InsideStress : Parisian subway tunnelelixandre
An InsideStress instrumentation to measure
the in-situ stresses inside a tunnel.
Cementys has been mandated by the RATP (the Parisian subway operator) for the surveillance of a tunnel located between two subway stations. As part of the implementation of a new behavior law for the masonry tunnels, the RATP would like make in-situ measurements to know the stresses states and the existing relation between stresses and strains of the structure.
Cementys suggested the InsideStess solution:
This solution uses the well-known incremental whole method used for the measurements of residual stresses inside metallic mechanic parts (normalized method ASTM E837). For concrete or masonry structures, InsideStress uses the method of incremental over-coring instrumented by vibrating wire sensors MicroVib® M54.
Using the real time strains measured by those robust and durable sensors during the coring, we can know the stresses. Indeed, during the coring the stresses are released (or created) and have a strain effect on the sensors. This strain is then transformed to stress using the elasticity properties of the material (determination of the Young modulus by normalized vibration testing).
By using this reliable, fast and relatively unobtrusive solution, the RATP knows the stress states on the outside of the tunnel (direction and major stresses), their evolution towards the inside of the tunnel, and the states of the auto compensated residual stresses.