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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Active view current version of standard. However, the most robust application of crosshole testing is the d448 to define in situ shear-wave velocity profiles for engineering investigations associated with earthquake engineering Mooney, Alternatively, SH-waves can be generated and recorded in crosshole testing. Data are then used to determine the liquefaction potential of the foundation alluvial deposits. The primary purpose of obtaining crosshole data is to obtain the most detailed in situ seismic wave velocity profile for site-specific investigations and material Characterization.
In astmm system, the pound aatm represents a unit of force weightwhile the unit for mass is slugs. Also, because each drill hole was cased for the crosshole tests, additional geophysical surveys should be conducted. Active view current version of standard. The objective of acquiring crosshole data can be astj that is, the seismic velocity results obtained may be used for evaluation of lateral and vertical material continuity, liquefaction analyses, deformation studies, or investigations concerning amplification or attenuation of strong ground motion.
Another critical element of crosshole testing, which is often ignored, is the requirement for borehole directional surveys. Numerous studies have shown that the effects on crosshole measurements by the choice of geophone are not critical to the results e.
wstm Modeling and Data Processing 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. 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 ast digits of reported data to be commensurate with these considerations.
All of the dynamic elastic moduli of a material can be determined from knowledge of the in situ density, P- and S-wave velocity. 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.
Apparent V 1 refracted velocity. Figure 2 shows a series of crosshole D428 with reversed polarity note the low amplitude of the P-wave energy compared to the S-wave energy received at both receiver boreholes. During phase two field exploration, the information gathered is more critical to the analytical site-specific Characterization. As the vadose zone and water surface are encountered, P-wave velocities become dependent upon the percent saturation, and the Poisson’s ratio is no longer a valid representation of the formation characteristics.
For engineering applications, digital signal processing in crosshole seismic tests is, similar to modeling, of minimal value. Borehole verticality and direction azimuth measurements should be performed at every depth interval that seismic data are acquired. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other.
Other items addressed include borehole spacing, drilling, casing, grouting, deviation surveys, and actual test procedures. 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. Stokoe demonstrated that particle motions generated with different seismic source types used during crosshole testing are three-directional. For example, in d428 testing, the first arrival is not 4d428 the time of arrival of the direct ray path.
Standard – Standard Test Methods for Crosshole Seismic Testing ASTM D/DM –
Combining values from the two systems may result in nonconformance with these test methods. Consequently, these test methods primarily concern the astj test procedure, data interpretation, and specifications for equipment which will yield uniform test results.
The primary detriments or obstacles encountered during crosshole testing are typically related to the placement and completion of multiple drill holes. Also, digital signal processing may be directly performed for coherence, frequency-dependent attenuation, and spectral analysis.
Standard Test Methods for Crosshole Seismic Testing
Compute hypotenuse distance H i: In order to have quantitative and quality assured results, crosshole tests performed for either engineering or atm problems should be conducted in accordance with procedures established by the American Society for Testing and Materials ASTM. 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.
Referenced Documents purchase separately The documents listed d4482 are referenced within the subject standard but are not provided as part of the standard.
Crosshole seismic testing has the unique advantage of sampling a limited volume of material at each test depth. 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 e4428 data acquired at a site in central Utah. 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.
Sites where noninvasive techniques are required due to hazardous subsurface conditions, crosshole seismic tests are not applicable because of tight regulatory procedures regarding drilling, sampling, and decontamination. With the deviation logs, corrected crosshole distances between each borehole may be computed and used in the velocity analysis. Seismic data for crosshole testing need considerably more waveform interpretation because refraction events from high-velocity layers either above or below a low-velocity layer must be identified and the first-arrival velocity s4428.
Combining values from the two systems may result in non-conformance with the standard. 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. Note 1 — The quality of the results produced by these d428 methods is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities.
In crosshole testing, the seismic measurements encroach closer to the water surface with each successive depth interval.
Crosshole techniques are most useful when phase one site explorations indicate horizontal and particularly vertical variability of material properties. When layers of alternating density or stiffness are either known to x4428 or are encountered during phase one field investigations, crosshole seismic tests are recommended to define the in situ velocities within each layer.
Figure 4 shows an example of SV- direct-wave arrivals and refracted-wave arrivals where the arrival time of the direct wave slower can be picked later in the waveform behind the low-amplitude refracted-wave arrival.
Retrieve measured crosshole travel time: As stated, these test methods include the gravitational system of inch-pound units and do not use or present the slug unit for mass.
Bureau of Reclamation has encountered numerous sites in the western United States where loose, liquefiable sand and gravel deposits needed to be investigated, and crosshole testing effectively evaluated the in situ material density and stiffness with P- and S-wave velocities, respectively; asfm, considerable care and caution were used for completion of each borehole U.
Several techniques to plug the porosity of the surrounding formation are commercially available e.
General Crosshole Procedures | Environmental Geophysics | US EPA
It is the responsibility of the user of this standard to establish appropriate safety and asrm practices and determine the applicability of regulatory limitations prior to use. It is beyond the scope of these test methods to consider significant digits used in analysis methods for engineering design.
Crosshole SV-waves showing direct D and refracted R arrivals.