At its coal mine near Underwood, North Dakota, Falkirk Mining noticed unusual vibrations occurring in its silo during certain periods. Concerned about the silo’s structural stability, the company asked Barr to investigate the cause.
Our structural engineers installed four vibration and displacement sensors at various heights on the silo to record data multiple times a second. Barr’s cloud-based data-warehousing system processed the high-frequency instrumentation data into hourly and daily averages for analysis. We then used statistical fingerprinting techniques to identify the specific characteristics of the vibrations when they occurred, and with the client’s assistance, identified previous dates on which those types of vibrations had taken place.
The real-time instrumentation data showed that the silos were swaying slightly and vibrating at a frequency centered on 1.25 Hz. Barr theorized that differences in the coal level in the silo were affecting the mass distribution and creating the vibrations, and conducted a dynamic structural analysis to test that theory. We used the results to (1) demonstrate that the vibrations were not caused by activities linked to specific days of the week or external loading conditions, and (2) help Falkirk Mining evaluate several hypotheses about the circumstances causing the vibration.
Our analysis of the vibrations and their inferred stresses indicated that the vibrations were likely the result of non-uniform vertical flow patterns in the coal mass inside the silo, and did not threaten the structure’s stability.