ABSTRACT:

The acoustic emission as additional parameter measured. during the stress strain measurement in uniaxial conditions is described in this paper. There are many factors influencing the acoustic emission activity. The petographic character of the material influences very strongly the AE activity, however the water content of the sample or the stratigraphy of the tested material influences the AE activity, too. These results are useful especially for the construction of the underground storages or estimation of the underground stability.

I.
INTRODUCTION

Uniaxial stress - strain measurements are one of the most important laboratory tests in geomechanics. However. the big disa vantage of these tests is the destruction of the samples. Because of this fact the system of additional measurement during the test is applied to obtain about the material during the laboratory measurement as complex information as possible. Volume changes calculated from the strain measurement or measurement of gas permeability during the process of deformation arc usually measured in Laboratory of mechanical properties of Institute of Geonics of Academy of Sciences of the Czech Republic. The method of measurement of acoustic emission activity was ap- plied in recent time, too. It seems to be very interesting addition- al method to characterize the properties of tested material (Konecny, 1998).

2.
APPARATUS

Stress strain measurement of coal and rocks is carried out on mechanical press ZWICK 1494 with computerised control system which allow the control of deformation or loading velocity In a. Wide range. This press is equipped with uniaxial cell with Strain gauges measurement of deformation. Two gauges situated symmetrical to the axis of cylindrical specimen measure the axial deformation. Lateral deformations are indicated in four symmetrical points in the lateral area of the cylindrical specimen in the half of its eight. The uniaxial cell enables the attachment of the sensor for AE measurement. As the acoustic sensor the gauges of type S 9223, produced by the Physical Acoustic Corporation, USA were used. They allowed measuring in the frequency range from 5 kHz up to 300 k hz. The schematic diagram of the measurement equipment is in Fig. I. Stress. axial and lateral deformation of the sample and AE are regisrated on the computer. The ASCII file is created. After that The Microsoft Excel program computes the ASCII file. The result of the measurement is the graph which shows the Dependence of the deformation (axial, lateral and volume), amount of the acoustic emission on the stress (see Figs. 2, 3, 4). The mechanical screw-type press ZWICK 1494 is presented in fig 1 as the mechanical unit MU which is able to create via the dynamometer D, the upper plate UP and the lower plate LP the force F onto the rock testing specimen RS. The computer PCI controls the unit MU via the control unit CU.

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