A characteristic study on the attenuation and velocity of ultrasonic waves propagating via grouted rock bolts.

摘要

Since rock bolts are widely used in mining and civil engineering as a ground anchorage, it is crucial to determine their quality after installation. To avoid destruction of rock bolts caused by destructive test methods such as Pull-out and Over-coring tests, non-destructive test methods are sought using techniques such as ultrasonic waves. This thesis investigates the characteristics of ultrasonic waves and its application to test the grouted rock bolts. Experiments were conducted to study the traits of ultrasonic waves propagating via grouted rock bolts. To simulate in-situ grouted rock bolts, specimens are comprised of rebar and grouted mortar with different compressive strengths with a diameter of 20 cm around the rebar. Using a variety of ultrasonic frequencies, a number of tests were conducted on five specimens in a month period after they were made. The effects of grouted mortar length, mortar air content and the mortar compressive strength on the attenuation and velocity of ultrasonic waves propagating through grouted rock bolts were also studied. The grouted mortar was then cut away in 10 cm increments reducing the mortar length from 70 to 30 cm, and the attenuations and velocities of ultrasonic waves were correspondingly measured at each length of grouted mortar. The results demonstrate that there is significant effect of grout mortar compressive strength, grout mortar length, grout mortar air content, and ultrasonic wave frequencies on velocities and attenuations. The research makes a contribution to the understanding of ultrasonic wave propagation in grouted rock bolts.