The results of overcore stress determinations and stratascope observations in the roof of the Colony Pilot Mine are presented and compared with results from numerical calculations. These results show compressive stresses in all horizontal directions and imply that movement has occurred on one or more bedding separations. Numerical modeling was used to simulate the roof behavior at the Colony Mine; the primary modeling'' technique used was a displacement discontinuity model developed by Crouch. To match the analytical results with the field measurements the structural model of the roof was perfected by varying the location and properties of the bedding separations as well as the regional stress field. Reasonable agreement between field and analytical results were obtained, using five bedding separations. A comparison with elemental beam theory is made, and the implications of applying the numerical analysis with the selected structural model to the design of roof spans in a prototype oil shale mine are discussed.
The Colony Pilot Mine is located in the Piceance Creek Basin in northwestern Colorado, approximately 250 miles west of Denver. Mining was conducted by the room-and-pillar method over a period of eight years, and an extensive rock mechanics program was carried out during the latter periods of mining. Operations ceased in 1972, but some geotechnical work has been conducted since then by the current Colony participants - Atlantic Richfield Company(Operator) and Tosco Corporation. Some of this work has been previously reported by Agapito, 1974 (1) and Agapito and Page, 1976 (2). Selection of appropriate roof spans is an important part of mine design since spans have a significant impact on resource recovery and productivity.
Roof Conditions and Stratascope Observations The mine roof is located at a natural parting that extends throughout the mine.