Abstract
Rock bolts ensure structural stability for tunnels and many other underground structures. The pre-load on a rock bolt plays an important role in the structural reinforcement and it is vital to monitor the pre-load status of rock bolts. In this paper, a rock bolt pre-load monitoring method based on the piezoceramic enabled time reversal method is proposed. A lead zirconate titanate (PZT) patch transducer, which works as an actuator to generate stress waves, is bonded onto the anchor plate of the rock bolt. A smart washer, which is fabricated by sandwiching a PZT patch between two metal rings, is installed between the hex nut and the anchor plate along the rock bolt. The smart washer functions as a sensor to detect the stress wave. With the increase of the pre-load values on the rock bolt, the effective contact surface area between the smart washer and the anchor plate, benefiting the stress wave propagation crossing the contact surface. With the help of time reversal technique, experimental results reveal that the magnitude of focused signal clearly increases with the increase of the pre-load on a rock bolt before the saturation which happens beyond a relatively high value of the pre-load. The proposed method provides an innovative and real time means to monitor the pre-load level of a rock bolt. By employing this method, the pre-load degradation process on a rock bolt can be clearly monitored. Please note that, currently, the proposed method applies to only new rock bolts, on which it is possible to install the PZT smart washer.
Highlights
Rock bolts are widely used to stabilize rock masses in tunneling and underground construction [1,2]
Please note that the proposed method applies to only new rock bolts, where it is possible the smart washer
Please note that the proposed method applies to only new rock bolts, where it to is install thetoPZT
Summary
Rock bolts are widely used to stabilize rock masses in tunneling and underground construction [1,2]. Rock bolt related accidents still happen [3,4] and people’s lives were taken because of the rock bolt failure caused tunnel collapse [5]. Many factors, such as insufficient length, improper grouting, corrosion, and insufficient pre-load, contribute to rock bolt failures [6,7,8,9]. The pre-load on a rock bolt plays an important role in stabilizing rock masses. The reduction or loss of the pre-load of a rock bolt significantly reduces its capacity to stabilize the rock masses. The rock bolt monitoring in general and the pre-load monitoring in particular are of great importance [10,11]
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