ABSTRACT:
The engineering and mechanical properties of macroporous rock are highly variable and exhibit considerable scatter when unconfined compressive strength or deformation modulus are plotted as functions of macroporosity. One approach to such describe such highly scattered data is to constrain them with derived upper and lower bounds. The data set for this investigation consisted of experimental data from plaster of Paris specimens containing Styrofoam macropores of various shapes and sizes. Two methods, traditional regression analysis and local regression analysis, were applied in an attempt to develop upper and lower bounds to unconfined compressive strength and deformation modulus data as a function of macroporosity . However, traditional regression analysis was not able to provide bounds to the majority of the experimental data and expected modulus behavior was not satisfactorily described. Local regression was able to provide bounds to the majority of the experimental data and could describe the expected behavior of the macroporous specimens.
1 INTRODUCTION
Rock contains both matrix material and void space. The amount of void space in rock has a considerable influence on its engineering properties. Specifically, an increase in porosity generally decreases the compressive strength and the elastic modulus of rock (Howarth 1987, Martin et al. 1994, 1995, Price et al. 1985). Porosity can be divided into two categories: microporosity and macroporosity. Microporous rocks are those containing voids too small to be seen with the unaided eye. Macroporous rocks, such as vesicular basalt, lithophysical tuff, and vuggy limestone contain voids large enough to be seen without any magnifying equipment. Studying the effects of void size and void shape on rock properties is difficult using natural rock specimens due to the inherent variability in the size and shape of the pores and defects in the mineral structure of natural rock.
