A microelectromechanical system digital 3C array seismic cone penetrometer

Abstract

A digital 3C array seismic cone penetrometer has been developed for multidisciplinary geophysical and geotechnical applications. Seven digital triaxial microelectromechanical system accelerometers are installed at 0.25-m intervals to make a 1.5-m-long downhole seismic array. The accelerometers have a flat response up to 2 kHz. The seismic array is attached to a class 1 digital seismic cone, which measures cone tip resistance, sleeve friction, pore-pressure, and inclination. The downhole 3C array can be used together with impulsive seismic sources and/or high-frequency vibrators that are suitable for high-resolution shallow applications. Results from two field experiments showed that a good data quality, including a constant source function within an array, and a dense depth-sampling allowed robust estimation of seismic velocity profiles in the shallow subsoil. Using horizontal and vertical seismic sources, downhole 9C seismic array data can be easily acquired. The quality of the shear-wave data is much superior when the surface seismic source is a controlled, high-frequency vibrator in stead of a traditional sledge hammer. A remarkable correlation in depth, in a fine scale, between low-strain seismic shear wave velocity and high-strain cone tip resistance could be observed. The array measurements of the full-elastic wavefield and the broad spectral bandwidth are useful in investigating frequency-dependent seismic wave propagation in the porous near-surface soil layers, which is informative of the in situ fluid-flow properties. Stable estimates of dispersive seismic velocity and attenuation can be obtained.

Wet and gassy zones in a municipal landfill from P- and S-wave velocity fields

“…This can be explained by the fact that V S is primarily controlled by rigidity of the waste skeleton, which is likely to be a strong determinant for the mechanical resistance. Better correlation between the tip resistance of cone penetration tests and V S has been reported in previous studies, especially in a depth-specific sense (Ghose, 2012). On the other hand, the correlation that we observe between the distribution of V P and that of the mechanical tip resistance of the landfill materials is determined by compressibility and density.…”

Earthquake-faulting-related deformation in soil evidenced in S-wave shallow reflection data: Field results from Portugal

“…Of the various geophysical methods, seismic reflections generally offer a good resolution to study the shallow fault zones (e.g., Woolery et al, 1993;Benson and Mustoe, 1995;Floyd et al, 2001;Williams et al, 2001;Sugiyama et al, 2003;Wang et al, 2004;Harris, 2009;. In case of soft soils, S-waves generally offer better results than P-waves not only because of the higher resolution due to much lower velocity and hence smaller wavelengths, but also owing to a greater sensitivity of S-waves to the subtle changes in the soil type or composition (e.g., Brouwer et al, 1997;Ghose and Goudswaard, 2004;Ghose, 2012). The vast majority of previous studies involving shallow seismic reflections to illuminate a fault zone relied on detecting a displacement in one or more reflection horizons due to faulting, generally observed in the stacked section.…”

Retrieving Higher-mode Surface Waves Using Seismic Interferometry by Multidimensional Deconvolution

“…The MDD scheme contains point-force responses only, which is advantageous for applications with contemporary field-acquisition geometries, and assumes illumination from one side. The scheme also requires one or more shallow vertical arrays of geophones, which may be made available by the presence of buried arrays, boreholes, or a seismic cone penetrometer (Ghose, 2012). We presented a numerical example with controlled sources having the same spectrum, but in principle the source spectra can be different.…”