Full-process deformation monitoring and failure characteristics analysis of damaged coal under 3D laser scanning technology

During underground coal mining, coal bodies are highly susceptible to deformation and damage under repeated excavation-induced disturbances, which significantly increases the risk of dynamic coal-rock disasters. To investigate the deformation and failure characteristics of coal under repeated excavation-induced disturbances and to improve disaster prevention and control capabilities, quasi-static uniaxial cyclic loading-unloading (L-U) tests, as well as dynamic axial compression tests under impact loading, were conducted on large-scale coal-like specimens. During the tests, three-dimensional (3D) laser scanning technology and high-precision total station measurements were employed to accurately capture the deformation data of the specimens at each testing stage. This enabled a systematic analysis of the deformation and failure evolution. Results indicate that: (1) During the quasi-static uniaxial cyclic L-U process, the maximum loading stress is the most critical factor affecting the deformation. With increasing cycle numbers, the specimens loaded to the yield stage exhibit progressively increasing deformation; those specimens loaded to the elastic stage show a trend of initial decrease followed by an increase; while specimens loaded to the compaction stage demonstrate a continuous decrease in deformation. (2) Acoustic emission (AE) monitoring results revealed a damage evolution mechanism characterized by the alternating dominance of crack compaction and propagation during cyclic loading. The damage contribution rate rose with both loading intensity and cycle number, showing that early-stage damage accumulation provided the basis for later dynamic failure. (3) After the application of dynamic impact loading, all specimens failed mainly by splitting failure. Specimens with lower levels of pre-existing damage experienced more severe failure, indicating that greater energy was accumulated during the preceding cyclic L-U process. (4) The deformation evolution patterns obtained by the 3D laser scanning technique were highly consistent with the axial displacement curves measured by the total station, with the maximum deviation less than 2.5%, which meets the permissible error requirements of laboratory testing. This direct comparison confirms the accuracy and reliability of the scanning data. Furthermore, the 3D laser scanning method demonstrates higher operational efficiency in field applications, highlighting its strong engineering applicability and potential for broader adoption.