Yukitoshi Oka

Determination of the tensile strength of rock by a compression test of an irregular test piece

Abstract The stress in an irregular test pair subjected to a pair of concentrated loads was analysed theoretically as well as experimentally. From the result of this analysis together with the experiments carried out on several kinds of rock, it was found that the tensile strength of rock could be approximately determined by 0·9 times the critical load under which the test piece broke, divided by the square of the distance between the points of loading.

Determination of the stress in rock unaffected by boreholes or drifts, from measured strains or deformations

Abstract The present paper treats the problems regarding determination of the stress in the rock unaffected by boreholes or drifts from measurements made in them. As the items of measurement, we can mention variations in borehole diameter, strains on the bottom surface of boreholes, strains of the wall surface of boreholes, variations in oblique dimension of boreholes and combinations of these as well as strains on the wall surface of drifts or shafts. The formulae to be used in practice to determine the stress in the rock from several measurements have been presented. On deducing them, the elastic constants of the rock, the rigidity of the measuring instruments used and the irregular distribution of strain within the range of each strain gauge were taken into account. The least number of boreholes or drifts necessary for each stress determination and the accuracy in the results obtained have also been discussed.

Precalculation of ground movements caused by mining

Abstract The present paper describes the principle and the technique of a new method for precalculating the ground movements caused by mining coal seams or ore bodies. In this method functions of influence which by integration give the influence factors are used. The features of this method are that the calculation is carried out more mathematically than the conventional methods and is therefore suited to the use of an electronic computer, that not only subsidences and horizontal displacements but also inclinations, strains and curvatures can be directly calculated, and that the nature of ground is able to be taken into consideration. The detail of numerical calculation is explained by taking an example.

Stress on the wall surface of levels with cross sections of various shapes

INTRODUCTION THE authors have published, previously, the results of investigations on the stress concentration in elastic rock around a level or a shaft, applying the theory of elasticity and photoelastic experiments under the conditions that before the excavation was made, the rock was in a general three-dimensional state of stress, i.e. the rock was subject to compression in all directions, and the directions of principal stresses were not always vertical and horizontal [1]. The stress on the wall of a level or a shaft under such conditions is very complicated. Therefore, in order to understand the relation between the shapes of cross section of levels, and stress concentrations around levels, it will be more convenient to study the latter under somewhat simpler initial conditions. For this reason, the stress concentrations around levels will be treated in this paper with the assumption that one of the smaller principal stresses took the direction of the axis of the level before the level was driven. As a matter of course, the analysis of stress under this condition is easier and needs only three two-dimensional photoelastic experiments for each shape of cross section, while the analysis of stress under general conditions requires five photoelastic experiments, three of them being two-dimensional and the other two three-dimensional. Referring to the results of investigations under the general conditions described above, it is supposed that the stress concentration under this special condition is greater than that under other conditions, so that the analysis of stress under this condition will contribute to the study of earth pressure.

A means of determining the complete state of stress in a single borehole

Abstract This paper sets out the equations and apparatus of an experimental means to determine the complete state of stress in a single borehole. We can determine displacement vectors axially and diametrically during stress relief overcoring of a borehole containing instrumentation as proposed. A proposed new device will measure three vectors of axial displacement Several diametral measuring devices are available. Computation of the in situ stress tensor employs coefficients derived from established formulae. Calibration of this complete state of stress measuring system can be done in appropriately oriented boreholes in four separate blocks under load. The elastic constants will then be unnecessary for determining the complete state of stress. Thus stress in inhomogenous rock can be determined. This arrangement permits the use of either a soft or a rigid type of measuring instrument. In both cases only stresses at equilibrium are involved, making such applications possible.

Determination of Tensile Strength of Concrete by Compressing Cylindrical Test Pieces Axially over Limited Areas

Recently the authors proposed a method of testing tensile strength of rocks with irregular test pieces subjected to a pair of concentrated loads.It is the object of the present investigation to examine whether or not a similar method can be applied to the test of concrete. From the theoretical analysis and experiments, it has been found that the tensile strength of concrete can be determined by compressing cylindrical test pieces axially over limited areas if it is conducted under suitable condition. It is found also that deviations of the test results are negligible. The suitable conditions are described in detail in the paper.