Abstract
This paper proposes a methodology to construct logs of rock strength from the cutting force signal recorded in scratch tests conducted in the ductile regime. The approach, which is based on the application of discrete wavelet transforms, recognizes the existence of two length scales ℓc and ℓr. The strength length scale ℓc represents the length over which it is meaningful to measure strength, while the repeatability length scale ℓr is related to the resolution at which the force signal must be observed to become insensitive to the stochastic micro-failure events triggered by the motion of the cutter. It is postulated that the original cutting force signal, assumed to be sampled at a high enough frequency, can be decomposed into a deterministic signal intrinsic to the rock and a stochastic one resulting from discrete rock failure events. The technique of multiresolution analysis based on the maximal overlap discrete wavelet transform is applied as a low-pass filter to the original cutting force signals so as to wipe out the high-frequency components associated with the stochastic rock failure events. A criterion to determine the optimum cutoff frequency of the low-pass filter and the corresponding repeatability length scale is discussed in terms of the correlation coefficients between different filtered signals. It is shown that the low-pass filtered signals obtained at the optimum cutoff frequency have two salient features: (i) repeatability over different tests conducted at the same depth of cut on the same sample, and (ii) variability along the cutting distance. The excellent repeatability reveals that the deterministic background trend of the original force signals is relevant to the rock strength property, and the variability of the background trend captures the spatial variation of the rock strength.
Original language | English (US) |
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Pages (from-to) | 1161-1170 |
Number of pages | 10 |
Journal | Journal of Rock Mechanics and Geotechnical Engineering |
Volume | 15 |
Issue number | 5 |
DOIs | |
State | Published - May 2023 |
Externally published | Yes |
Bibliographical note
Funding Information:The main funding for this research was provided by the National Science Foundation of USA (Grant No. 1742823). Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The research was also partially supported by the Theodore W. Bennett Chair in Mining Engineering and Rock Mechanics. These supports are gratefully acknowledged. The authors also acknowledge the technical support from EpsLog.
Funding Information:
The main funding for this research was provided by the National Science Foundation of USA (Grant No. 1742823 ). Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The research was also partially supported by the Theodore W. Bennett Chair in Mining Engineering and Rock Mechanics . These supports are gratefully acknowledged. The authors also acknowledge the technical support from EpsLog.
Publisher Copyright:
© 2023 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences
Keywords
- Intrinsic specific energy
- Rock heterogeneity
- Scratch tests
- Wavelet method