Standard Practice for Extensometers Used in Rock

Importancia y uso:

4.1 Extensometers are widely used in the field of engineering and include most devices used to measure displacements, separation, settlements, convergence, and the like.

4.2 For tunnel instrumentation, extensometers are generally used to measure roof and sidewall movements and to locate the tension arch zone surrounding the tunnel opening.

4.3 Extensometers are also used extensively as safety monitoring devices in tunnels, in underground cavities, on potentially unstable slopes, and in monitoring the performance of rock support systems.

4.4 An extensometer should be selected on the basis of its intended use, the preciseness of the measurement required, the anticipated range of deformation, and the details accompanying the installation. No single instrument is suitable for all applications.

4.5 In applications for construction in rock, precise measurements will usually allow the identification of significant, possibly dangerous, trends in rock movement; however, precise measurement is much less important than the overall pattern of movement.

4.6 Data collection of extensometers can be simple or low tech, such as manual readings at the instrument location, or complex or high tech where there are electronic readings taken at the site and either downloaded at the instrument locations or transmitted to a data collection and analysis center.

4.7 It is important to realize the pros and cons and costs between each type of extensometers. In the case of manual readings, not as much data may be collected, important data may be missed and the person taking the readings may be put in harm’s way and may not be able to safely continue collecting data just when the data is needed the most or becomes more important. Whereas, with electronic data collection as the system becomes more sophisticated, the data collected can be done more safely, provide important data that might be missed, and may allow for real-time data analyses that are timelier and more accurate.

4.8 When very accurate measurements are dictated by certain excavations, for example, the determination of the tension arch zone around a tunnel opening, extensometers which can be adjusted in the field after installation shall be used. In all cases, the accuracy of extensometers, either determined through calibration, should be given in addition to the sensitivity of the transducers.

Note 1: Notwithstanding the statements on precision and bias contained in this test method, the precision of this test method is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing. Users of these test methods are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable testing depends on many factors; Practice D3740 provides a means of evaluating some of those factors.

Subcomité:

D18.23

Referida por:

D4395-17, D4553-18, D4394-17, D6286_D6286M-20, D0420-18, D4506-21

Volúmen:

04.08

Número ICS:

93.020 (Earth works. Excavations. Foundation construction. Underground works)

Palabras clave:

convergence; data analysts; deformation; displacement; extensometers; field testing; installation; monitoring; rock; settlement; tunnels; underground environments;