Moving and building, a core competence of the building industry!

Or an attempt to square the circle?

Author: Axel-Björn Hüper, former Chief Executive Officer of DB ProjektBau

The marked increase in funds set aside for the necessary maintenance and replacement of existing rail infrastructure at DB AG has also resulted in restrictions on the availability of this infrastructure due to partial and full track possessions and the resultant diverted services under current site planning arrangements.

One of the core competences of the building industry, while working on existing assets, is to largely ensure the continued provision and availability of the operational rail infrastructure with the help of existing technologies and recognised process technology.

Composed of representatives of the building industry and employees of DB Netz AG, a joint expert group addressed the topic of "technological framework conditions for the permanent way" for the purpose of systematically optimising the fundamentals used in planning track renewal measures for rail infrastructure. This exercise was to provide specific criteria in support of taking decisions on defined planning parameters and thus to ensure high-quality construction while at the same time maintaining continued rail service.

Planning parameters in respect of

local conditions
single- or multiple-track sections or site access,

economic efficiency
length of renewal and train service in adjacent track as well as recycling of materials,

the environment
optimisation of the period of construction as well as reduction of noise and CO2,

safety
through assembly line technology,

have been included to this end.

Decision criteria for track renewal

Assistance in the selection of appropriate processes

The user has a decision chart which helps him choose the appropriate process technology. The construction process chosen in the early planning phase and the defined process technology form the basis for optimised track possession planning.

An explanatory catalogue (for excerpts see below) has been compiled to support the choice of appropriate processes and thus ensure a uniform understanding on how to apply specifically assigned premises.

Explanatory notes on the decision chart for track construction

Assistance in the selection of appropriate processes

Single- or multiple-track section

In conventional renewal work on only one track with the track to be renewed being in front of the machine, building materials must be handled several times including their temporary storage. In general, the conventional method is thus only applied to cases where at least two adjacent tracks can be used for renewal or where the entire site can be served via an additional access road. With the use of an assembly line process it is possible to manage the work site on only one track without affecting the output of the machine systems.

Installation independent of weather conditions (limitation on building pit)

The carrying capacity of the substructure will influence the choice of the process since the loads generated by the machines must be taken up and absorbed by the formation. If, as is the case with conventional construction methods, the formation is directly driven onto, special care must be taken to ensure that it has sufficient carrying capacity. Otherwise, uneven subsidence could occur and affect the quality of the work done and the service life of the infrastructure asset built.

Precipitation events, in turn, change the carrying capacity of the soil depending on the type of soil. The uncontrolled addition of water especially in cohesive soils (silt, clay, etc.) will result in reduced carrying capacity and make the application of conventional construction methods more difficult. The assembly line process presents an alternative technical solution.

In constant and heavy rainfall, the quality of ballast cleaning will be compromised without additional ballast treatment. Appropriate conclusions are to be drawn on site.

Site access (easy/difficult)

Access to the work site will influence site management in respect of transporting the necessary tools and materials to and from a work site. The assembly line method is basically a means of completing the entire site job on-track, making it virtually independent of access roads. By contrast, difficult site access conditions in conventional renewal operations will result in increasing requirements for logistics, storage options and construction processes.

The results of the optimisation analysis have shown that, with due regard to available process technologies in the early planning stage and based on reduced construction periods and continued train service in the adjacent track of multiple-track sections, it is possible to move and build on-track without full track possession and thus to increase the availability of the line’s capacity. If these principles are consistently applied by those responsible for planning, the objective of moving and building will no longer be an attempt to square the circle.