Kurzbeschreibung
(Englisch)
|
The proposed research is to explore the feasibility of geotechnical applications of the novel Brillouin echo distributed sensor technology (BEDS) in the areas of soil-structure interaction, soil displacements and structural crack monitoring. The great advantage of the BEDS technology is the reduction of the spatial resolution and the sampling interval, which allows for the feasibility study to be carried out on physical models of laboratory scale validated against analytical and numerical modeling. This will allow geotechnical engineering to benefit from the revolution in sensor technologies, especially in the area of safety of construction and maintenance of structures and their response to natural and manmade hazards.
|
Partner und Internationale Organisationen
(Englisch)
|
AT, BE, CH, CY, CZ, DE, DK, EL, ES, FI, FR, IE, IL, IT, N, PL, PT, RO, RS, SI, SK, UK
|
Abstract
(Englisch)
|
Distributed Fibre Optics (FO) technology represents an extremely powerful tool for monitoring thanks to its high adaptability to the environment in which it is applied, its insensitivity to electromagnetic fields and to the amount and accuracy of data provided. The development of Distributed FO technologies has now reached very high spatial resolutions, offering new monitoring opportunities in the field of geotechnical engineering: this project aims at examining such applications. The second year of the project focused on investigating further different aspects of the Rayleigh Optical Frequency Domain Reflectometry (OFDR) technology (millimetric resolutions over lengths of about 70m) applicability to selected geotechnical engineering problems; in particular, the group had the chance to apply it in the field thanks to the involvement in the Crossrail tunnelling project in London. The possibility to reliably quantify lateral soil displacements such as those due to creeping landslides or tunnelling was investigated by means of laboratory tests. Sensors embedded in sand were subjected to transversal displacements; these could be easily quantified if the sheared zone was large enough. Locating shear bands within the soil seems instead more challenging; however, their propagation with displacement could be observed and modelled. Improving the connection between cable and soil had beneficial effects. The study of the possibility to monitor local events such as cracks produced rather interesting results. Following last year's positive results, the OFDR technology was applied to a model tunnel lining ring; deformations were simulated, and the sensors proved very efficient in detecting and quantifying the opening/closing of joints between lining segments as well as the deformation of the segments themselves. Cables embedded in grout (boreholes) also showed very clearly the formation and opening/closing of cracks. The integrity of different types of cables was assessed with the pullout box by applying strains and observing the response; the strain measured along good quality cables was the same as that applied, and localised only along the length under elongation; poorer cables showed slippage between the different cable layers, the strain measured was lower than that applied and distributed also beyond the points where strain was applied. Finally, the IGT group had a unique opportunity to be involved in the Crossrail project for monitoring the deformations caused by the construction of a new railway tunnel beneath London. Deformations of the ground surface, displacements in the boreholes excavated in the proximity of the tunnel axis, and movements of an existing London Underground tunnel were monitored. The campaign was successful; the results gave a clear overview of the settlements induced by tunnel excavation and will give further insight to the prediction of such deformations by means of analytical models (planned for the final year of the project).
|
