Study On Non-destructive Testing Of GFRP Anchorage System In Earthen Sites For Whole Life Cycle

Glass-fiber Reinforced Plastic anchor bolt is widely used in the anchorage enginerring of earthen sites,the quality of anchoring will affect the safety of earth site.Quality evalution of anchoring of earthen sites is a problem which now we urgently awaits to be solved,since that traditional destructive detection methods are no longer suitable based on the principle of “minimum intervention” in the protection of cultural relics.Audio frequency stress wave method is applicable in assessing the anchoring quality of earthen sites,nevertheless,the nondestructive testing（NDT）method used in the field of earth site glass fiber anchorage system is still in its infancy stage.The research on evaluation of the safety of GFRP anchoring system during the curing and service period is inadequate,the application of sonic frequency stress wave method is restricted due to that many problems are have remained unclear.In this paper,based on the construction situations of GFRP anchoring system used in earthen sites,the entire lifetime of the anchoring system of earthen sites from construction period to service period is studied.The variation of testing indexes of anchor system with different anchoring mediums and length during the curing period and the influence of load action by using nondestructive testing method and traditional pull-out test during the service period are explored as well.The following conclusions can be drawn:（1）The relationship between the curing age and the nondestructive testing signal curve was established through the nondestructive testing in the curing stage.Under the condition of continuous monitoring,the time domain image of the detection signal can be used as the basis for judging the curing quality.（2）Through the research on nondestructive testing of the anchoring model,the law of the consolidating wave and the curing time of the anchorage system was established.It is clearly related to the physical and mechanical properties of the anchoring medium during the curing period.The consolidating wave can reflect the anchoring medium and the bolt.In addition,the well-cured anchorage is affected by the type of anchoring medium,which provides a basis for the quality control of the anchorage construction and curing stage.（3）Based on the study of the stress wave response of the anchoring model under different loads,the law of the external load on the response curve in the time domain and time spectrum was obtained,and the deformation and damage caused by the load will be reflected in the time domain image;The time spectrum of the anchor system was obtained by transformation,and the existence of small cracks was identified according to the difference in sensitivity of low-frequency and high-frequency signals to defects of different sizes.Affected by signal analysis methods,it is difficult to accurately locate the damage location,and the time domain and time spectrum analysis conclusions can only be used as a reference for service status monitoring and early warning.（4）In order to figure out the relationship between loads and fundamental frequency,the detected signal was analysed using the fast Fourier transform algorithm.Through the frequency domain analysis of the detection signal,record the fundamental frequency of the anchor system response under different loads,establish the relationship between the response curve and the load,and obtain a quadratic power relationship between the fundamental frequency and the load.The change of the fundamental frequency value is related to the damage of the first interface of the anchoring model,and the bonding of the interface affects the propagation of the stress wave,thus changing the fundamental frequency of the vibration of the system.The fundamental frequency value of the anchorage system can be used as a reliable parameter to measure the safety performance of the anchorage system in service state.