It is very important to study the mechanism of the behavior of a slope in order to assess its stability, to predict its future behavior, and to design countermeasure works. There is an unstable steep slope along a national road in Yamaguchi Prefecture, Japan, where heavy rain has sometimes caused large displacements. Local collapses have occurred in some areas of the slope. The GPS displacement monitoring system was installed in 2012 to continuously monitor the slope displacements. The groundwater level of the slope has also been monitored at a few well points. The slope is composed of mainly rhyolite and granite. The surface is covered with colluvial deposits that accumulated due to past collapses.
In this paper, a numerical analysis is conducted to understand the mechanism of the slope behavior considering both the measured displacements and the groundwater height. The Universal Distinct Element Code (UDEC) is employed to better understand the mechanism of the displacement behavior brought about by heavy rain. The numerical analysis reveals that when the groundwater rises and reaches the height of a discontinuity (the boundary between the rhyolite and the granite), the water pressure in the discontinuity increases, the stress reaches the failure criteria, and the displacements increase largely. As a countermeasure, several horizontal drains were drilled toward the locations of the discontinuities, and the displacements became stable.
Knowledge of the mechanism of the displacement behavior of a slope is essential for assessing the stability of the slope, for predicting its future behavior, and for designing countermeasures. Monitoring the real behavior is important to investigating such a mechanism. There is an unstable steep slope along a national road in Yamaguchi Prefecture, Japan, where heavy rain has sometimes caused large displacements. Local collapses have occurred in some areas of the slope. A continuous displacement monitoring system, using the Global Positioning System (GPS), has been applied to confirm the behavior of the slope and to assess its stability (Nakashima et al., 2018).
Hayashi, Hisashi (Yamaguchi University) | Nishiuchi, Mizuki (National Institute of Technology) | Kanazawa, Shinichi (National Institute of Technology) | Ishiyama, Koji (Nishimatsu Construction) | Morimoto, Shingo (Yamaguchi University) | Shinji, Masato (Yamaguchi University)
The glass solidified body reprocessed by the high level nuclear waste disposal in the process of nuclear fuel recycle was the final design condition to construct the underground disposal tunnel under the over 300m depth in Japan. The design methodology and construction technique of underground facilities had been discussed.
However, there has been 17,000 tons of spent nuclear fuel rods kept by the nuclear power plants at poresent. It is necessary to develop the research of the construction method of direct disposal of the spent nuclear fuel rod. In the direct waste disposal facilities, it is assumed to become tunnel section bigger because of workability of construction and operation and closing when consider with underground disposal facilities. Also, the dynamic influence of tunnel invert may be bigger when the waste transport and movement system operated because the weight of spent nuclear fuel rod is bigger than the glass solidified body.
Therefore, this study is performed about a dynamic stability of direct waste disposal facilities, during tunnel excavation, the influence of the ground specialty during excavation and the influence of the load from transport and movement system to tunnel invert. This study applied 2D and 3D numerical analysis.
The process of deep geological disposal of high-level nuclear radioactive waste reproducted by nuclear power plant is main disposal method in Japan. According to the report titled “The second progress report on research and development for the geological disposal of High Level Waste in Japan”, a basic idea of geological disposal is called “multiple barrier system”. In this system, waste liquid generated in the process of nuclear fuel recycle is fixed as the vitrification. The vitrified solid is covered with isolation material in the pit of disposal tunnel located deep underground. The geological disposal facility consists of vertical shafts, disposal tunnel and disposal pits. The design of this facility needs to consider the economic efficiency and the workability at each stage of operation on construction, operation and closure. In the design of a disposal tunnel where waste is transported and stored, there are three factors of design mechanical stability, workability of construction, operation, backfilling and economy. Then, the optimum sectional shape is proposed for the tunnel of the geological disposal facility.
In considering the safety performance of CO2 storage in oil reservoir or aquifer and deep geological repository of the nuclear wastes, the groundwater flow and the permeability should be estimated under various stress and thermal conditions.
In this paper, the permeability tests of single tensile fracture of granite cylindrical have been carried out under loading and unloading confining stress processes. In the experiments, the confining stress conditions of from 1.0 to 3.0 MPa and three types of thermal conditions, such as 20, 60, and 90 degree C have been applied to the specimen. The permeability of single fracture has been measured on each confining stress condition.
From the experimental results, the permeability in each thermal condition has decreased under loading process and it has also increased under unloading process. In cases of 20 and 60 degree C conditions, the rates of increase are the same and the reversible performances on loading and unloading process can be found. And, the permeability at each confining stress condition of 60 degree C is lower than that of 20 degree C. In case of 90 degree C, the permeability becomes smaller than that in other thermal conditions at each confining condition. The hysteresis on the loading and unloading process can be found. It is thought that the thermal expansion has occurred in the intact part of rock and the aperture becomes closed in case of 60 and 90 degree C. Moreover, in case of 90 degree C, it is also though that the thermal expansion and the geochemical response has been affected the structure of fracture and the permeability has been changed.
Considering the utilization of geothermal energy, the fluid circulated in the rock mass need to be focused. Especially the hydraulic and thermal performance in the low permeable granite basement rock .The effective normal stress and permeability acting on the fracture roughness surface has been studied for years . Some research indicates that with increasing the effective stress the permeability is decreasing, and the permeability would be reduced with time due to the fracture asperities deformation and the fracture creep . The differential confining stress has a great influence in the initial coefficient of permeability, and the compaction deformation has less influence than dilation on the monotonic loading creep test . Moreover, in the hydro-thermal processing of short-term permeability test, no minerals dissolution could be seen after the experiment, but when the experimental duration is longer, it need to be given special attention on the issue of dissolution . Some researchers found in a time interval about 400h, the thermal influence reduced the permeability due to the mineral mass removed from the fracture asperities . Although it is important to know the time dependence and mechanical creep behavior under hydro-thermal conditions in many engineering applications, it is difficult to measure the permeability during a long time by using the steady state flow for tight rock, few laboratory works had been conducted .
Yastika, P. E. (Yamaguchi University) | Ibara, T. (Yamaguchi University) | Shimizu, N. (Yamaguchi University) | Iwata, N. (Chuden Engineering Consultants Co., Ltd.) | Takahashi, Y. (Chuden Engineering Consultants Co., Ltd.) | Araki, Y. (Chuden Engineering Consultants Co., Ltd.)
Monitoring deformation due to volcanic activity is important for understanding volcanic behavior and for predicting eruptions. The Global Navigation Satellite System (GNSS) is sometimes used for such purposes. However, the system requires the installation of sensors at the site, and the installation and maintenance of these sensors are usually difficult and dangerous when volcanoes in the area are very active. On the other hand, Deferential Interferometry Synthetic Aperture Radar (DInSAR) can be used to measure the surface deformation of volcanoes without the installation of any devices on the ground. Moreover, the time-series DInSAR analysis has the potential to reveal the deformation behavior of volcanoes at the pre- and post-eruption stages. However, the DInSAR results can be greatly affected by the temporal variation in the refractivity in the tropospheric layer, especially when there are large differences in height in the target area of the measurements. Although it is a fundamental issue of DInSAR, it is still difficult and there are only a few methods for removing the errors caused by the tropospheric delays of radar pulse waves. This paper discusses this issue and proposes two simple methods for improving the measurement accuracy. The proposed methods were applied to Sakurajima Volcano in Japan. Ground surface deformation was observed for three years, from November 2014 to August 2017, by a time-series DInSAR analysis using Sentinel-1 data (operated by the European Space Agency). In this way, the effect of the tropospheric delays was successfully reduced.
As a country that is located in the “ring of fire”, Japan has dozens of the active volcanoes. A volcano can be disastrous when it erupts, especially one that lies near a city. Therefore, the monitoring of the volcano’s behavior is very important for safety and risk management. The activities of a volcano usually lead to ground surface deformation. Thus, a volcano’s behavior can be monitored through the observation of its surface deformation.
Monitoring of the ground surface deformation can be conducted using a traditional measurement method, i.e., leveling or modern technologies such as GPS. Using the proper GPS method (i.e., the method developed by Shimizu et al., 2014) for surface displacement monitoring enables the yielding of continuous and highly accurate results. However, the method necessitates the installation of GPS sensors at the monitoring site. The installation and maintenance of the devices on the ground involve high costs and a great labor force. In addition, the installation and maintenance of the devices under tough and harsh conditions, like active volcanoes, can be dangerous.
Tuzla is well known for salt mining. Previous research found that the massive exploitation activities of salt mining have caused up to 12 meters of ground subsidence. These results were obtained by an analysis of the time series topographical data from 1956 to 2003. Abandonment of salt exploitation in center of Tuzla was lasting from 2001 and finally finished in 2007. Subsidence causes damage to buildings and infrastructures. Other research using a GPS survey has revealed that subsidence was ongoing from 2004 to 2007. The GPS results showed that the subsidence was decreasing. However, the subsidence is still ongoing in center of Tuzla City, especially in an area near new salt-water lakes for swimming.
In this research, the Differential Interferometry Synthetic Aperture Radar (DInSAR) method was applied to measure the present subsidence in Tuzla. The main purpose of this research is to enhance the ground subsidence information on the spatial distribution and temporal transition. The Small Baseline Subset (SBAS) time series approach is employed. Sentinel-1 data from October 2014 to November 2017 is used to generate the time series of the ground subsidence. The DInSAR results show that the ground subsidence is still ongoing in some areas. The maximum subsidence velocity is about 40 mm/year. This means that continuous subsidence monitoring is very important. In addition, a comparison of the subsidence obtained by DInSAR and GPS is analyzed and discussed in this work.
Ground subsidence has been a major man-made hazard in Tuzla since 1950. The main factor in this ground subsidence is the salt mining activities (Mancini et al., 2009a). Ground subsidence of up to 12 meters was reported during the period of 1956 to 2003 (Mancini et al., 2009a). Research on ground subsidence was continued by means of static relative GPS positioning conducted four times between 2004 and 2007 (Stecchi, 2008). The GPS results from 2004 to 2005 show that the ground subsidence velocity was about 100-200 mm/year. From 2005 to 2006, the ground subsidence decreased to 0-50 mm/year. In a limited area near the salt-water swimming lakes, however, the subsidence velocity was still close to 200 mm/year. The subsidence gradually decreased from 2006 to 2007, except for the area near the salt-water swimming lakes where the subsidence velocity was about 100 mm/year.
Currently, three GNSS stations are installed and in operation to monitor the ground surface movement. The three stations are located in Tuzla (reference point), Tušanj, and Pannonica (Čeliković, 2016). These GNSS stations provide real-time ground subsidence monitoring. However, the subsidence monitoring results of GNSS lack spatial coverage. Spatial coverage is important to understanding the behavior of subsidence itself.
ABSTRACT: Laboratory tests were conducted in this study in order to examine the changes in aperture of an open single fracture in a granite core over time, under confining pressures of 1-3 MPa and temperatures of 20°C and 60°C. During the experiment, the fracture aperture was monitored with X-ray CT. For a quantitative evaluation of the fracture aperture, the CT images were processed with image co-registration by the Scale-Invariant Feature Transform (SIFT) method and fracture surface extraction using the Canny edge detection algorithm. Based on the fracture surface geometry data extracted from the CT images, the aperture and contact ratio were calculated and compared. The effect of the confining pressure and temperature on the aperture and contact ratio was not clear from the results. However, the trend of the fluctuation in the aperture and contact ratio over time was found to be consistent with the trend of the fluctuation in permeability.
The aperture of an open fracture can change over time. It largely depends on the properties of the rock minerals and the geometry of the fracture surface asperities, and is a function of pressure and chemical dissolution, precipitation, and/or mechanical deformation. Although the importance of the thermo-hydro-mechanical-chemical (THMC) effects on the aperture of a fracture is widely recognized, few experimental studies have been conducted that directly observe the evolution of the fracture pore space geometry and the resulting changes in permeability.
The primary objective of this study is to visualize the evolution of the rock fracture aperture and asperities due to long-term pressure loading and temperature using the X-ray CT (Computed Tomography) technique. X-ray CT is one of the few experimental techniques for visualizing the inner structure of rock samples in a non-invasive and non-destructive manner. Many researchers have employed X-ray CT in the rock engineering field to visualize the heterogeneous micro-structure of rocks and micro-crack propagation (Verhelst et al. 1995, Sugawara 1997), to visualize the fluid flow of sedimentary rocks (Sato et al. 2002), to measure the tracer diffusion and migration into the rock matrix and fractures (Nakashima et al. 2004, Sato et al. 2007), and to visualize the fluid flow within deformed rock (Hirono et al. 2003). X-ray CT has also been used to measure fracture apertures and to detect contact areas (Sato et al. 2007, Yoshino et al. 2003, Sato et al. 2004, Re and Scavia 1999, Nakashima et al. 2010).
ABSTRACT: In measuring rock fracture apertures from X-ray CT images, a binarization method has generally been used to separate the air void parts (fractures) from the rock parts. However, reasonable thresholding is often an essential problem in this method, especially for heterogeneous rock materials. This paper suggests a new method for detecting fracture surfaces from CT images using an edge detection algorithm that is known well in the field of image processing as Canny edge detection. Applying this edge detection method to the CT images of a single granite fracture, 15 mm in diameter and 30 mm in length, this study successfully measures the fracture surface geometry, the aperture distribution, and the contact ratio.
Taking precise measurements of the geometric characteristics of rock fractures, such as the elevation distribution of fracture walls, the distribution of apertures, and the contacting asperities within the fractures, is essential because of their significant influence on the mechanical and hydrological behaviors of rock fractures. On a laboratory scale, the elevation distribution of fracture walls can be measured with micrometer accuracy using a system that combines a laser displacement sensor and a high-precision automatic positioning stage (e.g., ).
However, the distribution of apertures and the contacting conditions within a fracture are rather difficult to measure experimentally. In previous researches, various techniques have been proposed, such as 1) the surface topography approach, in which the topography of a pair of fracture surfaces is measured separately by a laser beam profiler, while the aperture is computed indirectly as the distance between the two fracture surfaces [2, 3]; 2) the injection approach, in which the specimen containing the fracture is cut into slices after some resin has been injected, and the aperture is measured as the thickness of the injected resin [4, 5]; and 3) the casting approach, in which replicas of the fracture apertures are made by casting .
We designed the wave energy conversion system which consists of water chambers array aligned along the wave propagation direction and the float-type wave energy converters, each of which is installed in the chamber and utilizes the gentle up/down motion of the water in the chamber. This system aims to match conditions required for practical use, i.e., durability against wave load, workability in setting and maintenance, high performance of energy gain, and reduction of total cost. Calculation is made along our previous mathematical model, but consideration on the load resistance connected to the generator is added for the information to practical use. Also the effect of the total length of the systems set on the time history of the total energy is considered more strictly.
A rising demand for energy coupled with the problem of environmental pollution has led to investigations into potential of new energy resources. Wave energy is one of the most dependable and predictable sources of renewable energy available which is free from the variations present in wind or solar energy(Takahashi, S. (1993); Malm O., and Reiten A.(1985); Evans, DV. (1982)). Various mechanisms for extracting wave energy have been developed but not fully realized due to structural strength and economic problems.
For the practical use of wave energy, all the following factors should be satisfied at some level: durability of the device, workability (without difficulty in installation, maintenance and repair), high performance of energy gain, and low cost. The durability of the device includes those of both the external structure and the power converting portion of the device. It can be said with certainty that the lack of fulfilment of the above mentioned conditions is the main reason that the wave power conversion technology has not reached a commercially generating stage.
In order to meet these conditions, the first author et.al.(2013) designed the system which consists of water chambers array aligned along the wave propagation direction and the float-type wave energy converters each of which is installed in the chamber and utilizes the gentle up/down motion of the water in the chamber. In this system, neither the wall(s) of the chambers nor the energy conversion device(s) are exposed to the impulsive load due to water wave. Also since this system is profitable when set along the jetty or along a long floating body, installation and maintenance are done without difficulty and the cost is reduced. Waves near the jetty or a loosely moored long floating body will propagate toward the length of these structures. Therefore, an array of water chambers set along the jetty or a long floating structure is profitable in the sense that the outer wall is never exposed to severe wave loads.
ABSTRACT: It is important to consider the influence of temperature when evaluating the frictional behavior of a single rock joint since it may change due to the geochemical processes occurring at the asperity contacts such as mineral dissolution. It is thought that the chemical processes may be accelerated under thermal conditions. In this study, the direct shear tests under a slide-hold-slide process, using artificial rock (mortar), granite and andesite with a single natural rough joint, have been performed at 20 and 60 °C. Through the experiments results, the shear strength healings can be evaluated. Moreover, the log-linear equation and the rate- and state-dependent friction law are applied to the experimental results. In particular, the cutoff time of rate- and state-dependent friction law shows the response with the difference of the thermal conditions
The fluctuation of rock fracture friction has been recognized as one of the major causes in fault mechanical behavior. In previous studies, Dieterich (1979) and Ruina (1983) proposed a famous empirical rate- and state- dependent friction (RSF) law. This law could well describe the variation of rock friction as observed in the slide-hold-slide direct shear test. Since, then a large number of researches related to the earthquake’s occurrences were conducted based on this friction law [e.g. Stuart and Tullis, 1995, Marone 1998]. The authors has been carried out the Slide-Hold-Slide(SHS) type direct shear tests of rock fracture including natural joint surface roughness under relative low confining (Kishida et al., 2011; Kawaguchi et al., 2009). Kishida et al. (2011) have confirmed that the shear strength recovery during short-time holding may be attributed to a purely mechanical process, like creep deformation at the contacted asperities, while the shear strength recovery during long-time holding is affected by both mechanical and chemical processes. Kishida et al. (2011) and Kawaguchi et al. (2009) were conducted under room temperature, and then, the influence of various thermal conditions was not considered.
In this research work, direct shear tests have been carried out under two different temperature conditions following a SHS process in a residual state employing mortar replica specimen, granite and andesite with a single joint surface roughness. Then, the RSF law has been applied to the experimental results and the influence in temperature has been discussed.
GPS is now being used widely for monitoring rock displacements, and it has been a useful tool for various rock engineering projects. The most important technical issue for the practical use of GPS in monitoring displacements is to perform real-time and precise monitoring even under adverse observation conditions, i.e., steep slopes, the existence of trees and walls above/around the sensors, bad weather conditions, etc. The authors and their colleagues have developed a precise real-time displacement monitoring system using GPS and have established a method of data processing which can automatically reduce the errors caused by meteorological factors and obstructions above the antennas.
In this research, the GPS displacement monitoring system is applied to monitor the displacements of an unstable steep slope for the safe management of a national road in Japan over the long term. Three-dimensional displacement monitoring results are shown.
Monitoring rock displacements is important to assessing the stability of rock slopes. The Global Positioning System (GPS) can continuously measure three-dimensional displacements over extensive areas. The “ISRM Suggested Method for Monitoring Rock Displacements Using the Global Positioning System” was proposed (Shimizu et al., 2014) as technology which can be used by anyone.
In this research, the GPS displacement monitoring system developed by the authors is applied to assess the stability of an unstable steep slope along a national road in Japan. Since local slope failures have occurred in the slope several times over the last 20 years, displacement monitoring has been conducted by borehole inclinometers and surface extensometers. Some of the instruments, however, have occasionally not worked due to large deformations, and it has become difficult to perform the monitoring continuously. In order to overcome such trouble, the GPS monitoring system has been applied (Furuyama et al., 2014). In this paper, the results of three-dimensional displacement monitoring using GPS are shown, and the applicability of this system for assessing slope stability is discussed.