Method for determining velocity and confidence level of acoustic waves in penetrable ground
OwnerErick J. Baziwinventor
Life of this patent
Estimating the term…
Abstract
Seismic traces are singularly acquired, digitally converted, normalized according to mean and amplitude, visually displayed for qualitative evaluation, and recorded in conjunction with relevant environmental (acquisition) details. Related pairs of data with differential vertical offsets so recorded are digitally bandpassed according to user specification, limits of dominant waveforms determined with respect to time, crosscorrelated to determine time offset, and average waveform velocity estimated over the depth increment under study, based on the determined time offset and the estimated waveform travel path distance difference.
Claims6
A method for Seismic Cone Penetration Testing comprising the steps of inserting a seismic cone penetrometer to predetermined depths in the ground, generating a seismic source at the surface of the ground so that seismic waves propagate through the overburden adjacent the probe hole of the cone penetrometer which contains a seismic sensor, in addition to other sensors, employing said seismic sensor to provide an analogue signal in response to the seismic waves, converting analog seismic wave signal to digital seismic wave signal, and then,
- A) removing the D.C. shift of said digital seismic wave signal to force the mean amplitude of said signal to zero,
- B) normalizing the amplitude range of said digital seismic wave signal to a 1.0 to -1.0 unit range scale,
- C) displaying said digital seismic wave signal so the user can assess the quality of said digital seismic wave signal,
- D) recording said digital seismic wave signal in digital format on computer media for later processing,
- E) processing pairs of vertically offset and related digital seismic wave signals so recorded as in A) through D) above, by
- i) displaying the frequency spectra of said digital seismic wave signals by taking a Fast Fourier Transform of these inputs for user identification of desired spectra isolation, then digitally filtering these vertically offset and related pairs of digital seismic wave signals to remove unwanted frequencies, thereby isolating the waveforms of interest contained in a frequency range,
- ii) determining upper and lower bounds of the limits of said waveforms of interest so isolated with respect to time,
- iii) crosscorrelating with respect to the time difference, .tau., said waveforms of interest isolated in i) within the limits defined in ii) to determine the time difference, .tau.*, where the crosscorrelation value between said waveforms is maximum,
- iv) determining the actual distance difference travelled by said waveforms of interest from the horizontal displacement of the seismic source from the probe hole (X offset) and the vertical displacement of the seismic source from the surface of the ground (Y offset) to the respective depths of seismic cone data acquisition,
- v) determining from the time difference .tau.* and the travel distance difference of said waveforms of interest, the average velocity of said waveforms over the depth increment under study,
- vi) indicating an estimate of accuracy of said average velocity calculated by dividing the value of the crosscorrelation function at .tau.*, by the variances of said waveforms of interest calculated within the limits determined in (ii), and
- vii) recording the velocity and accuracy estimates obtained in i) through vi) above, as well as user-specified site information, in digital format on computer media for a permanent record for further processing, printing, or evaluation.
Dependencies are inferred from the claim text.