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Collaborating Authors
Japan
A New Simple Shear Test of Rock Prism Specimen by Torsional Shearing
Togashi, Yota (Graduate School of Science and Engineering, Saitama University, Japan) | Hirasawa, Riho (Oriental Consultants Corporation, Japan) | Osada, Masahiko (Graduate School of Science and Engineering, Saitama University, Japan)
ABSTRACT: This study proposes a new simple shear test method by torsional shearing of rock prism specimens. In this test, multiple radially placed prismatic specimens are torsional sheared under normal load. To validate the test method, a torsional loading apparatus capable of carrying 50 kN normal load and 300 kN cm torque was prepared, and the proposed test was conducted using prismatic mortar specimens which strength are equivalent to soft rock (UCS < 25 MPa). The size of the prismatic specimen is 20 mm height, 20 mm width, and 70 mm depth. The stress-strain characteristics of the mortar specimens were consistent with the previously conducted trends in uniaxial compressive and tensile strength. Peak shear stress in simple shear tests at under 0.9 MPa normal stress conditions equals tensile strength. Almost equal tensile strength was obtained when compared to the results of the proposed test. INTRODUCTION To evaluate the stability of rock masses during earthquakes and rock foundation for offshore wind turbines subjected to wave action, it is necessary to evaluate the mechanical properties of rock masses in simple shear mode. A typical simple shear mode test is a torsion test. Talesnick & Ringel (1999) carried out torsion tests using hollow cylindrical specimens of sedimentary rocks to determine the anisotropic elastic parameters. For the same purpose of identifying anisotropy, the authors also proposed a method of identifying anisotropic parameters using hollow torsion tests (Togashi et al. 2018). In addition, Paterson & Olgaard (2000) conducted torsion tests using solid specimens to clarify geoscientific phenomena. On the other hand, unlike the indirect shear test, which controls the principal stress, the simple shear test, in which the shear force (torque) is directly applied, has a problem in the transmission of the shear force. In the simple shear test using the soil material, the shear force is transmitted by making the cap uneven. However, the methods in the field of soil mechanics cannot be easily applied to rocks that are hard and have a low strain level until failure. In the above two previous studies (Talesnick & Ringel 1999 and Paterson & Olgaard 2000), the cap and the specimen were rigidly bonded with an adhesive and sheared by applying a confining pressure of several tens of MPa.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.54)
Using Webcam to Visually Observe the Mechanical Behaviors of Shirahama Sandstone Under Triaxial Compression
Asahina, Daisuke (Geological Survey of Japan, AIST, Japan) | Takemura, Takato (Geomechanics Lab. Nihon University, Japan) | Endo, Takahisa (Geomechanics Lab. Nihon University, Japan) | Tsukurimichi, Yu (Geomechanics Lab. Nihon University, Japan) | Aoji, Yu (Geomechanics Lab. Nihon University, Japan)
ABSTRACT: We present a newly developed monitoring system to directly visually observe the shear behavior of Shirahama sandstones under triaxial compression testing. The proposed visual monitoring system contains a commercially available webcam and a pressure-resistant steel housing device. The webcam records the video clip of the rock specimen surface during the triaxial compression test. The recorded video frames and their associated digital image correlation (DIC) results allow a better understanding of the evolution of the strain fields and fracture development. The implementation of the proposed monitoring system is simple, safe, and inexpensive, but allow new data to be measure and provides new insights into the progressive shear behavior under triaxial compression loads. INTRODUCTION Triaxial compression testing of rock samples provides fundamental information for understanding the deformation and fracture behavior of rock mass, which is related to underground engineering applications such as tunneling, nuclear waste disposal, and carbon dioxide sequestration. Triaxial compression tests have been widely conducted and are widely accepted as a reliable test method and measurement system because of their simplicity, robustness, and repeatability (ISRM 1983; Paterson and Wong 2005). However, in general, triaxial compression test of rock samples are performed in the steel pressure vessel, and it is difficult to visually capture and observe the behavior of rocks, as in uniaxial compression tests. We recently developed a new measurement system to directly visually observe the behavior of rock specimens from the inside of the pressure vessel of the triaxial test apparatus. This newly developed measurement system exhibited three primary advantages compared to the other conventional measurement system: (i) the measurement system allows direct observation of the mechanical behavior of the rock specimen from inside the pressure vessel under confining pressure, (ii) the measurement system is inexpensive. It requires only a commercially available digital camera and the simple steel housing, and (iii) the measurement system is safe and can be installed without any modification of the existing triaxial apparatus.
- Geology > Geological Subdiscipline > Geomechanics (0.99)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.65)
- Water & Waste Management > Solid Waste Management (0.89)
- Energy (0.70)
- Media > Photography (0.57)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (0.89)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.57)
- Health, Safety, Environment & Sustainability > Environment > Climate change (0.55)
Rock Evaluation of NATM Tunnel Face Using Deep Learning
Nakata, Masanari (Kansai University Graduate School of Science and Engineering, Japan) | Halim, Karnallisa Desmy (Kansai University Graduate School of Science and Engineering, Japan) | Yun, Yeboon (Kansai University, Japan) | Kusumi, Harushige (Kansai University, Japan) | Nishio, Akinobu (Construction Services in Kinki Region, Kinki Regional Development Bureau, Japan)
ABSTRACT: Because of the complexity of the geological features, when the NATM method is used in Japan, the rock mass is evaluated in nine categories (A. condition of tunnel face, B. condition of excavation face, C. compressive rock strength, D. weathering and alteration, E. spacing of discontinuities, F. condition of discontinuities, G. direction of discontinuities, H. presence of water inflow, I. deterioration due to water) The evaluation is graded on four levels. The objective of this study is to use deep learning to quantitatively evaluate the frequency, condition, and morphology of fractures, as well as weathering and alteration of the tunnel faces; CNN was used to grade the three criteria regarding fractures. Furthermore, ratio of weathering area was detected by HSV color space for categories regarding weathering and alteration. We also applied Grad-CAM to verify whether the CNN model could actually evaluate rock fractures as a decision criterion. INTRODUCTION In Japan, the New Austrian Tunneling Method (NATM) is a very popular tunnel construction method because it can adapt to the complex geological formation of Japan. This construction method relies on the surrounding rock mass to ensure the stability of the structure. Furthermore, to maximize safety and minimize costs, support structure (determined through support patterns) could be change from the original design based on the observed rock mass as stated in the "Index for Road Tunnels Observation and Measurement (2009)". Rock mass on tunnel face are evaluated and graded based on a set of criteria, and labelled with a support pattern. Rock mass evaluation are typically done by onsite engineers, but since these decisions are based on their individual experiences, there is a discrepancy in judgement resulting in differing evaluations. This study will apply a type of deep learning method, the Convolutional Neural Network (CNN), to the process of rock mass evaluation. This study will focus on evaluating the visually observable features of rock mass, namely the rock fractures. Finally, Gradient-weighted Class Activation Map (Grad-CAM) is implemented to visualize CNN. In addition to the evaluation of rock fractures, the weathering area of rocks is quantitatively extracted by using HSV color space.
Reinforcement Effect of Deformation-Controlled Tunnelling Supports Based on Three-Dimensional Tunnel Excavation Analysis
Yokota, Yasuhiro (Kajima Technical Research Institute Singapore, Kajima Corporation, Singapore) | Date, Kensuke (Kajima Technical Research Institute Singapore, Kajima Corporation, Singapore) | Sainoki, Atsushi (Faculty of Advanced Science and Technology, Kumamoto University, Japan) | Ishii, Masako (Kajima Technical Research Institute, Kajima Corporation, Japan) | Masumoto, Kazuhiko (Kajima Technical Research Institute, Kajima Corporation, Japan) | Utsuno, Mori (Kajima Corporation, Japan)
ABSTRACT: In recent years, many tunnel excavation projects are planned despite swelling ground conditions and/or great depths subjected to high ground pressure around the world. In such cases, there is a risk that the high ground pressure will exceed the loading capacity of the conventional rigid supports, leading to brittle failure. Accordingly, the authors have been developing new deformation-controlled supports that can reduce stress acting on steel supports, shotcrete, and rock bolts by gradually resisting high ground pressure while controlling tunnel deformation. Here, we report on a study of support specifications suitable for actual tunnel excavation, performed by developing the constitutive model of deformation-controlled supports and analyzing 3D tunnel excavation. INTRODUCTION Deep excavation in squeezing ground presents many challenges in tunnel engineering and construction. Adverse geological conditions, such as high overburden pressure, extremely shallow tunnel cover, unsymmetrical earth pressure / anisotropic stress condition and large cross-section certainly add complexity to this matter. As such, the role of the deformation-controlled (DC) tunnelling supports, which absorb certain displacement while effectively supporting the tunnel, has become more crucial and beneficial to ensure the tunnel stability as the conventional rigid tunnelling support systems may not work effectively with such tunnelling difficulties. Prior to this work, relevant studies were undertaken mainly for individual tunnelling support component. However, a holistic and comprehensive study of the complete support mechanism is required for a deep understanding and better application of the DC supports. In this paper, three-dimensional numerical analyses were performed using the FLAC3D 6.0 to study the effect of the DC supports to the overall tunnelling support system under the static load condition. Code scripts implemented in fish and python languages were developed and used in conjunction with the FLAC3D 6.0 to parametrically evaluate the mechanical state of each component (i.e., rock bolts, steel support, shotcrete) of the tunnelling support system. The effective utilization of the DC supports has also been discussed with the aim of optimizing the support system performance.
ABSTRACT: Consolidation property is an indicator of load bearing capacity of foundation and also reflects the process of geological evolution. In general, consolidation test has been performed for soil materials in geotechnical area, however we tried to conduct consolidation test using Mio–Pleistocene sedimentary rocks taken from a forearc basin located at a subduction zone. Consolidation yield stress almost increased as porosity decreases, however consolidation yield stress has variation in same porosity and it was increased with depth of sampling point, that indicates the consolidation line of this setting and the consolidation yield stress would record the maximum burial depth of the basin. SEM images show the consolidation fabric which has layer structure and high-resolution X-ray CT images show a deformation during the consolidation test. INTRODUCTION Consolidation property is one of the important mechanical properties of sedimentary rocks both in geoengineering and geologic fields. It is an indicator of load bearing capacity of foundation and also reflects the process of geological evolution. In general, consolidation test has been performed for soil materials in geotechnical area to examine the state of underground which is basement of building and to clarify the process of consolidation. Although the test may also be used for soft sedimentary rocks to investigate the tectonic process, e.g. the developmental process of the plate boundary where the crustal movement is violent (Morgan & Ask 2004), only a few such previous researches are available. To examine the excess pore pressure induced by the marine landslide, the one-dimensional consolidation tests were performed and the consolidation yield stress were estimated using a Pliocene sedimentary rock with around 40% porosity taken from a forearc basin located at a subduction zone (Kamiya et al., 2018). In this study, we report the properties in detail during the consolidation tests using a constant strain-rate loading system and discuss the results of the consolidation tests with the observation of the micro fabric and the consolidation deformation using SEM and X-ray CT images.
- Phanerozoic > Cenozoic > Quaternary > Pleistocene (0.36)
- Phanerozoic > Cenozoic > Neogene > Pliocene (0.35)
- Geology > Rock Type (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics (0.98)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.68)
Strategy and Application of Slope Monitoring Over Dam Basin in Regular Periods and During Emergencies Using SAR and GNSS
Shoji, Yukiko (Electric Power Development Co., Ltd., Japan) | Kikuchi, Teruyuki (J-POWER Design Co., Ltd., Japan) | Koike, Hitoshi (J-POWER Business Service Corporation, Japan) | Shimizu, Norikazu (Yamaguchi University, Japan)
ABSTRACT: Monitoring the behavior of slopes around the sites of hydroelectric power plants and dam reservoirs over dam basins is important for their stable operation and a reduction in the risks of accidents and disasters. However, since there are numerous slopes widely located over a dam basin, it is generally not feasible to efficiently monitor the behavior of all the slopes over such an extensive area. Satellite technology, SAR and GNSS, will contribute to overcoming this difficulty. In the present paper, a strategy is proposed for slope monitoring over a dam basin in regular periods and during emergencies using SAR and GNSS. Then, practical applications are demonstrated for regularly monitoring the slopes and for detecting unstable slopes during an emergency brought about by an extremely heavy rainfall in Japan. INTRODUCTION It is important to regularly monitor the behavior of slopes around the sites of hydroelectric power plants and dam reservoirs over dam basins from the viewpoints of their stable operation and a reduction in the risks of accidents and disasters. Moreover, during emergencies, such as earthquakes and heavy rainfalls associated with typhoons and storms, monitoring is expected to aid in the early detection and prediction of slope failures. However, since there are numerous slopes widely located over a dam basin, it is generally not feasible to efficiently monitor the behavior of all the slopes over such an extensive area. Satellite technology, SAR (Synthetic Aperture Radar) and GNSS (Global Navigation Satellite System), will contribute to overcoming this difficulty. SAR is a high-resolution radar device that is mounted on an artificial satellite. It can provide the displacement distribution over extensive areas of more than several hundred square kilometers without the use of any sensors on the ground surface. GNSS can continuously locate three-dimensional displacements in target slopes. In this paper, a strategy is proposed for slope monitoring over a dam basin in regular periods and during emergencies using SAR and GNSS. Practical applications are demonstrated for regularly monitoring the slopes around a dam basin in Japan and for detecting unstable slopes during an emergency brought by an extremely heavy rainfall event.
- Energy > Power Industry (1.00)
- Energy > Renewable > Hydroelectric (0.96)
ABSTRACT: The authors developed a measurement method by the fiber optic sensing which can evaluate vertical and lateral displacements ahead of the tunnel face. The method uses some fiber optic cable sensors named All Grating Fibers capable of evaluating the longitudinal strains along the cable with high positional resolution and accuracy by the Optical Frequency Domain Reflectometry method. The cable sensors are fixed with inflatable packer tubes in a square pipe inserted in a steel forepole drilled from the face and can be retrieved after the measurement. One advantage is therefore the fact that fibers can be repeatedly used in other pipes. This paper outlines the developed tunnel pre-displacement measurement method by the fiber optic sensing. Results of laboratory experiments and field measurements conducted in a motorway tunnel construction project are also presented. INTRODUCTION In tunnel construction projects, monitoring of ground behavior ahead of the tunnel face is often required especially when tunneling in poor rock conditions, or in urban areas where the influence on structures existing near the tunnel should be minimized. Based on the monitoring results, some auxiliary methods and pre-supports can be studied and installed to control the behavior if required. For this purpose, the ground displacement ahead of the tunnel face (tunnel pre-displacement) is often measured by in-tunnel instruments. For example, Sakai et al. (2016) reported a case study of an underground metro station construction project in a built-up area in which settlement ahead of the tunnel face at the crown level and tunnel longitudinal displacement were measured for evaluating the ground stability ahead of the face. Chain inclinometers named Shape Accel Array concatenating with a series of 50 cm long segments of MEMS acceleration sensors were used for settlement measurement. Schneider et al. (2018) reported two measurement results of settlement ahead of the tunnel face at the crown level in the Brenner Base Tunnel construction project. The chain inclinometers of 40 m length and concatenated with a series of 2 m long segments were installed in measurement holes above exploratory tunnels at the transition from larger to smaller excavation profiles to validate the longitudinal displacement profile assumed in the tunnel support design. Other authors also reported measurement results but mainly in shallow tunnels.
ABSTRACT: We carried out the centrifuge model test to evaluate the long-term behavior during the resaturation surrounding the deep geological disposal repository. The centrifuge model is the vertical emplacement concept repository and 1/50-size, and the sedimentary rock is drilled a single disposal tunnel and hole, and then the model-overpack, Na-type bentonite buffer, and backfill material are placed in. And the test was conducted at 50 G with the effective stress of 3 MP for equivalent to about 200 years based on centrifugal similarity law. As a result, the displacement of the overpack was measured to be several times larger than that of the tests without the backfill material and disposal tunnel. In addition, it was confirmed that the buffer significantly expanded to the disposal tunnel after the test and visual confirmation. Test results implied that the displacement of the overpack is affected by the stiffness of the backfill material. INTORODUCTION The high level radioactive waste (HLW) disposal repository in Japan will be built in deeper than 300 m in the underground (JNC, 2000). The vitrified waste is enclosed in a metallic overpack. It is then packed, surrounded by buffer material made of clay bentonite, into a disposal hole drilled deep into the bedrock. The near-field is composed of such a heterogeneous composite. In the near-field, various processes will occur under the effect of heat from the waste, rock stress and underground water. This thermal-hydraulic-mechanical (THM) transition will dominate and continue for hundreds of years in the initial construction, operation, and closure stage. These states are transition period of artificial disturbance and resaturation, and phenomena dominates THM, mechanically unstable. Long-term behavior in the near-field is finally evaluated by numerical analysis. In order to improve the reliability of the numerical analysis, it is necessary to validate the numerical analysis by comparing it with test results. To validate the numerical analysis, Nishimoto et al. (2016) conducted centrifuge model tests, which are time-acceleration tests based on the similarity law of static fields, and Sawada et al. (2017) compared the test results with those of the numerical analysis.
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.36)
- Health, Safety, Environment & Sustainability > Environment > Waste management (0.35)
Consideration to Evaluate Maintenance Process for Utilization of Non-Supported Underground Quarries
Huang, Rui (Utsunomiya University, Japan / Xihua University, China) | Seiki, Takafumi (Utsunomiya University, Japan) | Dong, Qinxi (Hainan University, China) | Noguchi, Shizuo (Utsunomiya office, Kawasaki Geological Engineering Co. Ltd., Japan) | Ohmura, Takeshi (Utsunomiya office, Kawasaki Geological Engineering Co. Ltd., Japan)
ABSTRACT: In this study, the authors focus on propose evaluation chart for checking stability and safety the underground quarries because of the underground quarries are unstable and worried about the corrupts. Additionally, it is necessary for those users, such as entrepreneurs to evaluate the stability of the underground spaces in case of utilizing those underground spaces in certain purpose. Field survey is very important and necessary to understand for the workers and entrepreneurs. Thus, the authors consider the stress distribution and deformation to simulate active and abandoned underground quarries. the authors will consider stability for individual structure of room and pillar type based on the numerical analysis with considering influence of adjacent underground spaces. Finally, the authors will discuss the maintenance process to utilize the underground quarries analysis. INTRODUCTION Background The authors have considered the stability of Oya underground quarry (Seiki, et al.2016), which is quarrying Oya tuff in Utsunomiya city, Tochigi Prefecture, Japan, to evaluate easily by using table for engineers to check the stability. Oya tuff is classified into pumice tuff geologically and it is called Oya stone. And it is used as building materials for fences and decorating plate for houses. Those underground space structures are almost non-supported and locate in Oya area about 5 km in north-south and 4 km in east-south. It has said that there are over 200 underground spaces after quarrying Oya tuff. Almost of them has room and pillar type structures some of them has long-wall type structures. Some of them has been unstable and had corrupted (Memories of Natural Disasters 2023). Objective for study In this study, the authors focus on propose evaluation indexes for checking stability and safety the underground quarries because of the underground quarries are unstable and worried about the corrupts. Additionally, it is necessary for those users, such as entrepreneurs to evaluate the stability of the underground spaces in case of utilizing those underground spaces in certain purpose. Field survey is very important and necessary to understand for the workers and entrepreneurs. At first, the authors propose the way of field survey to consider the table. Secondly, the authors try to propose the evaluation chart including indexes for novice users, especially entrepreneur to check the structural safety for business continuation easily because of being aware of unstable state according to daily use. Thus, the authors consider the stress distribution and deformation to simulate some of underground quarries. As roughly those quarries have two kinds of structure, room and pillar and long wall type structures, the authors will consider stability for individual structure based on the numerical analysis with considering influence of neighbor underground spaces. Finally, the authors will propose the maintenance concept to utilize the underground quarries based on filed survey and numerical analysis.
ABSTRACT: For the long-term stability assessment of underground structures, it is essential to understand the effects of water on the time dependent properties of rock, such as loading-rate dependence, creep, and relaxation. In this study, the relation between the loading-rate dependence of strength and the stress dependence of creep lifetime in dry and wet conditions was examined on the basis of the previous experimental results of a tuff. It was found that the results of strength and short-term creep tests in dry and wet conditions are consistently explained with the rate process theory, which indicates that creep lifetime can be estimated from the loading-rate dependence of strength in a dry or wet condition. Using these theoretical and experimental findings, the creep lifetime in the ongoing 25-year creep test was predicted. INTRODUCTION It is well known that rock demonstrates various time dependent behaviors such as loading-rate dependence, creep under constant stress, and relaxation under constant strain (Cristescu & Hunsche 1998 and Brantut et al. 2013) and that these are closely related to each other (Hashiba & Fukui 2016). Previous studies have reported that the deformation and failure of rock are influenced by water; for example, rock strength and Young's modulus are lower in wet conditions than in dry conditions (Kirby 1984), and the time dependent behaviors are accelerated by water (Hashiba & Fukui 2015). For the long-term stability assessment of underground structures, it is essential to understand the effects of both time and water on the deformation and failure of rock. Hashiba et al. (2018) explained the relation between the loading-rate dependence of strength and the stress dependence of creep lifetime in dry and wet conditions on the basis of the rate process theory and demonstrated that the results of an andesite are consistently elucidated with this theory. Hashiba et al. (2019) reported that the loading-rate dependence of strength of the andesite in various water saturation conditions are also consistently elucidated with this theory. These theoretical and experimental findings indicate that the effects of time and water are integrated and that creep lifetime can be estimated from the loading-rate dependence of strength and the results in arbitrary water saturation conditions can be estimated from the result in a certain water saturation condition. However, these studies examined the results of strength and short-term creep tests with a single type of rock, andesite, and hence it is not sure if this theory can be applied to other rocks or to long-term creep tests. In this study, the applicability of the theory derived from the results of the andesite was examined using the previous results of strength and short-term creep tests with a tuff. Then, the results of long-term creep tests with the tuff were used for comparative discussion with those of the short-term creep tests.