ASTM D7764-20

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Designation: D7764 − 12 D7764 − 20
Standard Practice for
Pre-Installation Acceptance Testing of Vibrating Wire
Piezometers
This standard is issued under the fixed designation D7764; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This practice describes two acceptance tests for a vibrating wire piezometer: a zero test and a down-hole test. The two tests
can help a user verify that the piezometer is operating properly before it is installed.
1.2 This practice offers an organized collection of information or a series of options and does not recommend a specific course
of action. This document cannot replace education or experience and should be used in conjunction with professional judgment.
Not all aspects of this practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace
the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied
without consideration of a project’s many unique aspects. The word “standard” in the title of this document means only that the
document has been approved through the ASTM consensus process.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
3. Terminology
3.1 Definitions:
3.1.1 For definitions of common technical terms in this standard, refer to Terminology D653.
This practice is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.23 on Field Instrumentation.
Current edition approved July 1, 2012Aug. 1, 2020. Published October 2012August 2020. Originally approved in 2012. Last previous edition approved in 2012 as
D7764–12. DOI: 10.1520/D7764-12. 10.1520/D7764-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
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D7764 − 20
3.2 Definitions:Definitions of Terms Specific to This Standard:
3.1.1 For general definitions, see Terminology D653.
3.1.2 absolute pressure, n—a pressure value that includes the effect of atmospheric pressure.
3.1.3 gauge pressure, n—a pressure value that excludes the effect of atmospheric pressure.
3.2.1 vibrating wire piezometer, n—a type of pressure sensor that is used to monitor pore-water pressure. Vibrating wire refers to
the mechanism by which pressure on the sensor’s diaphragm is converted to an electrical signal that is transmitted to a readout
device. A typical vibrating wire piezometer reports absolute pressure, rather than gauge pressure. In this standard, the words
“vibrating wire piezometer,” “piezometer,” and “sensor” will be used interchangably.
3.2.1.1 Discussion—
“Vibrating wire” refers to the mechanism by which pressure on the sensor’s diaphragm is converted to an electrical signal that is
transmitted to a readout device. A tensioned wire connected to the diaphragm is plucked by an electromagnetic pulse, and the
resulting natural frequency is monitored by the readout. Any change in pressure on the diaphragm changes the tension of the wire
and the resulting frequency. A typical vibrating wire piezometer reports gauge pressure, rather than absolute pressure. In this
standard, the words “vibrating wire piezometer,” “piezometer,” and “sensor” will be used interchangeably.
4. Significance and Use
4.1 Vibrating wire piezometers are typically not recoverable after installation. Replacement, which involves drilling a new
borehole, is expensive and sometimes impossible. Thus it is important to be certain that the sensor is operational before it is
installed.
4.2 Lacking sophisticated testing facilities, field testers must use equipment that is at hand. But in so doing, field testers should
not expect to achieve the same accuracy and precision that manufacturers state on the sensor calibration record. Instead, field
testers should look for obvious non-conformances, as explained in the procedures.
4.3 This standard practice is not meant to restrict the use of other appropriate acceptance tests and procedures.
NOTE 1—Notwithstanding the statements on precision and bias contained in this practice, the precision of this practice The quality of the result produced
by this standard 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.testing/sampling/inspection/etc. Users of this
practicestandard are cautioned that compliance with Practice D3740 does not in itself ensureassure reliable testing.results. Reliable testing dependsresults
depend on many factors; Practice D3740 provides a means of evaluating some of thesethose factors.
5. Equipment
5.1 A readout in good working condition and vibrating wire readout compatible with the sensor to be tested. Consult
manufacturer’s user manual to verify compatibility of the readout.
5.2 The calibration record for the sensor to be tested. Vibrating wire sensors typically have unique calibrations, so it is important
to match the calibration record to the sensor.
6. Zero-Reading Test Procedure
6.1 This procedure is used to verify that the sensor reads approximately zero when only atmospheric pressure is applied.
6.2 Ideally, this procedure is conducted in a temperature-stable location, since changes in temperature can affect the sensor. At
minimum, ensure that the sensor is kept out of direct sunlight and away from other sources of heat.
6.3 Prior to establishing a zero reading on site, the filter tip of the sensor should be saturated.
6.3.1 Remove the filter tip of the sensor by its twisting and pulling the filter end from the body of the instrument.
D7764 − 20
6.3.2 Once the filter tip end is removed, hold the body of the instrument upright with cable end down, and fill the upper chamber
with clean water.
6.3.3 Slowly push the filter tip back into the body of the instrument, allowing the water to force itself through the filter stone of
the tip. This process should be done carefully and slowly, so as to not over-range the pressure sensor.
6.4 Suspend the sensor in air by its signal cable Place the instrument into a water-filled container and allow approximately one
hour for the sensor to reach thermal equilibrium with the surrounding air. Do not handle the sensor during this time or during the
test.water in the container.
6.5 Prior to installation, connect the signal cable to the readout and suspend the sensor in air by its signal cable just above the
water-filled container. Do not handle the sensor during this time or during the test.
6.6 Connect the signal cable to the readout and
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