Stability Analysis of Shafts Used for Minewater Heat Recovery

Traditional heating using non-renewable energy resources contributes up to 50% of current carbon emission level. Different sources of renewable energy are being exploited and developed to lower the carbon emission level for continuity of healthy living environment. It is found that thermal energy is stored in minewater flooding abandoned mines. The minewater can be extracted through newly drilled boreholes or existing mineshafts. To ensure successful and sustainable operation, mineshafts have to be structurally stable. When the mines are abandoned, the water level tends to recover. Some of the configurations of the minewater heat recovery may change the temperature of part of the shaft wall. This research aims to provide some insight on the stability of mineshafts for minewater heat recovery through numerical sensitivity analyses on: (a) water level, (b) temperature fluctuations. In the presented research work, rock masses with different properties have been analyzed. Change in temperature is found to mainly change the static Young’s Modulus of intact rock and the joint roughness. However, the joint roughness is expressed indirectly using the Geological Strength Index, which has direct relationship with joint roughness and is used in stability analysis. It is found that an increase in water level reduces the integrity of the whole shaft. The degrees of stability deterioration are different at different depths and depend on the in situ stress state. Findings of this analyses can be assist in making a decision on the selection of the appropriate configuration for minewater heat recovery.