1、Designation: D 7400 08Standard Test Methods forDownhole Seismic Testing1This standard is issued under the fixed designation D 7400; 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 parentheses
2、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 ofthe interval velocities from arrival times and relative arrivaltimes of compression (P) and vertically
3、 (SV) and horizontally(SH) polarized shear (S) seismic waves which are generatednear surface and travel down to an array of vertically installedseismic sensors.Apreferred method intended to obtain data foruse on critical projects where the highest quality data isrequired is included. Also included i
4、s an optional methodintended for use on projects which do not require measure-ments of a high degree of precision.1.2 Various applications of the data will be addressed andacceptable procedures and equipment, such as seismic sources,receivers, and recording systems will be discussed. Other itemsaddr
5、essed include source-to-receiver spacing, drilling, casing,grouting, a procedure for borehole installation, and conductingactual borehole and seismic cone tests. Data reduction andinterpretation is limited to the identification of various seismicwave types, apparent velocity relation to true velocit
6、y, examplecomputations, use of Snells law of refraction, and assump-tions.1.3 There are several acceptable devices that can be used togenerate a high-quality P or SV source wave or both and SHsource waves. Several types of commercially available receiv-ers and recording systems can also be used to c
7、onduct anacceptable downhole survey. Special consideration should begiven to the types of receivers used and their configuration.Heavily-damped sensors should not be used so that spectralsmearing, phase shifting, and latency response between sensorsis avoided. These test methods primarily concern th
8、e actual testprocedure, data interpretation, and specifications for equipmentwhich will yield uniform test results.1.4 All recorded and calculated values shall conform to theguide for significant digits and rounding established in PracticeD 6026.1.4.1 The procedures used to specify how data are coll
9、ected/recorded and calculated in these test methods are regarded asthe industry standard. In addition, they are representative of thesignificant digits that should generally be retained. The proce-dures used do not consider material variation, purpose forobtaining the data, special purpose studies,
10、or any consider-ations for the users objectives; and it is common practice toincrease or reduce significant digits of reported data to becommensurate with these considerations. It is beyond the scopeof these test methods to consider significant digits used inanalysis methods for engineering design.1
11、.4.2 Measurements made to more significant digits orbetter sensitivity than specified in these test methods shall notbe regarded a nonconformance with this standard.1.5 This standard is written using SI units. Inch-pound unitsare provided for convenience. The values stated in inch poundunits may not
12、 be exact equivalents; therefore, they shall beused independently of the SI system. Combining values fromthe two systems may result in nonconformance with thisstandard.1.5.1 The gravitational system of inch-pound units is usedwhen dealing with inch-pound units. In this system, the pound(lbf) represe
13、nts a unit of force (weight), while the unit for massis 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/constructionprofession to concurrently use pounds to represent both a unitof mass (lbm) and of force
14、 (lbf). This implicitly combines twoseparate systems of units; that is, the absolute system and thegravitational system. It is scientifically undesirable to combinethe use of two separate sets of inch-pound units within a singlestandard. As stated, this standard includes the gravitationalsystem of i
15、nch-pound units and does not use/present the slugunit for mass. However, the use of balances or scales recordingpounds of mass (lbm) or recording density in lbm/ft3shall notbe regarded as nonconformance with this standard.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRo
16、ck and is the direct responsibility of Subcommittee D18.09 on Cyclic andDynamic Properties of Soils.Current edition approved June 1, 2008. Published July 2008. Originally approvedin 2007. Last previous edition approved in 2007 as D 7400 07.1*A Summary of Changes section appears at the end of this st
17、andard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1.6 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-p
18、riate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection
19、of Soil and Rock asUsed in Engineering Design and ConstructionD 4428/D 4428M Test Methods for Crosshole Seismic Test-ingD 5778 Test Method for Electronic Friction Cone andPiezocone Penetration Testing of SoilsD 6026 Practice for Using Significant Digits in Geotechni-cal Data3. Terminology3.1 Definit
20、ions:3.1.1 For definitions of terms used in these test methods, seeTerminology D 653.4. Summary of Test Method4.1 The Downhole Seismic Test makes direct measurementsof compression (P-) or shear (S-) wave velocities, or both, in aborehole advanced through soil or rock or in a cone penetrationtest sou
21、nding. It is similar in several respects to the CrossholeSeismic Test Method (Test Methods D 4428/D 4428M). Aseismic source is used to generate a seismic wave train at theground surface offset horizontally from the top of a casedborehole. Downhole receivers are used to detect the arrival ofthe seism
22、ic wave train. The downhole receiver(s) may bepositioned at selected test depths in a borehole or advanced aspart of the instrumentation package on an electronic conepenetrometer (Test Method D 5778). The seismic source isconnected to and triggers a data recording system that recordsthe response of
23、the downhole receiver(s), thus measuring thetravel time of the wave train between the source and receiv-er(s). Measurements of the arrival times (travel time fromsource to sensor) of the generated P- and S- waves are thenmade so that the low strain (104%) in-situ P-wave andS-wave velocities can be d
24、etermined. The calculated seismicvelocities are used to characterize the natural or man-made (orboth) properties of the stratigraphic profile.5. Significance and Use5.1 The seismic downhole method provides a designer withinformation pertinent to the seismic wave velocities of thematerials in questio
25、n (1). The P-wave and S-wave velocitiesare directly related to the important geotechnical elastic con-stants of Poissons ratio, shear modulus, bulk modulus, andYoungs modulus. Accurate in-situ P-wave and S-wave veloc-ity profiles are essential in geotechnical foundation designs.These parameters are
26、used in both analyses of soil behaviorunder both static and dynamic loads where the elastic constantsare input variables into the models defining the different statesof deformations such as elastic, elasto-plastic, and failure.Another important use of estimated shear wave velocities ingeotechnical d
27、esign is in the liquefaction assessment of soils.5.2 A fundamental assumption inherent in the test methodsis that a laterally homogeneous medium is being characterized.In a laterally homogeneous medium the source wave traintrajectories adhere to Snells law of refraction. Another as-sumption inherent
28、 in the test methods is that the stratigraphicmedium to be characterized can have transverse isotropy.Transverse isotropy is a particularly simple form of anisotropybecause velocities only vary with vertical incidence angle andnot with azimuth. By placing and actuating the seismic sourceat offsets r
29、otated 90 in plan view, it may be possible toevaluate the transverse anisotropy of the medium.NOTE 1The quality of the results produced by this standard isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities. Agencies that meet the criteriaof
30、 Practice D 3740 are generally considered capable of competent andobjective testing/sampling/inspection/etc. Users of this standard are cau-tioned that compliance with Practice D 3740 does not in itself assurereliable results. Reliable results depend on many factors; Practice D 3740provides a means
31、of evaluating some of those factors.6. Apparatus6.1 The basic data acquisition system consists of the fol-lowing:6.1.1 Energy SourcesThese energy sources are chosenaccording to the needs of the survey, the primary considerationbeing whether P-wave or S-wave velocities are to be deter-mined. The sour
32、ce should be rich in the type of energyrequired, that is, to produce good P-wave data, the energysource must transmit adequate energy to the medium incompression or volume change. Impulsive sources, such asexplosives, hammers, or air guns, are all acceptable P-wavegenerators. To produce an identifia
33、ble S wave, the sourceshould transmit energy to the ground with a particle motionperpendicular or transverse to the axis of the survey. Impulse orvibratory S-wave sources are acceptable, but the source mustbe repeatable and, although not mandatory, reversible.6.1.1.1 Shear BeamAshear beam is a commo
34、n form of anSH-wave energy source. The beam can be metal or wood, andmay be encased at the ends and bottom with a steel plate. Strikeplates may optionally be provided at the beam ends. Thebottom plate may optionally have cleats to penetrate the groundand to prevent sliding when struck. A commonly ut
35、ilized shearbeam has approximate dimensions of 2.4 m (8 ft) long by 150mm (6 in.) wide. The center of the shear beam is placed on theground at a horizontal offset ranging from 1 to 3 m (3 to 10 ft)from the receiver borehole (or cone insertion point). Thishorizontal offset should be selected carefull
36、y since boreholedisturbance, rod noise, and refraction through layers withsignificantly different properties may impact the test results.Larger horizontal offsets of 4 to 6 m (12 to 20 ft) for the2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
37、 serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.D7400082seismic source may be necessary to avoid response effects dueto surface or near-surface features. In this case the possibilityof raypath refraction must be t
38、aken into account. The ends ofthe beam should be positioned equidistant from the receiverborehole. The shear beam is typically then loaded by the axleload of vehicle wheels or the leveling jacks of the cone rig. Theground should be level enough to provide good continuouscontact along the whole lengt
39、h of the beam to ensure goodcoupling between the beam and the ground. Beam-to-groundcoupling should be accomplished by scraping the ground levelto a smooth, intact surface. Backfilling to create a flat spot willnot provide good beam-ground coupling and should beavoided. The shear beam is typically s
40、truck on a strike plate atone end using a nominal 1- to 15-kg hammer to produce aseismic wave train. Striking the other end will create a seismicwave train that has the opposite polarity relative to the wavetrain produced at the first end. Fig. 1 shows a diagram of thetypical shear beam configuratio
41、n that will produce SH-wavetrains. Fig. 2 shows an example of an impulse seismic sourcewave train that contains both P- and S-wave components.Although the shear beam of dimensions 2.4 m (8 ft) long by150 mm (6 in.) wide is commonly utilized, it may be desirableto implement beams of shorter length so
42、 that SH-source moreclosely approximates a “point source” for tests less than 20 m(60 ft) in depth. The “point source” SH-wave beam allows forthe accurate specification of the source Cartesian location (x, y,and z coordinates) which is required for the subsequent intervalvelocity calculation. For ex
43、ample, if a large SH-hammer beamis utilized, it becomes difficult to specify the exact location ofthe seismic source. In addition, it is preferable to initially excitea small area if complex stratigraphy exist and shorter SH-hammer beams mitigate problems arising from poor beam-ground coupling.6.1.2
44、 ReceiversIn the downhole seismic test, the seismicreceivers are installed vertically with depth within a boreholeor as part of the instrumentation in a cone penetrometer probe.The receivers intended for use in the downhole test shall betransducers having appropriate frequency and sensitivity char-a
45、cteristics to determine the seismic wave train arrival. Typicaltransducer examples include geophones, which measure par-ticle velocity, and accelerometers, which measure particleacceleration. Both geophones and accelerometers are accept-able for downhole seismic testing. High precision, low noise(op
46、erational amplifier integrated into sensor) accelerometersare generally more accurate due to their desirable transientresponse times (that is, delay, rise and peak times (10) andhigh bandwidths compared to geophones. Sensors with fasttransient response times are advantageous when carrying outdownhol
47、e seismic testing within hard rock stratigraphy andhigh energy ambient noise environments. The frequency re-sponse of the transducer should not vary more than 5 % over arange of frequencies from 0.5 to 2 times the predominantfrequency of the site-specific S-wave train. The geophonesshould not be hea
48、vily damped to minimize spectral smearing.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.Provision must be made for the container to be held in firmFIG. 1 Typical Downh
49、ole Shear Wave Source (Produces SH- Wave Train)D7400083contact with the sidewall of the borehole. Examples of accept-able methods include: air bladder, wedge, stiff spring, ormechanical expander. Using a wedge to hold the sensor inplace can result in erroneous data if the sensor is supported atthe bottom. If a wedge is used, it should be positioned near thecenter of the receiver container mass. The receiver packagescan also be grouted within the borehole (permanent array).When using the instrumented cone penetrometer probe, there isno borehole since the container is push
