3.1.4 Monolithic Designs
These designs are consisted of only a continuous monolithic concrete layer and direct rail fastenings adjusted on it. The sleeperless designs are established either as monolithic concrete layer produced by a concrete paver or as prefabricated slabs connected together (Esveld, Lichtberger). The direct rail fastenings used for this system are very effective in bridges making them lighter and eliminate problems associating the sleepers (Esveld5). The monolithic designs are stiff and rigid enough to behave structurally as a continuous supported elastic beam under traffic loading. The rigidity of this system makes it suitable for use in soft soils. The loads are distributed across a much longer and wider area (Esveld). Attention must be paid to the crack formation of the concrete bearing layer (CBL) and proper measures have to be taken to prevent cracking caused by the rail fastenings.
Figure 50: An example of a monolithic slab track design with direct rail fastenings (HeilitWörner) (Esveld)
3.1.4.1 Lawn Track or RASENGLEIS system
The Lawn track system consists of a water permeable concrete slab 30 cm thick and two longitudinal reinforced concrete beams of trapezoidal shape (cross section) which are connected onto the concrete bearing layer which supports and reassure the stability of the track (Lichtberger, Franz). Anchoring ties connect the longitudinal concrete beams and the concrete supporting layer (CBL) as shown in figure 51. The rail fastenings are fastened onto the longitudinal concrete beams by rail clamps cast in pre-drilled holes. The space between the concrete beams and their outer areas is filled with a substrate covered by oligotrophic grass (low vegetation) (Lichtberger).
Figure 51: Lawn track or RASENGLEIS construction (Darr & Fiebig)
3.1.4.2 FFC slab track system
The FFC (Feste Fahrbahn Crailsheim) slab track system is manufactured with high precision in preparation and installation. The supporting points (dowels) for the rail fastening system either are “shaken into” the fresh concrete during installation, or they may be inserted and glued in predrilled holes into the dried concrete slab (Franz). After the dowels are inserted the rail fastening system IOARV300 is positioned at the manufacturing stage as a profile in the form of an infinitive length concrete sleeper in the concrete bearing layer (CBL) (Lichtberger, Franz, UIC report). The concrete slab is made by a slipform paver and the fastening system is adjusted by a special machine following behind. The concrete base is normally 2.4 m wide as shown in figure 52, but it can reach a maximum of 3.2 m length according to Franz. Every third support point a notch is made in order to control crack formation and to let the water to let the rain water to run off.
Figure 52: FCC slab track design (Darr & Fiebig)
3.1.4.3 Hochtief/SHRECK-MIEVES/LONGO
The Hochtief system consists of a concrete bearing layer over the hydraulically bonded layer (HBL) and it uses concrete-embedded rail support points for rail fastening type 300 (UIC report, Franz). Four linking anchors are jiggled into the fresh concrete of the CBL for each individual support. Then each rail support is adjusted using a setting frame for accurate leveling and height adjustment (Mörscher). The use of steel fiber concrete in segments revealed fissure structures with almost invisible cracking (Franz). The surface of the concrete bearing layer
(CBL) has been designed with inclination to directly drain off the rain water (Mörscher). The exact dimensions and design characteristics of this system are illustrated in figure 53.
Figure 53: Hochtief/SHRECK-MIEVES/LONGO slab track system (Darr & Fiebig12)
3.1.4.4 BES system
The BES slab track system is consisted by a reinforced concrete bearing layer (CBL) with individual support points over the cement stabilized layer (HBL) (UIC report, Franz). This system was developed in Germany and uses the same process as the FFC in producing the form of the rail fastening at the installation of the CBL. The plugs for the rail screws are glued into pre-drilled holes in the dried concrete supportive layer (Franz).
Figure 54: BES slab track system (Darr & Fiebig)
3.1.4.5 BTE slab track system
The BTE system is a concrete supportive layer (CBL) with individual support points over a hydraulically bonded layer (HBL), very similar to BES system. A two-level plate machine system is used to achieve the desirable geometry of the concrete slab layer (CBL) (UIC report). Two different rail fastenings have been used for this system, Ioarg 336 and ERL (BWG). The concrete areas, where the rail fasteners are located, are manufactured with extra strength. Details of the BTE design system are shown in figure 55.
Figure 55: BTE slab track system (Darr & Fiebig)
3.1.4.6 PACT system
The PACT slab track system was developed in Britain and first constructed in 1969 at Radcliffe for testing purposes (Round8). It is consisted of a continuous paved unreinforced concrete layer on which a paved, profiled continuous reinforced track slab is based (Bastin). The connection between these two layers is achieved by shear links in the reinforcement of the upper slab (Round8). This system has a 22.9 cm thick concrete slab that is 2.43 m wide (Canadian Pacific Railway) (Bilow,Gene & Randich). After the curing of concrete is complete, holes are drilled (diamond-core) and the continuous welded rail is laid on a continuous rail pad and fixed to inserts embedded in the slab (Bilow,Gene & Randich, Bastin). Although it was designed for high speed lines, this has not happened. It has mainly used in tunnels (wet tunnels) because of its low construction height and low maintenance needs comparing to ballasted track. The maximum speed in a PACT system nowadays does not exceed the 150 km/h (Round). Although this system was at the forefront of slab track development, the lack of any significant new construction in Britain did not allow for many further developments. The PACT system is outdated for the current standards and high speed train demands (Bastin31). The advantages of this system are the low construction costs and the high quality geometry. The disadvantages are, that requires special laying equipment, the out-dated construction method (bottom-up) combined with the continuous support of the rail make it harder to achieve the levels of accuracy required for high speed, as well as that the drainage is often hindered resulting to debris collection which lead to corrosion of the railway fastenings (Round8, Bastin). The exact dimensions and structural features of the PACT system are schematically illustrated in figure 56.
Figure 56: PACT slab track system (* Depth D at real seat varies: typically 150-250 mm. Similarly depth of the base slab varies depending on site conditions: 300mm minimum) (Bastin).