GERMAN GEOSYNTHETIC manufacturer Huesker Synthetic has prov ided an alternative reinforcement solution for a new railway embankment on the extension to the UelzenStendal west-east rail link in northern Germany.
The firm's geogrids enabled a steep-sided embankment to be built within an existing embankment footprint.
Work is being carried out for Deutsche Bahn (German Railways) under the German unity transport projects initiative by a contracting consortium of firms Matthai, Bothe and Meyer.
Near Harper Muhlenbach a single line runs along a 440m long,6m high embankment on a 10m wide base. This had to be upgraded to support the new twin-track 140kph line. The embankment, which is underlain by peat, would not have been able to cope with the extra load caused by the new trains. The structure also had to be widened to make room for the extra track.
Widening the structure while retaining its natural slope angle was not possible for ecological and economic reasons, so it was decided to build a 3m high, steep sided embankment. The original plan was to secure the side slopes with anchored sheet pile walls, but this was expensive and was abandoned in favour of a new approach.
Huesker proposed building the embankment on 'piled' precast cemented stone columns covered with horizontal geogrid reinforcement and to use geogrid to reinforce the embankment slopes.
The geogrid increases the overall stability of the embankment and provides a 'virtually settlement-free foundation'for the steep-sided embankment. The firm had already used similar designs on projects for Deutsche Bahn.
During construction, part of the existing embankment was first removed. The 600mm diameter cemented compacted stone columns were then driven through the remaining structure at 1. 75m centres, down to loadbearing strata.
For the basal reinforcement, two types of Huesker's Fortrac geogrid were laid on top of a 200mm thick levelling course. Then 400kN/m geogrid was laid across the embankment and 150kN/m geogrid laid along the embankment axis.
The new embankment was built using more Fortrac to stabilise the compacted fill. A variety of strengths were used, depending on the height on the slope. To keep the side slopes at 45degrees they were faced with the firm's Textomur system. This consists of prefabricated sections of steel mesh backed with a non-woven material to support vegetation growth. Topsoil was placed on the slope faces and hydroseeding carried out.