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An explosive project: Modernisation of the Ostpark sports facilities at Frankfurt am Main
Dipl.-Ing. Bernd Schnabel, Landscape architect AKH BDLA Planungsbüro Lukowski + Partner
The Ostpark is an attractive green park in Frankfurt am Main, Germany, which is very popular due to its vicinity to the city centre. At the centre of the park, which was founded at the beginning of the 20th century, is the so-called Ostparkweiher, a small lake. Grouped around the lake are playing and sunbathing areas, a playground and a sports field. The sports field had suffered greatly over the years. The grass pitch, edged by a weedy mulch running track, was practically bald rendered made useless by rabbit burrows. The two tennis courts which remained in a useable state, no longer satisfied the requirements of modern sports use.
As the facilities were still used both for school sport and by a football club, the city of Frankfurt decided to modernise them, demolishing the playing field and track and starting again from scratch with a new installation.
The planning and renovation work presented particular challenges as the Ostpark is a listed monument of historic interest and the renovated and modernised sports field was required to suit the concept of historic interest.
The planning office Lukowski + Partner were awarded the task of further developing a preproject drawn up by the city authorities for public parks and to monitor implementation of the measures.
The planning, agreed on with the sports, historic and nature conservation authorities, included a sports field rotated by 90°, a 400m running track with four lanes and a synthetic turf pitch oriented from north to south in order to be more userfriendly and built on an existing large clay playing area At the northern end, two artificial turf minigolf courses were installed. These were equipped with specially designed and manufactured transparent boards made of acryl glass (Plexiglas) to maintain the generous, open character required by the historic conservation authorities.
The running track and the south segment of the arena, intended for field and track athletics, were given a green synthetic surface coating in order to adjust it better into the open character of the surrounding parkland. This also avoided the problem of green rubber granulate filling material from the synthetic turf looking untidy if it was transferred to a red standard running track surface. In the southern segment a combined long and triple jump pit with two approach tracks were installed for school sport – the centre approach track can be used for both pits. In addition, there is also room for a highjump site if required.
In the northern segment, two mini football fields (20 x 13 m) were built, - an important addition to the facilities given the special focus on youth work and school sport. Both pitches are completely surrounded by boards and equipped at both ends with ball stop nets. The football goals are integrated into the board surrounds. For the rest of the area, concrete block paving was laid to minimise maintenance work.
At both ends of the artificial turf football pitch, 5m-high nets were installed stretching nearly the whole width of the pitch. This was to stop balls being lost and also to prevent players from other games disturbing each other or causing injury.
A new 6-mast set of floodlights provide sufficient light for the artificial turf pitch and both segments while watering of the artificial turf is carried out by a fullyautomatic irrigation system sunk into the ground. Spectator barriers were built around the running track with bars close enough together to prevent rabbits from getting on to the pitches. In order to prevent vandalism and to ensure order, the whole new facilities were surrounded by a steel-mesh fence.
A very tight time schedule was decided on for the building measures as building work could not start before June 2012. The weather-sensitive synthetic surfaces needed to be installed before the end of September 2012 however.
Things were made even more difficult by the fact that the mainly clay or silt ground needed to be stabilised by milling in of a hydraulic bonding agent.
As the building ground was nearly impermeable to water, a draining system to remove the water was necessary. Disposal of the rain, surface and drainage water into the Ostparkweiher Lake was not approved and there was no existing connection to the canalization systems so it was intended to build infiltration shafts in the ground underneath the sports facilities. Up to a depth of two metres, the ground was practically solid making it nearly impossible for water to sicker down. Underneath this layer, the soil consistency changed and became permeable. To ensure sufficient drainage, the whole of this impermeable layer was removed for a wide area around the infiltration shafts and replaced with a mix of sand and gravel allowing the water to drain off the surface and into the groundwater via the drainage shafts. Due to the relatively high ground water level in the Ostpark, the infiltration system was able to be built of plastic halfpipes.
Further challenges appeared during the building process. The area had been bombed during the Second World War and it was to be expected that explosive remains would be discovered. During systematic tests demanded by regional authorities, numerous suspicious positions were identified.
Right at the start of the search, remains of explosive and intact incendiary devices were uncovered so that all construction work was immediately halted. All determined bomb craters which after the war had been filled in, mainly with rubble, were systematically dug out with heavy earth-moving machinery and probed. Several incendiary devices were found and one live 50 kg bomb needed to be defused, including a closing the nearby motorway A661 and the next railway station. The comprehensive clearing of the area finally resulted in a crater landscape with pits up to 3 m deep and 12 m wide – all needing to be refilled and compacted.
Due to the comprehensive planning preparations and good cooperation with the authorities responsible for public parts, planners and contracting companies - Strabag Sportstättenbau GmbH and Polytan GmbH – it was possible to complete all work on time in autumn of 2012. All construction requirements, such as the special draining systems and substrate problems, were satisfied and calculated costs were not exceeded.
Photos: Planungbüro Lukowski + Partner
Further information can be obtained from www.SL-plan.de