ANALYSIS OF THE DEFORMATION OF SATURATED POROUS ROCKS IN COMPRESSION

An investigation of the mechanical influence of interstitial fluids on the deformation process of saturated rocks was conducted. Equilibrium equations for fluid saturated materials in which the fluid is at rest or flows according to Darcy's law were derived. For this purpose, a new characterization of porosity was proposed. This derivation indicates that the bulk material (solid plus fluid) can be represented by an equivalent homogeneous continuum for which the mass density and the stress tensor at any point depend upon average stresses and average densities of both the solid matrix and the saturating fluid as well as upon the surface and the volume porosity. When the stress-strain relationship for the solid matrix, the fluid and the saturated rock are linear, a linear equation of state for the equivalent material was derived for undrained conditions (fluid at rest). The three effective stress theories previously proposed for the analysis of elastic deformation in saturated rocks were discussed in view of these results. It was shown taht, when the linear theory applies, the classical effective stress consept, as defined by Terzaghi in 1923, can be used to determine the bulk material deformations only when the influence of a hydrostatic pressure, applied in the interconnected pore space, is negligible. The two other effective stress theories were found inadequate in the elastic domain. In the post elastic domain, two features were investigated: the disintegration process, to determine the influence of hydrostatic pressure on post elastic deformation; and the interconnected pore space variation, to analyze the possible changes of pore fluid pressure during the disintegration process. Experimental results were found to be phenomenologically in good agreement with Irwin's theory of brittle fracture. It was concluded that the disintegration process results from the simultaneous occurrence of brittle fracture mechanisms, which correspons to local energy dissipation, plastic deformation, friction along internal discontinuities and elastic deformation. Accordingly, if the existence of a hydrostatic pressure in the interconnected pore space is not associated with any significant stress concentration, does not induce any noticeable elastic deformation and does not modify the rheological properties of the solid matrix, the post elastic deformation of saturated rocks can be analyzed in terms of the classical effective stress concept. The two other effective stress theories were found to be inapplicable. /Author/

  • Supplemental Notes:
    • This report was prepared for Geology, Soils and Materials Branch, Missouri River Division, Corps of Engineers, Omaha, Nebraska
  • Corporate Authors:

    University of Minnesota, Minneapolis

    Department of Civil and Mineral Engineering, 122 Civil and Mineral Engineering Building
    Minneapolis, MN  United States  55455-0220
  • Authors:
    • Cornet, F H
  • Publication Date: 1975-7

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 290 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00127406
  • Record Type: Publication
  • Report/Paper Numbers: MRD-4-75 Tech. Rpt.
  • Files: TRIS
  • Created Date: Dec 16 1975 12:00AM