Rocks containing clay minerals exhibit diminished strength and undergo physical and chemical deterioration of their texture due to the presence of these clay minerals. Specifically, rocks containing swelling clay minerals experience a significant decrease in strength when subjected to repeated drying and wetting compared to rocks with non-swelling clay minerals. This study conducted a comprehensive series of experiments (physical, uniaxial compressive, and swelling pressure tests) using artificial soft rock mixed with clay minerals. The primary objective was to elucidate the impact of the types of clay minerals present on the physical properties of rock materials under repeated drying and wetting. The clay minerals investigated in this study included Na-type and Ca-type smectites (swelling clay minerals) and mica (non-swelling clay minerals). The smectite-mixed specimen demonstrated higher swelling pressure than the mica-clay-mineral-mixed specimen. Moreover, the uniaxial compressive strength and P-wave velocity of the specimens were remarkably reduced due to repeated drying and wetting process. Hence, the difference in clay mineral content and type in the clay mineral-bearing rock material specimens directly influences the physical and mechanical properties of rock materials when subjected to dry and wet cycles. Furthermore, the outcomes suggest a close association between the reduction in rock material strength, inclusive of clay minerals, and the swelling pressure observed in the specimen.

Thermal conductivity is one of the important parameters to accurately predict temperature structures in the subsurface for various geoengineering applications such as geothermal development and underground disposal of radioactive wastes. Thermal conductivity varies with rock type and is anisotropic when rocks are layered, such as shale and schist. Sedimentary rocks, especially sandstone and mudstone, have layer structures formed by consolidation that reduces porosity. Although this porosity change may be linked with the anisotropy of thermal conductivity, the relationship has not been investigated previously. In this study, we quantitatively investigated the anisotropy of thermal conductivity of sedimentary soft rocks, then examined relationships between porosity and the anisotropy of thermal conductivity. In addition to thermal conductivity, the anisotropy of P-wave velocity was also examined as it is known to correlate well with thermal conductivity. Thermal conductivity and P-wave velocity were measured in both directions perpendicular and parallel to bedding plane in the specimen, respectively. The cubic specimens of sedimentary soft rocks taken from the Boso Peninsula, central Japan were used as the samples, whose porosity ranged approximately from 37% to 55%. As a result, thermal conductivity and P-wave velocity of the specimens parallel to bedding plane were higher than those in perpendicular direction, indicating that the anisotropies regarding to bedding plane were observed in these physical properties. The degrees of anisotropy regarding to bedding plane of both physical properties were then quantitatively evaluated by two indices. The results showed that the degrees of anisotropy of thermal conductivity and P-wave velocity were linked with porosity; the degree of anisotropy in low porosity specimens tended to be smaller than in high porosity specimens.

Strength loss of sedimentary rocks due to water content changes is an important issue in the civil engineering field. Assuming disasters associated with rainfall and drying, it is important to identify unsaturated strength properties for gradually varying moisture contents. Water retention curves are needed to describe unsaturated strength properties. The high suction acting in the case of rock presents a challenge in identifying the suction. In particular, identifying the water retention drying path is difficult. This study propose a method to identify the drying paths using uniaxial compressive strength and tensile strength of Brazilian test. Uniaxial compression and Brazilian tests were performed on specimens with varying water content in the drying pass to investigate changes in their mechanical properties. Strength and stiffness were found to be approximately halved in the wet condition compared to the dry condition. Simplified Mohr-Coulomb failure criteria are also identified using uniaxial compressive and tensile strength. The cohesion decreases with increasing water content, while the angle of shear resistance is independent of changes in water content. Suction at each saturation level was back-analyzed using the detected cohesion and shear resistance angles to identify the water retention drying curve. The water retention drying curves identified were compared with the water retention wetting curve identified by another method to confirm the validity of the proposed method.

It is important to understand the long-term migration of radionuclides when considering long-lasting rock engineering projects such as the geological disposal of radioactive waste. The network of fractures and pores in a rock mass plays a major role in fluid migration as it provides pathways for fluid flow. The geometry of such a network can change due to fracture sealing by fine-grained material over extended periods of time. Groundwater commonly contains fine-grained material such as clay minerals, and it is probable that such minerals accumulate within rock fractures during groundwater flow, thereby decreasing fracture apertures and bulk permeability. It is therefore essential to conduct permeability measurements using water that includes fine-grained minerals in order to understand the evolving permeability characteristics of rock. However, this has not been studied to date in in-situ rock mass. Therefore, in the present study, we perform permeability measurements in a granite rock mass to investigate the change of permeability that occurs under the flow of water that includes clays. Our findings show that clay particles accumulate in fractures and that the permeability (hydraulic conductivity) of the granite rock mass decreases over time. The decrease was more significant in the earlier time. We conclude that the accumulation of clay minerals in the fracture decreases the permeability of a rock mass. Furthermore, we consider that the filling and closure of fractures in rock is possible under the flow of groundwater that contains clay minerals.

In the context of engineering field operations, extracting the physical properties from rocks poses a challenge, necessitating fast and non-destructive remote sensing methods. The objective of this research is to characterize the rock hardness variations induced by the Heating and Quenching (HQ) cyclic experiment, utilizing photosensitivity differences generated during these cycles through multispectral imaging. Laboratory experiments were conducted to capture hardness changes and near-infrared spectral data of rocks subjected to HQ experiments, comparing degraded rocks to their undegraded counterparts. Furthermore, Maximum Information Coefficient (MIC) method is used in this study to explore the integration of hardness changes resulting from artificial degradation with spectral feature information, information and rock physical parameters. Elucidating the coordinated variations between spectral information and rock physical parameters. The paper discusses the potential of using a hyperspectral camera as a substitute for geological sketches and provides insights into its application.

Rock resistivity is essential for interpreting subsurface resistivity structures obtained from electromagnetic surveys. Using rock physics models, we can estimate water content from resistivity; however, the predicted results are strongly dependent on the choice of model with the assumption of the internal pore microstructure. In this study, we evaluated the relationship between resistivity and pore microstructure of clay-free sandstones based on Digital Rock Physics, with a particular focus on tortuosity. The simulation results demonstrated an increase in resistivity and its anisotropy with decreasing porosity. The tortuosity values calculated from the local electric current further explain the evolutions in resistivity. This suggests that the smaller pore volumes (i.e., porosities) prevent pore connectivity and enhance tortuosity, resulting in higher resistivity and anisotropy. The resistivity of high porosity data could be fitted by Archie’s equation with empirical parameters, whereas the resistivity of low porosity data could not. This suggests the difficulty of applying Archie’s equation to low porosity rocks. On the other hand, using the calculated tortuosity, the equivalent channel model reproduced the resistivity over a wide range of porosities. Our results suggest that tortuosity can be a key factor in demonstrating electrical properties.

In this paper, we use AI to predict the ground information at unknown points from the ground information at known points in Urayasu City, which has a large amount of reclaimed land and a very high liquefaction potential. The paper also introduces a liquefaction hazard map and a method for indicating liquefaction hazard using the PL method based on the predicted ground information. Damage to structures due to liquefaction was widely recognized after the 1964 Niigata and Alaska earthquakes. Since then, analysis of the mechanism of liquefaction has been conducted based on field surveys and experiments, and research has been conducted on the occurrence of liquefaction and countermeasures against it. Given the concern about the occurrence of large-scale earthquakes such as the Nankai Trough Earthquake in the near future, the evaluation of liquefaction hazards will become even more important. In order to establish ground investigation and countermeasure methods against liquefaction and subsidence, it is essential to obtain detailed information in the ground. It is essential to develop and establish a method to predict unknown points or unknown areas in the ground with high accuracy based on the limited results of ground investigation.

This paper aims to investigate the impact of low permeability layers in the ground on chemical infiltration by utilizing seepage flow analysis. Additionally, we present the outcomes of a multiple regression analysis conducted using the data obtained from the seepage flow analysis. The chemical injection method has experienced extensive usage in recent years for construction projects conducted near railroad lines, dams, rivers, mountain tunnels, and as a precautionary measure against ground liquefaction in the event of a large-scale earthquake. This technique involves drilling a hole to the desired location, injecting a chemical solution, and allowing it to permeate into the ground. However, the chemical injection method still faces several technical challenges. One of these challenges is the insufficient penetration of the chemical when low permeability layers are present in the ground. In the current chemical injection method, a uniform hydraulic conductivity is assumed based on the value obtained from a specific point in the ground, and the chemical is injected accordingly. However, this approach proves unreliable as it overlooks the existence of low permeability layers that hinder the sufficient infiltration of the chemical. Consequently, such limitations result in the failure of the improvement process. Therefore, it is crucial to enhance the reliability of the chemical injection method by thoroughly investigating the extent to which low permeability layers influence infiltration behavior.

Aluminum bolts used for fastening aluminum structural members must have high resistance to stress corrosion cracking (SCC) leading to thread damage while maintaining high 0.2 % proof stress. Generally, the bolts of 7050-aluminum alloy are manufactured in the order of Ⅰ: machining, Ⅱ: rolling, Ⅲ: solution heat treatment, and Ⅳ: aging treatment, which was labeled No.1 in this study. This paper presented the effects of manufacturing process order on the mechanical properties and the SCC damage morphologies with the aim of satisfying the required specifications for bolts. Two types of bolts were manufactured in order of Ⅰ→Ⅲ→Ⅱ→Ⅳ, and Ⅲ→Ⅳ→Ⅰ→Ⅱ, which were labeled No.2 and No.3, respectively. The mechanical properties and the damage morphologies were evaluated via tensile, Vickers hardness and salt spray tests, respectively. The values of tensile strength and 0.2 % proof stress of No.1 and No.2 were almost the same, however that of No.3 was lower than No.1 and No.2. The degree of SCC damage in No. 2 was smaller than that of No. 1 and No. 3. Finally, the results were discussed via XRD and EBSD analysis. MgZn₂ and Al₂CuMg of typical compounds and the randomly crystal orientation were detected in the bolts, which is indicated that the manufacturing process order does not affect the production of compounds and the crystal orientation. It is presumed that the mechanical properties and the degree of SCC damage are mainly dominated by the effect of the rolling process after solution heat treatment.

It is well known that the transverse cracks (TCs) generated in CFRP laminates are saturated, and the number of saturated TCs varies widely. This paper presents a stochastic approach for the TC saturation characteristics cumulated in a CFRP cross-ply laminate under tensile loading. An inverse analysis mechanics model was proposed on the basis of Markov process combined with a matrix cracking model which was derived on the basis of slow crack growth (SCG) concept in conjunction with the Weibull distribution. The analysis model is assumed that each discrete stage is assigned in the order of the TCs generation, and that it transits to two states i.e., continuously generated and saturated states from one state. The saturated TCs data was stochastically analyzed using the analysis model. The estimated TC saturation probability curves approached the experimentally obtained saturation TCs data with an increase in the number of TCs and ultimately agreed with them. The measured and estimated mean number of saturated TCs was in good agreement.

If a piping system in the reactor coolant circulation system of a nuclear power plant were to fail, the reactor would lose its cooling function, and radioactive materials would be discharged to the outside. In particular, the drainage plant of the Fukushima Daiichi NPP has many unknown parameters, such as the action of external forces and the state of the internal fluid, and there is uncertainty about the state of wall thinning progress and lifetime consumption status. Therefore, it is significant to control the wall thickness appropriately, and remote monitoring is desirable considering the work environment. However, the inspection data of wall thickness reduction by sensors has errors, and the number of measurement points is limited from the viewpoint of cost and other factors. Therefore, this study proposes a method to quantitatively evaluate engineering risk by considering the probability of failure of piping systems and the consequence of failure, based on the data from multiple fixed-point wall thinning monitoring. In this paper, the effectiveness of the proposed method is clarified for a piping system of a cooling water circulation system, and the effects of measurement error, number of measurement points, and candidate settings of wall thinning progression on the evaluation accuracy of wall thinning progression and failure probability are examined.