Non-Contact Ultrasonic Assessment of Rock Bolt Damage

Abstract

Rock bolts are an essential component of ground support in tunnels and underground mines. These bolts are subject to corrosion due to the presence of water, which affects their load-bearing capacity, leading to possible structural failure. Therefore, it is important to develop a method to assess the condition of rock bolts quickly and non-destructively.This thesis provides a detailed review of non-destructive methods such as ultrasonic, fiber optic, piezoelectric, electromagnetic, impact-echo, acoustic emission, and numerical algorithms to assess the condition of rock bolts and proposes a non-contact and non-destructive method for investigating damage in a rock bolt. Five types of rock bolts were tested: brand new rock bolts, slightly damaged rock bolts, severely damaged rock bolts, bent rock bolts, and corroded rock bolts. A laser vibrometer was used to record stress waves input into the rock bolts. The collected data are highly sensitive to the properties of the material, the presence of defects and the condition of the rock bolt. An in-depth study of stress wave properties revealed that rock bolts with large defects have significant differences in energy loss rate and total reflected signal amplitude. Small changes in stress wave velocity were also observed. Bent rock bolts also had a unique signature compared to brand new and damaged rock bolts. A third experiment involving induced corrosion in rock bolts also revealed significant changes in signal energy. These results show that the proposed non-destructive technique can assess the condition of rock bolts due to physical and chemical damage.