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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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.
CROSSIT is built for compatibility with laptop or desktop computers and dot matrix or laser-jet printers such that data reduction could be performed in the field as geophysical data are being acquired. Other items addressed include borehole spacing, drilling, casing, grouting, deviation surveys, and actual test procedures. Therefore, since procedures to determine material densities are standardized, acquiring detailed seismic data yields the required information to analytically assess a site.
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. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method.
Low-strain material damping and inelastic attenuation values can also be obtained from crosshole surveys. With the deviation logs, corrected crosshole distances between each borehole may be computed and used in the velocity analysis. However, the most robust application of crosshole testing is the ability to define in situ shear-wave velocity profiles for engineering investigations associated with earthquake engineering Mooney, General Crosshole Procedures Introduction 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.
Using source-receiver systems with preferential orientations in tandem i. In this case, the two horizontal axis geophones must remain oriented, radially and transversely, throughout the survey. In these soil conditions, computing an average velocity from the two direct velocities i.
Standard Test Methods for Crosshole Seismic Testing
A preferred test method intended for use on critical projects where the highest quality data must be obtained is included.
This becomes uniquely critical when only two drill holes are used i. Numerous studies have shown that the effects on crosshole measurements by the choice of geophone are not critical to the results e. The logic and flowt for this interpretation and data presentation program are designed to follow the typical field data acquisition process i.
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. 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 asstm.
Crosshole SV-wave paired borehole records at five depths. Further, several types of commercially available receivers and recording systems can also be used to conduct an acceptable crosshole survey. 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. Therefore, in order to generate and record SH-wave signals, horizontal impacts and geophones are required; also, the orientation of the source and receiver must be parallel while their respective orientation remains perpendicular to the axis of the boreholes transverse orientation.
Unlike surface seismic techniques, crosshole testing requires a more careful interpretation of the waveforms acquired at each depth. Furthermore, the program was fashioned around the ASTM conventions and test procedures outlined for crosshole seismic testing. In order to have quantitative and quality assured results, crosshole tests performed for either engineering or environmental problems should be conducted in accordance with procedures established by the American Society for Testing and Materials ASTM.
For crosshole tests, Butler, et al. 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. 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. Combining values from the two aastm may result in non-conformance with the standard.
Also included is an optional method intended for use on projects which do not require measurements of a high degree of precision. Several techniques to plug the porosity of the surrounding formation are commercially available asgm. Active view current version of standard.
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.
Poor coupling between the casing and the formation wstm delayed arrival times and attenuated signal amplitudes, particularly for higher frequency P-waves.
ASTM D / DM – 14 Standard Test Methods for Crosshole Seismic Testing
A seismic source with reversible impact directions is the key factor for quality crosshole S-wave data acquisition and interpretation. Hence, below the water surface, the P-wave is commonly termed the fluid wave, because its propagation velocity is governed by the pore fluid snot the formation density. Alternatively, SH-waves can be generated and recorded in crosshole testing. However, at sites where detailed in situ P- and S-wave velocities are required, drill hole completion must follow ASTM procedures, and when unusual conditions exist e.
Direct-wave arrivals are easily recognized even with low-amplitude refracted arrivals as long as the previously described field equipment is utilized for preferential generation of P-waves or polarized SV or SH-waves.