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Determining the change of stress in rock based on measurements of the deformation of a drill hole is a procedure that is increasing in popularity. A closely related procedure involves the application of this principle to determine the existing stresses in a rock medium by cutting free (core drilling) an annulus containing the drill hole.
In this report, expressions are derived from which one can calculate the stress ellipsoid—the three-dimensional change of stress or the existing three-dimensional stress field, as the case may be. Study of these equations shows that the stress components in three dimensions can be determined by measurements in only two drill holes and yields general principles that are useful in planning an efficient program of drilling and measurement.
The need for some method of averaging the measurements arises even in the simplest situation, because one usually has available several sets of measurements and wishes to combine them into a single set of average stress components. Procedures, therefore, are given for calculating the least squares estimates of the stress components and their standard errors, and for evaluating or comparing calculated values by means of standard statistical inferences.
rock (material), rock mechanics, drilling, core testing, earth pressure
Panek, L A
Supervisory physical research scientist, Bureau of Mines, College Park, Md.