Inter‐borehole Acoustic Measurements and Their Use in Engineering Geology*

McCann, D. M.; Grainger, P.; McCann, C.

doi:10.1111/j.1365-2478.1975.tb00680.x

Cited by 42 publications

(8 citation statements)

References 5 publications

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“…The tomography data consisted of 210 arrival times obtained using 15 sources in one of the boreholes and recorded at 14 receivers in the other borehole. The source, known as a 'sparker', was a downhole electrode assembly across which a capacitor bank was discharged (see McCann, Grainger & McCann 1975, for a description of the source). The sparker generates frequencies between 0.5 and 2 kHz.…”

Section: Geological Setting and Survey Specificationmentioning

confidence: 99%

Traveltime tomography in anisotropic media-II. Application

Pratt

Chapman

1992

Geophysical Journal International

144

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S U M M A R YCross-borehole seismic data have traditionally been analysed by inverting the arrival times for velocity structure (traveltime tomography). The presence of anisotropy requires that tomographic methods be generalized to account for anisotropy. This generalization allows geological structure to be correctly imaged and allows the anisotropy to be evaluated. In a companion paper we developed linear systems for 2-D traveltime tomography in anisotropic media. In this paper we analyse the properties of the linear system for quasi-compressional waves and invert both synthetic and real data. Solutions to the linear systems consist of estimates of the spatial distributions of five parameters, each corresponding to a linear combination of a small subset of the 21 elastic, anisotropic velocity parameters. The parameters describe the arrival times in the presence of weak anisotropy with arbitrary symmetries. However, these parameters do not, in general, describe the full nature of the anisotropy. The parameters must be further interpreted using additional information on the symmetry system. In the examples in this paper we assume transverse isotropy (TI) in order to interpret our inversions, but it should be noted that this final interpretation could be reformulated in more general terms.The singular value decomposition of the linear system for traveltime tomography in anisotropic media reveals the (expected) ill-conditioning of these systems. As in isotropic tomography, ill-conditioning arises due to the limited directional coverage that can be achieved when sources and receivers are located in vertical boreholes. In contrast to isotropic tomography, the scalelength of the parametrization controls the nature of the parameter space eigenvectors: with a coarse grid all five parameters are required to model the data; with a fine grid some of the parameters appear only in the null space.The linear systems must be regularized using external, a priori information. An important regularization is the expectation that the elastic properties vary smoothly (an ad hoc recognition of the insensitivity of the arrival times to the fine-grained properties of the medium). The expectation of smoothness is incorporated by using a regularization matrix that penalizes rough solutions using finite difference penalty terms. The roughness penalty sufficiently constrains the solutions to allow the smooth eigenvectors in the null space of the unconstrained problem to contribute to the solutions. Hence, the spatial distribution of all five parameters is recovered. The level of regularization required is difficult to estimate; we advocate the analysis of a suite of solutions. Plots of the solution roughness against the data residuals can be used to find 'knee points', but for the fine tuning of the regularization one has little recourse but to examine a suite of images and use geological plausibility as an additional criterion.The application of the regularized numerical scheme to the synthetic data reveals that the roughness penalty shoul...

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Section: Geological Setting and Survey Specificationmentioning

confidence: 99%

Traveltime tomography in anisotropic media-II. Application

Pratt

Chapman

1992

Geophysical Journal International

144

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“…ODonoghue and OFlaherty (1974) used the technique to investigate the spatial variation in rock properties encountered during tunneling and to assess the degree of rock damage in the rock mass caused by different excavation techniques. McCann, Grainger and McCann (1975) delineated interfaces between homogeneous media and detected localized, irregular features. Auld (1977) has described instrumentation for, and presented field results of, cross-hole acoustic measurements, which he used to determine the elastic properties of the rock mass.…”

Section: Introductionmentioning

confidence: 99%

Experimental Studies of Elastic‐wave Propagation in a Columnar‐jointed Rock Mass*

King

Myer

Rezowalli

1986

Geophysical Prospecting

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KING, M.S., MYER, L.R. and REZOWALLI, J.J. 1986, Experimental Studies of Elastic-Wave Propagation in a Columnar-Jointed Rock Mass, Geophysical Prospecting 34, 1185-1 199.Results are presented of a series of cross-hole acoustic measurements made between four horizontal boreholes drilled from a near-surface underground opening situated in a basaltic rock mass. The objectives of the program were to assess the extent of blast damage around the opening, and to evaluate the rock mass characteristics and their spatial variation around the opening. The acoustic velocity and attenuation data are indicative of an anisotropic, jointed rock mass, with a greater intensity of jointing along travel paths in the horizontal than the vertical direction. Low acoustic P-and S-velocities are indicative of blast damage and of zones of intense jointing or fracturing. In this case blast damage extends to approximately 1.5 m from the face. Attenuation data appear to be less sensitive in distinguishing between the blast-damaged zone and intense vertical jointing and fracturing in the virgin rock mass. Taken together with field data, laboratory measurements of P-and S-wave velocities on intact core samples suggest that the rock mass is probably water saturated.

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“…O'Donoghue et al (1974) employed the technique to investigate the spatial variation-in rock properties encountered during tunneling, and to assess the degree of damage in the rock mass caused by different excavation techniques. Using the cross-hole technique, McCann et al (1975) delineated interfaces between different strata and det~ted localized irregular features. Auld (1977) used cross-hole measurements to evaluate the elastic properties of a rock mass.…”

Section: Introductionmentioning

confidence: 99%

Cross-hole acoustic measurements in basalt

Myer

Rezowalli

1986

International Journal of Rock Mechanics and Mining Sciences &am

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A series of cross-hole acoustic measurements have been performed in a columnar-jointed basaltic rock mass around an underground opening mined by the drill-and-blast method. The purposes of the test program were: to evaluate the rock mass characteristics around the opening; to determine the zone of blast damage; and to evaluate seismic methods for anomaly detection ahead of mining in this type of rock. The cross-hole measurements were made between four 76-mm diameter horizontal boreholes diamond-drilled 12 m into a wall of the underground opening. Repetitive pulses of compressional (P) and shear (S) waves of frequencies in the range 1 kHz-100 kHz were propagated from a transmitter sonde through the rock mass to a receiver sonde, both of which w~re clamped hydraulically to the borehole wall. After amplification the received P-and S-wave signals were digitized at the surface by a digital oscilloscope and stored on floppy discs.The results indicate considerable reductions in P-and S-wave velocities at distances less than 2 m from the face. Clearly these low values are associated with blast damage. Beyond 2 m, the velocities in a vertical direction indicate almost constant values. The velocities in the horizontal direction beyond 2m appeared erratic, but showed a general tendency to increase as a function of distance from the face. Their maximum values remained, however, still lower in value than the corresponding velocities in the vertical direction. Near the face, the differences in velocities were considerably greater: with horizontal velocities considerably lower in value than those v~rtical.

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Inter‐borehole Acoustic Measurements and Their Use in Engineering Geology*

Cited by 42 publications

References 5 publications

Traveltime tomography in anisotropic media-II. Application

Traveltime tomography in anisotropic media-II. Application

Experimental Studies of Elastic‐wave Propagation in a Columnar‐jointed Rock Mass*

Cross-hole acoustic measurements in basalt

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