1991 Volume 107 Issue 7 Pages 461-466
In an abandoned coal mine, a test tunnel has been newly driven in the massive sandy-shale rock mass from the main roadway located at a depth of 365m from the surface, and several in-situ measurements and laboratory tests have been conducted. The Barton's Q-value to classify the rock mass was evaluated to be 11.1, which means there will be little problems accompanying the excavation and maintenance of the cavern. It should be noticed, however that the physical properties of the rock are sensitive to the water content due to some clay minerals contained in it. Therefore, sufficient countermeasures should be taken into account when designing the cavern.
Three types of test using boreholes were conducted to know the resistability for pressure and the stiffness of the rock mass. It was confirmed that the pressurized hole, when its surface is sealed, behaves elastically for the pressure up to 16 MPa and has a fatigue limit of more than 4.6 MPa. However, for unsealed condition, small value of 8 MPa was recorded as the breakdown pressure when the pressurized area was intersected by the fractures.
