Slope Stabilization with Multiple Anchors Monitored by Glass Fibre Technique-Paper

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The study investigates the use of distributed glass-fibre sensors to monitor load transfer and deformation in multiple-strand ground anchors used to stabilize slopes at a refinery construction site. The site’s proximity to a tectonic fault and volcanoes created highly variable ground conditions and pressurized groundwater, making anchor design and installation challenging.<br /><br />Two 25 m single-bore multiple anchors were instrumented and pull-out tested. Each contained three individual anchors with separate bond lengths. Sensors were installed directly on selected steel strands to measure their elongation and along the anchor grout to monitor deformation at the grout–ground interface. The cables were installed redundantly to reduce the risk of sensor failure. Measurements were recorded continuously during staged loading, with a resolution of approximately 1.0 µm/m.<br /><br />The strand measurements showed relatively uniform strain along the free length and decreasing strain through the bond length, consistent with expected load transfer. Measurements from independent sensors on the strands closely agreed, demonstrating the system’s reliability. Interface measurements revealed progressive cracking in the grout–ground bond as loads increased. These cracks shortened the effective bond length and, in turn, increased the anchors’ effective free length. Reloading also produced localized strain changes, indicating that unloading could contribute to further cracking.<br /><br />The trials demonstrate that fibre-optic monitoring can provide detailed, real-time insight into anchor behaviour that conventional measurements at the anchor head cannot capture. The authors conclude that the technique can help assess bond performance and improve future decisions about anchor bond lengths and spacing. Further testing in different soil types is recommended to better understand interactions among the sensors, strands, grout, and ground.

Keywords

distributed glass-fibre sensors

ground anchors

load transfer

slope stabilization

pull-out tests

grout-ground interface

strand strain measurement

bond length

fibre-optic monitoring

anchor deformation