Absolute heat sources as a method to check the accuracy of temperature prediction in underground structures within cryolithozone

Abstract

Forecasting the thermal regime of mine workings and the surrounding rock mass is a necessary element of the design of underground structures in cryolithic zone. This is particularly necessary when substantiating and selecting reliable methods and means of rock supporting, in order to ensure safe operation of underground structures during the entire standard service life. Changes in the temperature of discontinuous permafrost rocks in the range of negative values (below the ice point in the rock) can lead to a decrease in their strength characteristics, and consequently to a decrease in the stability of workings. The aim of the research was to compare two ways of considering absolute heat sources (point sources and sources uniformly distributed along the length of a mine working) when forecasting the thermal regime in mine workings of underground structures. The dependencies used to determine temperature differences in various methods of considering absolute heat sources were established. For the sake of generality, the dependencies were produced in dimensionless (criterial) form. The variants were calculated, and the results are presented in the form of graphs. The aim is to visually present the influence of the method of heat sources when considering the accuracy of air temperature prediction in an underground facility. Key qualitative and quantitative features of the formation of thermal regime in workings at different methods of considering absolute heat sources were established. It was shown in particular that during the transition from a negative temperature in a working to a positive one, incorrect consideration of the action of absolute heat sources can lead to an almost 30 % (1.26 times) difference (i.e., error) in the calculated depth of thawing of discontinuous rocks. It was also established that at a positive temperature, when the initial air temperature in a structure is more than 7.5 oC, there is no fundamental difference in engineering calculations results depending on the method of considering of absolute heat sources.

Keywords

• underground structure
• cryolithozone
• safety
• thermal regime
• forecast
• heat source
• method of considering
• temperature