Failure Properties and Stability Monitoring of Strip and Column Cemented Gangue Backfill Bodies Under Uniaxial Compression In Constructional Backfill Mining

The strip and column cemented gangue backfill bodies (CGBBs) are the main supporting components in the design of constructional backfill mining for coal mining, which determines the stability of goaf. Previous researches have mostly focused on the mechanical properties of column CGBB, but the mechanical properties of strip CGBB are still unclear. Herein, the uniaxial compression experiments for strip and column CGBBs were conducted to compare the failure properties. The acoustic emission (AE) and two types of resistivity monitoring were used to monitor the damage evolution. The effect of the length-height ratio on the mechanical characteristic of strip CGBB was analyzed by discrete element simulation. The results show that: the strength and peak strain of strip CGBB under uniaxial compression is higher than those of column CGBB, and the strip CGBB shows better ductility. The stress of column CGBB decreases significantly faster than that of strip CGBB at the post-peak stage. The strength and ductility of strip CGBB increase with the increase of length-height ratio. The strip CGBB is destroyed from both ends to the middle under uniaxial compression, and the core bearing area is reduced correspondingly. The AE signal evolution of CGBBs under uniaxial compression before the peak stress contains three stages, and the AE signals of strip CGBB at the peak stress will not rise sharply compared with column CGBB. The resistivity monitoring effect of the horizontally symmetrical conductive mesh is better than that of the axial. The horizontal resistivity increases gradually with the increase of stress under uniaxial compression, and increases sharply at the peak stress, and then drops after the peak stress. The damage constitutive models and the stability monitoring models of the CGBBs are established based on the experimental results. This work would be instructive for the design and stability monitoring of CGBB.

DEVELOPMENT OF A METHODOLOGY FOR STABILITY MONITORING OF A DEFENSE EMBANKMENT LOADED WITH FREQUENT TRAFFIC: THE EXAMPLE OF THE KOVIN MINE

In the present paper, the authors develop a methodology for stability monitoring of the hydrotechnicaldefensive embankment that is exposed to heavy frequent traffic. The proposed methodology envisages several phases of observation, work and monitoring: (1) macroscopic observations, (2) geophysicalgeoelectric tests, (3) group of exploration works, (4) model formation, (5) establishment of a monitoring system, (6) acquisition data processing and modeling. Four of the six proposed phases are illustrated by the example of the left-bank Danube embankment used by the Kovin coal mine for the needs of coal truck haulage. The results of the performed research indicate that there are no deformations that endanger the defensive function of the embankment. In order to ensure safe coal truck haulage and preserve the function of the embankment, it is proposed to establish a system for geophysical, hydrogeological and geotechnical monitoring, to form a model for simulating the behavior of the embankment for different hydrometeorological conditions (consequently, for different consistency states and material compaction), and for different load conditions.

Classification and Evaluation of Extended PICS (EPICS) on a Global Scale for Calibration and Stability Monitoring of Optical Satellite Sensors

Historically stable areas across North Africa, known as pseudo invariant calibration sites (PICS), have been used as targets for the calibration and monitoring of optical satellite sensors. However, two major drawbacks exist for these sites: first is the dependency on a single location to be always invariant, and second is the limited amount of observation achieved using these sites. As a result, longer time periods are necessary to construct a dense dataset to assess the radiometric performance of on-orbit optical sensors and confirm that the change detected is sensor-specific rather than site-specific. This work presents a global land cover classification to obtain an extended pseudo invariant calibration site (EPICS) on a global scale using Landsat-8 Operational Land Imager (OLI) data. This technique provides multiple calibration sites across the globe, allowing for the building of richer datasets in a shorter time frame compared to the traditional approach (PICS), with the advantage of assessing the calibration and stability of the sensors faster, detecting possible changes sooner and correcting them accordingly. This work identified 23 World Reference System two (WRS-2) path/row locations around the globe as part of the global EPICSs. These EPICSs have the advantage of achieving multiple observations per day, with similar spectral characteristics compared to traditional PICS, while still producing a temporal coefficient of variation (ratio of temporal standard deviation and temporal mean) less than 4% for all bands, with some as low as 2.7%.