A borehole extensometer using a conventional straddle-sliding-packer system has been developed as a method for evaluating the shear compliance of a fault. In this study, we re-evaluated the laboratory calibration experiment method for determining the compliance of the packer system which is required when applying the borehole extensometer method. The packer compliance measured by the previous method using a single packer was compared with that derived from a method using double packers, where the latter method more reproduces the actual in-situ test conditions. There is a difference between the results using a single packer and double packers, and the results showed that the previous method using a single packer may over- or under-estimate the packer compliance, and the difference between those from the methods using a single packer and double packers is greater with smaller packer pressure. We also found that the packer compliance depends on the packer pressure and increases with decreasing packer pressure. Therefore, it is desired to conduct laboratory calibration experiments using double packers at packer pressure close to the in-situ test conditions. The knowledge obtained by this study improves the reliability of the borehole extensometer measurement using a straddle-sliding-packer system.

This study introduces a novel method to quantify the weathering ratio of Ryukyu limestone by leveraging the potential difference generated within the stone during chemical degradation. We specifically shaped Ryukyu limestone into pillar-like specimens and immersed them in a dilute hydrochloric acid solution for 10, 20, and 30 days. Subsequently, we conducted Uniaxial Compressive Strength (UCS) tests on each sample, measuring its UCS, tangent Young's modulus, and the potential difference. The UCS test results clearly showed that the strength decreased quadratically over time under these accelerated weathering conditions. Furthermore, we observed a progressive decline in the maximum voltage over time, while the minimum voltage simultaneously increased, resulting in the voltage difference approaching zero after 30 days. Analyzing the relationship between potential differences and the tangent Young's modulus, we found that as potential differences increased, the tangent Young's modulus also consistently rose. These findings strongly suggest the feasibility of evaluating the degree of rock deterioration (weathering) by simply measuring the potential difference generated within the rock itself. In addition, microstructural observations indicate that weak, fine particles are likely selectively dissolved as weathering progresses. This dissolution likely explains the previously observed decrease in potential difference. As these fine particles dissolve, the bonds between larger particles loosen, leading to discontinuities within the material's structure. This process ultimately contributes to the overall degradation and strength reduction of the stone over time.

In order to understand mechanisms of rock failure under uniaxial tension, we analyzed permanent strains occurred post ultimate failure in uniaxial tension tests for several plutonic rocks included tonalite, granodiorite, granite and gabbro following our previous studies which just analyzed the test data until the ultimate failure. Usually, a specimen under uniaxial tension test broke locally, but the other part of the specimen looked no obvious visual changes with that before uniaxial tension test. From the post failure stress - strain curves, we found that extensional permanent strains occurred in apparently intact parts of the broken specimens, i.e., the tensile stress was unloaded completely. In addition, the permanent strain occurred in both axial and latera directions, i.e., in directions parallel and perpendicular to uniaxial tensile loading. We interpret that the extensional permanent strain occurred by mixed cumulative effects of new microcrack occurrence and developing and/or opening of pre-existing microcracks accompanying with increase of the tensile stress. Therefore, these extensional permanent strains implicate ‘damages’ that the specimens undergone in their failure process under uniaxial tension. Consequently, the failure process of uniaxial tension may be considered as that the minor damages occurred over the entire part of the specimen at first, then a concentrated damage zone was formed and finally proceeded to the ultimate failure.

The cement industry accounts for approximately 7% of global CO₂ emissions. Considering the anticipated increase in global cement demand, it is essential to implement measures to reduce CO₂ emissions from the perspective of decarbonization and achieving carbon neutrality. In recent years, the development of blast furnace cement, in which a portion of ordinary Portland cement (OPC) is replaced with blast furnace slag (BFS), a by-product of ironmaking in blast furnaces, has progressed. However, it has been concerned that increasing the mixing ratio of BFS may decrease the early strength of the cement. Therefore, this study aimed to investigate the effects of applying CO₂ nanobubbles (CO₂NB), which have been reported to promote the carbonation reactions in cement concrete, to blast furnace cement, in order to improve its strength and evaluate the influence of the carbonation reactions. In the experiments, mixtures of OPC and finely ground blast furnace slag (BFS4000) were prepared at cement replacement ratios of 100%, 70%, 50%, 30%, and 0%. Each mixture was blended with either tap water or CO₂NB water at a water-to-cement ratio (w/c ratio) of 50% to create the test samples. Flow tests, bleeding tests, uniaxial compressive strength tests, and X-ray diffraction (XRD) analyses were conducted on these samples. The results showed that the use of CO₂NB water not only promoted the carbonation reaction in blast furnace cement but also improved the compressive strength of the samples by approximately 10-20% after 28 days, in addition to enhancing early strength. Consequently, the application of CO₂NB to blast furnace cement enables the fixation of CO₂ within the samples while allowing for a higher BFS replacement ratio without compromising the strength of the samples. This approach is expected to significantly reduce CO₂ emissions and promote the environmentally sustainable use of cement-based materials.

High strength and ultra low permeability concrete (HSULPC) is considered as a material used to confine transuranic (TRU) waste for disposal in geological repositories. Therefore, information of the permeability of HSULPC is essential. In general, water migrates through the network of fractures and pores in a solid. It has been reported that the precipitation of calcium compounds occurred on the surfaces of fractures and pores in cementitious materials kept in water, which brought about the fracture closure. However, none has investigated the influence of such precipitation on the permeability. In this study, we have conducted permeability measurements on a macro-fractured HSULPC. In particular, we kept the macro-fractured HSULPC specimen in an artificial seawater, and investigated the influence of calcium compound precipitation on the hydraulic conductivity. It was shown that the introduction of macroscopic fracture increased the hydraulic conductivity. In addition, when the macro-fractured HSULPC was kept in artificial seawater, the fracture was filled partly by the precipitation of calcium compounds, which decreased the hydraulic conductivity. Especially, the fracture closure was observed mainly for the upstream part of the specimen. When HSULPC is put in the underground condition, the fracture closure in HSULPC can occur due to the existence of groundwater with high electrolyte concentration.

Fractures are the main pathways for groundwater flow and solute transport in rock. Modeling flow through hydraulically connected fractures is crucial for evaluating fractured rock environments. The Discrete Fracture Network (DFN) model is one approach to assess mass transport in fractured media. Recent advancements in DFN modeling allow flow simulation considering not only fracture connectivity but also heterogeneity within fractures. Continuous modeling using effective hydraulic conductivity is another approach to assess mass transport in fractured media. Estimating effective hydraulic conductivity also requires the evaluation of fracture connectivity and intra-fracture flow. Among them, fracture connectivity can be evaluated using conventional DFN modeling. However, the evaluation of intra-fracture flow remains challenging due to computational costs and uncertainties during modeling. To address this, this study utilized the fracture effective transmissivity derived by Landau–Lifshitz–Matheron formula, which accounts for both transmissivity heterogeneity and flow patterns within fractures without explicit modeling of intra-fracture flow. Combining effective transmissivity with a conventional DFN model enabled effective hydraulic conductivity estimation, considering both fracture connectivity and intra-fracture flow. The proposed approach was applied around the Horonobe Underground Research Laboratory. The resulting effective hydraulic conductivity was compared with that by conventional approach and the value directly derived from long-term inflow and hydraulic pressure data. Our approach estimated the directly derived effective hydraulic conductivity better than conventional approach.

Following the closure of underground facilities at geological disposal sites, groundwater infiltration may result in swelling and gap-filling behavior of bentonite buffer material. This behavior likely aids the sealing of fractures of rock in excavation-damaged zones. However, the chemical composition of groundwater can influence this swelling and sealing behavior. As a result, the effectiveness of fracture sealing may vary, potentially leading to significant differences in host rock permeability. To evaluate the effectiveness of properties of rock as a natural barrier, it is essential to understand the extent to which it intrudes into rock fractures. Determining the permeability of the rock once these fractures are filled with bentonite is also crucial. This study entailed permeability tests on Horonobe mudstone and Mannari granite samples with artificially induced fractures. The fractures were filled with bentonite chemically altered by immersion in different solutions simulating potential chemical interactions in geological disposal environments. The experimental results indicate that fractures increase the permeability of the rock. However, permeability reduces when the fractures are sealed with bentonite. The extent of this reduction depends on the chemical composition of solution and type of rock.

In preparation for upcoming activities on the Moon, such as facility construction and resource development, which constitute the next step in the ongoing lunar exploration projects, we have compiled thoughts on the development of rock fracturing techniques on the Moon. This includes considerations for selecting lunar rock simulants, that is terrestrial rocks to simulate lunar rocks necessary for rock experiments aiming at these lunar developing activities. In detail, we have investigated the types of lunar rocks, and their textures and fundamental properties using the information of returned samples from the Moon, and then selected the suitable terrestrial rocks for lunar rock simulants. As the specific plans for lunar development progress, discussions of this nature become increasingly crucial in the technological discourse. Based on the current knowledge, the types of lunar rocks on the surface appear to be limited, with two types of rocks, namely anorthosite in the highlands and basalt in the mare, seeming adequately suitable for technological development. It is speculated that, for the time being, there may be no need to utilize other types of rocks. To simulate lunar anorthosite, it is estimated that terrestrial anorthosite formed at Precambrian 3.0-3.5 Ga is suitable, and also terrestrial gabbro or norite, with relatively high proportions of plagioclase, and diabase are useful. To simulate lunar basalt, it is estimated that terrestrial basalt and diabase are useful, by considering the relatively high concentration of pyroxene in lunar basalt. It is considered desirable to choose rocks that have undergone minimal alteration and contain as little hydrous and/or clay minerals as possible when selecting lunar rock simulants. Furthermore, chrematistics, including uniaxial compressive strength and tensile strength, of some terrestrial rocks of which types are candidates of lunar rock simulants are investigated. It is estimated that the failure strength of lunar rocks is widely ranged.

Anisotropy of the physical properties in rocks is affected by factors such as the orientation of particles and the fracture directions. In sedimentary soft rocks, anisotropy relative to the bedding plane is developed due to preferred particle arrangement and compaction after deposition. We measured resistivity and calculated the degree of anisotropy using siltstone from the Mio–Pleistocene forearc basin. As a result, the samples exhibited anisotropy, in which the resistivity perpendicular to the bedding plane was larger compared to parallel to it. The degree of resistivity anisotropy is calculated using two parameters: anisotropic factor (AF) defined as the ratio of parallel over perpendicular value, and degree of anisotropy (DA, %) defined as the percentage difference between two directions. The anisotropy was found to be approximately 0.8 for AD and approximately -25% for DA, and tended to decrease with decreasing porosity in sedimentary soft rocks with high porosity (>35%). The anisotropy is thought to be due to the preferred orientation of mineral particles constituting the sedimentary soft rock, suggesting a layered structure. The anisotropic characteristics of resistivity are consistent with the anisotropy of P-wave velocity and thermal conductivity, and it was revealed that electrical conductivity can be detected more significantly than P-wave velocity or thermal conductivity.

The construction methods for mountain tunnels can be broadly classified into sheet pile and NATM. In the sheet pile method, the arch and the sidewall are constructed separately, which results in horizontal joints and transverse joints. These joints and joints tend to become discontinuous surfaces, and cracking and leakage often become apparent as the service life lengthens. Calcium leaching is a phenomenon in which calcium leaches out of the hardened cement and the area becomes brittle. However, this phenomenon has not been studied extensively because it takes a long time to develop. On the other hand, the Ca/Si molar ratio of calcium silicate hydrate, one of the hydration products of cement, is said to affect the strength of hardened cement. In this study, we hypothesized that calcium leaches out and propagates cracks when cracks with water leakage occur. We have continuously measured the amount of calcium leached into the water by immersing cement paste samples in ion-exchanged water over a long period of time. This study examines the relationship between the dissolution of calcium silicate hydrate and mechanical properties by analyzing the soaking water and samples used for soaking.

In this study, carbon-doped Y₂Ti₂O₇ and TiO₂ 22% - 1/2 (Y₂O₃) 78% (TiO₂ 22%-YTO) thin films were fabricated using mist CVD method under atmospheric pressure, and their structural analysis and electrical characteristics were evaluated. These films were formed using a low-temperature process with maximum heat treatment at 430°C and exhibited memory switching properties based on metal-insulator transition (MIT). The fabricated devices showed an initial low-resistance metallic state (Born-on characteristic) and demonstrated non-polar switching behavior, transitioning to a high-resistance insulating state when a voltage of approximately 0.7 V was applied. Furthermore, TiO₂ 22%-YTO maintained similar switching performance at 200°C as at room temperature, confirming operation over a wide temperature range. SIMS analysis confirmed approximately 0.4% carbon doping in the films, which is believed to create impurity levels that enable metal-insulator transitions in Mott-Hubbard insulators. The material system developed in this research is promising for applications in correlated electron random access memory (CeRAM) that operates at low voltages over a broad temperature range.

We applied scanning internal photoemission microscopy (SIPM) to characterize the uniformity of the Au/Ni/n-type β-Ga₂O₃ Schottky contacts under applied voltage of -126 V for 163 hours continuously. The standard deviation (σ) of the SIPM signal on the whole electrode using blue, bluegreen, green, and red laser beam under non-voltage application were less than 2%, and of the Schottky barrier height (qϕ_B) was 4.46 meV. This value was comparable for the n-SiC, n-GaN, and n-α-Ga₂O₃ Schottky contacts. After 163 h voltage application, the σ of qϕ_B on the entire electrode was 20 meV, and the decrease of the average value from 0.5 h was less than 10 meV. It shows no significant degradation and maintaining high qϕ_B values. We demonstrated that the SIPM method can be used to be in-situ observation for electrical uniformity of the Schottky contacts under applying high voltages.

The buckling state was reproduced in a compression test of a glass fiber reinforced plastic (GFRP) specimen. Furthermore, an effect of stiffness improvement by applying the adhesive was verified by the compression test. The load test was performed on the warmed thick plate of GFRP composites, and the state in which delamination due to buckling was produced. Compared to the non-damaged material, the stiffness of the two specimens was reduced to 16% and 22%, respectively. It was clarified in the test that the stiffness was improved by 2.5 times when the adhesive was applied to the vicinity of the buckling part, and the stiffness was restored to 66% of the initial value. Strain measurement by image correlation method (DIC) revealed that the strain in the buckling part was effectively reduced by applying the adhesive. In addition, the residual strain caused by buckling behavior can be quantitatively grasped, and the DIC can be effectively used to estimate the penetration range of adhesives.