Study on deformation monitoring and pre-failure information identification of coal samples based on OFDR-AE

Abstract

In order to obtain internal strain evolution during crack propagation and damage in coal samples, this paper proposes a combined monitoring approach using Optical Frequency Domain Reflectometry (OFDR) and Acoustic Emission (AE) technologies. Five optical fiber sensors and AE probes were installed on a cubic coal sample (100 * 100 * 100 mm), and uniaxial compression tests were conducted to examine the strain evolution under both uniaxially and the staged loading paths. The results indicate that OFDR accurately measures internal strain and captures strain evolution across various loading stages, including compaction, elastic, yield, and post-peak failure. A sharp increase in the non-uniform deformation index (Sw) during the yield stage and a “fluctuation-stabilization-decline” trend in the AE b-value serve as precursors to coal body failure. This research further introduces the Sw/b failure criterion, providing an effective basis for predicting the failure mode of coal bodies. By combining OFDR and AE techniques, this research addresses the spatial and temporal resolution limitations of traditional monitoring methods. The proposed Sw/b failure criterion offers valuable insights for monitoring coal body deformation and damage.