Performance Monitoring of a Glass Fiber-Reinforced Polymer Bar Soil Nail during Laboratory Pullout Test Using FBG Sensing Technology

Abstract

In this paper, the stress–strain state and the effectiveness of shear resistance of a glass fiber-reinforced polymer (GFRP) bar soil nail in a pullout test was studied in laboratory using fiber Bragg grating (FBG) sensing measurement. Both experimental study and numerical simulation were carried out and results are compared in this paper. In the pullout test, cement slurry was grouted into one predrilled borehole with a GFRP bar in a completely decomposed granite (CDG) soil mass, forming a cement-grouted GFRP bar soil nail. This GFRP bar soil nail was pulled out from the CDG soil mass in laboratory to investigate the performance of the GFRP bar soil nail during the pullout test process. Three loading cycles were applied to pull the GFRP bar soil nail out. Compared with traditional electricity-based strain gauges, FBG sensing technique is a relative novel technology to geotechnical structures health monitoring and has a number of advantages including high accuracy, multiplexing, electromagnetic interference resistance, and good repeatability. In the current study, one fiber line had a series of FBG strain sensors with a sequence of initial wavelengths. This fiber line with five FBG strain sensors was adhered on the pregrooved GFRP bar before grouting and was used to measure the strain distribution along this GFRP bar with cement grout during a pullout test. The mechanical behavior of the GFRP bar soil nail is evaluated by using the measured strain results in the paper. It is found that the pullout results of the GFRP bar soil nail are in good agreement with numerical calculation results. Test results also show that the FBG sensors are reliable for measuring the strain variation at all measured points under different loading stages. Furthermore, a simplified pullout resistance model originally proposed for GFRP pipe soil nails was employed to examine the laboratory pullout results of a GFRP bar soil nail. It is found that the simplified pullout resistance model is also applicable for the GFRP bar soil nail.