Katsuhiko Kaneko

Strain-rate dependency of the dynamic tensile strength of rock

Abstract Dynamic tension tests based on Hopkinson’s effect combined with the spalling phenomena were performed on Inada granite and Tage tuff to investigate the strain-rate dependency of the dynamic tensile strength of rock. The static tensile strengths were determined and compared with the dynamic tensile strengths. The fracture processes under various loading conditions were analyzed using a proposed finite element method to verify the differences between the dynamic and static tensile strengths and the strain-rate dependency. These analyses revealed that the differences were due to the stress concentrations and redistribution mechanisms in the rock. The rock inhomogeneity also contributed to the difference between the dynamic and static tensile strengths. An increase in the uniformity coefficient stimulated a reduction in the strain-rate dependency; i.e., the strain-rate dependency of the dynamic tensile strength was caused by the inhomogeneity of the rock. The fracture processes and principal stress fields in the specimens at high and low strain rates were analyzed to investigate fracture formations at various strain rates. Higher strain rates generated a large number of microcracks; the interaction of the microcracks interfered with the formation of the fracture plane. The observed dynamic tensile strength increase at a high strain rate was caused by crack arrests due to the generation of a large number of microcracks.

Slake durability and mineralogical properties of some pyroclastic and sedimentary rocks

Abstract Slake durability of rocks is an important property of rock-mass and rock-materials in geotechnical practice. The slake durability of rocks is closely related to their mineralogical composition. In this paper, mineralogical examinations and slake durability tests for argillaceous clastic rocks, especially pyroclastic rocks, sandstones and mudstones of Neogene Tertiary age from Japan, were performed in order to assess the slake durability and rock alteration process of these rocks as well as to understand the relationship between mineralogy and durability. The mineral composition and textural features of the rocks were studied by means of optical microscopy (OM), X-ray diffractometry (XRD), electron microprobe analysis (EPMA), and scanning electron microscopy (SEM). In addition, the slake durability test was carried out by using the standard testing method of ISRM [Int. J. Rock Mech. Min. Sci. 16 (1979) 148] in distilled water and in the aqueous solutions with dissolved electrolytes of NaCl and CaCl 2 . The pyroclastic rocks and tuffaceous sandstone, rich in di-octahedral and tri-octahedral Fe smectite, respectively, show distinctively different slaking behaviors. The pyroclastic rocks show relatively high slaking (Id 2 =55.5% and Id 10 =10.5%) than the tuffaceous sandstone (Id 2 =94.1% and Id 10 =87.8%, refer to text for Id 2 and Id 10 ). This difference in the slake durability observed in these rocks is due to the microscopic occurrences of smectite present in the interspaces between the particles (pyroclastic rocks) and zeolite cementing the interspaces (tuffaceous sandstone) as alteration minerals. In addition, the durability results of tuffaceous sandstone show that the slake durability decreases as the degree of weathering increases (weathered material Id 2 =88.7% and Id 10 =65.3%). Furthermore, two mudstones of Miocene and Pliocene ages, having different clay mineral compositions (smectite vs. illite+chlorite), show the lowest and the highest slake durability among the tested clastic rocks. Hard mudstone shows the highest (Id 2 =98.1% and Id 10 =95.5%) while the soft mudstone shows the lowest (Id 2 =33.9% and Id 6 =0.4%.) slake durability. Thus, the slake durability of pyroclastic and sedimentary rocks is greatly affected by their mineral composition and texture, and is closely related to their alteration history. Slake durability is also affected by the kind of dissolved electrolyte and its concentration in the aqueous solution, providing some useful information for geotechnical practice.

Measurement of local stress and estimation of regional stress associated with stability assessment of an open-pit rock slope

This paper discusses the concept of a new methodology for rock slope stability assessment. Then, results on rock stress measurement using the compact conical-ended borehole overcoring (CCBO) technique at Torigata limestone mine in Japan are presented. A procedure for back analysis of the regional strain and stress field with the 3-D finite element method, using the measured local stress, is suggested and demonstrated successfully in relation to Torigata limestone mine. Finally, to estimate the state of stress at the mine excavation level, 3-D finite element analyses were performed using boundary conditions from the analyzed regional strain and stress field. It is shown that the horizontal stress at the present excavation level is not reduced, and that the horizontal stress component cannot be disregarded in estimating the stability of rock slopes at this location, even though the mine is located near the top of a mountain.

Subcritical crack growth in rocks in an aqueous environment.

Subcritical crack growth is one of the main causes of time-dependent fracturing in rock. In the present study, we investigated subcritical crack growth in rock in distilled water (pH = 5–7) and in an aqueous solution of sodium hydroxide (NaOHaq, pH = 12), comparing the results to those in air. We also investigated the effect of the pH in an aqueous environment. We used andesite and granite for all our tests. We determined the relationship between the crack velocity and the stress intensity factor using the double-torsion test under conditions of controlled temperature. We showed that crack velocities in water were higher than those in air, in agreement with other research results indicating that crack velocity increases in water. When we compared our results for NaOHaq with those for water, however, we found that the crack velocity at the same stress intensity factor did not change even though the pH of the surrounding environment was different. This result does not agree with the accepted understanding that hydroxide ions accelerate subcritical crack growth in rocks. We concluded that the pH at the crack tip influences subcritical crack growth, and not the bulk pH, which has little effect.

The examination of fracturing process subjected to triaxial compression test in Inada granite

The behavior of a granite subject to a triaxial compression test ranging from the prefailure stage to the postfailure stage was studied using a fluorescent technique from the geological point of view. Microscopic observations of the specimens at different stages showed changes in the failure process. The start of formation of new microcracks paralleled the compression direction through their propagation until the onset of faulting and ended with the failure of shear zones after the strength failure point. Pores chiefly identified in the feldspar increased in length and width in the early stages, but not in number. It seems that the effect of pore spaces did not have any effect of failure. The microcracks generated on angular edges of quartz or feldspar grains and around biotite grains with increasing compression force. The phenomenon appearing on the crystal boundaries among biotite and quartz or feldspar agrees with the result calculated based on the theory on stress fields with ellipsoidal inhomogeneity suggested by Eshelby.

Methanoculleus horonobensis sp. nov., a methanogenic archaeon isolated from a deep diatomaceous shale formation.

A methanogenic organism from the domain Archaea, designated strain T10(T), was isolated from groundwater sampled from a deep diatomaceous shale formation located in Horonobe, Hokkaido, Japan. The strain utilized H2/CO2 and formate as substrates for methanogenesis. Cells were strictly anaerobic, Gram-negative-staining, flagellated, irregular coccoids, 0.7-1.6 µm in diameter, and occurred singly. The strain grew at 25-45 °C (optimum 37-42 °C), at pH 5.8-8.2 (optimum pH 6.7-6.8) and in the presence of 0-1.3 M NaCl (optimum 0.1-0.2 M NaCl). The G+C content of the genomic DNA was 62.9 mol%. 16S rRNA gene sequencing revealed that, although the strain is a member of the genus Methanoculleus, it clearly differed from all described species of this genus (95.5-98.3 % sequence similarity). Values for DNA-DNA hybridization with type strains of closely related Methanoculleus species were less than 50 %. Phenotypic and phylogenetic features of strain T10(T) clearly indicate that it represents a novel species of the genus Methanoculleus, for which the name Methanoculleus horonobensis sp. nov. is proposed. The type strain is T10(T) ( = DSM 21626(T) = JCM 15517(T)).

Methanosarcina subterranea sp. nov., a methanogenic archaeon isolated from a deep subsurface diatomaceous shale formation

A methanogenic archaeon, strain HC-2(T), was isolated from a deep diatomaceous shale formation. The strain grew on methanol, monomethylamine, dimethylamine, trimethylamine and dimethylsulphide, but not on acetate, H2/CO2, formate, 2-propanol, 2-butanol or cyclopentanol. Cells were Gram-stain-negative, non-motile, and coccus-like, 0.9-1.4 µm in diameter, and occurred singly, in pairs, or as aggregates. The strain grew at 10-40 °C (optimum 35 °C), pH 5.9-7.4 (optimum pH 6.6-6.8) and in 0-0.6 M NaCl (optimum 0.1-0.2 M). The genomic DNA G+C content was 41.5 mol% and the 16S rRNA gene sequence was closely related to those of Methanosarcina lacustris DSM 13486(T) (99.1%) and Methanosarcina siciliae DSM 3028(T) (98.3%). Values for DNA-DNA hybridization with these strains were less than 30%. The phenotypic and phylogenetic features of HC-2(T) indicate that it represents a novel species of the genus Methanosarcina , for which the name Methanosarcina subterranea sp. nov. is proposed. The type strain is HC-2(T) ( = DSM 22503(T) = JCM 15540(T) = NBRC 102578(T)).

Experimental and theoretical study on smooth blasting with electronic delay detonators

Abstract The effect of high delay time accuracy of electronic delay detonators (EDDs) on overbreak, remaining rock damage, and surface smoothness which are expected on smooth blasting was investigated by experimental and theoretical approach in comparison with that of pyrotechnically delayed detonators (PDDs). As an experimental approach, test-blasts were conducted in a deep iron mine. The test site region, those composed of very hard granodiorite. Five rounds were performed, EDDs were used in the holes on the perimeter of the right half, and PDDs were used on the perimeter of the left half. Following each shot, the cross section was measured by laser to determine amount of overbreak and surface smoothness. In situ seismic prospecting was used to estimate the depth of damage in the remaining rock, and the damage was further investigated by boring into both side walls. Perimeter charge initiation by the EDDs resulted in better smooth blasting results than the PDDs. As a theoretical approach, numerical simu...

Influence of Fracture Width on Sealability in High-Strength and Ultra-Low-Permeability Concrete in Seawater

For cementitious composites and materials, the sealing of fractures can occur in water by the precipitation of calcium compounds. In this study, the sealing behavior in a macro-fractured high-strength and ultra-low-permeability concrete (HSULPC) specimen was investigated in simulated seawater using micro-focus X-ray computed tomography (CT). In particular, the influence of fracture width (0.10 and 0.25 mm) on fracture sealing was investigated. Precipitation occurred mainly at the outermost parts of the fractured surface of the specimen for both fracture widths. While significant sealing was observed for the fracture width of 0.10 mm, sealing was not attained for the fracture width of 0.25 mm within the observation period (49 days). Examination of the sealed regions on the macro-fracture was performed using a three-dimensional image registration technique and applying image subtraction between the CT images of the HSULPC specimen before and after maintaining the specimen in simulated seawater. The temporal change of the sealing deposits for the fracture width of 0.10 mm was much larger than that for the fracture width of 0.25 mm. Therefore, it is concluded that the sealability of the fracture in the HSULPC is affected by the fracture width.

Numerical simulation of the fracture process in concrete resulting from deflagration phenomena

This paper investigated the mechanism of fracture in concrete due to the deflagration phenomenon. For this purpose, the electric discharge impulse crushing method was selected, with liquid nitromethane (NM) taken as the deflagration agent. Employing this technique, NM is set inside charge holes and initiated by electric discharge. The pressure generated by the deflagration of NM in a steel chamber was modeled using the Jones–Wilkins–Lee equation of state. The modeled and measured pressures agreed well and the applicability of the pressure model was validated. Then, assuming controlled splitting along the expected fracture surface in concrete, dynamic fracture process analysis (DFPA) based on two-dimensional dynamic finite element method was conducted. The results showed that fracture patterns predicted in the DFPAs agreed well with those obtained from experiments. The mechanism of fracture in concrete due to deflagration was then discussed in terms of the fracture process in the controlled splitting. Owing to stress interference from each charge hole, compressive stress zones (CSZs) formed above and below the middle regions between charge holes where maximum and minimum principle stresses were both in compression. The CSZs was found to be important in obtaining a flatter fracture surface in the case of controlled splitting. In conclusion, the proposed method was shown to be useful for the investigation of the fracture mechanism in the case of the use of deflagration agents and could be useful for the design optimization of such controlled splitting.