Ken-ichi Itakura

Fundamental Research on Drilling Processes Using Drag Bits

This paper proposes an analytical model to describe rock drilling processes using drag bits and rotary drills, and to induce relations among rock properties, bit shapes, and drilling parameters (rotary speed, thrust, torque, and stroke). In this model, a drilling process is divided into successive cycles. Each cycle includes two motions: feed and cutting. According to this model, drilling torque includes four components generated from cutting, friction, feed, and idle running respectively, the first three items are all proportional to the uniaxial compressive strength (UCS) when the penetration rate is constant. Laboratory tests verified the correctness and effectiveness of the proposed model qualitatively. Especially, the influence of friction on the flank face and the idle running was confirmed. Field experiments were performed. The results showed good correlation between the torque, penetration rate, and UCS. The proposed model and equations engender the possibility of eliminating useless components of cutting forces when investigating the relation between mechanical data and physical properties of rocks.

Laboratory Studies on Evaluation of Gasification Effect for Conversion of Coal Resources in Underground Coal Gasification (UCG) Reactors

Underground coal gasification (UCG) as a clean energy technology and efficient way for the conversion of the coal resources into energy in-situ has attracted wide public attention in recent years. Laboratory-scale experiments on coal blocks can provide significant insight into UCG process. The main goal of this study was evaluation of the gasification effect applying L-shape linking-hole and Coaxial-hole UCG models. Experimental results show the gas composition, AE activity and the temperature distribution inside the combustion reactors under similar operating parameters. Positive correlation was found between the temperature and cumulative AE events. The results shown that the gasification of L-shape linking-hole model obtained the average calorific value, as high as 11.3 MJ/m3, whereas in the Coaxial-hole model, the average calorific value of gas produced was only 5.79 MJ/m3 under the experimental conditions. Even so, the results of conducted Coaxial-hole UCG experiment provide the original and sorely lacking data base for future new-style UCG research.

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.

Ex Situ UCG model experiments with oxygen enriched air in an artificial coal seam

Underground Coal Gasification (UCG) demands precise evaluation of the combustion area in the coal seam. Especially, the monitoring of fracture activity in the coal seam and around rock is important not only for efficient gas production but also for estimation of subsidence and gas leakage to the surface. For this objective, laboratory experiments were conducted using the simulated UCG models. This paper also investigated gas energy for coal consumption, the production gas quantity and heat value, the application of oxygen element balance in the gasification reaction process, and the gas composition obtained in this study. During burning of the coal, temperatures inside the coal, contents of product gases and acoustic emission (AE) activities were monitored successively under the control of feeding gas (air/oxygen and steam) flow rate. Comparison of the temperature variation and accumulated AE event curves revealed a close correlation between them. The local change of temperature inside the coal induced fractures with AE. The AE activity was related closely to the local changes of temperature inside the model. The evaluation of gas energy recovery calculated from the obtained product gas provided a fair evaluation for the coal consumed, and the quantity of gas product and calorific value obtained from the UCG process.

Application of the Ultrasonic Propagation Time of a Core Sample for Stress Measurement of Underground Rocks.

Deformation rate analysis (DRA), although it has a poor theoretical basis, is a useful method for estimating rock stress in the laboratory using core samples. DRA is thought to be closely related to changes in the inner microstructure of rock samples undergoing a de formation process. Ultrasonic measurement is a useful technique for investigating structural changes in rocks. In this study, both methods were applied simultaneously to rock samples to confirm the applicability of ultrasonic measurement for the estimation of rock stress using a system of ultrasonic propagation time with accuracy in 10-2 nsec.In the experiments, core samples of sandstone were loaded up to a certain stress in order to artificially input memory of the stress into the samples, and the propagation time in the horizontal direction to the loading axis and the deformation rate were measured simultaneously. Consequently, the propagation time through the specimen was measured with high accuracy during deformation. Variations in the propagation time and lateral strain almost coincided during the loading-up process. Furthermore, the propagation time was drastically changed at the memorized stress corresponding to the deflection point of the deformation rate curve. These experimental results show that highly accurate measurement of the ultrasonic propagation time is useful, as is the DRA method using core samples, for examining changes in the microstructure inside rock samples under stress and applicable for estimating underground rock stress.

Effect of Pore Gas Pressure on Mechanical Behavior of Rocks under Confining Pressure.

The effect of pore gas pressure on the mechanical behavior of rocks has been investigated in order to confirm the validity of the effective confining pressure law among rocks. The triaxial compression tests of Noboribetsu welded tuff, Horonai sandstone (A), (B), Akabira sandstone and Akiyoshi marble were carried out with the strain rate 1.3 × 10-4/sec for confining and pore gas pressure combined with a conventional hydraulic testing machine. The stress strain curves of five kinds of rocks were determined under the condition of confining and pore gas pressure extending up to 50 MPa.The experiments show that the effective confining pressure law was valid for more porous and permeable rocks such as Noboribetsu welded tuff, Horonai sandstone (A), (B) and Akabira sandstone but Akiyoshi marble was not possible to adopt this law.The mechanical behavior of rocks whose pore are not fully saturated with gas pressure seems to largely depend on magnitude of the confining pressure acting on specimens.