The compressive creep of Sanjome andesite was examined under the confining pressure from 0 to 400 kg/cm².
The results are as follows:
(1) The creep behavior of the specimen can be divided into two stages. During the first period starting immediately after loading, creep rate is continuously decreasing with time and the logarithmic creeplaw fits for most part of this period. In the successive stage, creep rate is increasing monotonously toward the failure.
(2) The characteristic time, tc, at which creep rate takes its minimum is found tobe related to the lifetime of the specimen, tf, by the following equation, tf=2tc. In other word, the period of the first stage is nearly equal to that of the second.
(3) Comparing at the same elapsed time, creep rate increases with creep stress level under a given confining pressure, and increases with confining pressure under a given stress level.

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Deformation in roof rock was measured on an experimental tunnel in Matsumine mine. Two extensometers were installed in bore-holes drilled from an opening 15 meters above the experimental tunnel before its excavation. Therefore, the vertical displacement in the roof rock can be measured not only after, but also before the face passes under the measuring section.
The vertical displacement in roof rock consists of elastic part immediately after the blasting and time-dependent inelastic part. The inelastic displacement is considerably larger than elastic one. Total displacement and inelastic displacement in roof rock between two blastings increases with time following the power law, and the inelastic displacement rate decreases also following the power law. Through the measurement of such deformation behavior, it became clear that the rock mass around the experimental tunnel in Matsumine mine behaves as a visco-elastic body; a great part of the displacement is due to viscous or time-dependent behavior.

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In the 1st report, the authors presented two formulae of cutting force for two cutting mechanisms, that are the crack type and the shear type. And the applicable ranges for these two formulae are discussed.
In this report, the authors attempt to generdize these two formulae and to apply them to the results of experiments in two dimensions, using various gypsum and sand mixtures and a coal sample.
The generalized formulae are as follows,
P=2/n+2St·t·cos (α-φ)√1+2Stcos2φ/(n+2) Sc-cos (α-φ) for crack type cutting mechanism,
P=2/n+1St·t·cos (α-φ)·cosec1/2 (k+α-φ)/cos1/2 (k+α+φ)-cotk·sin1/2 (k+α+φ) for shear type cutting mechanism,
where
P=cutting force by unit length of blade
t=depth of cut
St=tensile strength of sample
Sc=compressive stength of sample
φ=friction angle between blade and chip
α=rake angle of cutting tool
n=stress distribution factor
cotk=Sc²-16St²/8Sc·St
Substituting experimental data inSc, St, φ, andk, the authors estimate the stress distribution factor “n” by means of each set of experimental values ofP/tandα.
In this culculation, W. E. DEMING'S method of statistical adjustment of data is applied. And then the applicable ranges of these two generalized formulae are discussed.
Under the experimentalconditions in this report, it is concluded that the formula for shear type cutting mechanism has a good agreement with the experimental results, but that the formula for crack typecutting mechanism does not agree with the experimental results.

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The effect of strain rate on the uniaxial and traxial compressive strength for Sanjome andesite is examined varying the strain rate from 0.85 to 850μ/sec. by a step of 10 fold change under the confining pressure up to 400kg/cm².
The preliminary uniaxial compression test shows that:
(1) the uniaxial compressive strength decreases with only small increase of moisture content in the test piece.
Therefore, a special care has been taken in preparing specimen for the following test programme. The test results are as follows:
(2) the increment of differential stress at the strength failure point is revealed to be about 75kg/cm² when the strain rate increased by a factor of 10;
(3) the square of the maximum principal stress at the strength failure point increases linearly with the confining pressure;
(4) the inelastic strain at the strength failure point increases linearly with the confining pressure. Though under a constant confining pressure, inelastic strain is almost constant regardless of strain rate.

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It is known empirically that the rock burst is due to the geometry of underground openings, the geological circumstances, the mechanical properties of rock and the stress conditionin rock. Considering only stress condition among these causes, it can be said that the rock burst occurs when the stress suddenly exceeds the strength of rock. On the viewpoint of stress condition in the triaxial compression test, the rock is failed by not only the increase of axial stress at constant confining pressure, but the decrease of confining pressure at constant differential stress.
In order to study the rupture of rock caused by the rapid reduction of confining pressure at constant differential stress, the triaxial compression test was undertaken on three kinds of rocks, namely IZUMI sandstone, BIBAI sandstoneand TOHOKU marble.
The testing apparatus shown in Fig. 4 is mainly consisted of a triaxial cell, an electromagnetic operation valve used in the rapid reduction of confining pressure, a diaphragm type pressure gauge for measuring the variation of confining pressure and arr electromagnetic oscillograph. The time required for reducing rapidly the confining pressure to the atmospheric one is about 0.2 second, as shown in Fig. 6.
The main results obtained in this investigation can be summarized as follows:
(1) To measure the relative violence of rupture of these rocks, the stiff loading test was undertaken on rock specimens. It becomes clear from this test that IZUMI sandstone and BIBAI sandstone fail violently, whereas TOHOKU marble fails gently as compared with other two kinds of sandstones. It is shown in Fig. 5.
(2) The rupture stress circles of these sandstones which are failed by rapid reduction of confining pressure exist beyond the Mohr's rupture envelope obtained by conventional triaxial compression test, as shown in Fig. 9-A and Fig. 9-B. This means that these sandstones fail violently in excessive elastic energy condition which is developed by rapid reduction of confining pressure. On the other hand, the complete stress-strain curve of TOHOKU marble is obtained as Fig. 5. Then the marble fails gently in the test. Besides, the rupture stress circle of the marble which is failed by rapid reduction of confining pressure exists near the Mohr's rupture envelope as shown in Fig. 9-C.

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In this report, the authors discuss on the fracture around a borehole under the biaxial compression and hydrostatic internal pressure.
The theory of linear fracture mechanics is applied to the shear fracture of borehole-wall, which is sometimes observed in the borehole drilled in the high stressed rockmass.
Then, the authors discuss on the application of hydrofracturing method to the measurement of in-situ rock stress, from the point of view of linear fracture mechanics. Theoretical analysis revealed some problems to be verified by some field and laboratory tests.

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Mining industry is now evaluating the rock bolting as a new suppor method because of its significant advantages: reduced storage and handling requirements, improved ventilation, negligible maintenance and soon. This study has been started to reveal the advantages and disadvantages of the rock bolt support over the conventional arch support and examine its applicability to mines of Kuroko are deposit on the basis of in-situ measurement carried out at Fukazawa mine in Akita.
In this first report, the measuring system and the results at roadway supported by rock bolts are described. The rock bolts were installed in a square grid at 1 m interval, and convergence, radial extension of rock wall and axial force of rock bolt have been measured. Up to this time (200 days after installation), measured values have been continuously increasing, and some are of the considerable amount. For example, convergences are in the order of 50-70mm against the roadway of 3.3m height and 4.5m width. However, rate of increase is descreasing monotonously and no trend of roof fall or wall spalling is observed. Among others, it is most interesting that the results of convergence, extension and axial force follow the semi-log relationship, linear increase of the measured value against log time, except the axial force above its yielding point.

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In-situ measurement were carried out in an experimental tunnel of Matsumine mine. Displacements in rock around the experimental tunnel were measured by five extensometers at a location, and convergences of the experimental tunnel were measured at two locations.
Displacement in rock around the tunnel increases rapidly with face advance at first, and these rates decrease gradually with face advance. And the face advance affect the displacement especially when the distance to face is less than one tunnel width. But it is interesting that the displacement continuously increases with time after the face advance was stopped, and that the displacement does not show a trend to level off at a certain value and increase continuously following the logarithmic law after quite long time has passed. Similar trend can be obtained by the result of convergence of tunnel.
Through the measurement of such displacement and convergence behaviors, it became clear that the rock mass around the experimental tunnel in Matsumine mine behaved as a visco-elastic body; a great part of the deformation is due to viscous or time-dependent bahavior.

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The non-linear rheological model is proposed in order to explain the time-dependent behavior of Sanjome andesite. The model consists of two units in series; i. e. a linear spring and a non-linear Voigt model. Considering various test results on the time-dependent behavior of sample rock, the constitutive equation for non-linear Voigt model is assumed as
ε_ν=ηexp{-δkε_ν(1-ε_ν/C)}
where σ is the stress applied to the model, ε_ν is the viscous strain and η, δ, k, c are the material constants.
This model is especially deviced to describe the following phenomena.
(1) In the constant strain-rate loading, the gradual increase of compliance toward the strength failure point and the strainrate dependency of the strength; the stress at the strength failure point increases by about 75kg/cm² as the strain rate is increased by a factor of 10.
(2) In the creep, a linear increase of the creep with logarithm of the elapsed time, and the subsequent accelated creep; creep strain-log time curves are of congruence in regardless of a creep stress.

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