Experimental and Numerical Studies on Bond Quality of Fully Grouted Rockbolt under Confining Pressure and Pull-Out Load

Abstract

In mining engineering, the in situ stress changes with the stress induced by the surrounding mining activities. It positively or negatively affects the propagation of ultrasonic guided waves in rockbolts. Therefore, the effect of in situ stress in rockbolt support was determined by applying confining pressure and pull-out load in a laboratory test and using ultrasonic guided waves to test the rockbolt. Furthermore, the propagation law of ultrasonic guided waves and bond quality of the rockbolt under the interaction of the pull-out load and confining pressure were studied. Numerical simulations were performed to deduce the guided wave propagation process in grouted systems, and the influencing mechanism of the pull-out load and confining pressure on the guided wave propagation was discussed. The laboratory test and numerical simulation results show that the confining pressure weakens the guided wave propagation without pull-out load. Under the same pull-out load, the guided wave propagation gradually strengthens with increasing confining pressure. A larger confining pressure weakens the weakening effect of the pull-out load and suppresses the discreteness of the guided wave propagation. Under the same confining pressure, the guided waves did not diffract well into the cement mortar and concrete with increasing pull-out load, the confining pressure restricted the radial vibration of the guided waves, and the guided wave propagation law weakened. Thus, the pull-out load plays a weakening role in the propagation law of ultrasonic guided waves.

Propagation Characteristics of Ultrasonic Guided Waves in Grouted Rockbolt Systems with Bond Defects under Different Confining Conditions

“…Figure 5 displays the propagation of ultrasonic guided waves in grouted rockbolt systems with bond defects in the absence of a pull-out load. The law of guided wave propagation gradually deteriorates with increasing confining pressure, and this phenomenon is the same as the propagation law of guided waves in grouted rockbolt systems without bond defects [18], while the echo wave packet at the bond defects fluctuates with increasing confining pressure, and the presence of bond defects cannot change the weakening effect of the confining pressure on the propagation law of guided waves. The variation of frequency in the guided wave with the confining pressure in absence of pull-out load is shown in Figure 6.…”

“…Yu et al [17] used ultrasonic guided waves to detect bond defects under different pull-out loads to determine bond quality but did not consider confining pressure. Yu et al [18] used ultrasonic guided waves to detect rockbolts under different pull-out loads and confining pressures and studied the bond quality of rockbolts but did not consider the influence of bond defects.…”

Axial Load Transfer Mechanism in Fully Grouted Rock Bolting System: A Systematic Review

“…However, the model's validity was limited to scenarios with constant confining pressure, typically applied in Hoek cells or biaxial cells. Yu, Zhu [77] found that increasing the confining pressure resulted in decreasing rock mass quality (Q) values, and the bond quality of rock bolts decreased, under the same pull-out loads. However, the Q values were increased by increasing the confining pressure if there were no pull-out loads (Figure 12).…”