Masuyuki Ujihira

Ultrasonic Measurement System for Detecting Penetration of Boulders by Autocorrelation Analysis

An elastic impact wave method is used as a typical nondestructive test method to investigate the depth of boulder penetration. However, in the elastic impact wave method using, for example, a hammer, the discrimination of the reflection wave produced by minute cracks is difficult. Theoretically, if it becomes possible to input the vibration of an ultrasonic domain into artificial structures, such as a concrete and a boulder, with a strong amplitude, deeper investigation depth compared to the conventional way with a high precision will be attained. In this study, a concrete block, with a known size, which was, unlike boulders, not buried under ground, was used as a test piece in a basic experiment. As analysis methods, a wavelet analysis for checking the reflection wave and an autocorrelation analysis for identifying the time lag of the reflection wave were used. As a result, the reflection wave was detected in a down chirp signal from 50 kHz to 40 kHz.

Two dimensional source location system for rock fall detection by using cable sensor and mobile multimedia network

Abstract Output characteristics of cable sensor which usually used for invader detection to atomic power station and others were tested. It was found that the cable sensor could be used instead of accelerometer, when high accuracy was not required. Two kinds of experiments for two dimensional source location of impact source of rock fall. It was confirmed that impact source could be evaluated from rise time of wave forms, amplitude array of wave forms and topography pictured by using amplitudes of wave forms. It can be said that two dimensional source location system by using cable sensor and mobile multimedia network is applicable for the rock fall detection.

An experimental study on the characteristics of the impact load of falling rock

Abstract An experimental study on rock falling was carried out to clarify the characteristics of impact load. For this study, a two dimensional dynamometer was constructed and validated to detect and record vertical and horizontal impact loads. Experimental results show that the ratio of horizontal impact load against vertical impact load is larger than expected. There are cases that the ratio is greater than 40%. Moreover, it has been revealed that the direction of horizontal impact loads are both in valley and mountain sides. These results are considered to be very important in evaluating the dynamic response of concrete structures, such as rock sheds, built at the foot of steep slopes.

Applicability of the Magnification Equation of Lens for Slope Survey

Photography is often used in geological survey, mining engineering or civil engineering to measure the length or width of an object by placing another object such as a scale, a hammer or a cigarette box next to the object. But, it is difficult to place a scale nearby the object when the object is too far and high or too dangerous to get to. In this study, practical applicability of the magnification equation of lens for indirect calculation of the length of a photographed object was examined. From this study, it was found that the applicable distance for the use of the magnification equation of lens was 84 m, even when the focal length was 36mm, and that the applicable distance was more than 300 m with the lens focal length being longer than 100 mm. Moreover, falling behavior, impact load and energy of a rock fall could be calculated readily using obtained information from a photograph.

A field test of a rock fall detection system using cable sensor and mobile multimedia network

ABSTRACT Cable sensor which is usually used for invader inspection of sensitive places such as atomic power stations and other high security buildings is considered to be available for rock noise and impact detection, because the sensor can detect vibration at any point of a string, and can be used with extending more than a hundred meter or more. From a field test using cable sensor and mobile multimedia network, it was found that the impact source caused by a steel ball dropping in the proximity of the sensing cable could be judged clearly from the order of rise time of signals of cable sensors, amplitudes of wave forms of signals and a topography pictured from peak values of signals transmitted by way of mobile multimedia network, This newly developed system is considered to be applicable not only to detect the resultant impact of fallen rocks but also to monitor the noise produced by the fracture of unstable rocks and sounds of falling rocks along a slope.

Numerical analysis of the impact load of falling rock by using the Distinct Element Method

ABSTRACT Theoretical analysis was carried out to clarify the impact load behavior of falling rock by using the Distinct Element Method (DEM). It was found that this method can simulate impact load behavior by comparing experimental with numerical results. The acting direction (mountain side or valley side) of a horizontal impact load was correctly simulated. The reason why the acting direction of horizontal impact load was unstable in the experiments was made clear by the results of numerical modelling. The DEM simulation can be used to estimate the resulting impact loads when the weight of a falling rock is too large to get experimental data.

The detection of a misfiring cylinder of diesel engines in excavation machinery using ALM analysis

Mechanical problems, common in large mining equipment, result in serious losses in operations efficiency and financial return. In this study, a minimum number of sensors was applied on the side of two cylinders of a diesel engine in order to build an abnormality diagnostic system that detects anomalous engine behaviour at an early stage. The study investigates whether or not the misfiring of an engine cylinder can be detected through analysis of acceleration results using an aggregative learning method (ALM). The results show that, using ALM, distinctive differences could be observed in almost every cylinder except those farthest from the accelerometer.

Improving the Rockfall Simulation by Measuring the Impact Acceleration of Rockfalls

For pertinent countermeasure of rockfalls, rockfall simulation was studied many times. Any rockfall simulation has not gotten consistency between the simulation result and real rockfall. There are a few causes. One is whether method of calculation used the simulation approaches the mechanics of real rockfall. Two is whether parameters using the calculation are assigned pertinent value in. This study suggests direct measurement of rockfalls detail motion which as method of closuring of the problems. It would be possible to determine pertinent value in parameter by comparing the detail motion to calculation result. In this research, 3-demensional rockfall simulation developing in this laboratory is explained. Then the problems and improvement of the simulation is shown. Finally the result of experiments on impact acceleration that applies to rockfalls is shown.

Grouping of Rock Shapes and Relationship between Rock Shape and Estimated Weight.

It is considered that shape of a rock is one of the factors which dominate the falling behavior of the rock along a slope. Rocks were decided to be grouped into three shapes, namely massive, tabular and columnar. Shapes of 200 pieces of rocks were judged visually by 40 persons. A diagram for shape grouping was made by using the judged results of the shapes and the measured ratios of the lengths of minor and intermediate axes against major axis. Then an estimation method of a rock weight was examined considering rock shapes, from whichfollowing two points were clarified. 1) Coefficients of the equation for weight estimationare not infuluenced by the changes of the rock shapes. 2) Weight of a rock can be estimated reasonablly giving adequate value to α which is the correction coefficient for weight. Where, the value of upper limit of confidential interval should be used.

Investigation of the Suitability of Simple Method for the Evaluation of Size Distribution of Fallen Rocks. Fundamental study on the evaluation of the largest rock size in a rock fall (2nd Report).

Evaluation of size distribution equation was carried out by eliminating some data that were obtained from a heap created along artificial and practical slopes, which has given the following results.(1) Simple sampling method from a heap becomes suitable when parameters of distribution equation are calibrated.(2) Deviation of rock size of 0.01% oversize estimated from calibrated distribution equation is 1.3-1.4 times larger than those estimated from distribution equation of feed.(3) This simple method is suitable to a practical heap in the field.(4) Size distribution equation can be used to estimate the maximum size of rocks under small probability by extending the distribution line.