Engineering Geology, 294, p.106369_1 - 106369_12, 2021/12
The transmissivities (T) of fractures can be related to the fracture roughness (), initial aperture (), effective normal stress ('), and the tensile strength (') of the intact rock, based on the Barton-Bandis model and their data, and the T (or ) can increase by shear-induced dilation. Previous studies revealed that the T of fractures in fault zones, detected as flow anomalies by borehole investigations at six sites, uniformly decreases with the increasing effective mean stress normalized to the '. If this uniform change in T can be explained by '-dependent fracture-normal-displacement following the Baron-Bandis model, the T represents the highest potential T of fractures in fault zones which can increase by shear-induced dilation. To verify this possibility, this study estimated the of the fractures using the T, ', and possible and '. Then, using this estimated , the changes in T were simulated, varying '. The results well reproduced the observed uniform change in T.
Engineering Geology, 275, p.105748_1 - 105748_12, 2020/09
A constant-head step injection test using a conventional straddle-packer system was performed for a normal fault in siliceous mudstone. The test applied a new method whereby axial displacements of isolated test sections in a borehole during injection are monitored by measuring the pressures of sliding packers and the pore pressure in the test section. The measured pressures and axial displacement, and the injection flow rate, were used to estimate the hydraulic aperture, shear displacement, normal compliance, normal stress, shear stiffness and hydraulic dilation angle of the fault during the test. The injection successfully yielded a large shear displacement during normal faulting of up to 13.3-49.5 mm (including the estimation error), which left residual shear displacement of 2.8-10.4 mm after a remarkable shear-slip event. The shear stiffness during faulting is estimated to be 2.3 10 to 8.4 10 Pa m (considering the estimation error), which is consistent with empirically predicted values based on previous studies. The hydraulic dilation angle was inferred to be effectively zero as the residual shear displacement did not leave any increase in hydraulic aperture. The experimental method applied here does not require specialized equipment and could aid in the investigation of the hydromechanical behavior of subsurface fractures or aquifers.
Mochizuki, Akihito; Ishii, Eiichi; Miyakawa, Kazuya; Sasamoto, Hiroshi
Engineering Geology, 267, p.105496_1 - 105496_11, 2020/03
The mechanical and hydraulic properties of rocks around mine drifts change significantly during the construction and operation of a radioactive-waste repository, with air intrusion causing the oxidation of rock and groundwater in excavation-damaged zones (EDZ). Redox conditions in such zones associated with niches excavated in mudstone at the Horonobe Underground Research Laboratory (URL), which is believed to be generally representative of conditions that could exist in the EDZ of a repository, were studied with the aim of improving our understanding of factors that control redox conditions in such rock-groundwater systems. Groundwater Eh values around the niches have reducing values of less than -150 mV. The SO concentration, regarded as an oxidation indicator, is consistently as low as 1 mol L. Gas occupies more than 50% of zone volumes, including CH and CO with traces of N and O. Cores drilled from host rock around a URL gallery were analyzed, with no pyrite dissolution or precipitation of calcium sulfates being found. It is concluded that oxidizing conditions do not exist in the excavation-damaged zones, which is attributed to the suppression of air intrusion by the release of CH and CO from groundwater as pressures decreased and their accumulation in fractures. The modeling of oxygen diffusion into host rock further indicates that a reducing environment is maintained around the URL drifts.
Niwa, Masakazu; Shimada, Koji; Ishimaru, Tsuneari; Tanaka, Yoshihiro*
Engineering Geology, 260, p.105235_1 - 105235_15, 2019/10
In order to identify specific chemical changes induced by recent, near-surface faulting, we compared two faults of different size and evolutionary history, the active Shiraki-Nyu Fault and a nearby minor, inactive fault in central Japan, in terms of their mineralogical and geochemical features. Our analyses suggest that (1) chemical changes such as depletion of NaO and CaO derived from smectite and illite formation, and that changes such as increase of U, Y and REEs derived from absorption to these clay minerals, occurred during the fault initiation and subsequent retrograde alteration and are identical in the two faults, and that (2) MnO increase accompanied by FeO depletion and a positive Ce anomaly can be a key to identify specific chemical changes due to recent, near-surface faulting, because this could be related to upward migration and oxidation of fault-driven reduced fluids from deep underground to the near-surface environment.
Engineering Geology, 259, p.105203_1 - 105203_9, 2019/09
Smectite-bearing shear zones are crucial in a variety of geoscientific and geoengineering fields due to the unique physicochemical properties of smectite. Although such shear zones worldwide occur in marine argillaceous/siliceous sediments, tephra-derived and host rock-derived are possible as their origin, and these shear zones potentially differ in amount of smectite, extent of the spatial distribution, and time of the formation. Nevertheless, it is hard to discriminate these origins by observation. This paper proposes a method utilizing the following two indicators for the discrimination: one is a proportion ratio of smectite to illite, sm/(ill+sm), in the clay fractions of the samples; the other is a concentration ratio of conservative elements, AlO/TiO (wt%/wt%), in bulk chemistry of the samples. Although high sm/(ill+sm) values can be an evidence indicating tephra-derived origin, the values may decrease by mineralogical disturbance/alteration during shear deformation, which make the discrimination difficult. The AlO/TiO values different from those of the host rock can also be an evidence of tephra-derived origin, based on previous studies, and the measurement error is also very small, compared to the analytical error of sm/(ill+sm). But the AlO/TiO values of shear zones may intrinsically be the same as those of the host rock even if those shear zones were derived from tephra layers. Application of these indicators to the protolith identification of bedding-parallel clay-rich shear zones in a folded siliceous mudstone (Hokkaido, Japan) demonstrates that combining sm/(ill+sm) and AlO/TiO is useful as a first diagnosis to identify the protolith more easily and more confidently.
Kubo, Taiki*; Matsuda, Norihiro*; Kashiwaya, Koki*; Koike, Katsuaki*; Ishibashi, Masayuki; Tsuruta, Tadahiko; Matsuoka, Toshiyuki; Sasao, Eiji; Lanyon, G. W.*
Engineering Geology, 259, p.105163_1 - 105163_15, 2019/09
Rock matrix permeability is mainly controlled by microcracks. This study aims to identify the factors influencing the permeability of the Toki granite, central Japan. Permeability of core samples, measured by a gas permeameter, largely increases in the fault and fracture zones. Although a significant correlation is identified between permeability and P-wave velocity, this correlation is enhanced by classifying the samples into two groups by the Mn/Fe concentration ratio. Thus, lithofacies is another control factor for permeability due to the difference in mineral composition. Moreover, permeability shows significant negative and positive correlations with Si and Ca concentrations, respectively. These concentrations are probably affected by dissolution of silicate minerals and calcite generation in the hydrothermal alteration process. Therefore, a combination of hydrothermal alteration and strong faulting are the predominant processes for controlling permeability.
Ishii, Eiichi; Furusawa, Akira*
Engineering Geology, 228, p.158 - 166, 2017/10
We present detailed mineralogical and geochemical analyses of clay-rich shear zones that are associated with bedding-parallel or bedding-oblique faults in drill cores of a siliceous mudstone from the Horonobe area, northern Hokkaido, Japan. The bedding-parallel shear zones are rich in smectite and some shear zones are characterized by melt inclusions hosted by plagioclase and quartz. The chemical compositions of melt inclusions in six shear zones are very similar, but distinct from those of melt inclusions in other shear zones. These six shear zones consistently occur in horizons 350 m shallower than a known tephra layer. These mineralogical characteristics and stratigraphic positions suggest that the six shear zones occur within the same tephra layer and that the smectite formed as a result of burial diagenesis of volcanic glass. Tephra-derived smectite-rich shear zones can be detected and correlated by analyzing melt inclusions preserved in mineral grains.
Engineering Geology, 221, p.124 - 132, 2017/04
Based on previous hydromechanical studies on fault zones, fault zones without development of tensile/hybrid damage-zone fractures have unlikely experienced faulting in highly brittle manner, and the highest potential transmissivity of fractures in such fault zones is assumed to be likely relatively low (transmissivity (T) 10m/s). To verify this assumption, this study investigated the relationship between the failure mode (tensile/hybrid/shear) of damage-zone fractures and the highest transmissivity of fractures in fault zones, using results from core logging and flowing-fluids electric conductivity logging in boreholes penetrating a Neogene siliceous mudstone of the Horonobe area, northern Hokkaido, Japan. In 96% (35/36) of fault zones where tensile/hybrid damage-zone fracture is not observed, the transmissivities of flow anomalies detected within the fault zones by FFEC logging are within a range of 10m/s. This result supports the above-mentioned assumption.
Niwa, Masakazu; Shimada, Koji; Aoki, Kazuhiro; Ishimaru, Tsuneari
Engineering Geology, 210, p.180 - 196, 2016/08
This study focused on microscopic features using particle size analysis, SEM and TEM and identified mineralogical and textural characteristics to improve our ability to discriminate between the active and inactive gouges. Particle size distribution analysis largely shows that fault gouge in an active fault, having the most abundant finer particles, experienced repetitive shearing whereas the inactive gouges did not. SEM examination of quartz particles shows that more particles retain their primary crystal structure in the active gouge than in the inactive gouges. In contrast, observation of very fine clay minerals using TEM shows the minerals in the active gouge are abraded and corroded in equal or higher degree as the aseismic gouges. Repetitive fault activities could result in the addition of new quartz particles from the granite with preservation of primary crystal structure, whereas relatively-soft clay minerals had been affected by abrasion and dissolution.
Ishibashi, Masayuki; Yoshida, Hidekazu*; Sasao, Eiji; Yuguchi, Takashi*
Engineering Geology, 208, p.114 - 127, 2016/06
Damage zone (DS) formed by faulting in crystalline rocks can act as significant transport pathway. Therefore, this paper describes the features of WCFs and their long-term behavior associated with faulting based on the results of investigations at the GL -300m and -500m in the MIU. The results of detailed investigations in and around DZ indicate that there are three stages in the development of hydrogeological structures: 1st stage) the formation of background fractures; 2nd stage) the formation of a DZ and corresponding increase in the hydraulic permeability as a result of formation of small fractures; and 3rd stage) the formation of fracture fillings and the hydraulic permeability of the DZ decrease. In the late 3rd stage, unconsolidated clayey fillings formed associated with faulting resulting in decreased permeability of fractures in the DZ. These results underline the importance of understanding the development stages for evaluating the effect of faulting in orogenic belt plutons.
Sasao, Eiji; Yuguchi, Takashi*; Ito, Yasuto*; Inoue, Takashi*; Ishibashi, Masayuki
Proceedings of 10th Asian Regional Conference of International Association for Engineering Geology and the Environment (IAEG ARS 2015) (USB Flash Drive), 6 Pages, 2015/09
Understanding of the fracture network is important for disposal of high-level radioactive waste. We present our hypothesis on the formative mechanism of inhomogeneous distribution of fracture in the Toki Granite. In the Toki Granite, low- and high-angle fractures are abundant at the shallower part, while less at the deeper part where high-angle fracture is dominant. Distribution of the high-angle fracture is inhomogeneous. Thermochronological study revealed that the rapid cooling occurred at the early stage of granite formation. Paleomagnetic directions of the intact granite were dispersed. This suggests granite was plastically deformed during rapid cooling period. The rapid cooling might cause inhomogeneous distribution of cooling strain. When the granite reached to brittle deformation field, inhomogeneous fracture distribution was formed by the inhomogeneous strain. If so, recognition of the cooling history is essential to understand the distribution of the fracture network.
Ishii, Eiichi; Hashimoto, Yuta; Inagaki, Daisuke*
Proceedings of 10th Asian Regional Conference of International Association for Engineering Geology and the Environment (IAEG ARS 2015) (USB Flash Drive), 4 Pages, 2015/09
This manuscript describes unpredicted inflow which occurred during tunnel excavation for a permeable fault zone with clay-rich gouge although the fault zone was pregrouted. Some observational evidence indicates that the gouge was increasingly washed out into the tunnel through the rockbolts penetrating the gouge and the boundary between the shotcrete and the gouge on the excavation side wall during excavation. The resultant piping/erosion of the gouge probably accelerated groundwater flow from the outer aquifer of the pregrouted zone to the tunnel. After an excavation outcrop exposing the fault zone was temporarily shotcreted, major inflow occurred from the nucleated flow channel in the fault zone, breaking the shotcrete. When a fault zone including such clay-rich gouge is pregrouted, washout of the gouge during tunnel excavation should be fully cared because the gouge itself is not cemented by pre-grouting due to its low-porosity.
Yuguchi, Takashi; Tagami, Masahiko*; Tsuruta, Tadahiko; Nishiyama, Tadao*
Engineering Geology, 149-150, p.35 - 46, 2012/11
This paper describes the spatial distribution of fractures in the Toki granitic pluton, Central Japan and their evaluation with respect to the pluton's cooling behavior. Three-dimensional frequency distributions of entire fractures, based on borehole television data collected from 19 boreholes, shows that (1) the central region of the granite has a high fracture frequency and (2) fracture frequency decreases with decreasing elevation (datum is mean sea level), with the exception of the west side of the body. The development of sub-solidus reaction features was measured at two neighboring positions, and the difference was divided by the distance between the two positions. The resulting quantity is here defined as "local cooling rate". We observed a significant correlation between the distribution patterns of entire fracture frequency and local cooling rate; the region with a high local cooling rate corresponds to the region with a high frequency of entire fractures, and vice versa. This correlation indicates that fracture genesis can be explained by "local cooling rate", combined with the concept of thermal stress. Thus, the three dimensional pattern of local cooling rate is a potential diagnostic tool for quantifying the distribution of fracture frequency.
Ishii, Eiichi; Sanada, Hiroyuki; Iwatsuki, Teruki; Sugita, Yutaka; Kurikami, Hiroshi
Engineering Geology, 122, p.215 - 221, 2011/09
In a massive siliceous mudstone at the Horonobe Underground Research Laboratory site, a "hard part" showing remarkably high unconfined compressive strength was observed at the top of the siliceous mudstone (opal-CT zone) bounding overlying diatomaceous mudstone (opal-A zone). The "hard part" corresponds to a transition zone where opal-A and opal-CT coexist. Bulk chemistry and SEM images indicate that the "hard part" results from the stronger framework/cementation by the coexistence of opal-A and opal-CT. A transition zone can be generally stronger and more brittle and, if it is deformed, have significant impact on fluid flow.
Niwa, Masakazu; Kurosawa, Hideki; Ishimaru, Tsuneari
Engineering Geology, 119(1-2), p.31 - 50, 2011/04
Fracture zone development has a substantial impact on long-term changes in the underground environment because fracture zones are leading candidates as groundwater flowpaths as well as a locus for mechanical disturbance by fracturing. For understanding fracture zone development we surveyed the spatial distribution and characteristics of fracture zones in an area 4 km to the north and 6 km to the south from the western part of the Atotsugawa Fault, a long-lived active fault in central Japan. This study suggests that fracture zones along the Atotsugawa Fault act as a major conduit controlling regional groundwater flow. Based on rock features and deformation fabrics at meso- and microscopic scales, once fracture zones had formed, epigenetic deformation was concentrated in the ancient fracture zones.
Sawada, Atsushi; Uchida, Masahiro; Shimo, Michito*; Yamamoto, Hajime*; Takahara, H.*; Doe, T. W.*
Engineering Geology, 56(1-2), p.75 - 96, 2002/00
Metcalf; ; Hama, Katsuhiro; Yoshida, Hidekazu;
Quarterly Journal of Engineering Geology and Hydrogeology, (35), p.189 - 201, 2002/00
Sato, Toshinori; Kikuchi, Tadashi; Sugihara, Kozo
Engineering Geology, 56(1-2), p.97 - 108, 2000/00
Mikake, Shinichiro; Yoshida, Hidekazu; Koide, Kaoru; ; ; Yanagizawa, Koichi
Engineering Geology, 56(2), p.185 - 195, 2000/00
; Yoshioka, Naoya; ; Sato, Toshinori
Engineering Geology, 35, p.223 - 228, 1996/00