Abstract
Pre-stress degradation or looseness of rock bolts in mining or tunnel engineering threatens the stability and reliability of the structures. In this paper, an innovative piezoelectric device named a “smart washer” with the impedance method is proposed with the aim of developing a real-time device to monitor the pre-stress level of rock bolts. The proposed method was verified through tests on a rock bolt specimen. By applying high-frequency sweep excitations (typically >30 kHz) to the smart washer that was installed on the rock bolt specimen, we observed that the variation in impedance signatures indicated the rock bolt pre-stress status. With the degradation of rock bolt pre-stress, the frequency in the dominating peak of the real part of the electrical impedance signature increased. To quantify the effectiveness of the proposed technique, a normalized root mean square deviation (RMSD) index was developed to evaluate the degradation level of the rock bolt pre-stress. The experimental results demonstrated that the normalized RMSD-based looseness index, which was computed from the impedance value detected by the “smart washer”, increased with loss of the pre-stress of the rock bolt. Therefore, the proposed method can effectively detect the degradation of rock bolt pre-stress, as demonstrated by experiments.
Highlights
Thanks to their low cost, simplicity, and ease of installation, rock bolts, as a major measure to enhance the bearing capacity of surrounding rock and foundations, have been widely used in mining, tunnel, and geotechnical engineering [1]
An electro-mechanical impedance (EMI)-based damage detection technique using lead–zirconate–titanate (PZT) patches is becoming a promising tool for detecting local damage in a wide variety of structures [17,18,19]
Smart washer-based bolt pre-tension monitoring using piezoelectric measurement measurement consists of three parts: hydraulic jack, frame, and animpedance electrical impedance measurement consists of rock three parts: aahydraulic jack,aaloading loading frame, and an electrical impedance measuring system
Summary
Thanks to their low cost, simplicity, and ease of installation, rock bolts, as a major measure to enhance the bearing capacity of surrounding rock and foundations, have been widely used in mining, tunnel, and geotechnical engineering [1]. A test method based on the frequency response of rock bolts was developed to determine encapsulation conditions [5]. An electro-mechanical impedance (EMI)-based damage detection technique using lead–zirconate–titanate (PZT) patches is becoming a promising tool for detecting local damage in a wide variety of structures [17,18,19]. By integrating the piezoelectric impedance method with the smart washer, the pre-tension looseness of a rock bolt was monitored. Based on this formula, the change of electrical impedance of host structure can be detected through the bonded PZT. With a high frequency excitation, very small damage can be detected
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