1、Designation: D 7400 07Standard 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 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 boreholeand seismic cone actual test conduct. Data reduction andinterpretation is limited to the identification of various seismicwave types, apparent velocity relation to true velocity, e
6、xamplecomputations, 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 condu
7、ct 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 the ac
8、tual 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 collecte
9、d/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, or a
10、ny 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.1.4.2
11、 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 be
12、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) represents
13、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 (lb
14、f). 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 inch-
15、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.1.6 This standard does not purport to address all of thesafety concerns, if any, a
16、ssociated 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.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direc
17、t responsibility of Subcommittee D18.09 on Cyclic andDynamic Properties of Soils.Current edition approved Nov. 1, 2007. Published November 2007.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2. Referenced Documents2.1 ASTM Standards
18、:2D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and ConstructionD 4428/D 4428M Test Methods for Crosshole Seismic Test-ingD 5778 Test Method for
19、Performing Electronic FrictionCone and Piezocone Penetration Testing of SoilsD 6026 Practice for Using Significant Digits in Geotechni-cal Data3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in these test methods, seeTerminology D 653.4. Summary of Test Method4.1 The Downhole Seism
20、ic 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 sounding. It is similar in several respects to the CrossholeSeismic Test Method (Test Methods D 4428/D 4428M). Aseismic source is used
21、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 seismic wave train. The downhole receiver(s) may bepositioned at selected test depths in a borehole or advanced aspart of the instrumenta
22、tion package on an electronic conepenetrometer (Test Method D 5778). The seismic source isconnected to and triggers a data recording system that recordsthe response of the downhole receiver(s), thus measuring thetravel time of the wave train between the source and receiv-er(s). Measurements of the a
23、rrival 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 determined. The calculated seismicvelocities are used to characterize the natural or man-made (orboth) properties of the stratigraphi
24、c profile.5. Significance and Use5.1 The seismic downhole method provides a designer withinformation pertinent to the seismic wave velocities of thematerials in question (1). The P-wave and S-wave velocitiesare directly related to the important geotechnical elastic con-stants of Poissons ratio, shea
25、r 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 used in both analyses of soil behaviorunder both static and dynamic loads where the elastic constantsare input variables into the mo
26、dels defining the different statesof deformations such as elastic, elasto-plastic, and failure.Another important use of estimated shear wave velocities ingeotechnical design is in the liquefaction assessment of soils.5.2 A fundamental assumption inherent in the test methodsis that a laterally homoge
27、neous medium is being characterized.In a laterally homogeneous medium the source wave traintrajectories adhere to Snells law of refraction and Fermatsprinciple of least time. Another assumption inherent in the testmethods is that the stratigraphic medium to be characterizedcan have transverse isotro
28、py. Transverse isotropy is a particu-larly simple form of anisotropy because velocities only varywith vertical incidence angle and not with azimuth.NOTE 1The quality of the results produced by this standard isdependent on the competence of the personnel performing it, and thesuitability of the equip
29、ment and facilities. Agencies that meet the criteriaof 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 de
30、pend on many factors; Practice D 3740provides a means 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-wav
31、e or S-wave velocities are to be deter-mined. The source 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 al
32、l acceptable P-wavegenerators. To produce an identifiable S wave, the sourceshould transmit energy to the ground primarily by directional-ized distortion. Impulse or vibratory S-wave sources areacceptable, but the source must be repeatable and, although notmandatory, reversible.6.1.1.1 Shear BeamAsh
33、ear beam is a common form of anSH-wave energy source. The beam can be metal or wood, istypically encased at the ends and bottom with a steel plate.Strike plates should be provided at the beam ends. The bottomplate should have cleats to penetrate the ground and to preventsliding when struck. A common
34、ly utilized shear beam hasapproximate dimensions of 2.4 m (8 ft) long by 150 mm (6 in.)wide. The center of the shear beam is placed on the ground ata horizontal offset ranging from 1 to3m(3to10ft)from thereceiver borehole (or cone insertion point). This horizontaloffset should be selected carefully
35、since borehole disturbance,rod noise, and refraction through layers with significantlydifferent properties may impact the test results. The ends of thebeam should be positioned equidistant from the receiverborehole. The shear beam is typically then loaded by the axleload of vehicle wheels or the lev
36、eling jacks of the cone rig. Theground should be level enough to provide good continuouscontact along the whole length of the beam to ensure goodcoupling between the beam and the ground. The shear beam istypically struck on a strike plate at one end using a nominal 5-to 15-kg hammer to produce a sei
37、smic wave train. Striking theother end will create a seismic wave train that is oppositely2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Sum
38、mary page onthe ASTM website.D7400072polarized relative to the wave train produced at the first end.Fig. 1 shows a diagram of the typical shear beam configurationthat will produce SH-wave trains. Fig. 2 shows an example ofan impulse seismic source wave train that contains both P- andS-wave component
39、s. Although the shear beam of dimensions2.4 m (8 ft) long by 150 mm (6 in.) wide is commonly utilized,it is desirable to implement beams of shorter length so thatSH-source more closely approximates a “point source.” The“point source” SH-wave beam allows for the accurate specifi-cation of the source
40、Cartesian location (x, y, and z coordinates)which is required for the subsequent interval velocity calcula-tion. For example, if a large SH-hammer beam is utilized, itbecomes difficult to specify the exact location of the seismicsource. In addition, it is preferable to initially excite a smallarea i
41、f complex stratigraphy exist and shorter SH-hammerbeams mitigate problems arising from poor beam-groundcoupling.6.1.2 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 re
42、ceivers intended for use in the downhole test shall betransducers having appropriate frequency and sensitivity char-acteristics to determine the seismic wave train arrival. Typicaltransducer examples include geophones, which measure par-ticle velocity, and accelerometers, which measure particleaccel
43、eration. Both geophones and accelerometers are accept-able for downhole seismic testing. High precision accelerom-eters (operational amplifier integrated into sensor) are prefer-able due to their low noise, fast response times, and highbandwidths compared to geophones. The frequency responseof the t
44、ransducer must not vary more than 5 % over a range offrequencies from 0.5 to 2 times the predominant frequency ofthe site-specific S-wave train. The geophones should not beheavily damped to minimize spectral smearing. The transduc-er(s) shall be housed in a single container (cylindrical shapepreferr
45、ed) not exceeding 600 mm (24 in.) in length. Provisionmust be made for the container to be held in firm contact withthe sidewall of the borehole. Examples of acceptable methodsinclude: air bladder, wedge, stiff spring, or mechanical ex-pander. The receiver packages can also be grouted within thebore
46、hole (permanent array). When using the instrumented conepenetrometer probe, there is no borehole since the container ispushed directly through the soil so there is always firm contact.The diameter of the cone penetrometer at the location of theseismic instrumentation package (transducers) should beg
47、reater than that of the sections immediately below theinstrumentation package to promote good coupling betweenthe instrument and the surrounding soil.6.1.2.1 Preferred MethodEach receiving unit will consistof at least three transducers combined orthogonally to form atriaxial array, that is, one vert
48、ical and two horizontal transduc-ers mounted at right angles, one to the other. Two receivingFIG. 1 Typical Downhole Shear Wave Source (Produces SH- Wave Train)D7400073units should be available for deployment, either as separateunits operating independently or separated vertically in thesame contain
49、er.6.1.2.2 Optional MethodA single uniaxial receiver maybe used. Care should be taken to make sure the transducer isoriented in the direction most nearly parallel to the direction ofthe source for S-waves or radially for P-waves.6.1.3 Recording SystemThe system shall consist of sepa-rate amplifiers, one for each transducer being recorded, havingidentical phase characteristics and adjustable gain control. Aseparate anti-aliasing filter for each seismic sensor utilizedwithin the downhole array will be required. The anti-aliasingfilters are set to 1/3 of the specified sampli
