Correlation between volumetric strain and porosity in saturated limestones

Porosity and permeability are two of the most important parameters regarding the knowledge about how rock masses are affected in terms of their geology and physical and mechanical behavior, whether in Mining or Petroleum Engineer. This matter is quite debated in both theoretical and practical studies. Laboratory analysis about the influence of different stress states in both porosity and permeability is a recurrent method to study, in a more profound way, what causes changes in these properties’ behavior and what are the consequences it brings to rock masses. This work involves triaxial testing under drained and undrained conditions in saturated limestones from Serra de Aire e Candeeiros. The specimens were submitted to anisotropic stress states of 20-40 MPa of deviatory stress with confinement stresses of 10, 20 and 30 MPa. During the tests, pressurized water was introduced (about 33% of confinement stress). The properties measured during the laboratory tests were deviatory stresses, axial, horizontal and volumetric strains, pore pressure, changes in porosity and permeability. It was concluded that the measured parameters show correlations between themselves which are worthy of being mentioned, namely with deviatory stress and volumetric strain.

The laboratory tests subjected saturated limestones specimens to variable triaxial stress states under drained and undrained conditions, while simultaneously measuring the main properties of interest in the mechanical characterization of the selected geological formation. These properties of interest relevant to the study were deviatory stresses, axial, horizontal and volumetric strains, pore pressure, changes in porosity and permeability.