Recent examples of applied fibre optic sensors in geotechnical areas to evaluate and monitor structural integrity

摘要

Different types of fibre optic sensors are used in civil and geotechnical engineering to monitor the stability of load-bearing structure components such as anchors, dams, ropes. Mostly, mechanical quantities such as deformation, strain or vibration are requested. However, measurement of chemical quantities in materials and structure components such as pH value in steel reinforced concrete members also provides information about the integrity of concrete structures. Different measurement tasks as well as the use of different sensor technologies require special application techniques. The paper presents the use of different fibre optic sensor types in geo-engineering. One example concerns the assessment of ultimate bearing capacity and the bearing behaviour of large concrete piles in existing foundations, or during and after installation. Highly resolving fibre Fabry-Perot sensors were used to design concrete-embeddable AE sensors for analysis of concrete pile integrity as well as bearing capacity. They were installed over the pile length and deliver more precise pile response when established testing methods are applied. This sensing method allows with only one measuring device the monitoring of pile deformations during dynamic low-strain, high-strain and static load testing. FBG sensors were attached to anchor steels (micro piles) to measure the strain distribution during pull-out tests. On the basis of measurement results, load distribution and load transfer to the soil was evaluated. Geotextiles are increasingly used to stabilize dams, dykes, slopes, railway embankments against damage and failure.Several Kilometres long sensor fibres integrated into textiles allow early detection of beginning damage during flooding or in sliding areas. If strain above 1% until about 40 % has to be detected, polymer optical fibre sensors provide outstanding characteristics. Investigations with sensor-equipped geotextiles will be presented; experiences from field tests are described. Steel reinforcement in concrete structures is susceptible to corrosion if the pH value approaches 9.5 and less.Therefore pH monitoring in chemically highly loaded areas is needed. Fibre optic pH sensors have been developed and installed in the fixing area of anchors. Long-term measurements over 2 year reveal amazingly well function. This pH sensor is being prepared for commercial applications.