SOIL NAIL MONITORING USING FIBER BRAGG GRATING SENSORS DURING PULLOUT TESTS

The authors have developed a Fiber Bragg grating (FBG) based monitoring system. FBG sensors were used to form quasi-distributed and automatic sensing array and special packaging methods were adopted. Calibration tests were conducted on bare, surface mounted and aluminum tube packaged FBG in laboratory. The sensors can measure average strain of host material as well as localized strain and show excellent linearity. Recently, FBG sensors have been successfully applied to monitor strain distributions along soil nails in Hong Kong, together with electrical strain gauges. During two pullout tests, the strain measured by FBG sensors and strain gauges are found to be in good agreement. This demonstrates the feasibility and reliability of FBG sensors in field soil nail monitoring. RESUME Les auteurs ont developpe un systeme de surveillance base du râpage de Bragg de fibre (FBG). Des sondes de FBG ont ete utilisees a la forme quasi-distribuee et la rangee de sensation automatique et les methodes de empaquetage speciales ont ete adoptees. Des essais d'etalonnage ont ete effectues sur et exterieur FBG emballe par tube monte et en aluminium nu dans le laboratoire. Les sondes peuvent mesurer la contrainte moyenne du materiel de centre serveur aussi bien que la contrainte localisee et montrer d'excellentes linearites. Recemment, des sondes de FBG ont ete avec succes utilisees pour surveiller la distribution de contrainte le long des ongles de sol sur un emplacement a Hong Kong, ainsi que les jauges de contrainte electriques. Pendant deux essais de degagement, la contrainte a mesure par des sondes de FBG et des jauges de contrainte s'averent en bon accord. Ceci demontre la praticabilite et la fiabilite des sondes de FBG dans la surveillance d'ongle de sol de champ.