Mechanical behaviors and failure characteristics of coal-rock combination under quasi-static and dynamic disturbance loading: a case based on a new equipment

The dynamic disasters of deep mining coal and rock mass are frequent and easy to be instable. Aiming at the deformation of coal-rock roadway under the coupled static and dynamic load, a new equipment which can simulate the actual situation dynamic environment is used to carry out the coupled static-dynamic loading test of coal-rock combination. The failure law and mechanical behavior of combination are studied. Test results show that weak structure significantly affects mechanical response of coal-rock combination. The coal part with lower strength firstly reaches the crack initiation stress. The strength of the combination is dominated by the coal part. The post-peak stage of the stress-strain curve under the coupled static and dynamic load presents a stepped reduction, which shows yield process. The dynamic load level has a significant effect on the mechanical behaviors of the combination. The elastic modulus decreases under dynamic loading. The peak stress of the combination is positively correlated with the dynamic load level in a certain range, and the peak strain was negatively correlated. The energy accumulation and dissipation are closely related to the failure of the samples. The strain energy is more concentrated in the area where the failure occurs first. The AE energy under dynamic load is developed from the traditional "four-stages" characteristic under static load to three stages. The interval release stage appears because of the appearance of intermittent disturbance load makes the AE energy of the sample change intermittently. The dynamic instability of samples accompanies a sudden increase in AE energy rate, hysteresis loop area and strain. Compared with the shear failure of single lithology sample, the failure mode of the combinations is mainly tensile, and it turns into tensile-shear failure under dynamic load. The fragmentation of samples is different under different failure modes. The fragmentation index can characterize the failure mode and crack propagation characteristics of coal-rock combination. The research provides reference for large deformation dynamic disasters of surrounding rock. The coupled static and dynamic load test is carried out used the self-developed creep and dynamic disturbance impact loading test system.The stepped stress reduction of the stress-strain curve of coal-rock combination, the precursor information of the failure and the characterization of the failure mode are obtained.Mechanical response and failure analysis of deep coal-rock combination are studied by acoustic emission and DIC technology.