Methods and systems for ultrasonic rock bolt condition monitoring
AssigneeNational Research Council of Canada
InventorsZhigang Sun, Kuo-Ting Wu, Silvio Elton Kruger
Life of this patent
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Abstract
Methods and systems for determining a change in condition of a rock bolt. Some methods may comprise, at a first point in time, propagating shear and longitudinal ultrasonic waves along the rock bolt to measure a first time of flight for each of the shear and longitudinal waves, at a second point in time after the first point in time, propagating shear and longitudinal ultrasonic waves along the rock bolt to measure a second time of flight for each of the shear and longitudinal waves, and using the relative changes of the first and second time of flights, determining the change in condition of the rock bolt section.
Claims6
A method for determining a change in condition of a section of a shank of an installed rock bolt, the section of the shank being less than an entirety of the rock bolt, wherein determining the change in condition of the section of the shank comprises determining a change in axial stress that the section of the shank is experiencing, the method comprising,
- at a first point in time, propagating shear and longitudinal ultrasonic waves along the shank of the rock bolt to measure a first time of flight for each of the shear and longitudinal waves, and determining an average temperature of the section of the shank at the first point in time;
- at a second point in time after the first point in time, propagating shear and longitudinal ultrasonic waves along the shank of the rock bolt to measure a second time of flight for each of the shear and longitudinal waves, and determining an average temperature of the section of the shank at the second point in time;
- using the relative changes of the first and second time of flights, determining the change in condition of the section of the shank;
- wherein the shank of the rock bolt is experiencing either non-uniform loading, non-uniform temperature, or both non-uniform loading and non-uniform temperature;
- and
- wherein a change in axial stress of the section of the shank is determined according to
- 〈
- σ
- 〉
- -
- 〈
- σ
- 0
- 〉
- =
- β
- σ
- e
- (
- Δ
- Tc
- r
-
- e
-
- l
-
- τ
- L
- -
- Δ
- Tc
- r
-
- e
-
- l
-
- τ
- S
- )
- β
- σ
- e
- -
- 1
- /
- C
- σ
-
- L
- e
- ,
- where (σ)−(σ0) is the difference in axial stress between the first and second points in time, ΔTcrelτS is the temperature-corrected relative change in the first and second time of flights of the shear ultrasonic waves, ΔTcrelτL is the temperature-corrected relative change in the first and second time of flights of the longitudinal ultrasonic waves, βσe is a ratio of a stress coefficient for the longitudinal ultrasonic waves to a stress coefficient for the shear ultrasonic waves, and CσLe is the stress coefficient for the longitudinal ultrasonic waves.
Dependencies are inferred from the claim text.