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LABORATORY TESTING OF THE PRECISION AND ACCURACY OF THE TM-71 DILATOMETER

Jan Balek

Abstract

The TM-71 dilatometer is a device manufactured in the 60s of the 20th century in the Institute of Rock Structure and Mechanics of the Czech Academy of Sciences. It has been developed as a reliable and easy-to-use rock crack monitoring facility capable of working even in the least favorable climatic conditions. It is a purely mechanical system capable of determining relative shifts and rotations in all three axis of two monitored blocks. The device is read out using two pairs of overlapping optical patterns, which are firmly connected to the rock blocks. Their mutual shifts and rotations changes the structure of image emerging on the overlap of the patterns based on moir? effect. The device is currently widely used to study geodynamic processes such as slow slope movements or movements on fracture structures. This article describes laboratory testing of the TM-71 device to determine the precision and accuracy, which is essential for reliable evaluation of the data measured. At present, the accuracy of reading the instrument is well known, which directly depends on the properties of the moire patterns used and is readily quantifiable by the mathematical way. The purpose of the instrument testing was primarily to determine the accuracy from the mechanical point of view. Namely, accuracy of the response of the optical patterns to the induced displacement of the monitored blocks. For several series of laboratory tests, standard deviations of measured displacements were determined.

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DOI resolver: doi.org/10.5593/sgem2018/1.2/s02.055

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