An Experimental Study on Measurement Methods of Bulk Density and Porosity of Rock Samples

摘要

Density and porosity are fundamental andimportant physical properties of rocks in various geological problems, andaffect the other physical properties. Therefore, measurements of density andporosity of rock samples are important investigation items in both geo-scienceand geo-engineering areas. Several measurement techniques of the density andporosity are available and being applied currently. To ensure the data qualityand to conduct its quality assessment, comparison of measurement results bydifferent measurement techniques is necessary since the techniques are based ondifferent principles and test procedures. In this study, we collected eighttypes of rock samples including a gabbro, a granite, four sandstones, a weldedtuff and a mudstone as study materials, and also prepared several metalspecimens for the experimental comparison. The porosities of the eight rockscovered a very wide range from 0.3% to 50% approximately. We employed threemethods (caliper, buoyancy and helium-displacement pycnometer) to measurevolumes of regularly-shaped specimens and to determine their bulk densities andporosities. As a result, the three techniques yielded almost same bulkdensities and porosities for all the specimens. In addition, we also appliedmercury intrusion porosimetry to measure density and porosity as well as todetermine pore size distribution of the rock samples. Porosity values obtainedby the porosimetry method were underestimated in the case of high-porosity(soft) rock samples and overestimated for the very low-porosity rock samples.Ability to determine pore size distribution, however, is a very importantadvantage of the porosimetry method.