The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass.Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt.In this study,bas...The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass.Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt.In this study,based on laboratory experiments,ultrasonic guided wave propagation in fully grouted rockbolt under different pull-out loads was investigated in order to examine the resultant debonding of rockbolt.The signals obtained from the ultrasonic monitoring during the pull-out test were processed using wavelet multi-scale analysis and frequency spectrum analysis,the signal amplitude and the amplitude ratio(Q)of low frequency to high frequency were defined to quantify the debonding of rockbolt.In addition to the laboratory test,numerical simulation on the effect of the embedment lengths on ultrasonic guided wave propagation in rockbolt was conducted by using a damage-based model,and the debonding between rockbolt and cement mortar was numerically examined.It was confirmed that the ultrasonic guided wave propagation in rockbolt was very sensitive to the debonding because of pull-out load,therefore,the critical bond length could be calculated based on the propagation of guided wave in the grouted rockbolt.In time domain,the signal amplitude in rockbolt increased with pull-out load from 0 to 100 kN until the completely debonding,thus quantifying the debonding under the different pull-out loads.In the frequency domain,as the Q value increased,the debonding length of rockbolt decreased exponentially.The numerical results confirmed that the guided wave propagation in the fully grouted rockbolt was effective in detecting and quantifying the debonding of rockbolt under pull-out load.展开更多
基金This work is funded by the National Science Foundation of China(Grant Nos.U1906208,52104157,51904056 and 51874069)and the Fundamental Research Funds for the Central Universities of China(Grant Nos.N2101028 and N2101015).
文摘The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass.Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt.In this study,based on laboratory experiments,ultrasonic guided wave propagation in fully grouted rockbolt under different pull-out loads was investigated in order to examine the resultant debonding of rockbolt.The signals obtained from the ultrasonic monitoring during the pull-out test were processed using wavelet multi-scale analysis and frequency spectrum analysis,the signal amplitude and the amplitude ratio(Q)of low frequency to high frequency were defined to quantify the debonding of rockbolt.In addition to the laboratory test,numerical simulation on the effect of the embedment lengths on ultrasonic guided wave propagation in rockbolt was conducted by using a damage-based model,and the debonding between rockbolt and cement mortar was numerically examined.It was confirmed that the ultrasonic guided wave propagation in rockbolt was very sensitive to the debonding because of pull-out load,therefore,the critical bond length could be calculated based on the propagation of guided wave in the grouted rockbolt.In time domain,the signal amplitude in rockbolt increased with pull-out load from 0 to 100 kN until the completely debonding,thus quantifying the debonding under the different pull-out loads.In the frequency domain,as the Q value increased,the debonding length of rockbolt decreased exponentially.The numerical results confirmed that the guided wave propagation in the fully grouted rockbolt was effective in detecting and quantifying the debonding of rockbolt under pull-out load.
