These test methods are limited to the determination of the velocity of two types of horizontally travelling seismic waves in soil materials. GEOPHYSICAL SYSTEMS. NDE ™» One Platform – Multiple NDE Tests geo- Crosshole/Downhole Seismic» ASTM D/DM/D(DS). Crosshole seismic test procedures are outlined in ASTM test designation D M (). The ASTM procedures provide specific.
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A preferred test method intended for use on critical projects where the highest quality data must be obtained is included. Reporting of test results in units other than SI shall not be regarded as x4428 with this test method.
Figure 2 shows a series asrm crosshole SV-waves with reversed polarity note the low amplitude of the P-wave energy compared to the S-wave energy received at both receiver boreholes. All of the dynamic elastic moduli of a material can be determined from knowledge of the in situ density, P- and S-wave velocity.
Inch-pound units are provided for convenience. Several techniques to plug the porosity of the surrounding formation are commercially available e. The effect of increasing velocity with depth is greatest within thick homogeneous soil deposits. Data Acquisition Recording instruments used in crosshole testing vary considerably, but there are no standard requirements other than exact synchronization of the source pulse and instrument trigger for each recording.
With three-component geophones, there is one vertically oriented geophone and two horizontal geophones.
ASTM D / DM – 00 Standard Test Methods for Crosshole Seismic Testing
Typically, crosshole surveys are a geophysical tool for performing explorations during what are considered phase two field investigations where phase one field investigations include surface geophysical surveys, follow-up drilling, trenching, and sampling of the in situ materials. Since seismic wave travel times should be measured to the nearest tenth of a millisecond, relative borehole positions should be known to within a tenth of a foot.
Recently, sites of particular concern for obtaining P- and S-wave velocities are liquefaction studies where the subsurface contains considerable unconsolidated coarse-grained material, and standard geotechnical test procedures blow counts and material sampling cannot effectively d442 in situ properties. Direct-wave velocities computed for the far receiver R2 at each depth will always be slightly higher than the near receiver R1 ; hence, the interval velocity will be even higher.
Also, lithologic information such as stratigraphy and material type are determined from the drilling and sampling program prior to seismic data acquisition; this allows reliable constraints, or boundary conditions, to be placed on the field data along the boundaries of the material between the boreholes. Aatm of Reclamation, Also, because each drill hole was cased for the crosshole tests, additional geophysical surveys should be conducted. Furthermore, the program was fashioned around the ASTM conventions and test procedures outlined for crosshole seismic testing.
The primary detriments or obstacles encountered during crosshole testing are typically related to the placement and completion of multiple drill holes. Referenced Documents purchase separately The documents listed below are referenced within the subject standard but are not provided as part of the standard. Crosshole SV-wave paired borehole records at five depths. Assuming that the boreholes are vertical and plumb leads to computational inaccuracies and ultimately to data that cannot be quality assured.
For engineering applications, there is not much advantage in determining via modeling the ray coverage or residual velocity resolution because crosshole testing at the engineering scale utilizes a simple horizontal, straight-ray path f4428 to determine average velocity. Stokoe demonstrated that particle motions generated with different seismic source types used during crosshole testing are three-directional.
Standard Test Methods for Crosshole Seismic Testing
Crosshole techniques are most useful when phase one site explorations indicate horizontal and particularly vertical variability of material properties. Active view current version of standard. Therefore, the following sequence of eight steps equations will confirm detection of refracted-wave travel time or direct-wave travel time at each recording depth ASTM Data are then used to determine the liquefaction potential of the foundation alluvial deposits.
Jump to main content. Based on this discussion, to ensure that astmm in situ velocities are presented, d4248 measurements should be performed a minimum of four measurement intervals below the zone of concern to adequately define the velocity profile.
The comparative technique for defining the refractor velocities outlined above assumes that the velocities are constant within each layer; however, occasionally this is an oversimplification.
The standard assumes that the method used to analyze the data obtained is based on first arrival times or interval arrival times over a measured distance. It is beyond the scope of these test methods to consider significant digits d4482 in analysis methods for engineering design. Measurements made to more significant digits or better sensitivity than specified in these test methods shall not be regarded a nonconformance with this standard.
Coupling detailed site information obtained from the crosshole tests with the overall acceptance of the validity of the velocity data, these standards use both empirical correlations for liquefaction and specific input parameters for deformation or ground motion analyses U. Since considerable confidence can be placed on engineering scale crosshole seismic data, computation of in situ low-strain elastic constants Shear and Young’s modulus, Poisson’s ratio, etc.
The recorded trigger aatm from zero-time geophones or accelerometers mounted ast the downhole impact hammer allows accurate timing for the first arrival at each drill hole.
Due to the effect refracted waves have on crosshole data sets, ASTM procedures require a three-borehole array because velocity corrections can be made for refracted arrivals. Typically, either forward or inverse modeling for cross-borehole seismic investigations consists of computing synthetic travel times to test ast ray path coverage and resolution of either unknown or identified velocity anomalies, respectively.
For crosshole tests, one horizontal geophone remains oriented parallel to the axis between the boreholes radial orientationand the other one remains oriented perpendicular to the borehole axis transverse orientation. Sites where noninvasive techniques are required due to hazardous subsurface conditions, d4248 seismic tests are not applicable because of asttm regulatory procedures regarding drilling, sampling, and decontamination. Also, depending upon the velocity contrast across layer boundaries, direct arrivals through low-velocity layers are generally larger amplitude and thereby recognizable.
Due to the different particle motions along the seismic ray path, it is crucial asmt use optimal source-receiver systems in order to best record crosshole P- or S-waves Hoar, V 2 across the seismic interface determine if the refracted wave will arrive before the direct wave.
It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Acquiring crosshole seismic data resolves hidden layer velocity anomalies that cannot be detected with conventional surface methods, allows both final interpretation of other surface geophysical data seismic or electricaland permits both empirical and theoretical correlation with other geotechnical material parameters.
It is paramount that the polarity of each geophone be known prior to data acquisition because the direct arrivals of S-waves with reversed polarity can be easily misinterpreted.
When layers of alternating density or stiffness are either known to exist or are encountered during phase one field investigations, crosshole seismic tests are recommended to define the in situ velocities within each layer.
Reliable results depend on many factors; Practice D provides a means of evaluating some of those factors. This technique of reducing data in the field has proven its value because of the ability to determine optimal testing intervals and adjust the program as necessary to address the site-specific problem.
Note 1 — The quality of the results produced by these test methods is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities.