1、Designation: D7764 12Standard Practice forPre-Installation Acceptance Testing of Vibrating WirePiezometers1This standard is issued under the fixed designation D7764; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes two acceptance tests for avibrating wire piezometer: a zero test and a down-hole test. Thetwo tests
3、 can help a user verify that the piezometer is operatingproperly before it is installed.1.2 This practice offers an organized collection of informa-tion or a series of options and does not recommend a specificcourse of action. This document cannot replace education orexperience and should be used in
4、 conjunction with professionaljudgment. Not all aspects of this practice may be applicable inall circumstances. This ASTM standard is not intended torepresent or replace the standard of care by which theadequacy of a given professional service must be judged, norshould this document be applied witho
5、ut consideration of aprojects many unique aspects. The word “standard” in thetitle of this document means only that the document has beenapproved through the ASTM consensus process.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstan
6、dard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referen
7、ced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and Construction3. Terminology3.1 Definitions:3.1.1 For general definiti
8、ons, see Terminology D653.3.1.2 absolute pressure, na pressure value that includesthe effect of atmospheric pressure.3.1.3 gauge pressure, na pressure value that excludes theeffect of atmospheric pressure.3.1.4 vibrating wire piezometer, na type of pressure sensorthat is used to monitor pore-water p
9、ressure. Vibrating wirerefers to the mechanism by which pressure on the sensorsdiaphragm is converted to an electrical signal that is transmit-ted to a readout device. A typical vibrating wire piezometerreports absolute pressure, rather than gauge pressure. In thisstandard, the words “vibrating wire
10、 piezometer,” “piezometer,”and “sensor” will be used interchangably.4. Significance and Use4.1 Vibrating wire piezometers are typically not recoverableafter installation. Replacement, which involves drilling a newborehole, is expensive and sometimes impossible. Thus it isimportant to be certain that
11、 the sensor is operational before itis installed.4.2 Lacking sophisticated testing facilities, field testers mustuse equipment that is at hand. But in so doing, field testersshould not expect to achieve the same accuracy and precisionthat manufacturers state on the sensor calibration record.Instead,
12、 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 ofother appropriate acceptance tests and procedures.NOTE 1Notwithstanding the statements on precision and bias con-tained in this practice, the precisio
13、n of this practice is dependent on thecompetence of the personnel performing it and the suitability of theequipment and facilities used. Agencies that meet the criteria of PracticeD3740 are generally considered capable of competent and objectivetesting. Users of this practice are cautioned that comp
14、liance with PracticeD3740 does not itself ensure reliable testing. Reliable testing depends onmany factors; Practice D3740 provides a means of evaluating some ofthese factors.1This practice is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommitt
15、ee D18.23 on Field Instrumen-tation.Current edition approved July 1, 2012. Published October 2012. DOI: 10.1520/D7764-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refe
16、r to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Equipment5.1 A readout in good working condition and compatiblewith the sensor to be tested. Consult manufacturers usermanu
17、al 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 itis important to match the calibration record to the sensor.6. Zero-Reading Test Procedure6.1 This procedure is used to verify that the sens
18、or readsapproximately 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 thesensor. At minimum, ensure that the sensor is kept out of directsunlight and away from other sources of heat.6.3
19、Suspend the sensor in air by its signal cable and allowapproximately one hour for the sensor to reach thermalequilibrium with the surrounding air. Do not handle the sensorduring this time or during the test.6.4 Connect the signal cable to the readout and obtain areading according to the manufacturer
20、s instructions. Typically,the reading will be in Hz or Hz2/1000. Check that the readingis stable and repeatable. Readings that vary 62Hzor612Hz2/1000 should be regarded as unstable. If the reading isunstable, check that the excitation setting is correct.Also checkif other sensors of the same type re
21、turn similar readings. If onlyone sensor is unstable, it should probably be rejected. If othersensors are unstable as well, the environment may be electri-cally noisy. Try moving to a different location.6.5 Convert the Hz or Hz2/1000 reading to units of pressureby applying the calibration factors su
22、pplied by the manufac-turer. The result will be called a “zero reading.”6.6 Correct the zero reading for elevation, as necessary.Calibration records are typically referenced to sea level or 1atmosphere, but atmospheric pressure decreases at elevationsabove sea level. Thus a zero reading at sea level
23、 is likely to benegative value at higher elevations. To correct for this, add 1.15kPa for every 100 m of elevation above sea level. Thiscorrection factor is suitable to elevations of 1500 m above sealevel.6.7 Compare the elevation-corrected zero reading with zero.If the value differs by more than 1
24、% of the rated range of thesensor, the sensor should be set aside. For example, a differ-ence of 3.5 kPa is at the limit for a sensor rated to 350 kPa. The1 % limit allows for variations barometric pressure,temperature, and the sensitivity of various ranges of sensors.6.8 Sensors that exceed the 1 %
25、 limit may still be usable.The sensors may have experienced a one-time zero-shift duringshipping, but are otherwise functioning correctly. Since pi-ezometers are generally used to monitor changes in pressure,rather than absolute pressure, the zero-shift is of little concernin practice. Assuming that
26、 they produce stable readings, asdefined above, such sensors are still candidates for the down-hole test.7. Downhole Test Procedure7.1 The downhole test is used to verify that the sensorperforms adequately over its range. Ideally, this procedure isperformed in a water-filled borehole that is deep en
27、ough to testthe full range of the piezometer. If the water table is well belowthe surface, then only a partial range can be tested.7.2 Flush the borehole with clean water to remove heavydrilling mud.7.3 Determine the depth to the water surface, as measuredfrom a selected index, such as the top of th
28、e drill casing.7.4 Calculate the range of the sensor in meters-head-of-water. 1 kPa is approximately 0.10197 meters of water.7.5 Lay the sensor on the ground and uncoil the signal cable.Mark the signal cable in three places: a shallow mark, amid-range mark, and a deep mark. Place the shallow mark so
29、that the tip of the sensor will be at least 1.5 m below the surfaceof the water when it is lowered into the borehole. Place thedeep mark as close as possible to the maximum range of thesensor. The mid-range mark should be somewhere between theother two marks.7.6 Measure the distance between the shal
30、low mark and thedeep mark. Also measure the distance between the shallowmark and the mid-range mark. Keep these measurements forlater use.7.7 Pull the filter off the piezometer, fill the chamber in frontof the diaphragm with clean water, and then replace the filter.Hold the piezometer filter-end dow
31、n and check that water doesnot immediately drain out of the chamber. If necessary, tie thepiezometer, filter-end up, to its signal cable, and note thechanged distance between the sensor tip and the marked depthson the cable.7.8 Lower the piezometer to the deepest depth. Wait about20 min to allow the
32、 piezometer to reach thermal equilibriumwith the surrounding water. Obtain a reading and check that itis repeatable.7.9 Draw the piezometer upwards to the middle depth.Obtain a reading and check that it is repeatable.7.10 Draw the piezometer upwards to the shallowest depth.Obtain a reading and check
33、 that it is repeatable.7.11 Convert the three readings to units of pressure usingthe calibration factors provided by the manufacturer.7.12 Subtract the shallow pressure from the deep pressure.Convert the result to meters of water head.7.13 Subtract the shallow pressure from the mid-rangepressure. Co
34、nvert the result to meters of water head.7.14 Correct the two values for displacement of water by thecable. As the piezometer and cable are lowered into theborehole, the water level in the borehole rises, resulting inhigher pressure readings. To calculate the correction value,divide the volume of wa
35、ter displaced by cable by the cross-sectional area of the borehole. Subtract the correction valuefrom the result from the calculated length.D7764 1227.15 The corrected calculated distances and the measureddistances should differ by no more than 1 %. This allows forvariations due to depth control and
36、 the specific gravity of thewater. Piezometers that exceed this limit are candidates forreturn to the manufacturer.8. Keywords8.1 acceptance test; vibrating wire piezometersASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentione
37、din this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and
38、must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of
39、theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C
40、700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D7764 123
