Possibilities of oil shale mining under the Selisoo mire of the Estonia oil shale deposit

摘要

The paper presents results of the study on oil shale mining (Estonia underground mine) possibilities under the Selisoo mire. The Selisoo area is 2,051 ha in extent, and most of the mire is in natural state. Peat layer consists of thick (4.4-6.5 m) oligotrophic peat. Mining under Selisoo will go at depths 65-70 m under the surface. The mining field of the Estonia mine was planned between Ahtme and Viivikonna fault zones. The lowest hydraulic conductivity of carbonate rocks 0.11 1/day per m~2 is found in the Oandu layer and for peat it is 0.35-0.0002 m/day. Therefore, together they form a good aquitard. When the annual rainfall amount is the highest, the difference between horizontal water inflow and runoff is positive with 127,000 m~3. Positive water balance is guaranteed in case of precipitation being at least 540 mm/year. The positive water balance is important for preserving the ecological system of Selisoo mire. For guaranteeing long-term stability of mine pillars, a new calculation method has been elaborated, based on the conventional calculation scheme, where the factor of safety is more than 2.3. Rheological processes are out of question, collapse of the pillars is impossible. Stability of the underground constructions and overburden rocks must be "eternal". The criteria were elaborated for oil shale mining and will guarantee preservation of mires in natural or close to natural state.