The methodology used for the laboratory measurements of the heat capacity and diffusivity of the rocks interesting a mine having an anomalous terrestrial gradient is presented, explicating the necessity to extend the research to some in situ determination both of the diffusivity and of the surface heat transfer coefficient. A comparative analysis of the values obtained in situ and in laboratory, on different scale, and some correlations between thermal characteristics and physical and texture properties of the examined rocks are attempted and conclusions are outlined about the influence of the measurement precision in forecasting the thermal regime of the mine.
Investigation on thermal properties of rocks may have some interest both for geophysical problems and for exploitation of deep and hot mines, as well as for geothermal power production and thermal comminution. As the authors measured these properties in connection with some climatization problems of Campiano mine (Tuscany, Italy - see Ref.1971) where terrestrial temperature gradient is higher than usual and rocks can be studied as deep formations from several point of view- they discuss the meto dology and related experimental values.
Rocks are typical materials, where often solid, liquid and gaseous phases can be coexist and anisotropy influences physical parameters: therefore it is necessary for rock investigation purposesto develop special essays or to modify the existing methods, evaluating moreover the results in a statistical way. Two thermal properties are generally con sidered: heat capacity and conductivity (or related diffusivity); in mine climatization problems the surface heat coefficient is al so required. In this research heat capacity (C) was determined with a Regnault calorimeter (the accuracy was 0.01 °C for temperature and 0.01 g for mass measurements); repeatibility was estimated into the second decimal figure. Conductivity depends upon temperature and can be influenced by porosity, fluid content and fissuration; it can be measured by steady or variable state experiments, directly or through the correlated diffusivity (a = λ/C). The former methods are considered more accurate, but less expeditive; accuracy of temperature measurement must be 0.01–0.1 for high precision or technical purpose respectively. The known experimental methods for conductivity measurement were analysed in connection with the characteristics of the Campiano rocks: finally we resorted to two procedures, not too complex nor expensive, that might satisfy the operational features of the research. Method (1) is more suitable for poor conductors (i.e. gangues): a rock disc R (fig. 1a), 50 mm in diameter and 10 - 20 mm thick, is pressed between a copper plate H, that acts as a heat source (its temperature To is mantained constant by a water flux, circulating from a thermostatic apparatus) and a copper cylinder P that acts as a heat sink. The rock disc and the cylinder are thermically insulated by a cork jacket J.
The error sources of the above described tests derive from the following causes.
