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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The requirement for multiple drill holes in crosshole testing means that care must be taken when completing each borehole with casing and grout.
Data are then used to determine the liquefaction potential of the foundation alluvial deposits.
Hoar provides an excellent description of picking P- and S-wave arrivals off recorded crosshole signals. Crosshole seismic testing has the unique advantage of sampling a limited volume of material at each test depth.
For engineering applications, digital signal processing in crosshole seismic tests is, similar to modeling, of minimal value. Other items addressed include borehole spacing, drilling, casing, grouting, deviation surveys, and actual test conduct.
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.
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. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method. Crosshole seismic testing has the definitive advantage of assessing a complex layered velocity structure with alternating high and low relative velocities.
Standard Test Methods for Crosshole Seismic Testing
Also, because each drill hole was cased for the crosshole tests, additional geophysical surveys should be conducted. 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 The comparative technique for defining the refractor velocities outlined above asym that the velocities are constant within each layer; however, occasionally this is an oversimplification.
Compute travel times through both materials: 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.
Therefore, since procedures to determine material densities are standardized, acquiring detailed seismic data yields the required information to analytically assess a site. Some deposits have linearly increasing velocity with depth, primarily due to vertical pressures, where the apparent velocity for each depth can be computed with.
Apparent V 1 refracted velocity. Compute abscissa distance Y i: Direct and fairly straightforward computation of the S-wave velocity profile, which is correlated with the liquefaction potential of both the materials and depth intervals d428 engineering concern for the safety of the structure.
Active view current version of standard. In addition, they are asym of the significant digits that should generally be retained. 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. 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.
Retrieve measured crosshole travel time: That is, the ray path is horizontal but the shear particle motion along the ray path is in the vertical plane.
A preferred test method intended for use on critical projects where the highest quality data must be obtained is included. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Further, several types of commercially available receivers and atsm systems can also be used to conduct an acceptable crosshole survey.
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. Another critical element of crosshole testing, which is often ignored, is the requirement for borehole directional surveys. 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.
Recently, sites of particular concern for obtaining P- and S-wave velocities are liquefaction studies where the subsurface contains considerable unconsolidated coarse-grained material, s4428 standard geotechnical test procedures blow counts and material sampling cannot effectively evaluate in situ properties.
Because boreholes are required, there is the opportunity to obtain more site-specific geotechnical information, which, when integrated with the seismic data, yields the best assessment for aetm engineering application liquefaction, deformation, or strong motion Characterization. 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.
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. 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.
Other items addressed include borehole spacing, drilling, casing, grouting, deviation surveys, and actual test procedures.
ASTM D / DM – 07 Standard Test Methods for Crosshole Seismic Testing
This, of course, assumes field data are acquired properly and no analog filtering or digital aliasing was performed prior to recording seismic data from each depth. Stokoe demonstrated that particle motions generated with different seismic source types used during crosshole testing are three-directional. Figure 4 shows an example of SV- direct-wave arrivals wstm 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.
S-waves generated in crosshole testing may be split into two wave types, each with different particle motions–SV- and SH-waves, vertical or horizontal particle motions, respectively. Active view current version of standard. The logic and flowt for this interpretation and data presentation program are designed to follow the typical field data acquisition process i.
This is accomplished with loading poles or with geophones that can be electronically oriented. Because of this, the crosshole f4428 permits much easier interpretation of direct arrivals in the recorded waveforms.
Therefore, a systematic comparison of measured travel times, computed asym velocities, and interval velocities at each recording depth enables interpretation of true in situ velocity at all measurement depths. Hoar’s dissertation shows that with proper borehole completion, digital recording equipment, and a preferential source-receiver system, clean reversed polarized and interpretable S-wave signals x4428 relatively easy to acquire.
Data Acquisition Recording instruments used in crosshole testing vary considerably, but there are no standard requirements other than exact synchronization of c4428 source pulse and instrument trigger for each recording. In these soil conditions, computing an average velocity from the two direct velocities i.
Apparent V 1 refracted velocity Comparing both sets of direct wave velocities, that is, source to receiver No. Furthermore, the program was fashioned around the ASTM conventions and test procedures outlined for crosshole seismic testing.
In this case, the two horizontal axis geophones must aztm oriented, radially and transversely, throughout the survey.