Monitoring of railway structures of the high speed line BPL with bituminous and granular sublayers

Abstract

Ballast deterioration, under dynamic loads, remains an important issue on high-speed tracks that can lead to high maintenance costs. This ballast deterioration leads to settlements. Several studies have shown that these settlements were linked to high accelerations produced in the ballast by high-speed train (HST) passages. The solution with bituminous underlayment was used since 1980s in several countries like United States, Italy, Spain, especially on high-traffic and high-speed lines (HSL). In France, the interest in this technique is recent. Following the East European HSL satisfactory behavior, a layer of asphalt concrete was used under the ballast layer of the Bretagne-Pays de la Loire (BPL) HSL. It is intended, in addition to the schedule savings and the protection of the subgrade during the construction phase, to reduce acceleration amplitudes produced at the passage of HST, to ensure moisture stability in the subgrade and thereby to decrease the maintenance costs of the tracks. BPL HSL includes 105 km of innovative track with an asphalt concrete (GB) ballast sublayer, and 77 km with a granular layer under the ballast (UGM). Out of the instrumented sections of the BPL track, 3 sections are constructed with GB subballast layer and one with a layer of UGM as a subballast layer. A total of 127 sensors that includes accelerometers, anchored displacement sensors, temperature and humidity probes, and extensometers are used. Sensors are placed at various positions and depths in the track structures. Data were first acquired during a speed up test phase, under controlled conditions, with the same train passing at speeds ranging from 160 to 352 km/h. This paper presents the different sensors used for the instrumentation as well as the acquisition system installed to collect all measurements. Data treatment and processing is explained in details. Finally, results obtained for different speeds are presented, with a focus on accelerometer and anchored displacement sensor measurements, on two sections, allowing, among others, comparisons between the response of structures with and without asphalt concrete. The role of the GB, as a subballast layer, in damping the vertical displacement of the sub ballast structure and reducing the accelerations peaks in the ballast layer for ballasted tracks is demonstrated.

A Critical Review of Sensors for the Continuous Monitoring of Smart and Sustainable Railway Infrastructures

“…While strain gauges have been widely used in rails, pads and bearing courses to measure elastic and plastic micro-deformations at a reasonable cost (in comparison with the other sensors), its application in sleepers could also be a viable way to measure the performance of this component and the evolution of its fatigue life. Nonetheless, it must be considered that this application has not been studied to date, and therefore, further study will be required [27,[43][44][45][46][47]. Additionally, although these micro-deformations are normally correlated with fatigue failure, a strain gauge would also be able to identify other failures in an indirect way, such as traffic loads [43], by correlating the strain measured with the stress applied by using the Young's modulus and Poisson ratio of the material.…”

“…Finally, there are also specific gauges (H-gauges) designed to be embedded in asphalt mixtures for bituminous sub-ballast. These H-gauges were used by Khairallah et al [47] in order to determine the deformation that appeared in a bituminous layer located in an experimental section in the line Bretagne-Pays de la Loire, France. This is a high-speed line in which two different substructures were studied: bituminous and granular sublayers.…”

“…Khairallah et al [47] used accelerometers to measure the vertical dynamic behavior of a railway track. To achieve this, accelerometers were placed under a sleeper and at the top of a bituminous sub-ballast layer with the aim to compare the differences in levels acceleration between a conventional section and a section with a bituminous sub-ballast layer.…”

Multifractal Analysis of the Common Crossing Track-Side Measurements

“…The system can detect the danger of track buckling of rail break and is integrated in the railway signaling system. Monitoring of railway ballast and sublayers on the highspeed railways of SNCF is provided on test sections with 127 sensors that includes accelerometers, anchored displacement sensors, temperature and humidity probes, and extensometers [12]. The distributed acoustic sensor technology, that is based on optical fiber real-time monitoring and positioning, is tested on heavy-haul railways of China Railways [13].…”

Long-Term Monitoring for Track Slab in High-Speed Rail via Vision Sensing

“…In this regard, long-term monitoring for the structural conditions can be a good way to detect the initiation and development of potential defects and schedule maintenance works accordingly. Deformation monitoring for track structure is usually achieved with linear variable differential transformer (LVDT)-based system [10][11][12][13], which can measure structural displacement with transducers, mounted on the track and external data acquisition instrument. However, as it needs fixed installation on the structure, the in-situ installation can cost a long time and a lot of manpower.…”