It is well known that rock porosity reduces rock Young’s modulus of intact rock specimens. However, it is not well understood how different types and amount of macroporosity in forms of non-connected or isolated cavities (e.g., vesicular basalt, lithophysal tuff) or interconnected vugs (e.g., vuggy limestone) affect rock elastic properties. Such macroporosity leads to challenges in deriving engineering properties of rock. This paper compiles an existing database for porosity and Young’s modulus of macroporous rocks. The database includes Young’s modulus determined from unconfined compression testing on intact rock specimens and analogue specimens used to prepare rock-like test samples and numerical simulations of compression testing on similar materials. The database is used to develop the relationship between porosity and Young’s modulus. In addition to the porosity, the macropore shapes, sizes, locations, and proximity of a macropore to its neighboring macropore play a role in how porosity affects intact rock Young’s modulus.


Macroporosity, which is the porosity due to visible large voids or cavities, impacts mechanical properties, such as strength and Young’s modulus (E). Examples of such rocks are primarily volcanic (e.g., vesicular basalt, lithophysal tuff, lithophysal rhyolite, pumice, and scoria) and sometimes sedimentary (e.g., vuggy limestone and coquina). Engineering characterization of such rock is challenging due to macroporosity variation within the rock mass, distribution (void-to-void proximity, void alignment), and shape of the macropores (Jespersen et al., 2010; Davis et al., 2017). Preparing test specimens of standard sizes from rock cores or outcrop blocks can be difficult due to macroporosity. Obtaining a representative specimen is also challenging as the size of the macropores becomes too large to prevent large macropores from being sampled. For example, the lithophysal tuffs of Yucca Mountain, Nevada, had macropores ranging in size from approximately 1 to 50 cm, with a maximum size up to 1 m (CRWMS M&O 2000). When laboratory compression tests are carried out on these limited number of specimens, the distribution of data is typically scattered.

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