Keywords: tamping scheduling, heuristic, forecasting, optimisation.

The maintenance of railway tracks is a task with a high impact on service quality and safety, that demands large amounts of both technical and human resources. An optimal deployment of the available resources is therefore determining for the cost-effectiveness of railway operation. Furthermore, the track geometry maintenance activities need to be planned up to one year in advance. For this reason the French railway operator SNCF has been measuring periodically the geometrical characteristics of its high speed network since its commissioning, i.e. for more than twenty years now.

One of the most important maintenance activities is the reduction of the track geometry irregularities, which is basically achieved by means of tamping. Currently, most of the tamping intervention plans are made manually, basing on expert knowledge. In this paper we present a method for automatic optimal planning and scheduling of tamping activities on railway tracks.

We consider two types of tamping interventions: preventive and corrective. By means of forecasting the geometry deviations, the maintenance needs for the next planning period (typically six to twelve months) can be predicted, which in turn allows the optimal balance between preventive and corrective interventions to be estimated. Implementing the method enables the minimisation of maintenance costs without a drawback in the achieved track geometry condition, i.e. to find the optimal schedule while complying with the current track quality requirements.

Maintenance planning is based on forecasts of the development of the geometry irregularities in each track sector. In order to achieve good forecasting quality and reliability, this paper presents a method for making middle term (i.e. up to one year) predictions of the railway geometry ageing process. The method relies on a process model describing the track geometry ageing as an exponential function. The function identification is achieved with the help of the Levenberg-Marquardt procedure for the sum of squares minimisation of non-linear functions.

The maintenance scheduling is calculated by means of an in-house developed optimisation algorithm. Its main novel aspect is the implementation of a heuristic for the problem resolution instead of commercial optimization packages. This results in a twofold benefit, as both the need for model simplification and the calculation times are dramatically reduced.

The method is finally validated by means of a case study on real data of a French TGV high speed line, where the optimal number of preventive and corrective interventions for the next planning period is assessed.

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