The heat transfer in the rock mass around mine openings is studied with reference to the Campiano Mine (Grosseto, Italy), where the geothermal gradient was measured to be approximately 0.08°C per meter depth. The following problems are considered:
Laboratory tests carried out in order to determine the thermo-physical properties of the rock.
In situ tests performed to measure the temperature distribution in the rock mass around mine openings and to evaluate the most important thermo-physical parameters of the rock mass.
Analytical and numerical modelling performed in order to interpret the in situ tests and to predict the temperature distribution in the rock mass around mine openings.
On etudie la diffusion de la chaleur dans la roche autour des vides miniers dans le cas de haut gradient de temperature (0.08°C/m) dans la mine de Campiano (Grosseto, Italie). L'etude a ete realisee par: 1) essais en laboratoire pour deduire les proprietes thermo-physiques de la roche; 2) essais in situ pour mesurer la distribution de la temperature dans la roche autour des vides miniers et d'evaluer les plus importants paramètres thermiques au niveau de la roche in situ; 3) mise au point des modèles analytiques et numeriques ayant pour but d'interpreter les essais in situ et de predire la distribution de la temperature dans la roche.
Der Warmeaustausch im Gebirge um bergmannische Hohlraume wird in Bezu auf die Campiano Grube (Grosseto, Italien) untersucht, wo der geothermische Gradient einer Temperaturzunahme von 0.08°C je Meter Tiefe - nach eigenen Messungen - zu enbsprechen scheint. Man hat deswegen die folgenden Untersuchungen durchgefuehrt: 1) Laborversuche, um die Warmeeigenschaften des Felsens zu bestimmen. 2) In situ Messungen, um die Warmeverteilung in der Umgebung von bergmannischen Hohlraumen festzustellen und die wichtigsten Warmeparameter des Gebirges abzuschatzen. 3) Analytische und numerische Modelle wurden hergestellt, um die in situ Messungen wissenschaftlich zu erklaren und um die Ternperaturverteilung um Grubenhohlraume vorhersagen zu können.
A number of very important engineering problems relate to heat transfer in rock masses. Among the most interesting examples, the following may be recalled: 1. the stabilization of rock by artificial freezing, for the purpose of excavation of wells and tunnels; 2. the industrial use of geothermal reservoirs; 3. the choice of underground spaces for radioactive waste storage; 4. the exploitation of minerals in deep mines, with high temperature conditions. With reference to the problem of evaluating the thermomechanical behavior of rock masses (i.e.) stress analysis and heat transfer of rock masses), the present state of knowledge is limited. For example, rock thermo-physical properties (e.g. thermal diffusivity and/or thermal conductivity; specific heat) are less known than mechanical properties (e.g. stress-strain laws, failure criteria, etc.). The need for obtaining additional data on rock thermo-physical properties in the laboratory and in situ is therefore well recognized. At the same time, appropriate analytical and numerical methods and solutions are to be developed for the study of heat transfer in rock masses around underground openings. This paper describes a number of problems relating to the analysis of heat transfer around underground openings in a deep mine near to Grosseto (Italy). The purpose is to obtain the basic data needed for predicting the temperature distribution in the rock mass and in the air where a mine opening is being excavated. The following problems are considered:
Laboratory tests carried out in order to determine the rock thermo-physical properties.
In situ tests performed to measure the temperature distribution in the rock mass around mine openings and to evaluate the rock mass thermo-physical parameters.
Analytical and numerical modelling performed in order to interpret the in situ tests and to predict the temperature distribution in the rock mass around mine openings.
The mineral deposit is formed of pyrite, mixed (Pb, Zn, Cu) sulphurs, and pyrite and magnetite, with a total of 25 Mt presently estimated reserve. An evaporitic series, made mostly of anhydrite with dolomites, is above the deposit, with phyllitic rocks being below. A very high geothermal gradient (approximately 0.08 °c per meter-depth) is present. It is to be noted that Campiano is located approximately 20 km away from the well known Larderello geothermal reservoirs. In addition to the high temperature of the virgin rock mass (75°C at 500 m depth below sea level, near to 800 m below ground surface), a strong influence on the temperature conditions underground is that due to the heavy mechanized systems used for excavation purposes. For the purpose of the present study, the heat transfer problem in situ was examined, mainly by considering the rock mass thermal behavior around a drift (spiral decline) of a 20 m2 cross section, created in order to reach the orebody, Fig. 2. However, in a few cases, also the openings located in the ore and neighbouring rocks were considered.
