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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For crosshole tests, Butler, et al. Data reduction and interpretation axtm limited to the identification of various seismic wave types, apparent velocity relation to true velocity, example computations, effective borehole spacing, use of Snell’s law of refraction, assumptions, and computer programs. Other items addressed include borehole spacing, drilling, casing, grouting, deviation surveys, and actual test conduct.
Figure 2 shows a series of 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. If an Asmt source is selected, then horizontal geophones must be used and oriented as previously described to detect the SH-wave arrivals. 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.
Crosshole seismic testing has the unique advantage of sampling a limited volume of material at each test depth. Referenced Documents purchase separately The documents listed below are referenced within the subject standard but are not provided as part of the standard. Also included is an optional method intended for use on projects which do not require measurements of a high degree of precision.
Further, several types of commercially available receivers and recording systems can also be used to conduct an acceptable crosshole survey.
With three-component geophones, there is one vertically oriented geophone and two horizontal geophones. Link to Active This link will always route to the current Active version of the standard. Matching the formation density with a grout mix is not too difficult, but in open coarse-grained soils, problems arise during grout completion with losses into the formation.
Low-strain material damping and inelastic attenuation values can also be obtained from crosshole surveys. Consequently, these test methods primarily concern the actual test procedure, data interpretation, and specifications for equipment which will yield uniform test results.
Figure 1 illustrates a general field setup for the crosshole seismic test method. When V I is much greater than the two computed direct-wave velocities, then refracted-wave arrivals are being timed as first arrivals at the second receiver borehole.
Increasing velocity with depth implies the seismic ray path is nearly circular between source and receiver, thereby sensing deeper higher velocity material as the source-receiver separation increases. These SV-waves are easiest to generate because of commercially available borehole impact hammers that have reversible impact directions up or downand they are also the easiest to record because only one vertically oriented geophone is required in each receiver borehole.
Combining values from the two systems may result in nonconformance with these test methods. 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.
Recently, sites of particular concern for obtaining P- and S-wave velocities are liquefaction studies where the subsurface contains d4428 unconsolidated coarse-grained material, and standard geotechnical test procedures blow counts and material sampling cannot effectively evaluate in situ properties. Based on 10 years of experience, since the inception of the ASTM standard incrosshole geophysical surveys have become more widely used and accepted for engineering as well as environmental applications.
Crosshole seismic testing has the definitive advantage of assessing a complex layered velocity structure with alternating high and low relative velocities. Data are then used to determine the liquefaction potential of the foundation alluvial deposits. Utilizing digital recording equipment affords the operator the ability to store d4428 data on magnetic adtm for analysis at a later date; but more importantly, digital data can be filtered, smoothed, and time-shifted during analysis.
Example Problem To illustrate the effect of a high S-wave velocity layer overlying a low S-wave velocity layer on crosshole waveforms, the following sample problem is presented using data acquired at a site in central Utah. In this case, the two horizontal axis geophones must remain oriented, radially and transversely, throughout the survey. The pages found under Surface Methods and Borehole Methods are substantially ba sed on a report produced by the United States Department of Transportation: In order to have quantitative c4428 quality assured results, crosshole tests performed for either engineering or environmental problems should be conducted in accordance with procedures established by the American Society aatm Testing and Materials ASTM.
S-waves generated in crosshole testing may be split into two wave types, each with d428 particle motions–SV- and SH-waves, vertical or horizontal particle motions, respectively.
Standard Test Methods for Crosshole Seismic Testing
For successful engineering analysis of coarse-grained materials, crosshole testing is one of axtm most acceptable geophysical techniques available. Borehole verticality and direction azimuth measurements should be performed at every depth interval that seismic data are acquired.
Measurements made to more significant digits or better sensitivity than specified in these test methods shall not be regarded a nonconformance with this standard. Numerous studies have shown that the effects on crosshole measurements by the choice of geophone are not critical to the results e. For crosshole tests, one horizontal geophone remains oriented parallel to the axis between the boreholes asym orientationand the other one remains oriented perpendicular to the borehole axis transverse orientation.
dd4428 As the vadose zone and water surface are encountered, P-wave velocities become dependent upon the f4428 saturation, and the Poisson’s ratio is no longer a valid representation of the formation characteristics. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the users objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations.
A preferred test method intended for use on critical projects where the highest quality data must be obtained is included. Compute hypotenuse distance H i: Data Interpretation For interpretation of direct ray path travel times between two or three boreholes, the Bureau of Reclamation Sirles, Custer, and McKisson, has published a computer program that is designed specifically for reducing crosshole seismic data.
Stokoe demonstrated that particle motions generated with different seismic source types used during crosshole testing are three-directional.
ASTM D / DM – 00 Standard Test Methods for Crosshole Seismic Testing
Further, several types of commercially available d4428 and recording systems can also be used to conduct an acceptable crosshole survey. Poor coupling between the casing and the formation yields delayed arrival times and attenuated signal amplitudes, particularly for higher frequency P-waves.
Since 4d428 wave travel times should be x4428 to the nearest tenth of a millisecond, relative borehole positions should be known to within a tenth of a foot. Typically, either forward or inverse modeling for cross-borehole seismic investigations consists of computing synthetic travel times to test the ray path coverage and resolution of either unknown or identified velocity anomalies, respectively.
Also included is an optional method intended for use on projects which do not require measurements of a high degree of precision. When approaching seismic interfaces, refracted-wave asstm begin to be timed as the first arrival, which could easily be misinterpreted as direct-wave arrival.
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 geometry to determine average velocity.