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Collaborating Authors
Ohnishi, Yuzo
Abstract In order to conduct disaster-prevention inspections without overlooking falling-rock sources, in this paper, we aim to establish a disaster-prevention inspection method using microtopography highlight maps and verify its effectiveness. First, we create the map using the data obtained from a high-density aerial laser. In our study, measurements were carried out using a measurement helicopter loaded with a laser measuring machine capable of irradiating 80,000 to 400,000 points per second. For creating a microtopographical representation, grid data, contour maps, inclination-amount diagrams that calculate the amount of inclination for each grid datum and change the lightness accordingly to express the topography, and wavelet-analysis diagrams that emphasize the change in the unevenness through wavelet analysis, are generally used. However, it is difficult to extract sources of falling rocks, because it is impossible to express the topographic change point between the contour lines in a contour map. It is also difficult to distinguish between ridges and valleys in the inclination-amount diagram because there is no information indicating the height difference. Furthermore, it is difficult to distinguish the microtopography in the wavelet-analysis diagram, because there is no information indicating the height difference or inclination. Therefore, in this study, we created a microtopography highlight map by overlaying 50 cm of grid data, the inclination-amount map, contour diagram, and wavelet-analysis diagram created from the measured laser data. A field survey verified that, by using this map, it was possible to detect a steep cliff of height 2 m or more, which is a possible source of falling rocks. In our study, we were able to extract sources of falling rocks from a microtopography highlight map. 1. Introduction The necessity of tackling falling-rock projects is increasing, especially, because of the recent heavy rains and earthquakes in Japan. In September 2017, a man riding a bike in the Hualien County in East Taiwan was hit by a falling stone and died. To avoid such painful accidents, improvements in countermeasure projects for falling rocks are necessary. In Japan's rock-fall countermeasure projects, visual tools (drawings) such as basic forest maps and aerial photographs are used to investigate slopes and grasp the locations of falling rocks. However, on slopes covered by trees, it is difficult to prepare a plan view by actual measurement. As a background of investigation using these drawings, this is because these can be made relatively easily. However, in the current countermeasure projects, it is difficult to grasp accurately the positions of the falling-rock origins, from the surveys using these drawings. This leads to a decrease in the investigation efficiency, which is caused by poor positioning accuracy during the survey and because of overlooking objects. In addition, there are problems related to the safety of investigators at the time of investigation, because survey routes must be selected using these drawings and reliable research routes cannot be obtained from them. To solve these problems, it is necessary to improve the accuracy of the drawings used for the survey.
The examined region is surrounded by mountains formed by a bowl shaped depression in the Paleozoic strata and Granite. The Paleozoic strata basin rock is an impermeable bed upon which there are a permeable diluvium and then alluvium. It is estimated a lot of groundwater is saved. In the past research, we performed pumping simulation analysis for the pumping well of waterworks in order to consider the influence on the groundwater level by pumping quantitatively. As a result, the fluctuation of water level by many pumping wells was able to be estimated by the pumping simulation analysis. However, in some wells, the tendency for a groundwater level decreasing was not able to be estimated, despite of having fixed or stopped the pump discharge. If a pumping well continues to pump groundwater for a long time, various groundwater obstacles like the fall of the groundwater level or required amount of water can not be acquired and others will surface. One of the possible reasons for this is the weakening of temporal well capability which originates from a clogging in a screen in many cases. The purpose of this study is to examine quantitatively the characteristics of water-decline-level of an aging of well by improving the past model and performing pumping simulation analysis.
Development of Grouting Technologies for HLW Disposal in Japan(5) - Development and Application of Numerical Model for Grout Injection Process during In-situ Grouting Test -
Koyama, Tomofumi (Kyoto University) | Katayama, Tatsuo (KANSOTechnos, Co. Ltd.) | Tanaka, Tatsuya (Obayashi Corporation) | Kuzuha, Yuji (Japan Atomic Energy Agency (JAEA)) | Ohnishi, Yuzo (Kyoto University)
ABSTRACT Grouting is commonly used to decrease the hydraulic conductivity of the fractured rock masses and control the groundwater inflow. Since underground facilities were constructed in various geological conditions, different types of grout material and mixing/injection methods were developed for effective and economical grout injection. It is also important to evaluate the grout arrival distance and the range of altered hydraulic conductivity field after grout injection. However, the mechanism of grout injection process has not been clarified sufficiently yet due to complicated chemical and physical processes of grout. In this study, to simulate the grout injection process, the three-dimensional numerical model based on equivalent continuum approach was developed and applied to the in-situ grout injection tests at the Grimsel test site, Switzerland. In the simulations, the injection pressure and/or injection rate was given as a boundary condition and total amount of injected grout (silica sol) was calculated. The breakthrough curves (grout arrival time and time evolution of grout density) at the observation boreholes and the distribution of altered hydraulic conductivity field were also investigated. The simulation results were also compared with the ones obtained from in-situ measurements/monitoring and show qualitatively good agreement.
Development of Grouting Technologies for HLW Disposal in Japan (4) – Planning and Results of In-situ Grouting Test –
Tanaka, Tatsuya (Obayashi Corporation) | Uyama, Masao (Obayashi Corporation) | Ishida, Tomoko (Obayashi Corporation) | Nakanishi, Tatsuro (Japan Atomic Energy Agency (JAEA)) | Ohnishi, Yuzo (Kyoto University)
ABSTRACT This paper describes the planning, material selection, execution and interpretation of the grout injection test carried out FY 2011 at the Grimsel Test Site (GTS) in Switzerland as part of the grouting technology project of the Japan Atomic Energy Agency (JAEA). Based on the findings of the rockmass characterization part of this study (Nakanishi et al, 2012, Bruines et al., 2012), it was decided to perform the grout injection test in a 5m interval with the highest expected hydraulic conductivity. Three 5m sections in three boreholes located 2m from the injection section were selected for observation. Colloidal silica grout was selected due to the low permeability of the rockmass. Before the grouting test, tracer tests were carried to determine the transport parameters of the test section, and the final silica grout composition for the grouting test. During the grouting test, the change of viscosity of the grout was continuously measured. Both flow rate and pressure in the injection section were recorded. In the observation sections, the pressure over time as well as the grout concentration, by means of electric conductivity measurements, was recorded. The grout reached two of the three observation intervals before the grout hardened, which makes the gathered dataset suitable for validating numerical grout penetration models.
Development of Grouting Technologies for HLW Disposal in Japan (2) In-situ Grouting Test Program and Site Investigation Results at the Grimsel Test Site in Switzerland
Nakanishi, Tatsuro (Japan Atomic Energy Agency) | Tsuda, Hidenori (Japan Atomic Energy Agency) | Abumi, Kensyo (Obayashi Corporation) | Uyama, Masao (Obayashi Corporation) | Ohnishi, Yuzo (Kyoto University)
ABSTRACT The Japan Atomic Energy Agency (JAEA) has been developing advanced grouting technologies and grout materials to seal fractures in the host rock of an underground disposal facility (repository) for the geological disposal of high level waste (HLW) in Japan. As a part of the JAEA Grout Project (JGP), this paper describes the in-situ grout injection test program carried out in the fractured granite of the Grimsel Test Site (GTS) in Switzerland with the aim of improving grouting design, in order to reduce unnecessary grout penetration into rock mass and investigate appropriate site investigation techniques. The in-situ grout injection test project at the GTS was carried out in three stages over three years. In the first stage, two parallel boreholes were drilled and surveyed by borehole TV (BTV). In the second stage, a third borehole was drilled, similarly surveyed and additional single borehole and cross-borehole hydraulic tests were conducted. The site investigation results were then used to determine the best configuration for the final stage of the grout injection test. The staged approach proved to be a good way to determine the best location for the grout injection test and to determine the next stages by identifying and mitigating possible problems before they occurred.
- Geology > Geological Subdiscipline (0.50)
- Geology > Rock Type > Igneous Rock (0.35)
Development of Grouting Technologies for HLW Disposal in Japan (3) – Development of a Hydro-geological Model using a Discrete Fracture Network –
Bruines, Patrick A. (Obayashi Corporation) | Tanaka, Tatsuya (Obayashi Corporation) | Hashimoto, Shuji (CFC Inc.) | Kuzuha, Yuji (Japan Atomic Energy Agency (JAEA)) | Ohnishi, Yuzo (Kyoto University)
ABSTRACT To better understand the grouting process and the effect of grouting on the performance of a nuclear waste repository, the Japanese Atomic Energy Agency has initiated a grouting test carried out in the fractured granite of the Grimsel Test Site in Switzerland. This paper describes the characterization of the rock mass carried out over a three year period, and how the data obtained has been used to make a discrete fracture network (DFN) model that attempts to account for as much known knowledge as possible (e.g. the location and orientation of fractures observed in the boreholes and the measured hydraulic transmissivity of 46 short intervals). Based on the DFN model developed, an equivalent continuous porous media (ECPM) model is generated for the purpose of numerical simulation of the grout injection process. The results of tracer testing have been used to optimize the specific storage and porosity distribution of the ECPM model.
Development of Grouting Technologies for HLW Disposal in Japan(1) Overall Program and Key Engineering Technologies
Fujita, Tomoo (Japan Atomic Energy Agency) | Kawaguchi, Masanao (Japan Atomic Energy Agency) | Walker, Colin S. (Japan Atomic Energy Agency) | Sasamoto, Hiroshi (Japan Atomic Energy Agency) | Yui, Mikazu (Japan Atomic Energy Agency) | Ohnishi, Yuzo (Kyoto University)
ABSTRACT The Japan Atomic Energy Agency (JAEA) started the JAEA Grout Project (JGP) in 2007, to investigate new grouting technologies and grout materials and to develop models for handling grout effects in performance assessment (PA), prediction of the long-term radionuclide migration and of host rock alteration. This paper presents an overview of the JGP and an example of how to apply key engineering technologies to the construction and operation of a purpose built underground facility (repository) for the geological disposal of high level nuclear waste (HLW). Further details of the outcome of the JGP can be found in papers (2–5) of the same series (Nakanishi et al., 2012, Bruineset al., 2012, Tanaka et al. 2012, and Koyama et al. 2012).
- Geology > Rock Type (0.47)
- Geology > Geological Subdiscipline > Geomechanics (0.31)
- Water & Waste Management (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Power Industry > Utilities > Nuclear (0.48)
The behaviors and stress distributions of the inclined jointed rock masses with different dip angles obtained from DDA are compared to the results of laboratory tests. By calculating the block stress distributions, it is confirmed that DDA can reproduce the arching around the trap door when lowering the trap door. The shapes of arching change with the angles of inclined layers. In addition, the earth pressures acting on the trap door shows non-symmetrical distributions when the layers are not horizontal. The stress concentration occurs in one side of the rock masses close to the trap door. Furthermore, the surface settlements are also related to the inclined angle, and the loosening zone in rock masses can be different from Terzghi's theory [1]. Since, simulations have good agreements with the laboratory test, it demonstrates the applicability of DDA to explain the mechanical behaviors of tunnel, such as arching phenomenon, non-symmetrical earth pressure distributions acting on the trap door, and the surface settlement profile in the jointed rock masses. Dans cet article est decrite l'etude numerique du perçage d'un tunnel dans un massif de couches rocheuses jointes inclinees. La simulation à l'aide de l'Analyse de Deformation Discontinue (DDA), en faisant varier l'angle d'inclinaison des couches de roche, nous apporte des resultats en termes de distributions de contraintes et de comportement des couches, resultats qui sont ensuite compares avec des resultats de tests en laboratoire. Les resultats confirment le fait que la DDA est capable de reproduire le phenomène d'arcage autour de la trappe lorsque la trappe s'abaisse. Les formes d'arcage varient selon l'angle d'inclinaison des couches de roche. Par ailleurs, lorsque les couches ne sont pas horizontales, la distribution de pression agissant sur la trappe est assymmetrique. La concentration de contraintes se produit du cote proche de la trappe. De plus, les tassements de surface dependent eux aussi de l'angle d'inclinaison. En consequence, les resultats de simulation sont en accord avec les tests en laboratoire, ce qui prouve que la DDA permet d'expliquer des comportements mecaniques du tunnel tels que l'arcage, les distributions assymmetiques de pression du sol sur la trappe, ainsi que le profil du tassement de surface dans la masse de roches jointes. Dieser Beitrag beschreibt eine numerische Studie ueber Tunnel im geklueftetem Fels. Das Verhalten und die Druckverteilungen in den unterschiedlich geneigten und gekluefteten Felsenmassen wird mit Hilfe des Discontinuous Deformation Analysis Programms (DDA) simuliert, und mit Laborversuchen verglichen. Die Resultate bestatigen, dass DDA der Gewölbewirkung im „Trapdoor" Experiment gut reproduzieren kann. Die Form des Gewölbes, andert sich mit unterschiedlichen Neigungswinkeln der Schichten. Bei _ geneigten Schichten entstehen unsymmetrische Druckverteilungen. Auch die Oberflachenabsenkung ist von dem Neigungswinkel abhangig. Die gute Übereinstimmung der Simulationen mit den Laborversuchen zeigt, dass die DDA-Methode gut geeignet ist, um das mechanische Verhalten von Tunneln, wie z.B. den Effekt der Gewölbewirkung, die unsymmetrischen Druckverteilungen bei geneigten Schichten, oder die Oberflachenabsenkung in gekluefteten Felsenmassen, zu erklaren. INTRODUCTION Many underground constructions, such as tunnel excavations and mining have to be constructed not only in the intact, stable rock mass, however, sometimes in the place with joints, faults, inclined strata and weak zones, etc. During the mountain tunnel constructions, specifically, it is pointed out that the discontinuities affect the behaviors of rock mass very much [2]. To complete the excavations in jointed rock mass successfully, it is necessary to not only guarantee the tunnel stabilities but also understand the mechanical behaviors of jointed rock mass. To solve the problems mentioned above, a discontinuous numerical analysis method named Discontinuous Deformation Analysis (DDA) is introduced in this study. By comparing the simulation results to the laboratory tests, the applying of DDA to solve the two major issues of tunneling, including loosened earth pressure and the characteristics of ground subsidence are discussed. Laboratory Test with Inclined Layers Testing Apparatus Park (2001) [3] and Park et. al. (2001) [4] performed the trap door tests to the inclined layers. The rock mass with inclined layers can be simplified and modeled as assemble of blocks in Fig. 1(a). Two predominant discontinuous planes exist in the model Fig. 1(b).
ABSTRACT: In this paper, we present the approaches of applying Discontinuous Deformation Analysis (DDA), a powerful numerical method, to practical problems related to slope stability analysis in three aspects: 1) calculation of factor of safety, 2) simulation of failure process and 3) rock fall analysis. The theory and the mechanism of modeling rock failure in DDA is briefly introduced. The factor of safety is directly defined based on the failure mechanism and is easily to be obtained in DDA calculation. Two practical applications have been presented to show how to use the method in practice. One application is the simulation of a slope rock mass collapse happened in Hokkaido, Japan. The other is rock fall simulation of a slope located in Niigata, Japan. It has been shown from two practical applications that DDA is a very effective numerical method for slope stability analysis. INTRODUCTION General speaking, slope stability analysis includes the following three major aspects. 1. Calculate factors of safety, which are very useful for investigating the weak or potential failure surfaces. 2. Simulate failure processes such as slope collapse. This work is very helpful in investigating the failure mechanism by reproducing the accident scene after the event happened or in estimating the damage that a slope collapse will bring about beforehand. 3. Analyze rock fall events. The knowledge of rock fall characteristics is very helpful in the design of protective structures for stopping the falling stones. It is obvious that numerical methods used for slope stability analysis should meet the requirements from above three aspects. Since discontinuity and rigid body movement are involved in this kind of problems, the widely used numerical methods such as Finite Element Method and Boundary Element Method are no longer effective. For this reason, we present the approaches of applying Discontinuous Deformation Analysis (DDA), a powerful numerical method, to slope stability analysis for above three aspects, since the method has the following merits: 1. It can be used for strain and stress analysis like Finite Element Method. 2. It can be used to deal with problems in which large deformations and rigid body movements are involved. 3. It can be used to simulate coupling or failure status between contacted rock blocks. Furthermore, in order to make DDA method to meet the practical requirements, we have made the following major improvements on the original DDA (Ohnishi et al, 1996). 1. Solve the problem of block expansions due to rigid body rotation error. 2. Add damping term so that the resistance from the air and drag force from plants can be simulated in rock fall analysis. 3. Energy loss from block collision can be taken into account, which is important for simulating the plasticity of the soft layer on the slope surface. 4. A practical software called DDAWorkTool has been developed, which makes it easy for engineers to apply DDA to their practical problems. In this paper, at first, the theory and discontinuity processing approaches are briefly introduced. And then, the factor of safety is defined directly based on the failure processing mechanism. Finally, two practical DDA applications to slope stability analysis in Japan are presented. One is the simulation of a rock slope collapse event, which happened at Hokkaido, Japan in Feb., 1996. The other is a rock fall analysis using DDA. It has been shown from these practical applications that DDA is a very
ABSTRACT: This paper presents a way to apply discontinuous deformation analysis (DDA) technique to rock fall simulations. In order to make the method meet the practical requirements, the original DDA has been improved in the following aspects: 1). reducing error from large rigid body rotation; 2). considering damping effect due to resistance in the air and drag force from plants on the surface; 3). considering energy loss from collision. It has been shown that the improved DDA is very efficient in rock fall analysis. The velocity and jump height of each falling stone can be easily estimated in detail for the whole falling path by DDA simulation. They are very helpful in the design of protective structures. A practical rock fall analysis has been made. The results are quite good in agreement with the experiment made on the same slope, and they were used to design new concrete walls to stop possible rock fall blocks coming into the adjacent road and railway. 1 INTRODUCTION In the mountainous country like Japan, rock fall is a very serious problem for maintaining roads, buildings and houses. Rock sheds, retaining walls and prevention nets and fences are usually used to mitigate the hazards. It is obvious that the knowledge about the motion behavior of falling stones, such as the falling paths, velocities and jump heights, is necessary for the design of these structures. Many experiments of falling stones on real slopes have been made in Japan. Some good experiences and empirical formulas have been obtained, even the Manual of the Countermeasure against Rock Falls (in Japanese) was drawn up by Japan Road Association in 1983. However, since the motion behavior of falling stones is closely related to the detail shape of a slope, it has been found that the manual is helpless for some slopes. According to this formula, one can find that it is almost impossible to make a prevention structure to stop a falling stone of 60tƒ from a height over 40m because of too large energy from the estimated velocity of 27m/sec. Therefore, the knowledge about the distribution of velocities and jump heights in the whole falling path is necessary for the analysis of rock fall. For this reason, we present a way to simulate the rock fall by use of the discontinuous deformation analysis (DDA) technique (Shi, 1989). In order to make the method meet the practical requirements from rock fall simulations, we, at first, make some improvements on the original DDA. This includes reduction of the error due to large rigid body rotation, consideration of motion damping effect due to resistance in the air and drag force from plants on the surface, and consideration of energy loss due to collision. It has been shown that the improved DDA is very efficient in rock fall simulations. The velocity and jump height of each falling stone can be easily estimated in detail for the whole falling path. They, obviously, are very useful in the design of protective structures.