Experimental Study On Nondestructive Testing And Optical Fiber Monitoring Of GFRP Anchorage System For Earthen Sites

In the anchoring technology of earthen archaeological sites,GFRP(Glass Fiber Reinforced Polymer)anchor rods,with their excellent durability,outstanding weather resistance,and significant tensile strength,have demonstrated extensive application value and practical significance in the protection and reinforcement projects of important cultural sites such as Jiaohe Ancient City,Western Xia Imperial Tombs,and Qiaowan City.However,quality issues of the anchoring system caused by anchor rod defects,construction environment,and construction techniques have led to occasional uncontrolled conditions of the earthen site.At present,short-term destructive anchoring pull-out tests are mainly employed as the primary means to evaluate anchoring effects.This method is simple to operate and provides reliable data but cannot be used for universal testing and is destructive to cultural relics.In addition,non-destructive testing technology based on acoustic stress wave methods is gradually being applied to anchoring system detection.By collecting time-domain signals of complete anchoring system models and grout void defect models during the curing and service stages,characteristics such as consolidation wave velocity and natural frequency can be obtained.Then,through signal processing methods such as Fast Fourier Transform,the bottom of the rod and the void reflection signals can be effectively identified,thus achieving the inversion of anchoring length,void location,and void unit length.However,there are drawbacks,such as stringent requirements for anchor rod end conditions and excitation,severe stress wave attenuation,and the inability to automatically collect data for real-time health monitoring.Based on a comprehensive analysis of the current research status of anchoring technology in earthen archaeological sites,this paper addresses the structural problems commonly found in such sites by focusing on the embedded fiber optic sensor glass fiber anchor rod anchoring system.Through the establishment of complete anchoring models and grout void defect anchoring models simulating real-world site conditions,non-destructive testing and fiber optic monitoring techniques are used to study the characteristic patterns of the anchoring system during the curing period and under pullout service conditions.The main contents are as follows:(1)Based on the principle of fiber Bragg grating(FBG)sensing,a highly sensitive and stable FBG temperature and strain monitoring system has been developed using the glass fiber anchor rod groove as the substrate.The sensing performance of the FBG sensor,such as linearity,sensitivity,hysteresis error,repeatability error,and crosssensitivity,was analyzed,providing important data support for the continuous real-time monitoring of temperature and strain at the interface of the glass fiber anchoring system in earthen archaeological sites.(2)The aging rules of the anchoring system during the curing stage were investigated.Complete anchoring models and anchoring models with grout void defects at different locations were used to conduct an in-depth study of the changes in timedomain,frequency-domain,time-frequency domain,and consolidation wave velocity of non-destructive testing signals during the curing period.In addition,the temperature change patterns during the grout solidification process along the anchor rod optical cable in each anchoring system were explored,forming a distributed temperature monitoring network.The effects of room temperature and curing time on the fiber optic sensor temperature were studied,providing experience references for the promotion and application of distributed fiber optic sensing technology in earthen archaeological site anchoring projects.(3)Pull-out tests were conducted to study the stress characteristics of the interface of homogeneous and locally debonded intelligent anchor rods,obtaining loaddisplacement curves,axial strain distribution,and interface damage patterns for complete anchoring systems and anchoring systems with void defects at different locations.The effects of pull-out load size and grout void defect anchoring models on the acoustic stress wave method’s non-destructive testing signals were analyzed,providing valuable practical implications and theoretical references for the design,optimization,and safety evaluation of actual earthen archaeological site anchoring projects.