1、Designation: D7400 08D7400 14Standard Test Methods forDownhole Seismic Testing1This standard is issued under the fixed designation D7400; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parent
2、heses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 These test methods are limited to the determination of the interval velocities from arrival times and relative arrival timesof compression (P) and ver
3、tically (SV) and horizontally (SH) polarized shear (S) seismic waves which are generated near surfaceand travel down to an array of vertically installed seismic sensors. A preferred method intended to obtain data for use on criticalprojects where the highest quality data is required is included. Als
4、o included is an optional method intended for use on projectswhich do not require measurements of a high degree of precision.1.2 Various applications of the data will be addressed and acceptable procedures and equipment, such as seismic sources,receivers, and recording systems will be discussed. Oth
5、er items addressed include source-to-receiver spacing, drilling, casing,grouting, a procedure for borehole installation, and conducting actual borehole and seismic cone tests. Data reduction andinterpretation is limited to the identification of various seismic wave types, apparent velocity relation
6、to true velocity, examplecomputations, use of Snells law of refraction, and assumptions.1.3 There are several acceptable devices that can be used to generate a high-quality Por SV source wave or both and SH sourcewaves. Several types of commercially available receivers and recording systems can also
7、 be used to conduct an acceptabledownhole survey. Special consideration should be given to the types of receivers used and their configuration. Heavily-dampedsensors should not be used so that spectral smearing, phase shifting, and latency response between sensors is avoided. These testmethods prima
8、rily concern the actual test procedure, data interpretation, and specifications for equipment which will yield uniformtest results.1.4 All recorded and calculated values shall conform to the guide for significant digits and rounding established in PracticeD6026.1.4.1 The procedures used to specify h
9、ow data are collected/recorded and calculated in these test methods are regarded as theindustry standard. In addition, they are representative of the significant digits that should generally be retained. The proceduresused do not consider material variation, purpose for obtaining the data, special p
10、urpose studies, or any considerations for the usersobjectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with theseconsiderations. It is beyond the scope of these test methods to consider significant digits used in analysis methods for eng
11、ineeringdesign.1.4.2 Measurements made to more significant digits or better sensitivity than specified in these test methods shall not beregarded a nonconformance with this standard.1.5 This standard is written using SI units. Inch-pound units are provided for convenience. The values stated in inch
12、pound unitsmay not be exact equivalents; therefore, they shall be used independently of the SI system. Combining values from the two systemsmay result in nonconformance with this standard.1.5.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In this system, t
13、he pound (lbf)represents a unit of force (weight), while the unit for mass is slugs. The rationalized slug unit is not given, unless dynamic (F = ma)calculations are involved.1.5.2 It is common practice in the engineering/construction profession to concurrently use pounds to represent both a unit of
14、mass (lbm) and of force (lbf). This implicitly combines two separate systems of units; that is, the absolute system and thegravitational system. It is scientifically undesirable to combine the use of two separate sets of inch-pound units within a singlestandard. As stated, this standard includes the
15、 gravitational system of inch-pound units and does not use/present the slug unit formass. However, the use of balances or scales recording pounds of mass (lbm) or recording density in lbm/ft3 shall not be regardedas nonconformance with this standard.1 This test method is under the jurisdiction of AS
16、TM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.09 on Cyclic and DynamicProperties of Soils.Current edition approved June 1, 2008Nov. 1, 2014. Published July 2008November 2014. Originally approved in 2007. Last previous edition approved in 20072008 asD7400 07.D
17、7400 08. DOI: 10.1520/D7400-08.10.1520/D7400-14.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurate
18、ly, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Dri
19、ve, PO Box C700, West Conshohocken, PA 19428-2959. United States11.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the appl
20、icability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and Contained FluidsD3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used inEngineering Design and Construc
21、tionD4428/D4428M Test Methods for Crosshole Seismic TestingD5778 Test Method for Electronic Friction Cone and Piezocone Penetration Testing of SoilsD6026 Practice for Using Significant Digits in Geotechnical Data3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in these test methods,
22、 see Terminology D653.4. Summary of Test Method4.1 The Downhole Seismic Test makes direct measurements of compression (P-) or shear (S-) wave velocities, or both, in aborehole advanced through soil or rock or in a cone penetration test sounding. It is similar in several respects to the CrossholeSeis
23、mic Test Method (Test Methods D4428/D4428M). A seismic source is used to generate a seismic wave train at the groundsurface offset horizontally from the top of a cased borehole. Downhole receivers are used to detect the arrival of the seismic wavetrain. The downhole receiver(s) may be positioned at
24、selected test depths in a borehole or advanced as part of the instrumentationpackage on an electronic cone penetrometer (Test Method D5778). The seismic source is connected to and triggers a data recordingsystem that records the response of the downhole receiver(s), thus measuring the travel time of
25、 the wave train between the sourceand receiver(s). Measurements of the arrival times (travel time from source to sensor) of the generated P- and S- waves are thenmade so that the low strain (104 %) in-situ P-wave and S-wave velocities can be determined. The calculated seismic velocitiesare used to c
26、haracterize the natural or man-made (or both) properties of the stratigraphic profile.5. Significance and Use5.1 The seismic downhole method provides a designer with information pertinent to the seismic wave velocities of the materialsin question (1). The P-wave and S-wave velocities are directly re
27、lated to the important geotechnical elastic constants of Poissonsratio, shear modulus, bulk modulus, and Youngs modulus. Accurate in-situ P-wave and S-wave velocity profiles are essential ingeotechnical foundation designs. These parameters are used in both analyses of soil behavior under both static
28、 and dynamic loadswhere the elastic constants are input variables into the models defining the different states of deformations such as elastic,elasto-plastic, and failure. Another important use of estimated shear wave velocities in geotechnical design is in the liquefactionassessment of soils.5.2 A
29、 fundamental assumption inherent in the test methods is that a laterally homogeneous medium is being characterized. Ina laterally homogeneous medium the source wave train trajectories adhere to Snells law of refraction.Another assumption inherentin the test methods is that the stratigraphic medium t
30、o be characterized can have transverse isotropy. Transverse isotropy is aparticularly simple form of anisotropy because velocities only vary with vertical incidence angle and not with azimuth. By placingand actuating the seismic source at offsets rotated 90 in plan view, it may be possible to evalua
31、te the transverse anisotropy of themedium.NOTE 1The quality of the results produced by this standard is dependent on the competence of the personnel performing it, and the suitability of theequipment and facilities. Agencies that meet the criteria of Practice D3740 are generally considered capable o
32、f competent and objectivetesting/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliableresults depend on many factors; Practice D3740 provides a means of evaluating some of those factors.6. Apparatus6.1 T
33、he basic data acquisition system consists of the following:6.1.1 Energy SourcesThese energy sources are chosen according to the needs of the survey, the primary consideration beingwhether P-wave or S-wave velocities are to be determined. The source should be rich in the type of energy required, that
34、 is, toproduce good P-wave data, the energy source must transmit adequate energy to the medium in compression or volume change.Impulsive sources, such as explosives, hammers, or air guns, are all acceptable P-wave generators. To produce an identifiable S2 For referencedASTM standards, visit theASTM
35、website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.D7400 142wave, the source should transmit energy to the ground with a particle motion perpendicular or tran
36、sverse to the axis of the survey.Impulse or vibratory S-wave sources are acceptable, but the source must be repeatable and, although not mandatory, reversible.6.1.1.1 Shear BeamAshear beam is a common form of an SH-wave energy source. The beam can be metal or wood, and maybe encased at the ends and
37、bottom with a steel plate. Strike plates may optionally be provided at the beam ends. The bottom platemay optionally have cleats to penetrate the ground and to prevent sliding when struck. A commonly utilized shear beam hasapproximate dimensions of 2.4 m (8 ft) long by 150 mm (6 in.) wide. The cente
38、r of the shear beam is placed on the ground at ahorizontal offset ranging from 1 to 3 m (3 to 10 ft) from the receiver borehole (or cone insertion point).This horizontal offset shouldbe selected carefully since borehole disturbance, rod noise, and refraction through layers with significantly differe
39、nt properties mayimpact the test results. Larger horizontal offsets of 4 to 6 m (12 to 20 ft) for the seismic source may be necessary to avoid responseeffects due to surface or near-surface features. In this case the possibility of raypath refraction must be taken into account. The endsof the beam s
40、hould be positioned equidistant from the receiver borehole. The shear beam is typically then loaded by the axle loadof vehicle wheels or the leveling jacks of the cone rig.The ground should be level enough to provide good continuous contact alongthe whole length of the beam to ensure good coupling b
41、etween the beam and the ground. Beam-to-ground coupling should beaccomplished by scraping the ground level to a smooth, intact surface. Backfilling to create a flat spot will not provide goodbeam-ground coupling and should be avoided. The shear beam is typically struck on a strike plate at one end u
42、sing a nominal 1-to 15-kg hammer to produce a seismic wave train. Striking the other end will create a seismic wave train that has the oppositepolarity relative to the wave train produced at the first end. Fig. 1 shows a diagram of the typical shear beam configuration thatwill produce SH-wave trains
43、. Fig. 2 shows an example of an impulse seismic source wave train that contains both P- and S-wavecomponents. Although the shear beam of dimensions 2.4 m (8 ft) long by 150 mm (6 in.) wide is commonly utilized, it may bedesirable to implement beams of shorter length so that SH-source more closely ap
44、proximates a “point source” for tests less than20 m (60 ft) in depth. The “point source” SH-wave beam allows for the accurate specification of the source Cartesian location (x,y, and z coordinates) which is required for the subsequent interval velocity calculation. For example, if a large SH-hammer
45、beamis utilized, it becomes difficult to specify the exact location of the seismic source. In addition, it is preferable to initially excite asmall area if complex stratigraphy exist and shorter SH-hammer beams mitigate problems arising from poor beam-groundcoupling.6.1.2 ReceiversIn the downhole se
46、ismic test, the seismic receivers are installed vertically with depth within a borehole or aspart of the instrumentation in a cone penetrometer probe. The receivers intended for use in the downhole test shall be transducershaving appropriate frequency and sensitivity characteristics to determine the
47、 seismic wave train arrival. Typical transducerexamples include geophones, which measure particle velocity, and accelerometers, which measure particle acceleration. Bothgeophones and accelerometers are acceptable for downhole seismic testing. High precision, low noise (operational amplifierintegrate
48、d into sensor) accelerometers are generally more accurate due to their desirable transient response times (that is, delay,rise and peak times (2) and high bandwidths compared to geophones. Sensors with fast transient response times are advantageousFIG. 1 Typical Downhole Shear Wave Source (Produces
49、SH- Wave Train)D7400 143when carrying out downhole seismic testing within hard rock stratigraphy and high energy ambient noise environments. Thefrequency response of the transducer should not vary more than 5 % over a range of frequencies from 0.5 to 2 times thepredominant frequency of the site-specific S-wave train. The geophones should not be heavily damped to minimize spectralsmearing. The receiver section should be housed in a single container (cylindrical shape preferred) so that multiple axis sensors(transducers) are located within 10 cm (4 in.) of each other
