Abstract
Hard rocks on the earth's surface are frequently observed at places as severely deformed and folded without fractures. How much would rocks flow under how large external forces through how long period of time of their application? The present experiments have been intended to answer this question. As for the rocks of the test-piece materials, granite was employed that forms the upper layer of the crust under the continents. Two large test-pieces of granite from one block were shaped into straight beams of 215cm length with rectangular cross-sections of 12.3cm width and 6.8cm thickness. These two test-pieces are separately mounted freely on end supports of blunt knife-edges at a distance of 210cm, which are made of granite quite similar to the materials of the test-pieces.
One of the two test-pieces called the unloaded beam bends under its own weight and the other called the center-loaded beam does under its own weight plus an extra center-load of 22.06kg. The maximum bending stress produced in the unloaded beam is 12.8kg/cm2 and that in the center-loaded 24.8kg/cm2. The experiments started on August 7, 1957. Since then, the experiments have been continued and until today (end of Feb., 1965) a time of seven and a half years has elapsed. Our experiments are the experiments that shall be carried on without end.
For finding vertical displacements of 11 measuring points at the upper surface of each of the test-pieces on end supports that would continue its secular bending, a dial guage of 0.01mm/div is used to measure vertical coordinates of them which slides along a straight steel beam (SSB) of 103cm length which is horizontally placed in the middle portion of the upper surface of the test-piece with SSB's three legs at fixed points. When the measurements are not performed, SSB is removed from the test-piece. Prior to the commencement of these measurements, the test-piece was mounted horizontally on two supports specially positioned as shown in Fig. 4 to produce no appreciable elastic bendings and the initial values of the vertical coordinates of the measuring points were found.
Influences upon the measurements of those vertical coordinates that should be produced from the circumstance that SSB might not be set constantly in each of the continuing experiments are obtained to get corrections, and also the corrections due to additional displacements of the measuring points by mounting SSB are likewise determined from a measurement by a level of a small inclination of the test-piece produced at its end by the mounting of SSB. This measurement of the small inclination of the test-piece enabled us to calculate instantaneous Young's modulus under a small stress of the test piece at the time of each experiment carried out on it.
The results obtained for the first 7 years since the beginning of the experiments are as follows:
(1) Since about 50 days after the beginning of the experiments, the upper surface of both test-pieces show very minute folds. They display gradual growth for the first 3 to 4 years since the beginning of the experiments and hereafter remain almost stationary until today. For both test-pieces the forms of the folds are unsymmetrical with respect to the central point P0, the wavelengths being much larger than the spacing of 10cm of the measuring points and the average amplitudes of the folds being in the order of 0.01mm. These folds may be seen as laboratory midget-models of synclinorium. The center-loaded beam shows stronger folds than the unloaded does.
(2) Both test-pieces display very strange phenomena of sags that oscillate with time with periods differing from one year-temperature of the laboratory is kept constant within the range of±2°C but humidity is not done so and does annual changes. Analyses of these oscillating sags will be published in the next paper.
