a model for compaction of wet porous solids, recently proposed by Drumheller, which shows that prediction of wet rock response requires characterization of the elastic constants and inelastic deformation of the same rock in the dry condition. A secondary objective in fulfilling this requirement was to characterize the material with as few tests as possible by increasing the complexity of the test methods. The principal result from the investigation was development of a functional relationship between values for the elastic constants and the porosity. This correlation defines the change in elastic constants with inelastic compaction, for wave propagation analysis, and can also be used to estimate elastic properties of tuffs with different initial porosity values. Our ability to relate stress induced changes to unstressed states with different porosity values is new. Elastic constant values for various states of compaction can now be estimated for a mineralogically similar porous rock with a different initial porosity. Our new approach requires an absolute minimum of laboratory results, thus reducing the need for a large, costlymore » testing program. Analysis of the inelastic parts of the compaction tests confirmed the applicability of mathematical forms used by Drumheller to describe hydrostatic loading and unloading. A strong relationship between shearing and work hardening during compaction was also observed, that made increases in deviatoric stresses highly dependent on the loading history of the rock.« less