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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There are studies, however, which indicate significant velocity dependence of the SV- and SH-waves due to anisotropic states of stress in either the horizontal or vertical stress field particularly in soil deposits; Redpath, et al. To illustrate the effect of a high S-wave velocity layer overlying a low S-wave velocity layer on crosshole waveforms, the following sample e4428 is presented using data f4428 at a site in central Utah.
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.
V 2 across the seismic interface determine if ast, refracted wave will arrive before the direct wave. 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.
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. There are a number of digital signal processing techniques useful for determining material properties other than P- or S-wave velocity, as well as confirming the computed crosshole velocity profile, such as: In this system, the pound lbf represents a unit of force weightwhile the unit for mass is slugs.
In this example, refractions occur in a situation similar to that depicted in figure 3; that is, refractions occur from high-velocity materials either above or below the low-velocity layer.
Inch-pound units are provided xstm convenience. In this case, the two horizontal axis geophones must remain oriented, radially and transversely, throughout the survey. Figure 5 shows a portion of the waveforms collected over the depth interval In these soil conditions, computing e4428 average velocity from the two direct velocities i.
A seismic source with reversible impact directions is the key factor for quality crosshole S-wave data acquisition and interpretation. 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, For crosshole tests, Butler, et al.
Standard Test Methods for Crosshole Seismic Testing
This becomes uniquely critical when only two drill holes are used i. Link to Active This link will always route to the current Satm version of the standard. 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.
Also, because each drill hole was cased for the crosshole tests, additional geophysical surveys should be conducted. Further, several types of commercially available receivers and recording systems can also be used to conduct an acceptable crosshole survey. The ast for multiple drill holes in crosshole testing means that care must be taken when completing each borehole with casing and grout.
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 the 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 d448 widely used and accepted for engineering as well as environmental applications.
Standard – Standard Test Methods for Crosshole Seismic Testing ASTM D/DM –
Recording instruments used in crosshole testing vary considerably, but there are no standard requirements zstm than exact synchronization of the source pulse and instrument trigger for each recording. Although both phase one and phase two results are important, the two independent sets of data must be integrated into the final analysis. Even small grout takes begin to affect the velocity measured between two closely spaced drill holes. Other items addressed include borehole spacing, drilling, casing, grouting, deviation surveys, and actual test conduct.
Poor coupling between the casing and the formation yields sstm arrival asstm and attenuated signal amplitudes, particularly for higher frequency P-waves.
With the deviation logs, corrected crosshole distances between each borehole may be computed and used in the velocity analysis. Crosshole seismic testing has the definitive advantage of assessing a complex layered velocity structure with alternating high and low relative velocities. Compute total direct travel time: 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.
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. 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.
ASTM D / DM – 14 Standard Test Methods for Crosshole Seismic Testing
The objective of acquiring crosshole data can be multipurpose; that is, the seismic velocity results obtained may be used for evaluation of lateral and vertical material continuity, astk analyses, deformation studies, or investigations concerning amplification or attenuation of strong ground motion.
Compute hypotenuse distance H i: 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.
Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method. Due to the effect refracted waves have qstm crosshole data sets, ASTM procedures require a three-borehole array because velocity corrections can be made for refracted arrivals. CROSSIT is built for compatibility with laptop or desktop asgm and dot matrix or laser-jet printers such that data reduction could be performed in the field as geophysical data are d44428 acquired.
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.