Innovative geophysical investigations of railroad infrastructure using discrete sensors and fiber optics

Summary We have developed a system based on the combination of a robust acquisition and processing system with an innovative geophysical methodology, able to provide permanent and reliable measurements of the surface waves velocity in the near-surface below railway platforms. We have proven that trains can be used as seismic sources to compute virtual seismic traces by means of interferometry, and that the area of interest can be covered accurately using the adapted design of receivers. Thanks to the system’s permanent recording of the seismic signal, a S-waves velocity volume of the near-surface underground (from 0 to about 50 m in depth) can be produced every day. These daily results can be directly interpreted to track the genesis and growth of cavities due to leakage and dissolution phenomena As a whole, the system is able to alert railway maintenance managers, allowing to provide preventive and accurately targeted maintenance operations; and to avoid accidents. Different instrumental techniques can be applied in order to accommodate variations in sites and train track geometries: dense accelerometer arrays for high resolution measurements, optical fiber layouts using DAS technology for long range and lower-resolution monitoring — or a combination of both.