Examination of a Rock Failure Criterion Based on Circumferential Tensile Strain

Abstract

Uniaxial compression, triaxial compression and Brazialian tests were conducted on several kinds of rock, with particular attention directed to the principal tensile strain. In this paper we aim to clarify the effects of the experimental environment -such as confining pressure, loading rate, water content and anisotropy-on the critical tensile strain, i.e., the measured principal tensile strain at peak load.It was determined that the chain-type extensometer is a most suitable method for measuring the critical tensile strain in uniaxial compression tests. It is also shown that the paper-based strain gage, whose effective length is less than or equal to a tenth of the specimen's diameter and glued on with a rubber-type adhesive, can be effectively used in the Brazilian tests.The effect of confining pressure P C on the critical tensile strain m TC in the brittle failure region was between −0.02× 10 −10 Pa −1 and 0.77 × 10 −10 Pa −1 . This pressure sensitivity is small compared to the critical tensile strain values of around −0.5×10 −2 . The strain rate sensitivities (m TC /({log(dm/dt)} were observed in the same way as the strength constants in other failure criteria. They were found to be from −0.10× 10 −3 to −0.52× 10 −3 per order of magnitude in strain rate in the triaxial tests. The average magnitude of the critical tensile strain m TC increased due to the presence of water by 4% to 20% for some rocks, and decreased by 22% for sandstone. It can at least be said that the critical tensile strain is less sensitive to water content than the uniaxial compressive strength under the experimental conditions reported here. An obvious anisotropy was observed in the P-wave velocity and in the uniaxial compressive strength of Pombetsu sandstone. It was not observed, however, in the critical tensile strain, although the data do show some variation.A ''tensile strain criterion'' was proposed, based on the above experimental results. This criterion signifies that stress begins to drop when the principal tensile strain reaches the critical tensile strain. The criterion is limited to use within the brittle failure region. The critical tensile strain contains an inelastic strain component as well as an elastic one. It is affected by the strain rate, however, it is relatively insensitive to the confining pressure, the presence of water and anisotropy.

Experimental Study on Mechanical Characteristics and Fracture Patterns of Unfrozen/Freezing Saturated Coal and Sandstone

“…Attributed to the bonding effect of ice crystals, the UCS was higher for rock samples with a higher ice content, and the UCS increase was not significant under −4 °C because of the constant frozen water content. With the temperature decrease, the UCS of the rocks increased and the critical compressive strain decreased [38]. In Figure 3, we can see that the specimens became brittle with the decrease of temperature.…”

Fractured Rock Permeability as a Function of Temperature and Confining Pressure

“…Not on permeability but it was also clarified that the critical extensile strain (extensile strain at peak load point [Fujii et al, 1998]) of Kimachi sandstone and Inada granite was much less sensitive to temperature than critical compression strain (compressive strain at peak load point).…”

“…No significant influences were observed in the tangent modulus and the residual strength. No significant effects of temperature on the critical extensile strain (CES, circumferential or lateral extensile strain value at peak load point) [Fujii et al, 1998]) were observed. However, the critical compressive strain (CCS, axial strain value at peak load point) at 353 K was larger than that at 295 K (Fig.…”

“…8). Fujii et al (1998) showed that critical extensile strain was much less sensitive to confining pressure, water content or anisotropy than peak stress or critical axial strain. The present results showed that critical extensile strain was also less sensitive to temperature.…”

Evaluation of excavation‐induced relaxation and its application to an arch dam foundation

“…Stacy also suggests the value of permissible tensile strain: ε l = 0.0073% for a certain congloment reef and ε l = 0.0175% for a diabase. Further researches are continued by Sakurai et al 19, 20, Fujii et al 21, Li et al 22, concerning the improvement of the criterion and the evaluation of the corresponding parameter ε l , which is reported to range between ε l = 0.1–1% according to the different laboratory test resources 17.…”