Analysis of excavation induced stress distributions of GFRP anchors in a soil slope using distributed fiber optic sensors

Abstract

In this work, a slope reinforcement system using glass fiber reinforced polymer (GFRP) anchors with pressure grouting was adopted in a field project in Hong Kong. The performance of the GFRP anchor during slope excavation was measured using a novel distributed strain sensing technology, known as Brillouin Optic Time Domain Analysis (BOTDA). The full strain profiles along the GFRP anchor under different excavation stages were obtained using specially protected fiber optic sensors. In addition to fiber optic sensors, traditional strain gauges were installed in the same GFRP anchor. Comparisons show that the BOTDA sensors have good accuracy. In addition, the measured results indicate that the maximum tensile strains and forces occurred at one-third of the GFRP anchor length from the slope surface. The tensile force distribution within the active zone is curvilinear which is confirmed by elastic theory analysis. Shear stress distributions along the GFRP anchors were obtained by differentiating the strain data numerically. The theoretical analysis results were consistent with the measured data at the initial excavation stage. However, the theoretical analysis underestimated the shear stress at the final excavation stage where the slope undergoes plastic deformation. Based on the field measurement results and theory analysis, we conclude that the BOTDA sensing technology provides an alternative and effective approach to identifying distributed strains along anchors and shear zones in reinforced slopes.