Measurement of Permanent Rotation and Tilt of Ground Surface on Mine Shaft Event Mine Ore

摘要

The rotation and tilt of the ground surface was measured at eight locations on two radii, 37 and 55 feet, from the Mine Ore ground zero. Rotation and tilt measurements were made on 24-inch diameter, 1-inch thick steel plates fastened to the granite surface with steel rock bolts. Only nine of the sixteen monuments emplaced could be used for measurements. The remainder were either torn loose by the detonation or lost in the removal of crater debris. Results of measurements on the nine intact monuments showed a maximum rotation counterclockwise of 0 deg. 49 sec. 25 min. at 37 feet from ground zero and a minimum of 0 deg. 00 sec. 16 min. at 55 feet. Tilting of the monuments was random, reflecting the behavior or the granite blocks to which the monuments were attached. The monuments with the largest radial and vertical displacement had the largest variation in tilt angle. All the monuments on the 37-foot radius indicated a positive or upward tilt of the position nearest ground zero and the monuments at 55 feet all showed a downward tilt at the same position. In general, the movement at the ground surface far exceeded the preshot qualitative arguments on how granite would behave compared with the behavior of a alluvium under similar conditions. (Author)