Novel monitoring system to diagnose rail track foundation problems

Abstract

A low cost, remote monitoring system has been developed to diagnose rail track subgrade failures. The portable monitoring system consists of five liquid vertical settlement probes, one piezometer, a small data acquisition system and laptop, and an Internet communication with remote control capabilities. The probes are designed to be small, easily installed (within railbeds using a one-man auger), easily manufactured, and low cost. The sensors and data acquisition have been rigorously tested and calibrated in the laboratory. The settlement probes and piezometer are sensitive to changes in the atmospheric pressure and temperature, and calibration curves have been obtained to correct for these effects. The settlement probes are further subjected to silicone oil density changes due to differential temperature between the atmosphere and the ground, and these effects are minimised by a proposed correction method. The prototype monitoring system was installed through a two phase installation exercise at the bridge approach site in FAST (Facility for Accelerated Service Testing) at Transportation Technology Centre Inc (TTCI), Pueblo, Colorado, USA. Since there are virtually no settlements at the stiff, sandy bridge approach site, the sensors are evaluated for ideal stability and robustness while being subjected to well-defined Heavy Axle Train (HAL) loadings. A detailed evaluation of the prototype system found that probes installed at depths 1.0 to 1.5m within the subgrade did not achieve satisfactory measurement stability (i.e. measurements have a spurious drift), due principally to manufacturing defects. The prototype probes were sufficiently robust to survive installation within the subgrade but not within the ballast itself.

(cont.) The probe designs have subsequently been refined to eliminate sources of drift, and have undergone more extensive calibration to account for differential temperature effects. These second generation probes are scheduled for field deployment as part of the on-going research.