Experimental Study of Strain Rockburst considering Temperature Effect: Status-of-the-Art and Prospect

In deep mining and excavation of tunnels with high geothermal, the surrounding rock is not only subjected to high ground stress but also subjected to high temperature. Temperature will change mechanical characteristics and energy storage capacity of rocks, as well as increase the destructiveness and randomness of rockburst. To reveal the mechanism of high-temperature strain burst in deep rock, the rockburst tests from uniaxial compression to three-dimensional compression were reviewed, and the research results of the minimum principal stress rapid unloading, true-triaxial loading with one free face, and dynamic disturbance triggered pre-heated granite rockburst simulation tests were focused on. According to the occurrence state of country rock for deep high-temperature and stress state in the whole process during excavation, six development directions for high-temperature strain rockburst simulation tests were proposed: (1) constructing the damage constitutive models of high-temperature rocks according to linear energy dissipation law; (2) developing the true triaxial rockburst simulation testing system accomplishing the function of “real-time high temperature + unloading + dynamic disturbance”; (3) considering the true triaxial rockburst simulation test after microwave irradiation; (4) developing the real-time high-temperature rockburst simulation testing device for large-size specimens and internal unloading; (5) focusing on the energy actuating mechanism for deep high-temperature rock failure via rockburst simulation tests; and (6) implementing the three-dimensional rockburst simulation test on the basis of deep in situ coring.

Research on Deformation and Failure Evolution of Deep Rock Burst Drivage Roadway Surrounding Rock under Dynamic Disturbance

In order to explore the deformation and failure evolution characteristics of the surrounding rock during the connection process of the deep rock burst drivage roadway under the dynamic load disturbance, and based on this, the catastrophe mechanism of the roadway is analyzed, taking the rock burst accident of Longyun Coal Industry in Shandong Province on October 20, 2018, as the engineering background. FLAC3D was used to study the distribution evolution law of displacement, plastic zone, and stress field in the whole process of “Roadway Drivage-Deformation and Failure-Instability and Disaster” in the surrounding rock of deep roadway. The research results show that under the conditions of high stress and dynamic load disturbance, the surrounding rock deformation and failure are significant during the connection of the thick-top-coal roadway in deep, the roof is the most, the two ribs are the second, and the roadway top-coal is in an “inverted trapezoid” sag pattern. When the length of the bolts is limited or the anchoring force of the cables is not enough to effectively restrain the roof, the impact of dynamic disturbance on the plastic damage of the roof is greater than that of the two ribs and the floor, and the plastic damage of the coal seam roof affecting the surrounding rock deformation of the roadway drivage played a leading role.

Effects of External Dynamic Disturbances And Structural Plane On Rock Fracturing Around Deep Underground Cavern

The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities. Thus, a combined finite-element approach was employed to simulate the failure process of an underground cavern, which provided insights into the failure mechanism of deep hard rock affected by factors such as the dynamic stress-wave amplitudes, disturbance direction, and dip angles of the structural plane. The crack-propagation process, stress-field distribution, displacement, velocity of failed rock, and failure zone around the circular cavern were analyzed to identify the dynamic response and failure properties of the underground structures. The simulation results indicated that the dynamic disturbance direction had less influence on the dynamic response for the constant in situ stress state, while the failure intensity and damage range around the cavern always exhibited a monotonically increasing trend with an increase in the dynamic load (stress-wave amplitudes). The crack distribution around the circular cavern exhibited an asymmetric pattern, possibly owing to the stress-wave reflection behavior and attenuation effect along the propagation route. Geological discontinuities significantly affected the stability of nearby caverns subjected to dynamic disturbances, during which the failure intensity exhibited the pattern of an initial increase followed by a decrease with an increase in the dip angle of the structural plane. Additionally, the dynamic disturbance direction led to variations in the crack distribution for specific structural planes and stress states. These results indicate that the failure behavior should be the integrated response of the excavation unloading effect, geological conditions, and external dynamic disturbances.

Acceleration-based disturbance compensation for elastic rack-and-pinion drives

Rack-and-pinion drives are mainly used for large machine tools and are often operated with indirect position control. Due to the lack of state information on the output side, this results in reduced accuracy regarding the table position. In addition, the system can only react inadequately to disturbances outside the control loop, meaning that often insufficient results can be achieved in typical application scenarios such as milling. To meet the increasing dynamic and accuracy requirements of the modern manufacturing industry, this paper presents a highly dynamic acceleration-based disturbance compensation method. For this purpose, the table acceleration is estimated using a dynamical model of the drive train and compared to the signal from an additional acceleration sensor attached to the machine table. Based on the resulting difference, an additional compensation torque is provided, which suppresses the disturbance in counterphase. The approach is tested experimentally on an open control platform with industrial drive components and the behavior is investigated based on compliance frequency responses and externally applied milling forces. At the same time, a standardized parametrization methodology is developed and the robustness is evaluated by varying table masses. In summary, a considerable improvement of the dynamic disturbance behavior can be achieved compared to the conventional system without compensator.