'Optical-acoustic-stress' responses in failure progress of cemented gangue-fly ash backfill material under uniaxial compression

Cemented gangue-fly ash backfill material (CGFBM) is made of coal gangue, fly ash, cementation materials and additives. It has been widely used in the field of backfill mining to control surface subsidence and to protect the environment. Partial backfill mining technology attracts much attention for its lower cost, and a large number of unconfined backfill structures (UBS) are formed based on it. Aimed at the stability monitoring of UBS in partial backfill, the failure progress of the CGFBM were obtained by uniaxial compression tests. The 'optical-acoustic-stress' responses of the specimens were monitored by Digital Image Correlation (DIC) technique, Acoustic Emission (AE) technique, Ultrasonic Testing (UT) technique and embedded pressure sensors. The advantages of each method in the stability monitoring of UBS was discussed. It is found that different monitoring methods have different sensitivity to different failure characteristics. The AE ringing count signal response is more sensitive to the pore compression and micro-crack generation in initial compaction stage and elastic compression stage. The central stress can be used to acquire the bearing capacity of the core bearing area after the top stress. The DIC response and UT response can be used to quantitatively evaluate the damage degree of the specimen. The stability of the UBS can be monitored by the jointly methods of 'optical-acoustic-stress' in partial backfill mining.