Deliverables Fibre bragg grating inclinometer Optical Fibre Bragg grating-based uni-angular inclinometers have been designed, realised and tested by CEA-LETI. A hanging mass submitted to gravitation is allowed to rotate with respect to an upper part fixed to the inclinometers body itself moving with the structure. The angle is turned into a proportional strain applied to two pre-strained FBGs that behave differentially (one FBG is strained while the other is compressed). Angular rotation effect is thus doubled whereas temperature and pressure effects are cancelled out therefore providing environmental compensation. Inclinometer prototypes have been tested with respect to required accuracy, detection limit and mechanical hysteresis. Angle resolution is about ± 10 arc seconds that corresponds to a 1meter high wall displacement of 50 mm. The range is +/- 2.5 degrees and the residual temperature sensitivity is lower than the angle resolution. Several inclinometers, in compact and waterproof packaging have been tested along with traditional inclinometers on a field trial at Toulon, France and interrogated with the portable CEA FPI-based logging unit. This field trial have shown better performance in comparison with usual inclinometers opening the way to intelligent public work methods (compensation grouting) thanks to the accuracy and portability of the instrumentation. Exploitable results Fibre bragg grating industrial logging unit A logging unit was designed for signal acquisition and recording for Fibre Bragg Gratings (FBG) sensors. Two different types of Elementary Detection Modules (EDM) have been developed and show good performances: -Wavelength tracking based on sensor-receiver grating pairs: the receiver grating is bonded onto a piezoelectric actuator and is used as a tuneable filter. The spectra of both gratings are kept superimposed using a tracking circuit. -Scanning Fabry-Perot Interferometer (FPI). The logging unit integrates an optical board with 4 receiver FBGs mini-piezo, couplers, optical source and power electronics. The CEA-LETI Logging Unit is integrated into a rugged portable PC, incorporates a FPI-based EDM in a modular and flexible design (source-FPI-switch-board) , and has a large multiplexing capacity (8 fibres x 4 to 8 sensors/fibre). It includes a user-friendly data acquisition and display software based on the Lab-View environment. Modelling tools for simulation of TBM excavations During shield tunnelling operation, a shield machine is driven forward by applying mechanical jack forces behind the machine tail and excavating the soil in front of the machine with its cutting face. A research orientated 3D soil-pore water coupled finite element program, which can simulate the advancement and excavation processes of the shield tunnelling operation, was developed in order to investigate the effect of various construction processes on the ground response. A new excavating finite element, which models the disturbed soil in front of the cutting face, is proposed. The operation of shield advancement and excavation is simulated using the finite element re-meshing technique at each time-step of the analysis. The developed program was used to simulate a tunnelling project in Tokyo and the numerical results are compared with the field measurements. The program allows us to examine the soil deformation mechanisms associated with the shield tunnelling operation in detail. Real-time observational compensation grouting method Objective of Compensation Grouting is to control the risk of soil subsidence on tunnelling sites. The strategy consists to introduce very small quantities of grout as close as possible to the origin of soil displacements, in such a way that the whole soil body remains as close as possible to the at-rest condition. The innovative approach of the COSMUS project is to implement an adaptive feedback loop including the following elements in a single operative network: A predictive numerical model to estimate on a daily basis the amount of settlements due to tunnelling, and to estimate the necessary grouting quantities. A precise control of grouting operations. Automatic remote acquisition of soil/structures movements. Software and methods to operate a daily adjustment of the predictive model from observations made on the site. Soil situations are generally complex and very heterogeneous. The adaptive process is the only feasible way to deal with this difficulty and obtain the best economical compromise between objectives of cost/safety on the tunnelling site. The concept and the software system were fully validated on several construction sites. The latest test was operated in the COSMUS project, and allowed to validate the general concept of Real-Time Observations and the corresponding software. This validation test will be used as a reference in further tenders. Fibre bragg grating strain sensor The fibre optic strain-cable measures displacement or strain between several fixation points along a borehole in order to monitor strain and /or settlement in rock, concrete and soils with a very high accuracy and long-term stability. This cable interconnects in series and in the borehole with several fibre optic displacement cells (the transducers). The diameter of the displacement cells being as small as 20mm, the borehole diameter can be reduced, thus decreasing the cost of drilling. But the displacement cells can be implemented in two other ways: 1) In a bundle of anchored displacement sensors or rod-extensometers. The fibre optic rod-extensometers perform basically the same measurements as the strain cable along a borehole but the displacement fibre optic cells are mounted externally of the structure, allowing them to be retrieved and repaired in case of damage. 2) In a chain of surface displacement sensors, the fibre optic surface displacement chain measures displacements between different anchors mounted into a rock or concrete wall. This configuration is particularly suited to the convergence monitoring of a tunnel or a cavity. The fibre optic displacement cell can be dimensioned to fulfil the end-user requirements. In addition, the cells are multiplexed in the optical wavelength domain. The measurements are thus centralised by a remote interrogating unit and the monitoring is flexible and user friendly. Monitoring software (GEOSCOPE WEB) GEOSCOPE-WEB is a chain of software which provides all functions of a real-time GIS for the instrumentation and control of soil/structure movements on construction sites. Its main feature is that it is fully compatible with Internet operations. It is composed of the following modules: -GW INTEGRATOR: acquisition of movements data on remote PC stations and collation of data in a remote technical room -GW ALERT: detection of alarms and triggering alert actions -GW MONITOR: GIS type mapping of sensors / alarms -GW PROCESSOR: reporting (graphs, tables, maps, etc) -GW ENGINE: remote administration, data base replication, data base query via Internet by technical staff, management of the company, the engineer, the client -GW WEB: Internet communication is integrated into all other modules. Modelling of grouting Modelling of compensation grouting operations is necessary to make an efficient design of compensation work, where decisions are needed for grout spacing, injection volume and injection rate. A conceptual model of grouting operation within the framework of tunnel construction analysis was developed in order to upscale the local injection phenomenon to global tunnel-soil interaction problem. In this model, a concept of grout efficiency has been introduced and the method of its numerical implementation into a finite element/difference code has been proposed. Both numerical and laboratory investigations were conducted to validate the proposed conceptual model of compensation grouting. Particular attention was made to estimate grout efficiency from the soil condition (e.g. soil, type, overconsolidation ratio). Grout injection tests were performed in the laboratory on reconstituted and natural clays to investigate the long-term effect of compensation grouting in clays. Using the proposed model, three-dimensional finite element analysis was performed to simulate compensation grouting operation performed in Tokyo and good agreement between the calculated values to the measured data was found. Searching for OpenAIRE data... There was an error trying to search data from OpenAIRE No results available
