Kazuhiko Sato

Source Mechanism of a Large Scale Gas Outburst at Sunagawa Coal Mine in Japan

On January 29ty, 1986, the third largest gas outburst in Japan took place at Sunagawa Coal Mine, which is the only hydraulic mine in Japan. It occurred at a face of a cross-cut, just after a coal seam was outcropped by blasting for drivage of the cross-cut. The site of the gas outburst was located 1,180 m below the surface. No workers were injured, but the cross-cut was plugged with 1,600 m3 of coal fragments extending over 100 m behind the face and 60,000 m3 of methane gas was emitted.The site of the gas outburst was investigated in detail to clarify the geological features. A normal and a reverse fault existed at the site. The area of the ejected zone was about 400 m2 and extended upward along the normal fault. The shape of the ejected zone suggests a great role of the normal fault on the gas outburst.Digital seismograms, recorded by a mine-wide seismic array at the coal mine, consisting of 27 microseismic events were used to investigate the gas outburst. Magnitude, seismic energy release, distribution of hypocenter and focal mechanism were analyzed. Taking the shape of the ejected zone together with results of the seismological investigation into consideration, it appears that the seismicity started with left-lateral faulting of the reverse fault and then right-lateral faulting of the normal fault followed. The faulting of the normal fault might be the direct cause and be the predominant mechanism of the gas outburst.

Induced seismicity associated with longwall coal mining

Abstract This paper describes the influence of mining parameters and geological conditions on seismicities associated with longwall coal mining. Microseismic activities were observed by using a mine-wide seismic array at 13 mining panels in the deepest coal mine in Japan. Most microseismic events were located in the vicinity of coal faces. In this case where a coal face was advanced along the rib-side of an old working, the tail entry T-junction suffered the most severe seismicity in the panel. The seismicity also intensified during the widening of a coal face. The seismicity at a panel was significantly alleviated by the presence of old workings above the panel, but intensified by a coal pillar left in an old working above the panel. The seismicity was also controlled by a fault. Stress analysis using a numerical model was attempted and the results offered good interpretation of the distribution of seismic energy density.

Design and implementation of partial mesh community wireless network in Himalayan region

Infrastructure-based CWN (Community Wireless Networks) are emerging as an affordable, robust, flexible, scalable and spreading technology in difficult terrain land distribution focusing in low income regions and communities having less or no density of wired networks. This paper studies how wireless broadband networks fill the void of network services in rural area. In order to address the proper implementation mechanism, we have deployed a CWN in the rural village of Kaski District of Nepal providing the community with Internet and related services as extra contribution. This research provides researchers a real-world test-bed for exploring the technical and social issues entailed in deploying CWNs in the heart of a small community of Himalayan region in Nepal. The model is used to analyze the tangible and intangible contribution of community and contributors that support the establishment of community networks. Also the result from the research is used to measure the problem in network design, sustainable network management and proper utilization.

9. Microseismic activity associated with hydraulic mining

Abstract Microseismic activity induced by the hydraulic mining of steeply inclined coal seams has been monitored in order to clarify the strata mechanics of hydraulic mining. A mine-wide seismometer network detected 652 microseismic events, with local magnitudes greater than −2.5, during mining of the panel which is situated at 1000 m below the surface. The largest microseismic event with a local magnitude of 0.1 was felt both on the surface and underground. The magnitude-frequency relation of seismic events followed Gutenberg-Richters formula, in which the b-value was estimated as 0.92. The seismic energy release rate varied with face advance due to changes in the mining geometry and configuration. A majority of hypocentres concentrated on the coal pillar which had been left in the old workings and was bounded by the active mining panel. Another group of seismic foci clustered on a pre-existing fault which runs through the border of the panel. The other events were distributed around the coal face and moved with the face advance. The spatial distribution of the seismic energy suggests that microseismic activity associated with hydraulic mining is mainly induced by collapse of coal pillars and fracture of the front abutment of coal face, and also partly caused by the roof caving into the goaf and by floor heave.

Polarization of crack waves along an artificial subsurface fracture

We analyze three-dimensional (3D) particle motions of crack waves which propagate along a fracture to determine fracture orientation. Crack waves were measured at an artificial subsurface fracture at a depth of approximately 370 m in the Higashihachimantai Hot Dry Rock model field in Japan. Dispersion was observed in crack waves. Velocities of crack waves below 100 Hz are 100 m/s–150 m/s along this artificial fracture. Therefore, crack waves arrived after compressional wave and shear wave. A coherence matrix is used to analyze the 3D particle motions in the frequency domain. Noise, which is outside of the band of the detector, is excluded in the coherence matrix analysis. We examine the polarization of 3D particle motions of crack waves using Principal Component Analysis. The longest axis of an ellipsoid which approximates the 3D particle motions shows a direction consistent with estimates obtained by core-sample measurements and tectonic stress measurements. The differences in fracture orientation obtained from the crack-wave analysis and the core sample analysis are less than 16° in azimuth and less than 20° in dip.

Kinematics, Dynamics and Statics of Wheel Loader during Scooping Process. Study on implementing machine intelligence into wheel loader. (1st Report).

In order to provide capability of intelligent control to the wheel loader, its motion during the scooping progress is modeled and analyzed on the basis of robotics. Motion of bucket linkage along with translation of wheel loader itself is presented by means of mechanical manipulator with three-degree-of-freedom, though the bucket linkage consists of twelve joints and ten links, and it involves three closed loops. The modeling of wheel loader enables us to plan a set of trajectories of three active joints in advance preceding scooping. The modeling provides not only kinematical information, but also a computational tool to evaluate dynamical forces to actuate all active joints in advance preceding scooping. In addition to kinematics and dynamics, the present paper also covers statics of the bucket linkage, which formulates the reaction at active joints against payload imposed on the bucket during scooping.The results of motion analysis and statics are integrated into a computer program, which is capable of simulating the progress of scooping materials piled with various angle of slope. This paper finally describes the results obtained from a series of computer simulation in which the slope angle of piled material is varied from 25 to 45 degrees.

Coal Mining Technology. Visualization System for Roof Rock using the Mechanical Data of Roofbolter.

It is important to obtain information about geostructure of roof rock for effective rock bolting at the roadway in underground coal mine. Information on the variation in rock types and the distribution of discontinuities, such as layer boundaries, separation of strata and cracks, is especially important. For in situ evaluation of roof rock, we developed a measurement-while-drilling (MWD) system using mechanical data obtained from a drilling machine. The hardware of this system detects the torque, thrust, revolution and stroke of the machine as the mechanical data, and the software analyzes the mechanical data log and displays the locations of discontinuities by Neural Network techniques. This system also enables estimation of the 3-D geostructure of roof rock with regard to the change in rock types and distribution of discontinuities in the case of an array arrangement of drill holes. For displaying images inside the 3-D geostructure, animation consisted of slicing images and/or a 3-D model describing the boundary plane of layers by VRML(virtual reality modeling language) in virtual space are employed. We conducted some feasibility studies of this system using a pneumatic and a hydraulic drilling machine in roadways of Taiheiyo Coal Mine, Japan. The results of feasibility studies confirmed that the 3-D geostructure, including the distribution of crack density, can be reconstructed by the analysis system. Animation and display by VRML for the 3-D geostructure were useful for understanding inner structure of rocks.

A Practice for Training IT Engineers by Combining Two Different Types of PBL

PBLs signifies both problem-based learning and project-based learning; we clearly distinguish between the two types of PBLs. The former PBL involves finding ways to solve problems under unfavorable conditions. In the curriculum at our institute, problem-based learning has been conducted since 2006. By contrast, project-based learning involves a student team undertaking an actual project, devised by a company. We did not adopt project-based learning in our curriculum. In 2016, our institute joined the Education Network for Practical Information Technology project of Japan’s Ministry of Education, Culture, Sports, Science and Technology. In that project, around 40 universities are engaged in developing a cooperative network. Each university develops practical education using PBL; its knowledge and resources obtained are shared among other universities in the network. For our part of the project, we added 3 practical exercises based on project-based learning. By combining the two different types of PBL, our curriculum provides exercises that introduce better problem-solving skills, instill a challenging spirit, and provide practical experience for students. In this paper, we report our exercises and practical results for 2017.

Implementation of Collaborative E-Learning System for Unstable Environment

We design a collaborative e-learning system for stable operation in an unstable environment of developing countries. The proposed system is used for providing a collaborative learning among local schools of rural area in Nepal. The stable operation of the system is realized by the redundant robustness in three different levels: network arrangement, energy management,, replicative database. In this paper, we present an overall design of the system, its use case. Then, methods adopted for achieving the redundancy in each level are described.

A Support Method for Programming Education Based on Analysis of Each Learner’s Mental States

This paper describes a support method for programming education in self-learning style and its implementation. It is difficult and important for learners to keep their motivation. In this research, methods for catching the learning data, which cope with four learning steps; reading text, check test, coding and compile, are developed. Psychological agent, which analyzes the learning data and grasps each learner’s state based on ARCS model, is also developed. According to the diagnosis by psychological agent, interface agent gives advice and hints to the learner in visual and auditory way. Implementation of prototype system, an experiment with the prototype and its results are reported. Finally, the efficiency of proposed method and further problems are discussed.